JP5143104B2 - Switching power supply - Google Patents

Description

  The present invention relates to an insulation type switching power supply apparatus that makes an output voltage constant by pulse width control.

  As a control method of the switching power supply device, an output voltage signal obtained by amplifying an error between the output voltage and the reference voltage is compared with a predetermined reference triangular wave voltage, and pulse width modulation (PWM) is performed so that the output voltage becomes constant. There is a pulse width control that automatically controls the on / off time ratio of the main switching element. Here, in the case of an insulating switching power supply in which the input side and the output side are separated by a main transformer, an error amplifier circuit that generates an output voltage signal is generally provided on the output side in order to detect the output voltage with high accuracy. Therefore, when performing pulse width control, it is necessary to transmit an output voltage signal or the like to the main switching element on the input side through some insulating means.

  Conventionally, as this type of switching power supply device, for example, as disclosed in Patent Document 1, an error amplification circuit is provided on the output side, and a PWM circuit including a drive circuit for the main switching element is provided on the input side, There is a switching power supply circuit configured to transmit an output voltage signal output from an error amplifier circuit to an input side via a transmission means that is an insulation means. This switching power supply circuit has a configuration in which a predetermined bias voltage is always applied to the transmission means, and fluctuations in the output voltage due to sudden changes in the load can be kept relatively small.

  Further, as disclosed in Patent Document 2 as a conventional example, an error amplification circuit and a PWM circuit are provided on the output side, and a rectangular driving pulse output from the PWM circuit is input to the input side via an insulating transformer of the driving circuit. There is a DC-DC converter configured to transmit to the main switching element. In addition, this DC-DC converter is provided with a dedicated auxiliary power supply (switching power supply) for supplying operation power to the error amplifier circuit and PWM circuit on the output side.

  Further, as disclosed in the invention according to Patent Document 2, an error amplifier circuit is provided on the output side, a PWM circuit and a drive circuit for the main switching element are provided on the input side, and an output voltage signal is supplied to the main transformer. There is a DC-DC converter configured to transmit from the third winding provided to the input side through the fourth winding. In the drawing for explaining the embodiment of Patent Document 2, an AC voltage obtained by converting an output voltage signal output from the error amplifier circuit is applied to the third winding, and the AC voltage generated in the fourth winding is used as a diode. A circuit that averages with a capacitor and performs pulse width modulation (PWM) on the averaged voltage with a reference triangular wave voltage is described.

  Further, as disclosed in Patent Document 3, an on-period control circuit and a ramp wave generation circuit corresponding to the above-described error amplification circuit and PWM circuit are provided on the output side, and the main switching element is turned off at regular intervals. There is an insulated DC-DC converter having a configuration in which a drive circuit (PWM control circuit) that is turned on is provided on the input side and an off-timing signal output from the on-period control circuit is transmitted to the drive circuit via a pulse transformer . In the drawing for explaining the embodiment of Patent Document 3, a ramp for generating a reference triangular wave voltage (ramp wave) for performing pulse width modulation using a rectangular wave voltage generated at both ends of an inductor of a rectifying and smoothing circuit is shown. The configuration of the wave generation circuit is described.

JP 2002-186254 A JP 59-178969 A JP 2009-124849 A

  The switching power supply circuit of Patent Document 1 generally uses a photocoupler as a transmission means. However, the general-purpose photocoupler used for this type of application causes a phase delay when transmitting a signal in a high frequency band of several kHz or more, and causes the entire control circuit of the switching power supply device to oscillate. In order to avoid this oscillation, consideration must be given to correcting the phase characteristics in the entire control circuit and keeping the gain in the high frequency band low. For example, a method of increasing the capacity of the smoothing capacitor in order to keep the high frequency cutoff frequency of the output smoothing circuit of the LC filter configuration low, or adding a circuit for phase correction to the error amplifier circuit etc. can be considered. However, each method has a problem that the apparatus becomes large and the circuit configuration becomes complicated.

  In addition, the gain of the photocoupler itself is defined by the conversion efficiency (ratio of the current flowing through the light emitting element to the current flowing through the light receiving element), but this conversion efficiency varies depending on the usage environment and usage conditions, and varies from element to element. Is also big. Therefore, when setting the gain in the high frequency band of the entire control circuit, the center value must be set sufficiently low in consideration of fluctuations in the conversion efficiency of the photocoupler and individual differences in order to ensure an oscillation margin. The design and evaluation of was difficult.

  In addition, when the gain of the high frequency band is set low as described above and a certain phase delay is approved, the output voltage can be controlled against a transient change (such as a sudden change in load) of the external environment of the switching power supply. Control that suppresses fluctuations cannot be performed at high speed. Therefore, even in a configuration in which a predetermined bias is applied to the photocoupler as in the switching power supply device of Patent Document 1, the fluctuation of the output voltage cannot be remarkably reduced.

  On the other hand, in the DC-DC converter according to the conventional example of Patent Document 2, it is necessary to start up the PWM circuit on the output side first in order for the main switching element to start on / off operation. (Switching power supply) and a battery must be provided. Therefore, there is a problem that the apparatus is increased in size or cost. Furthermore, since the DC-DC converter according to the invention of Patent Document 2 performs a process of averaging the output voltage signal, a large phase delay occurs at that stage. Therefore, similarly to the switching power supply circuit of Patent Document 1, there is a problem that control for suppressing fluctuations in output voltage cannot be performed at high speed.

  In the insulated DC-DC converter disclosed in Patent Document 3, a reference triangular wave voltage (ramp wave) for performing pulse width modulation is generated using a rectangular wave voltage across the inductor of the rectifying and smoothing circuit. However, the rising and falling speeds of the rectangular wave voltage change depending on the magnitude of the output current, and the amplitude of the rectangular wave voltage also changes when the input voltage varies. Therefore, the instability of the reference triangular wave voltage causes the entire control circuit to oscillate. Furthermore, when a diode is used instead of the synchronous rectifier, it is necessary to drive the main switching element with a very short on-width when the output current is small. In the configurations of the on-period control circuit and the ramp wave generation circuit, There is a possibility that the ON width of the main switching element cannot be narrowed to a certain time or less, and the output voltage increases due to the inability to control.

  The present invention has been made in view of the above-described background art, and an object thereof is to provide a small and inexpensive isolated switching power supply device including a highly stable control circuit having high-speed response.

  According to the present invention, a DC input voltage is intermittently generated by turning on and off a main switching element to generate an AC voltage, and an AC voltage generated by the inverter circuit is applied to an input winding. A main transformer that transforms and outputs from the output winding; and a rectifying and smoothing circuit that rectifies and smoothes the voltage across the output winding, generates a DC output voltage, and supplies power to the load. An insulation type switching power supply device that makes the output voltage constant by controlling on / off pulse width, and compares the output voltage with a reference voltage and outputs an output voltage signal obtained by amplifying the error. An amplification circuit, a comparator, and a triangular wave generation circuit that generates a reference triangular wave voltage that repeats at a predetermined cycle, and the output voltage signal and the reference triangular wave voltage are A PWM circuit that outputs a PWM signal obtained by pulse-width-modulating the output voltage signal by comparing with a comparator, and an OFF signal that is a short-width pulse that is generated at a timing for turning off the main switching element based on the PWM signal An OFF signal generating circuit for generating the signal, a signal transformer for inputting the OFF signal to the secondary winding, transmitting it to the insulated primary winding and outputting it, and a fixed period generated at the timing of turning on the main switching element A basic pulse generating circuit that generates an ON signal that is a rectangular pulse of the above, and a triangular wave reset signal that is a short-width pulse for resetting the reference triangular wave voltage to an initial value at a timing when the ON signal is generated, A triangular wave reset output to the triangular wave generation circuit via the primary winding and the secondary winding of the signal transformer. Based on the ON signal and the OFF signal, and a drive pulse generation circuit that generates a rectangular drive pulse for turning on and off the main switching element, the error amplification circuit, the PWM circuit, and the An OFF signal generation circuit is a switching power supply configured to generate the OFF signal after the triangular wave reset signal is generated and the period of the pulse width has elapsed and before the next triangular wave reset signal is generated. Device.

  The drive pulse generation circuit includes a latch circuit including a set / reset flip-flop, and the set / reset flip-flop receives the ON signal as a set signal and outputs the OFF from the primary winding. An inversion signal is input as a reset signal to perform processing, and a period in which the drive pulse is at a high level to turn on the main switching element is after the ON signal is generated and the period of the pulse width has elapsed. The gate is set to start, and the pulse width of the ON signal is set wider than the sum of the pulse width of the triangular wave reset signal and the pulse width of the OFF signal.

