JP5255902B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device that outputs a DC stabilized voltage / current that is insulated from an input power supply side, and more particularly to a switching power supply that achieves a reduction in switching element loss, a reduction in size and cost, and a stable startability. Relates to the device.

  Conventionally, a composite resonance type series converter circuit is known as a small-sized and high-efficiency switching power supply as described above. FIG. 10 shows a main circuit configuration according to the prior art, and FIG. 11 shows waveforms of main parts.

  In this switching power supply device, a series circuit of switching elements Q1 and Q2 (hereinafter referred to as power MOSFET) is connected between both terminals of the DC input power supply E, and a capacitor C0 is connected. A series resonant circuit of an inductor L, a primary winding L11 of the output transformer T, and a resonant capacitor C1 is formed between the connection point of the power MOSFETs Q1 and Q2 and one end of the DC input power supply E, and the power Capacitor C2 is connected in parallel with either MOSFET Q1 or Q2 (in FIG. 10, one end of DC input power source E is connected to the low voltage side, and capacitor C2 is connected in parallel to power MOSFET Q2). Also, diodes D1 and D2 are connected in antiparallel to power MOSFETs Q1 and Q2, respectively (in many cases, they are also used as body diodes for power MOSFETs Q1 and Q2).

  Further, an intermediate tap is provided in the output winding of the output transformer T and divided into two (L21, L22), and a full-wave rectifier circuit is formed by diodes D3 and D4 that rectify their outputs, and between the intermediate taps. A smoothing capacitor C3 and a DC load Load are connected. The power MOSFETs Q1 and Q2 are alternately turned ON / OFF at a preset frequency in consideration of the complex resonance condition by the control unit 1 shown as a block. Therefore, the control unit 1 has a high