  The triangular wave reset signal generating circuit includes a differentiating circuit for differentiating the ON signal, and a differential signal output from the differentiating circuit is input between its own drive terminal and a ground terminal, and the differential signal is at a high level. The primary winding of the signal transformer is connected at one end to the voltage source for the primary side control circuit, and the other end that outputs the OFF signal is the collector of the transistor element. The error amplification circuit is configured to invert and amplify an output voltage to output an output voltage signal, and the triangular wave generation circuit of the PWM circuit includes a series circuit of a charging resistor and a timer capacitor, A second transistor element connected to both ends of the timer capacitor, and one end of the secondary winding of the signal transformer, wherein the primary winding It is composed of one end connected to the voltage source for the secondary control circuit and a second transistor drive circuit connected to one end on the same polarity side, and the comparator of the PWM circuit is input to the non-inverting input terminal Comparing an output voltage signal with a reference triangular wave voltage input to an inverting input terminal and outputting a rectangular PWM signal, the OFF signal generation circuit includes a differentiation circuit for differentiating the PWM signal, and the differentiation A buffer circuit that operates in response to a differential signal output from the circuit, an anode terminal connected to the voltage source for the secondary side control circuit, and a cathode terminal at a connection point between the secondary winding and the second transistor drive circuit The output of the buffer circuit is connected to one end of the secondary winding on the side to which the second transistor drive circuit is not connected, and the differential signal is high-level. The second transistor drive circuit is configured to output a power supply voltage of a secondary-side control voltage source at a low level and to output a low level voltage when the differential signal is at a low level. When the potential of the connection point between the line and the second transistor drive circuit exceeds the power supply voltage of the secondary control voltage source when the first transistor element is turned on, the second transistor The device is configured to turn on.

The present invention also provides an inverter circuit that generates an AC voltage by intermittently switching a DC input voltage by turning on and off the main switching element, and an AC voltage generated by the inverter circuit is applied to the input winding. A main transformer that transforms the voltage and outputs it from the output winding; and a rectifying and smoothing circuit that rectifies and smoothes the voltage across the output winding, generates a DC output voltage, and supplies the load to the load. An insulation type switching power supply device that makes the output voltage constant by controlling the pulse width of on / off of the element, compares the output voltage with a reference voltage, and outputs an output voltage signal in which an error is amplified An error amplifier circuit, a comparator, and a triangular wave generation circuit that generates a reference triangular wave voltage that repeats at a predetermined cycle, and the output voltage signal and the reference triangular wave voltage A PWM circuit that outputs a PWM signal obtained by pulse-width-modulating the output voltage signal by comparing with the comparator, and an OFF that is a short-width pulse generated at a timing for turning off the main switching element based on the PWM signal An OFF signal generation circuit for generating a signal, a first signal transformer in which the OFF signal is input to the secondary winding, transmitted to the insulated primary winding, and output; and the timing at which the main switching element is turned on A basic pulse generation circuit that generates an ON signal that is a rectangular pulse having a fixed period, and a triangular wave reset signal that is a short-width pulse for resetting the reference triangular wave voltage to an initial value at the timing when the ON signal is generated. A triangular wave reset signal generation circuit to generate,
Based on the ON signal and the OFF signal, the main switching element based on the second signal transformer that the triangular wave reset signal is input to the primary winding and output from the insulated secondary winding to the triangular wave generating circuit And a drive pulse generation circuit that generates a rectangular drive pulse for turning on and off the switching power supply device.

  The drive pulse generation circuit includes a latch circuit including a set / reset flip-flop, and the set / reset flip-flop receives the ON signal as a set signal and outputs the OFF signal from the primary winding. A period in which the inverted pulse is input as a reset signal to perform processing and the drive pulse shows a high level to turn on the main switching element starts after the ON signal is generated and the pulse width period elapses. The ON signal pulse width is set wider than the sum of the triangular wave reset signal pulse width and the OFF signal pulse width.

  In addition, the switching current flowing through the main switching element is detected for each switching period, and an overcurrent signal is output to the set / reset flip-flop when the peak value of the switching current exceeds a reference value. The drive pulse generation circuit includes a circuit, receives the overcurrent signal, operates the set / reset flip-flop, and inverts the drive pulse so that the main switching element is turned off.

  According to the switching power supply of the present invention, when the OFF signal generated by the output-side OFF signal generation circuit is transmitted to the input-side drive pulse generation circuit via the signal transformer, signal transmission is performed. No phase lag occurs. Further, the reference triangular wave voltage is also a waveform that is generated in a fixed manner, and does not include an element that has a large gain variation or variation, such as the photocoupler described above. Therefore, oscillation of the entire control circuit can be easily avoided, and high-speed response can be realized. A triangular wave reset signal for operating the triangular wave generation circuit of the PWM circuit in synchronization with the drive pulse generation circuit can also be transmitted from the input side to the output side through the signal transformer. It is not necessary to provide a plurality. Furthermore, since the triangular wave reset signal and the OFF signal that pass through the signal transformer are pulse voltages that are sufficiently short with respect to the switching period, the signal transformer can be realized in a small size.

  In addition, the drive pulse generation circuit is configured with a latch circuit that includes a set / reset flip-flop, and the on-pulse width for driving the main switching element can be gradually reduced to zero, making it impossible to control. Therefore, even when the main switching element operates with a narrow ON width, it is possible to perform almost linear and stable control. Moreover, if this set / reset flip-flop is used, a pulse-by-pulse high-speed overcurrent protection circuit that limits the peak value of the switching current of the main switching element can be easily configured.

  Further, since the ON signal is generated in the input side control circuit portion and the OFF signal is generated in the output side control circuit portion, a dedicated auxiliary power source (switching power source) or battery is used as in the conventional example of Patent Document 2 described above. The switching power supply device can be started up without providing such as.

  According to the switching power supply device according to claims 4 to 6 of the present invention, a signal transformer that allows the triangular wave reset signal and the OFF signal to pass is provided separately while realizing the same high-speed response as the switching power supply device. Thus, there is no operational interference between the triangular wave reset signal generation circuit and the OFF signal generation circuit. Therefore, circuit means for preventing the interference is not required, and the configuration of the two signal generation circuits can be simplified.

1 is a block diagram showing a first embodiment of a switching power supply device of the present invention. It is a circuit diagram which shows the specific structure of 1st embodiment. 3 is a time chart for explaining the operation of the circuit of FIG. 2. It is a time chart explaining the operation | movement from which the ON time of the main switch element of 1st embodiment becomes zero. It is a circuit diagram which shows the structure which added the overcurrent detection circuit to 1st embodiment. It is the circuit diagram (a) on the input side which shows the concrete structure of the circuit of 2nd embodiment of the switching power supply device of this invention, and the circuit diagram (b) on the output side. 7 is a time chart for explaining the operation of the circuit of FIG. 6. It is a block diagram which shows 3rd embodiment of the switching power supply device of this invention. It is a circuit diagram which shows the specific structure of 3rd embodiment. 10 is a time chart for explaining the operation of the circuit of FIG. 9.

  Hereinafter, a first embodiment of a switching power supply device of the present invention will be described with reference to FIGS. The switching power supply device 10 of the first embodiment includes a power conversion circuit portion that converts an input voltage into an output voltage and supplies power to a load, and an output voltage by controlling on / off operation of a main switching element by pulse width control. Is provided with a control circuit portion for making the voltage constant.

  As shown in FIG. 1, the power conversion circuit portion is supplied with an input voltage from a DC input power supply 12, and the input circuit is intermittently connected with an inverter circuit 16 that interrupts the input voltage by ON / OFF operation of the main switching element 14. Is provided to the input winding 18a, and the output transformer 18b is provided with a main transformer 18 that outputs an insulated AC voltage. The main switch element 14 is preferably, for example, a transistor element such as an N-channel MOS FET, and is turned on when a high level voltage exceeding an ON threshold is applied between the gate and source terminals, and the low level voltage is When applied, it turns off. Further, the output winding 18 b is connected to a rectifying / smoothing circuit 22 that rectifies and smoothes the AC voltage generated at both ends thereof to generate a DC output voltage Vout and supplies power to the load 20.

  The control circuit portion is composed of an input side control circuit portion and an output side control circuit portion that are insulated from each other, and the two control circuit portions are connected via a primary winding 24a and a secondary winding 24b of the signal transformer 24. ing. The input side control circuit portion is composed of a basic pulse generation circuit 26, a triangular wave reset signal generation circuit 28, and a drive pulse generation circuit 30. The basic pulse generation circuit 26 generates and outputs an ON signal Va, which is a rectangular pulse having a predetermined period and having a predetermined pulse width that is generated when the main switching element 14 is turned on.

  The triangular wave reset signal generation circuit 28 generates and outputs a triangular wave reset signal Vb, which is a short pulse for resetting the reference triangular wave voltage Vd1 to the initial value at the timing when the ON signal Va is generated, and outputs the triangular wave reset signal Vb. Is transmitted from the primary winding 24a to the triangular wave generating circuit 42 described later via the secondary winding 24b. The drive pulse generation circuit 30 receives the ON signal Va from the basic pulse generation circuit 26 and the OFF signal Vg output from the primary winding 24a of the signal transformer 24, and receives a rectangular drive pulse that turns the main switching element 14 on and off. Vi is generated. The OFF signal Vg will be described later.

  On the other hand, the output side control circuit portion is constituted by an error amplification circuit 34, a PWM circuit 36, and an OFF signal generation circuit 38. The error amplification circuit 34 is an amplification circuit that compares the output voltage Vout with a reference voltage and outputs an output voltage signal Vd2 obtained by amplifying an error from the reference voltage. The PWM circuit 36 includes a comparator 40 and a triangular wave generation circuit 42 that generates a sawtooth reference triangular wave voltage Vd1 that is repeated at a predetermined cycle. The comparator 40 generates the output voltage signal Vd2 and the reference triangular wave voltage Vd1. By comparison, the output voltage signal Vd2 is subjected to pulse width modulation, and the PWM signal Ve which is a rectangular pulse that is inverted at the timing of turning off the main switching element 14 is output. Based on the PWM signal Ve, the OFF signal generation circuit 38 generates and outputs an OFF signal Vf, which is a short pulse indicating the timing for turning off the main switching element 14, and the OFF signal Vf is output from the secondary winding 24b. It is converted into an OFF signal Vg having a different voltage value via the primary winding 24b and transmitted to the drive pulse generation circuit 30 described above. Further, the input side control circuit portion operates by receiving the power supply voltage Vcc1 from the input side control circuit voltage source 32, and the output side control circuit portion operates from the power supply voltage Vcc2 from the output side control circuit voltage source 44. Operates in response to supply.

  The switching power supply device 10 of FIG. 1 can be configured with specific circuit elements as shown in FIG. 2, for example. Hereinafter, the configuration of the switching power supply device 10 shown in FIG. 2 will be described. In the inverter circuit 16 of the power conversion circuit portion, the main switching element 14 is connected to both ends of the DC input power supply 12 via the input winding 18a of the main transformer 18, and the input winding 18a is turned on when the main switching element 14 is on. An input voltage Vin is applied to both ends of the input winding 18a, and the input winding 18a is opened when it is off. The rectifying / smoothing circuit 22 includes a rectifying circuit 22a composed of two diode elements for rectifying a voltage generated in the secondary winding 18b when the main switching element 14 is ON, and a high-frequency cutoff filter having an LC filter configuration. And a smoothing circuit 22b for smoothing. That is, this power conversion circuit part is a general single-ended forward type single-stone converter circuit.

  The triangular wave reset signal generation circuit 28 includes a differentiating circuit 50 for differentiating the ON signal Va and a first transistor element 52 to which a triangular wave reset signal Vb, which is a differential output of the differentiating circuit 50, is input between the base and emitter terminals. Has been. When the ON signal Va is input, the differentiating circuit 50 outputs a triangular wave reset signal Vb that is a pulse having a shorter width than the ON signal Va at a timing when the signal is inverted from a low level to a high level. Here, the differentiation circuit 50 in which a low-frequency cutoff filter is configured by a series circuit of a capacitor and a resistor is used. However, for example, a configuration of a pulse width shortening circuit formed by combining various gate circuits and passive elements may be used. . Here, an NPN transistor is used as the first transistor element 52, and is turned on when the triangular wave reset signal Vb is at a high level and turned off when the triangular wave reset signal Vb is at a low level.

  The primary winding 24 a of the signal transformer 24 has one end connected to the dot-side control circuit voltage source 32 and the other end connected to the collector terminal of the first transistor element 52. Therefore, when a high-level triangular wave reset signal Vb is input to the first transistor element 52, a pulse voltage having the same pulse width as that of the triangular wave reset signal Vb and a peak value of Vcc1 is generated at both ends of the primary winding 24a. .

  A diode 54 connected in parallel to the primary winding 24a is a diode that operates during reset to release the excitation energy of the signal transformer 24. The primary and secondary windings 24a and 24b are in the negative direction (on the dot-attached side). By preventing the occurrence of a high voltage on the opposite side), a reset operation that suppresses the occurrence of a ringing voltage in the forward direction (the side with dots) and prevents the signal transformer 24 from being demagnetized is performed. Helps to ensure smooth operation. The diode 54 may be deleted as necessary.

  The drive pulse generation circuit 30 has a configuration of a latch circuit using a general set / reset flip-flop 55 (hereinafter referred to as RS-FF 55) and an AND gate 56 (hereinafter referred to as AND 56). . The RS-FF 55 is composed of a knot gate 1 (hereinafter referred to as NOT 1) and two NAND gates 1 and 2 (hereinafter referred to as NAND 1 and 2) in which inputs and outputs are connected to each other. The output of NOT1 is connected to the second input of NAND1. The output of the basic pulse generation circuit 26 is connected to the input of NOT1, and the ON signal Va is handled as a set signal. Further, the second input of the NAND 2 is connected to one end of the primary winding 24a of the signal transformer 24 on which the dot is not attached, and the OFF signal Vg is handled as an inverted signal of the reset signal.

  At the output of NAND1, a voltage signal Vh is generated as a result of the logical operation. The voltage signal Vh can be directly used as a drive pulse for the main switching element 14, but here, an AND 56 is further provided, and the output of the NAND 1 and the output of the NOT 1 are input to the AND 56 and output from the AND 56. This voltage signal is used as the drive pulse Vi for the main switching element 14. By configuring the gate using the AND 56 in this manner, the high level period of the drive pulse Vi (the period in which the main switching element 14 is turned on) starts after the high level period of the ON signal Va has elapsed. Is set.

  In the output side control circuit portion, the output voltage Vout is used as the power supply voltage Vcc2. In the switching power supply device 10, when the input voltage Vin is input, the input-side control circuit voltage source 32 that receives power supply from the input voltage Vin generates the power supply voltage Vcc1, and the above-described input-side control circuit portion operates. Start. That is, the on / off operation of the main switching element 14 can be started regardless of the operation state of the output side control circuit portion. Therefore, since the output-side control circuit voltage source 44 may be established after the main switching element 14 starts to be turned on / off, a dedicated auxiliary circuit as in the DC-DC converter according to the conventional example of Patent Document 2. There is no need to provide a power supply (switching power supply). Therefore, here, a simple output-side control circuit voltage source 44 that uses the output voltage Vout as it is as the power supply voltage Vcc2 is provided. When the output voltage Vout has a voltage value that is not suitable as the power supply voltage Vcc2, the power supply voltage Vcc2 may be obtained by a simple method such as providing a third winding in the main transformer 18. The error amplifying circuit 34 includes an operational amplifier 57 that operates by receiving power supply from the output-side control circuit voltage source 44, and outputs of two voltage dividing resistors 58 that divide the output voltage Vout are applied to the inverting input terminal of the operational amplifier 57. It is connected. Further, a Zener diode 60a having a cathode terminal connected to the non-inverting input terminal of the operational amplifier 57 and an anode terminal connected to the ground, and a resistor 60b for supplying a bias current from the output-side control circuit voltage source 44 to the Zener diode 60a A reference voltage generation circuit 60 is provided, and the reference voltage generation circuit 60 supplies a reference voltage determined by the Zener voltage of the Zener diode 60a toward the non-inverting input terminal of the operational amplifier 57. Further, a feedback circuit 62 for adjusting the gain and phase of signal amplification is connected between the inverting input terminal and the output terminal of the operational amplifier 57. The error amplifying circuit 34 outputs an output voltage signal Vd2 that is an analog signal that is a voltage obtained by inverting and amplifying an error between the output voltage Vout and the reference voltage, and that continuously changes in a range equal to or lower than the power supply voltage Vcc2. .

  The comparator 40 of the PWM circuit 36 receives the output voltage signal Vd2 from the output of the error amplifier circuit 34 at the non-inverting input terminal. On the other hand, the reference triangular wave voltage Vd1 is input from the output of the triangular wave generating circuit 42 to the inverting input terminal. The comparator 40 outputs a high level during a period when the reference triangular wave voltage Vd1 is lower than the output voltage signal Vd2, and outputs a low level during a high period. At this time, since the comparator 40 operates by receiving power supply from the power supply voltage Vcc2, the high level voltage becomes substantially equal to the power supply voltage Vcc2.

  The triangular wave generating circuit 42 of the PWM circuit 36 includes a timer capacitor 64 connected between the inverting input terminal of the comparator 40 and the ground, and a charging resistor for supplying a charging current from the output-side control circuit voltage source 44 to the timer capacitor 64. 66, a second transistor element 68 that is an NPN transistor connected in parallel to the timer capacitor 64, and a second transistor element drive circuit 70 that drives the base terminal of the second transistor element 68.

  The second transistor element drive circuit 70 includes a Zener diode 70a having a cathode terminal connected to one end of the secondary winding 24b of the signal transformer 24 on the dot-attached side, an anode terminal of the Zener diode 70a, and a ground. The voltage dividing resistor 70 b is provided between the two voltage dividing resistors 70 b, and the connection point between the two voltage dividing resistors 70 b is connected to the base terminal of the second transistor element 68. The triangular wave reset signal Vc applied to the cathode terminal of the Zener diode 70a is set so that the second transistor element 68 is turned on when the first transistor element 52 is turned on and exceeds the power supply voltage Vcc2. ing.

  The second transistor element 68 is turned on by being driven by the second transistor element driving circuit 70, and the voltage across the timer capacitor 64 is instantaneously reduced by short-circuiting both ends of the timer capacitor 64 to reset the voltage. Thereafter, when the second transistor 68 is turned off and both ends of the timer capacitor 64 are released, a charging current flows into the timer capacitor 64 via the charging resistor 66, and the voltage across the timer capacitor 64 aims at the power supply voltage Vcc2. To rise. By repeating this operation, a sawtooth basic triangular wave voltage Vd1 is generated at both ends of the timer capacitor 64 and output to the comparator 40. Accordingly, the basic triangular wave voltage Vd1 has a constant waveform that does not depend on the input voltage Vin or the output current supplied to the load 20.

  The OFF signal generation circuit 38 receives a differentiation circuit 72 for differentiating the PWM signal Ve, and a differentiation signal from the differentiation circuit 72, and outputs a signal to one end of the signal transformer 24 on the side of the secondary winding 24b where no dot is attached. And a diode 76 having an anode terminal connected to the secondary-side control circuit voltage source 44 and a cathode terminal connected to one end of the secondary winding 24b on the dot-attached side. Yes.

  When the PWM signal Ve is input, the differentiating circuit 72 outputs a differential signal that is a low-level pulse having a width shorter than that of the PWM signal at the timing of inversion from the high level to the low level. Here, the differentiation circuit 72 in which a low-frequency cutoff filter is configured by a series circuit of a capacitor and a resistor is used. However, for example, a configuration of a pulse width shortening circuit formed by combining various gate circuits and passive elements may be used. .

  The buffer circuit 74 is a buffer element that operates by receiving a voltage supply from the voltage source 44 for the secondary side control circuit, and outputs the input voltage to a low impedance. Therefore, the OFF signal Vf which is the output signal becomes the power supply voltage Vcc2 which is a high level voltage when the output of the differentiating circuit 72 is at a high level, and becomes almost zero voltage only during a period in which the differential signal is at a low level.

  The diode 76 is provided on the side where the dots of the secondary winding 24b of the signal transformer 24 are attached during the period excluding the period in which the first transistor element 52 is turned on and the triangular wave reset signal Vc is generated in the secondary winding 24b. One end of the power supply voltage is held at the power supply voltage Vcc2. Therefore, when the OFF signal Vf indicates a short low level, the power supply voltage Vcc2 is generated in the positive direction (dotted side) at both ends of the secondary winding 24b, and the positive direction is applied to the primary winding 24a. A voltage is generated at the doted side. Then, the positive voltage generated in the primary winding 24 when the OFF signal Vf is at the low level is input to the drive pulse generation circuit 30 as the above-described OFF signal Vg.

  Next, the operation of the switching power supply device 10 shown in FIG. 2 will be described based on the time chart of FIG. Here, for convenience of explanation, it is assumed that the power supply voltage Vcc1 and the power supply voltage Vcc2 are equal to Vcc, and the number of turns of the primary and secondary windings 24a and 24b of the signal transformer 24 is equal to each other. Further, each transistor element in the control circuit portion is ignored because the saturation voltage when turned on is sufficiently small and the forward voltage of the diode 76 is also sufficiently small. The outputs of the comparator 40 and the buffer circuit 74 have a low level of zero voltage. Similarly, the high level is equal to the power supply voltage Vcc, and the delay time of output inversion is sufficiently short and can be ignored.

  As shown in FIG. 3, the switching power supply device 10 operates at a constant switching frequency (period T). Hereinafter, the operation within one cycle T will be described by being divided into periods T1 to T5.

  In the period T1, the ON signal Va output from the basic pulse generation circuit 26 is inverted from the low level to the high level. The ON signal Va is a fixed signal that is inverted from the low level to the high level every time the period T1 starts and that is inverted to the low level when a predetermined time tck elapses. The differentiating circuit 50 of the triangular wave reset signal generating circuit 28 passes the high level ON signal Va and generates a high level triangular wave reset signal Vb between the base and emitter of the first transistor element 52. Then, the first transistor element 52 is turned on, and a positive voltage Vcc is generated at both ends of the secondary winding 24b of the signal transformer 24.

  At this time, the voltage at one end of the secondary winding 24b to which no dot is attached is Vcc by the operation of the buffer circuit 74 as shown in the waveform of the OFF signal Vf. The triangular wave reset signal Vc that appears as a voltage at one end on the side to which the dot 24b is attached has a peak value that is twice as high as Vcc. Then, the second transistor element driving circuit 70 turns on the second transistor element 68, and the reference triangular wave voltage Vd1, which is the voltage across the timer capacitor 64, drops to the initial zero voltage, which is a so-called reset state.

  When the reference triangular wave voltage Vd1 drops to zero voltage, the output voltage signal Vd2 generated in a DC manner becomes a higher voltage, so that the PWM signal Ve output from the comparator 40 is inverted from the low level to the high level. . However, even if the PWM signal Ve is inverted, the output of the buffer circuit 74 continues to be at a high level, and the OFF signal Vf remains at a high level. Therefore, a signal for turning off the main switching element 14 is not generated in the primary winding 24a.

  As shown in the waveform of the OFF signal Vg, the voltage at one end where the dot of the primary winding 24a is not attached is changed from the high level (voltage Vcc) to the low level when the first transistor element 52 is turned on. Invert. Then, the low level OFF signal Vg is input to the drive pulse generation circuit 30. When the ON signal Va and the OFF signal Vg are input to the drive pulse generation circuit 30, the output signal Vh of the RS-FF 55 is inverted from the low level to the high level. However, since the drive pulse Vi remains at a low level by the above-described operation of the AND 56, the main switching element 14 continues to be turned off.

  In the period T2, the ON signal Va continues to be high level, but the triangular wave reset signal Vb is inverted to low level by the operation of the differentiating circuit 50. When the triangular wave reset signal Vb becomes low level, the first transistor element 52 is turned off, and the primary winding 24a of the signal transformer 24 is opened. At this time, one end of the secondary winding 24b on the side to which the dot is attached is held at the voltage Vcc by the conduction of the diode 76, and the voltage on the other end on the side to which the dot is not attached is also increased by the operation of the buffer circuit 74. Since it is Vcc, the voltage across the windings 24a and 24b is almost zero. The voltage value of the triangular wave reset signal Vc that appears as the voltage at one end of the secondary winding 24b to which dots are attached becomes Vcc. Then, the second transistor element driving circuit 70 turns off the second transistor element 68, and the reset state of the timer capacitor 64 is released.

  When the second transistor element 68 is turned off, a charging current flows into the timer capacitor 64 via the charging resistor 66, and the reference triangular wave voltage Vd1 starts to rise according to a time constant determined by the timer capacitor 64 and the charging resistor 66. However, since the output voltage signal Vd2 is higher than the reference triangular wave voltage Vd1 during the period T2, the PWM signal Ve, which is the output of the comparator 40, continues to be at a high level, and the output of the buffer circuit 74 is also high. The level continues, and the OFF signal Vf remains high and does not change.

  When the first transistor element 52 is turned off, the voltage at both ends of the primary winding 24a becomes substantially zero voltage as the voltage at both ends of the secondary winding 24b. As shown in the waveform of the OFF signal Vg, the voltage is inverted from the low level to the high level. Even if the ON signal Va and the inverted OFF signal Vg are input to the drive pulse generation circuit 30, the output signal Vh of the RS-FF 55 continues to be at a high level by the latch function, and the drive pulse Vi that is the output of the AND 56 also has a low level. continue.

  In the period T3, the ON signal Va is inverted from the high level to the low level. At this time, since the high-level triangular wave reset signal Vb is not output from the differentiating circuit 50 of the triangular wave reset signal generation circuit 28, the first transistor element 52 continues to be turned off. Therefore, the output side control circuit portion and the signal transformer 24 continue the operation in the period T2, and the OFF signal Vg does not change. When the ON signal Va and the OFF signal Vg are input to the drive pulse generation circuit 30, the output signal Vh of the RS-FF 55 continues to be high level, but the output of NOT1 is inverted from low level to high level. As a result, the drive pulse Vi is inverted from the low level to the high level. Then, the main switching element 14 turns on.

  In the period T4, the rising reference triangular wave voltage Vd1 exceeds the output voltage signal Vd2, and the PWM signal Ve output from the comparator 40 is inverted from the high level to the low level. Then, the PWM signal Ve is input to the buffer circuit 74 through the differentiation circuit 72, the output of the buffer circuit 74 is inverted from the high level to the low level, and the OFF signal Vf becomes zero voltage. Further, the voltage at one end of the secondary winding 24b on which the dots are attached is held at the voltage Vcc as shown by the waveform of the triangular wave reset signal Vc.

  On the other hand, since the ON signal Va and the triangular wave reset signal Vb are kept at the low level, the first transistor element 52 is kept off. Accordingly, the voltage at both ends of the primary winding 24a is generated in the positive direction as the voltage Vcc at both ends of the secondary winding 24b, and the voltage at one end of the primary winding 24a without the dot is applied to the OFF signal Vg. As shown in the waveform, the high level is inverted to the low level. When the ON signal Va and the OFF signal Vg are input to the drive pulse generation circuit 30, the output signal Vh of the RS-FF 55 is inverted from the high level to the low level, and the drive pulse Vi output from the AND 56 is also changed from the high level to the low level. Invert to. Therefore, the main switching element 14 turns off.

  In the period T5, the PWM signal Ve continues to be at the low level, but the input of the buffer circuit 74 is inverted to the high level by the operation of the differentiating circuit 72. Therefore, the output of the buffer circuit 74 is inverted from the low level to the high level, and the OFF signal Vf becomes Vcc. In addition, the voltage at one end of the secondary winding 24b on which the dots are attached is held at the voltage Vcc as shown by the waveform of the triangular wave reset signal Vc.

  On the other hand, since the ON signal Va and the triangular wave reset voltage Vb are kept at the low level, the first transistor element 52 is kept off. Therefore, the voltage across the primary winding 24a is zero voltage, as is the voltage across the secondary winding 24b, and the voltage at one end of the primary winding 24a without a dot is shown in the waveform of the OFF signal Vg. Thus, the low level is inverted to the high level. When the ON signal Va and the OFF signal Vg are input to the drive pulse generating circuit 30, the output signal Vh of the RS-FF 55 continues to be low level, and the drive pulse Vi that is the output of the AND 56 also continues to be low level. Accordingly, the main switching element 14 continues to be turned off.

  Then, the operation in the above-described periods T1 to T5 is repeated, the time ratio between the on-period (periods T3, T4) and the off-time (periods T1, T2, T5) of the main switching element 14 is controlled, and the output voltage Vout It becomes.

  As described above, the switching power supply 10 transmits the OFF signal Vf generated by the OFF signal generation circuit 38 to the drive pulse generation circuit 32 on the input side via the signal transformer 24. At this time, the phase delay of the transmission is transmitted. Therefore, high-speed response can be realized, and oscillation of the entire control circuit can be easily avoided.

  By the way, when the input voltage Vin increases or the output current decreases, the switching power supply 10 shortens the period T3 by reducing the output voltage signal Vd2 that is the output of the error amplifying circuit 26. Control to narrow the ON width is performed to suppress the output voltage Vout from rising. Then, when the on-time of the main switching element 14 is controlled in a very short state, a characteristic operation as shown in FIG. 4 is performed. Hereinafter, an operation in which the ON time of the main switching element 14 is controlled to be narrowed and the ON time becomes zero will be described with reference to FIG.

  In the time chart of FIG. 4, there is no ON period (T3, T4) of the main switching element 14. Further, the operations in the period 1 and the period 5 are the same as those in FIG. However, the operation in the period (period T2) from when the triangular wave reset signal Vb is inverted from the high level to the low level until the ON signal Va is inverted from the high level to the low level is different from that in FIG. Hereinafter, the period T2 in which the characteristic operation is performed will be described by being divided into periods T21, T22, and T23.

  Note that the switching power supply device 10 is configured such that the total value of the pulse width tb (high level period) of the triangular wave reset signal Vb and the pulse width Vf (low level period) of the OFF signal Vf is the pulse width Tck of the ON signal Va. It is set to be shorter than (high level period). Further, the OFF signal Vf is set so as to be generated after the triangular wave reset signal Vb changes from the high level to the low level, so that the OFF signal Vf and the triangular wave reset signal Vb do not overlap. These are conditions for performing an appropriate operation, and the purpose and action thereof will also be described in the following operation description.

  In the period 21, an operation similar to that in the period 2 in FIG. 3 is performed. That is, the ON signal Va continues to be high level, but the triangular wave reset signal Vb is inverted to low level by the operation of the differentiation circuit 50. Then, the triangular wave reset signal Vc, which is the voltage at one end of the secondary winding 24b, is lowered to the voltage Vcc, the reset state of the timer capacitor 64 is released, and the reference triangular wave voltage Vd1 starts to rise. However, since the output voltage signal Vb is always set to be higher than the reset triangular voltage value of the reference triangular wave voltage Vd1, the output voltage signal Vd2 is always higher than the reference triangular wave voltage Vd1 during the period T21. High voltage. Therefore, the PWM signal Ve continues to be at the high level, and the OFF signal Vf remains at the high level Vcc. Since the voltage at both ends of the primary winding 24a becomes almost zero voltage as the voltage at both ends of the secondary winding 24b, the OFF signal Vg is inverted from the low level to the high level. When the ON signal Va and the OFF signal Vg are input to the drive pulse generation circuit 30, the output signal Vh of the RS-FF 55 continues to be high level, and the drive pulse Vi that is the output of the AND 56 also continues to be low level.

  In period T22, the rising reference triangular wave voltage Vd1 exceeds the output voltage signal Vd2 before the ON signal Va is inverted to the low level, and the PWM signal Ve output from the comparator 40 is inverted from the high level to the low level. To do. Then, the PWM signal Ve is input to the buffer circuit 74 through the differentiation circuit 72, the output of the buffer circuit 74 is inverted from the high level to the low level, and the OFF signal Vf becomes zero voltage. Further, the voltage at one end of the secondary winding 24b on which the dots are attached is held at the voltage Vcc as shown by the waveform of the triangular wave reset signal Vc.

  On the other hand, the ON signal Va continues to be high level, the triangular wave reset signal Vb continues to be low level, and the first transistor element 52 continues to be turned off. Therefore, the voltage Vcc in the positive direction is generated in the voltage across the primary winding 24a, as is the voltage across the secondary winding 24b, and the voltage at one end of the primary winding 24a without the dot is OFF. As shown in the waveform of the signal Vg, the high level is inverted to the low level. When the ON signal Va and OFF signal Vg are input to the drive pulse generation circuit 30, the output signal Vh of the RS-FF 55 is inverted from the high level to the low level, but the drive pulse Vi that is the output of the AND 56 continues to be at the low level. To do. Therefore, the main switching element 14 continues to be turned off.

  In the period T23, the PWM signal Ve continues to be low level, but the input to the buffer circuit 74 is inverted to high level by the operation of the differentiating circuit 72. Therefore, the output of the buffer circuit 74 is inverted from the low level to the high level, and the OFF signal Vf becomes Vcc. Further, the voltage at one end of the secondary winding 24b on which the dots are attached is held at the voltage Vcc as shown by the waveform of the triangular wave reset signal Vc.

  On the other hand, since the ON signal Va continues to be high level and the triangular wave reset signal Vb continues to be low level, the first transistor element 52 continues to be turned off. Therefore, the voltage across the primary winding 24a is zero voltage, as is the voltage across the secondary winding 24b, and the voltage at one end of the primary winding 24a without a dot is shown in the waveform of the OFF signal Vg. Thus, the low level is inverted to the high level. When the ON signal Va and the inverted OFF signal Vg are input to the drive pulse generation circuit 30, the output signal Vh of the RS-FF 55 continues to be low level, and the drive pulse Vi that is the output of the AND 56 also continues to be low level. Therefore, the main switching element 14 continues to be turned off. Also in the period T5, as in the period T5 in FIG. 3, the main switching element 14 continues to be turned off.

  With the above operation, the drive pulse Vi becomes a low level in all the periods T1, T2 (T21, T22, T23) and T5, and the ON width of the main switching element 14 can be made zero. Therefore, in the process in which the output voltage signal Vd2 shifts from the high state shown in FIG. 3 to the low state shown in FIG. 2, the operation of gradually reducing the ON width to zero is performed. There is no case where the ON width cannot be shortened below a certain level and control becomes impossible unlike the DC-DC converter. Further, even when the main switching element 14 operates with a narrow ON width, it is possible to perform a substantially linear and stable pulse width control.

  As can be seen from the above description of the operation, the pulse width tb (high level period) of the triangular wave reset signal Vb and the OFF signal Vf are used in order to linearly control the operation of gradually reducing the ON width to zero. The drive pulse Vi is set while the total value with the pulse width Vf (low level period) is set shorter than the pulse width Tck (high level period) of the ON signal Va and the ON signal Va is high level. This is realized by applying a gate with AND 56 of the drive pulse generation circuit 30 so as not to invert to the high level. However, for example, in the case of a switching power supply device or the like in which the rectifier circuit 22a is configured by a synchronous rectifier capable of conducting in both directions and the main switching element 14 does not operate with a narrow on-width, the above conditions need not be satisfied. Therefore, the configuration in which the gate is gated by the AND 56 may be deleted, and the output signal Vh of the NAND 1 may be used as it is as the drive pulse Vi.

  As can be seen from the above description of the operation, the condition for setting the OFF signal Vf to be generated after the triangular wave reset signal Vb changes from the high level to the low level is that two signal transformers 24 have two conditions. This is a condition necessary for preventing the signals Vf and Vb from interfering with each other. Further, when the RS-FF 55 of the drive pulse generation circuit 30 receives the high level ON signal Va and the low level OFF signal Vg at the same time, there is also a problem that the output becomes unstable. Therefore, this condition must be satisfied in order to avoid malfunction of the main switching element 14.

  Further, the triangular wave reset signal Vb and the OFF signal Vf are preferably short pulses. Here, the short width means the pulse width tb (high level period) of the triangular wave reset signals Vb and Vc determined by the differentiation circuit 50 and the pulse width tf (low level) of the OFF signal Vf determined by the differentiation circuit 72. ) Is as short as possible. If the pulse widths tb and tf are shortened, the magnetic flux generated in the magnetic core of the signal transformer 24 can be kept small. Therefore, the signal transformer 24 having a predetermined inductance and saturation characteristics is small with a relatively small magnetic core. The number of windings 24a and 24b can be used, and the signal transformer 24 can be realized in a small size at low cost. On the other hand, the triangular wave reset signal Vb and the OFF signal Vf can be distinguished from noise and must not be able to be accurately transmitted as a signal even if there is a parasitic capacitance in the signal transformer 24. Therefore, it is necessary to secure a certain pulse width. Therefore, it is desirable to set the triangular wave reset signal Vb and the OFF signal Vf to a short width of about 10 to 100 nsec.

  In addition, by shortening the pulse widths tb and tf, the pulse width tck (high level period) of the ON signal Va can be set shorter. Since the switching power supply 10 is a period in which the main switching element 14 cannot be turned on during the period of the pulse width tck, the maximum on-width of the main switching element 14 can be increased by reducing the pulse width Tck. Therefore, the controllable range of the pulse width control can be expanded by setting the pulse widths tb, tf and tck short and widening the maximum ON width of the main switching element 14.

  Next, a modification of the switching power supply device 10 of FIG. 2 will be described based on FIG. Here, the same components as those in FIG. The switching power supply 10 of the modification shown in FIG. 5 is added with a pulse-by-pulse overcurrent protection circuit that monitors the switching current flowing in a pulsed manner in addition to the configuration of FIG.

  A general switching power supply device is provided with an overcurrent protection circuit that limits an output current to a predetermined value or less in order to prevent a load burnout accident when the load fails. Although the location where the overcurrent is detected can be selected in various ways, it is often performed by observing the switching current flowing through the main switching element. This is because if the increase in the switching current is limited, the output current can be limited, and at the same time, the failure of the switching power supply itself including the main switching element can be avoided. In particular, the pulse-by-pulse overcurrent protection that observes the switching current every pulse for each switching cycle and instantaneously turns off the main switching element when the peak value exceeds a predetermined reference value provides excellent high-speed response. It is suitable for protecting semiconductor elements such as main switching elements.

  As shown in FIG. 5, the switching power supply device 10 is provided with an overcurrent detection circuit 80 that detects whether or not it is in an overcurrent state by observing a switching current flowing through the main switching element 14. The overcurrent detection circuit 80 is inserted between the source terminal of the main switching element 14 and the ground, divides the current detection resistor 82 that converts the switching current into a voltage, the comparator 83, and a constant power supply voltage Vcc, A voltage dividing resistor 84 that supplies a reference voltage to the non-inverting input terminal of the comparator 83 and an RC filter 86 that removes noise superimposed on the voltage across the current detection resistor 82 and outputs it to the inverting input terminal of the comparator 83. It is configured. The output of the comparator 83 is connected to the third input of the NAND 2 of the drive pulse generating circuit 30. Other configurations are the same as those in FIG.

  In the current switching power supply device 10 of FIG. 5, when an appropriate switching current flows, the output of the comparator 83 continues to be at a high level and does not hinder the operation described with reference to FIGS. 3 and 4. However, when the switching current increases due to a load failure or the like, the peak value of the pulse voltage generated in the current detection resistor 82 increases, and when the voltage exceeds the reference voltage output by the voltage dividing resistor 84, the output of the comparator 83 is increased. Is instantaneously inverted, and a low level is input to NAND2. Then, the drive pulse Vi output from the AND 56 is inverted from the high level to the low level, and the main switching element 14 is turned off. When the main switching element 14 is turned off, the switching current stops flowing, so the output of the comparator 83 is inverted from the high level to the low level. However, the ON signal Va is set to the high level by the latch operation of the drive pulse generation circuit 30. The main switching element 14 continues to be turned off until the next period T to be reversed starts. This operation is performed regardless of the state of the OFF signal Vg, which is a signal for making the output voltage constant, and when an overcurrent is detected, the output voltage Vout also decreases simultaneously.

  As described above, the drive pulse generation circuit 30 has a configuration of a latch circuit including the RS-FF 55. Therefore, by adding the overcurrent detection device 80 having a simple configuration, a high-speed pulse-by-pulse method The current protection circuit can be easily configured. In addition, since the ON width of the main switching element can be reduced to zero in principle, it is possible to easily avoid the problem that the output current rapidly increases when the output voltage droops, that is, the problem of the output current. be able to.

  Next, a second embodiment of the switching power supply device according to the present invention will be described with reference to FIGS. Here, the same configuration as that of the above-described switching power supply device 10 is denoted by the same reference numeral, and description thereof is omitted. As shown in FIG. 6, the switching power supply device 90 of the second embodiment includes an inverter circuit 16, a main transformer 18, and a rectifying / smoothing circuit 22, which are power conversion circuit portions, in a general half-bridge type two-stone type. It has a converter circuit configuration. Further, the input side control circuit portion includes a two-output drive pulse generation circuit 94 for driving the two main switching elements 92a and 94b, and further includes an overcurrent detection circuit 96. Other configurations are the same as those of the switching power supply circuit 10.

  As shown in FIG. 6A, the inverter circuit 16 has a series circuit of main switching elements 92a and 92b connected to both ends of the DC input power supply 12, and the high side is the main switching element 92a and the low side is the main circuit. This is a switching element 92b. Similarly, it has a series circuit of two capacitors 96a and 96b connected to both ends of the DC input power supply 12, with the high side being a capacitor 96a and the low side being a capacitor 96b. The input winding 18a of the main transformer 18 is connected between the connection point of the main switching elements 92a and 92b and the connection point of the capacitors 96a and 96b.

  Further, as shown in FIG. 6B, the main transformer 18 has two secondary windings 18b, and the rectifying / smoothing circuit 22 generates all voltages generated in the two secondary windings 18b by two diodes. A rectifier circuit 98a that rectifies the wave and a smoothing circuit 98b that smoothes the rectified voltage with a high-frequency cutoff filter of an LC filter configuration are provided.

  The main switching elements 92a and 92b operate alternately every switching period T, and the on / off operation performed in one period T is the same as the operation performed by the main switching element 14 of the switching power supply device 10. Further, in the period T in which the main switching element 92a is turned on / off, the other main switching element 92b is continuously turned off. Conversely, in the period T in which the main switching element 92b is turned on / off, the other The main switching element 92a is continuously turned off. Then, the switching power supply device 90 applies the same pulse width control as that of the switching power supply device 10 to the main switching element 92a and the main switching element 92b alternately at every switching period T, thereby making the output voltage Vout constant. be able to. Therefore, the signal transformer 24, the triangular wave reset signal generation circuit 28, the error amplification circuit 34, the PWM circuit 36, and the OFF signal generation circuit 38 (not shown) in the switching power supply 90 have the same configuration as that of the switching power supply 10. .

  The drive pulse generation circuit 94 generates drive pulses Vk and Vj that cause the main switching elements 92a and 92b to operate alternately every switching period T. Specifically, in addition to the configuration of the RS-FF 55 and AND 56 included in the drive pulse generation circuit 30 described above, a trigger flip-flop 100 (hereinafter referred to as T-FF 100) and two AND gates 102 and 104 (hereinafter referred to as “T-FF 100”). ANDs 102 and 104) are connected as shown in FIG. Then, drive pulses Vk and Vj are generated at the outputs of the ANDs 102 and 104, and the drive pulse Vk is input to the drive terminal of the main switching element 92a via the high-side drive means 106 such as an insulating transformer. Directly input to the drive terminal of the element 92b.

  In addition, the switching power supply 90 is provided with a pulse-by-pulse overcurrent protection circuit that monitors the switching current that flows in a pulsed manner. Each of the switching currents of the main switching elements 92a and 92b flows in the input winding 18a of the transformer 18, and the flowing direction is inverted every switching period T. Therefore, in addition to the configuration of the overcurrent detection circuit 80 described above, the overcurrent detection circuit 96 includes a current transformer 108 that outputs the switching current flowing through the input winding 18a of the main transformer 18 by performing a turns ratio conversion, and a current transformer. A rectifier circuit 110 for full-wave rectifying the output current 108 is connected as shown in FIG. 6, and the current output from the rectifier circuit 110 is converted into a voltage by the current detection resistor 82 and input to the RC filter 86. ing. Accordingly, the switching current flowing through the two main switching elements 92a and 92b can be observed by one overcurrent detection circuit 96.

  The operation in which the switching power supply 90 performs the pulse width control is as shown in the time chart of FIG. That is, the operations of the signals Va, Vb, Vc, Vd1, Vd2, Ve, Vf, Vg, Vh, Vi of each part are the same as those shown in FIG. 3, but the drive pulse generation circuit 90 further includes an ON signal. Va and the output signal Vi are input to the T-FF 100 and the ANDs 102 and 104 for processing, and drive pulses Vj and Vk for the two main switching elements 92a and 92b are generated. Then, as shown in FIG. 7, the drive pulse Vj generated during the previous cycle T shows the same operation as the signal Vi of the previous cycle T, and the drive pulse Vk generated during the subsequent cycle T. Indicates the same operation as the signal Vi of the subsequent period T.

  In this way, even if the power conversion circuit portion has a configuration of a two-stone converter circuit exemplified as a half-bridge type, if configured in a latch circuit including the RS-FF 55 such as the drive pulse generation circuit 94, The same excellent effect as described in the one-stone converter circuit such as the switching power supply device 10 can be obtained. Further, even if the configuration of the four-stone converter circuit exemplified by the full bridge type is used, the same effect as the switching power supply devices 10 and 90 can be obtained if a four-output drive pulse generation circuit of the same concept is configured. Can be obtained.

  Next, a third embodiment of the switching power supply device according to the present invention will be described with reference to FIGS. Here, the same configuration as that of the above-described switching power supply device 10 will be described with the same reference numerals. As shown in FIG. 8, the power conversion portion of the switching power supply 110 of the third embodiment has an inverter circuit 16, an input winding 18a, and an output winding 18b, similar to the switching power supply 10 described above. It comprises a transformer 18 and a rectifying / smoothing circuit 22.

  The control circuit part is composed of an input side control circuit part and an output side control circuit part which are insulated from each other, and the two control circuit parts are a primary winding 112a and a secondary winding 112b of the first signal transformer 112, and The second signal transformer 114 is connected via a primary winding 114a and a secondary winding 114b. The input side control circuit portion is composed of a basic pulse generation circuit 26, a triangular wave reset signal generation circuit 28, and a drive pulse generation circuit 30. The basic pulse generation circuit 26 is the same as that of the switching power supply device 10 described above.

  The triangular wave reset signal generation circuit 28 generates and outputs a triangular wave reset signal Vb, which is a short pulse for resetting the reference triangular wave voltage Vd1 to an initial value at the timing when the ON signal Va is inverted to a high level, and resets the triangular wave. The signal Vb is transmitted from the primary winding 114a of the second signal transformer 114 to the triangular wave generation circuit 42 via the secondary winding 114b. The drive pulse generation circuit 30 receives the ON signal Va from the basic pulse generation circuit 26 and the OFF signal Vg output from the primary winding 112a of the first signal transformer 112, and turns the main switching element 14 on and off. Drive pulse Vi is generated.

  On the other hand, the output side control circuit portion is configured by an error amplifier circuit 34, a PWM circuit 36, and an OFF signal generation circuit 120. The error amplifier circuit 34 is an amplifier circuit that compares the output voltage Vout with a reference voltage and outputs an output voltage signal Vd2 obtained by amplifying an error from the reference voltage. The PWM circuit 36 includes a comparator 40 and a triangular wave generation circuit 42 that generates a sawtooth reference triangular wave Vd1 that is repeated at a predetermined period. The comparator 40 compares the output voltage signal Vd2 with the reference triangular wave Vd1. As a result, the output voltage signal Vd2 is subjected to pulse width modulation, and the PWM signal Ve, which is a rectangular pulse that is inverted at the timing of turning off the main switching element 14, is output. Based on the PWM signal Ve, the OFF signal generation circuit 120 generates and outputs an OFF signal Vf that is a rectangular pulse that is inverted when the main switching element 14 is turned off. The OFF signal Vf is output from the first signal transformer. The secondary winding 112 b of 112 is converted to an OFF signal Vg via the primary winding 112 b and transmitted to the drive pulse generation circuit 30. Further, the input side control circuit portion operates by receiving the supply voltage Vcc1 from the input side control circuit voltage source 32, and the output side control circuit portion receives the supply voltage from the output side control circuit voltage source 44. The operation is performed with the supply of Vcc2.

  The switching power supply device 110 can be configured with specific circuit elements as shown in FIG. 9, for example. Hereinafter, the configuration of the switching power supply device 110 shown in FIG. 9 will be described. The inverter circuit 16, the main transformer 18, and the rectifying / smoothing circuit 22 in the power conversion circuit portion are general single-ended forward type one-stone converter circuits. The triangular wave reset signal generation circuit 28 has a function of receiving the ON signal Va of the basic pulse generation circuit 26 in the input side control circuit portion and outputting the triangular wave reset signal Vb, and has the same configuration as that of the switching power supply device 10. .

  The primary winding 114a of the second signal transformer 114 has one end connected to the dot-side control circuit voltage source 32 and the other end connected to the collector terminal of the first transistor element 52. ing. Therefore, when the triangular wave reset signal Vb is input to the first transistor element 52, a pulse voltage having the same pulse width as that of the triangular wave reset signal Vb and a peak value of Vcc1 is generated at both ends of the primary winding 24a.

  The drive pulse generation circuit 30 is the same as the switching power supply device 10 described above. The output of the basic pulse generation circuit 26 is connected to the input of NOT1, and the ON signal Va is handled as a set signal. The second input of the NAND 2 is connected to one end of the primary winding 114 a of the second signal transformer 114 on the side where no dot is attached, and the OFF signal Vg is handled as an inverted signal of the reset signal. And the drive pulse Vi for driving the main switching element 14 is output from the output of AND56.

  In the output side control circuit portion, the output voltage Vout is used as the power supply voltage Vcc2. If this is the configuration of the switching power supply device 110, the switching element 14 can start the on / off operation when the input is turned on without providing a dedicated auxiliary power supply (switching power supply) as in Patent Document 2. Because. The error amplifying circuit 34 is a voltage obtained by inverting and amplifying an error between the output voltage Vout and the reference voltage, and has a function of outputting an output voltage signal Vd2 that continuously changes in a range equal to or lower than the power supply voltage Vcc2. The configuration is the same as that of the power supply device 10. The comparator 40 of the PWM circuit 28 receives the output voltage signal Vd2 from the output of the error amplifying circuit 34 at the non-inverting input terminal and the triangular wave generating circuit 42 at the inverting input terminal, as in the switching power supply device 10. A reference triangular wave voltage Vd1 is input from the output. Therefore, a high level (voltage Vcc) is output during a period when the reference triangular wave voltage Vd1 is lower than the output voltage signal Vd2, and a low level is output during a high period. The triangular wave generation circuit 34 of the PWM circuit 28 receives the triangular wave reset signal Vc, the second transistor element 68 resets the voltage across the timer capacitor 64, and then the second transistor 68 is turned off and the both ends of the timer capacitor 64. And has a function of generating a sawtooth reference triangular wave voltage Vd1, and the configuration is the same as that of the switching power supply device 10 described above.

The secondary winding 112 b of the first signal transformer 112 has one end connected to the dot side connected to the output-side control circuit voltage source 44 and the other end connected to the output of the buffer circuit 74. Similarly to the switching power supply device 10, the OFF signal generation circuit 120 receives a differential circuit 72 for differentiating the PWM signal Ve and a differential signal of the differential circuit 72, and a dot of the secondary winding 24 b of the signal transformer 24 is attached. A buffer circuit 74 for outputting a signal is provided at one end of the non-side, but the diode 76 is omitted. Therefore, the OFF signal Vf which is the output signal becomes the power supply voltage Vcc2 which is a high level voltage when the output of the differentiating circuit 72 is at a high level, and becomes almost zero voltage only during a period in which the differential signal is at a low level.
The primary winding 112 a of the first signal transformer 112 has one end with a dot attached to the input side control circuit voltage source 32 and the other end connected to the input of the NAND 2 of the drive pulse generation circuit 30. . Accordingly, when the OFF signal Vf indicates a short low level, a voltage is generated in the primary winding 112a in the positive direction (dotted side). The positive voltage generated in the primary winding 112a when the OFF signal Vf is at a low level is input to the drive pulse generation circuit 30 as the OFF signal Vg described above.

  The operation in which the switching power supply 110 performs the pulse width control is as shown in the time chart of FIG. The operation of each signal Va, Vb, Vc, Vd1, Vd2, Ve, Vf, Vh, Vi is the same as that shown in FIG. 3, but only the OFF signal Vg is different, and the triangular wave reset signal Vc is sent to the signal transformer 114. The generated period T1 also maintains the high level. This is because the signal transformer for transmitting the triangular wave reset signal and the signal transformer for transmitting the OFF signal are provided separately and do not interfere with each other.

  As described above, since the switching power supply device 110 includes the two signal transformers 112 and 114, there is no operational interference between the triangular wave reset signal generation circuit 28 and the OFF signal generation circuit 120. It is not necessary to add an auxiliary circuit for avoiding unstable operation due to the above, and the circuit configuration can be further simplified. Further, since the two signal transformers 112 and 114 only need to have a performance capable of passing a short-width pulse, both can be configured to be small and inexpensive.

  The switching power supply device of the present invention is not limited to the above embodiment. For example, the triangular wave reset signal generation circuit and the OFF signal generation circuit may be any circuit that has a function of generating a predetermined pulse signal at both ends of the winding of the signal transformer based on the input pulse signal. The transformer excitation circuit can be selected as appropriate. Further, the triangular wave generating circuit can be freely changed as long as it is configured to generate a reference triangular wave voltage for PWM modulation that can be reset based on a triangular wave reset signal.

  Further, the logic of each signal for control is not necessarily the same as the operation illustrated in FIG. 3, FIG. 7, and FIG. 10, and a predetermined logic for turning on / off the main switching element 14 by the drive pulse Vi is shown. If the time during which the high level voltage is applied to the secondary winding of the signal transformer is short, the circuit configuration may be such that the high level and the low level of each signal are in opposite phases. .

  Further, the input side control circuit portion and the output side control circuit portion may be integrated and provided in a microcomputer provided with an analog / digital converter (A / D converter), a clock, a CPU, a memory, and the like.

10, 90, 110 Switching power supply device 14, 92a, 92b Main switching element 16 Inverter circuit 18 Main transformer 18a Input winding 18b Output winding 22 Rectifier smoothing circuit 22a, 98a Rectifier circuit 22b, 98b Smoothing circuit 24 Signal transformer 24a Primary winding Line 24b Secondary winding 26 Basic pulse generation circuit 28 Triangular wave reset signal generation circuit 30, 94 Drive pulse generation circuit 32 Voltage source for input side control circuit 34 Error amplification circuit 36 PWM circuit 38, 120 OFF signal generation circuit 40 Comparator 42 Triangular wave generation circuit 44 Output side control circuit voltage source 50 Differentiation circuit 52 First transistor element 54 Diode 58 Voltage dividing resistor 57 Operational amplifier 60 Reference voltage generation circuit 62 Feedback circuit 64 Timer capacitor 66 Charging resistor 68 Second transistor element 70 Second run Star element drive circuit 72 differentiation circuit 74 buffer circuit 76 diode 80 overcurrent detection circuit 82 current detection resistor 83 comparator 84 voltage dividing resistor 86 RC filter 96a, 96b capacitor 106 high side drive means 108 current transformer 110 rectifier circuit 112 first Signal transformer 112a Primary winding 112b Secondary winding 114 Second signal transformer 114a Primary winding 114b Secondary winding Va ON signal Vb, Vc Triangular wave reset signal Vd1 Reference triangular wave voltage Vd2 Error amplification circuit Ve PWM signals Vf, Vg OFF signal Vi, Vk, Vj Drive pulse Vcc, Vcc1, Vcc2 Power supply voltage

Claims (6)

An inverter circuit that generates an AC voltage by intermittently switching a DC input voltage by turning on and off the main switching element;
An AC voltage generated by the inverter circuit is applied to the input winding, a main transformer that transforms the AC voltage and outputs it from the output winding;
A rectifying / smoothing circuit for rectifying and smoothing the voltage across the output winding, generating a DC output voltage and supplying power to the load;
In an insulation type switching power supply device that makes the output voltage constant by controlling on / off of the main switching element by pulse width control,
An error amplification circuit that compares the output voltage with a reference voltage and outputs an output voltage signal obtained by amplifying an error; and
Comprising a comparator and a triangular wave generating circuit for generating a reference triangular wave voltage that repeats at a predetermined cycle, and comparing the output voltage signal and the reference triangular wave voltage with the comparator, the output voltage signal is pulse width modulated. A PWM circuit for outputting the PWM signal,
An OFF signal generation circuit that generates an OFF signal that is a short pulse generated at a timing of turning off the main switching element based on the PWM signal;
A signal transformer for inputting the OFF signal to the secondary winding and transmitting the OFF signal to the isolated primary winding;
A basic pulse generating circuit for generating an ON signal which is a rectangular pulse having a fixed period generated at a timing of turning on the main switching element;
A triangular wave reset signal that is a short pulse for resetting the reference triangular wave voltage to an initial value at a timing when the ON signal is generated is generated, and the triangular winding reset signal is transmitted through the primary winding and the secondary winding of the signal transformer. A triangular wave reset signal generating circuit for output to the triangular wave generating circuit;
A drive pulse generation circuit that generates a rectangular drive pulse for turning on and off the main switching element based on the ON signal and the OFF signal;
The error amplifying circuit, the PWM circuit, and the OFF signal generation circuit are configured so that the OFF signal is generated after the triangular wave reset signal is generated and the period of the pulse width has elapsed, and before the next triangular wave reset signal is generated. A switching power supply device configured to generate The drive pulse generation circuit includes a latch circuit including a set / reset flip-flop, and the set / reset flip-flop receives the ON signal as a set signal and outputs the OFF signal from the primary winding. An inverted signal is input as a reset signal and processed
In order to turn on the main switching element, the period in which the drive pulse is at a high level is gated to start after the ON signal is generated and the period of the pulse width has elapsed,
2. The switching power supply device according to claim 1, wherein a pulse width of the ON signal is set wider than a sum of a pulse width of the triangular wave reset signal and a pulse width of the OFF signal. The triangular wave reset signal generation circuit is turned on when a differentiation circuit for differentiating the ON signal and a differentiation signal output from the differentiation circuit are input between its own drive terminal and ground terminal, and the differentiation signal is at a high level. It is composed of a first transistor element,
One end of the primary winding of the signal transformer is connected to a voltage source for a primary side control circuit, and the other end that outputs the OFF signal is connected to a collector terminal of the transistor element,
The error amplifier circuit is configured to invert and amplify an output voltage to output an output voltage signal,
The triangular wave generating circuit of the PWM circuit includes a series circuit of a charging resistor and a timer capacitor, a second transistor element connected to both ends of the timer capacitor, and one end of the secondary winding of the signal transformer. A first transistor connected to the primary-side control circuit voltage source of the primary winding and a second transistor drive circuit connected to one end of the same polarity side,
The comparator of the PWM circuit is configured to compare the output voltage signal input to the non-inverting input terminal with the reference triangular wave voltage input to the inverting input terminal and output a rectangular PWM signal.
The OFF signal generation circuit has a differentiation circuit that differentiates the PWM signal, a buffer circuit that operates in response to a differentiation signal output from the differentiation circuit, and an anode terminal connected to a voltage source for a secondary side control circuit, It consists of a diode whose cathode terminal is connected to the connection point between the secondary winding and the second transistor drive circuit, and the output of the buffer circuit is connected to the second transistor drive circuit of the secondary winding The power supply voltage of the secondary control voltage source is output when the differential signal is high level, and the low level voltage is output when the differential signal is low level. And
The second transistor drive circuit is configured such that a potential at a connection point between the secondary winding and the second transistor drive circuit is such that when the first transistor element is turned on, the secondary-side control voltage source 3. The switching power supply device according to claim 1, wherein the second transistor element is turned on when a power supply voltage is exceeded. An inverter circuit that generates an AC voltage by intermittently switching a DC input voltage by turning on and off the main switching element;
An AC voltage generated by the inverter circuit is applied to the input winding, a main transformer that transforms the AC voltage and outputs it from the output winding;
A rectifying / smoothing circuit for rectifying and smoothing the voltage across the output winding, generating a DC output voltage and supplying power to the load;
In an insulation type switching power supply device that makes the output voltage constant by controlling on / off of the main switching element by pulse width control,
An error amplification circuit that compares the output voltage with a reference voltage and outputs an output voltage signal obtained by amplifying an error; and
Comprising a comparator and a triangular wave generating circuit for generating a reference triangular wave voltage that repeats at a predetermined cycle, and comparing the output voltage signal and the reference triangular wave voltage with the comparator, the output voltage signal is pulse width modulated. A PWM circuit for outputting the PWM signal,
An OFF signal generation circuit that generates an OFF signal that is a short pulse generated at a timing of turning off the main switching element based on the PWM signal;
A first signal transformer, wherein the OFF signal is input to the secondary winding and transmitted to the insulated primary winding for output;
A basic pulse generating circuit for generating an ON signal which is a rectangular pulse having a fixed period generated at a timing of turning on the main switching element;
A triangular wave reset signal generating circuit that generates a triangular wave reset signal that is a short-width pulse for resetting the reference triangular wave voltage to an initial value at a timing when the ON signal is generated;
A second signal transformer that inputs the triangular wave reset signal to the primary winding and outputs the insulated secondary winding to the triangular wave generating circuit;
A switching power supply device comprising: a drive pulse generating circuit that generates a rectangular drive pulse for turning on and off the main switching element based on the ON signal and the OFF signal. The drive pulse generation circuit includes a latch circuit including a set / reset flip-flop, and the set / reset flip-flop receives the ON signal as a set signal and outputs the OFF signal from the primary winding. An inverted signal is input as a reset signal and processed
In order to turn on the main switching element, the period in which the drive pulse is at a high level is gated to start after the ON signal is generated and the period of the pulse width has elapsed,
5. The switching power supply device according to claim 4, wherein a pulse width of the ON signal is set wider than a sum of a pulse width of the triangular wave reset signal and a pulse width of the OFF signal. An overcurrent detection circuit that detects a switching current flowing through the main switching element for each switching period and outputs an overcurrent signal toward the set / reset flip-flop when a peak value of the switching current exceeds a reference value; Prepared,
6. The drive pulse generation circuit according to claim 2, 3 or 5, wherein the drive pulse generation circuit receives the overcurrent signal and operates the set / reset flip-flop to invert the drive pulse so that the main switching element is turned off. The switching power supply device described.

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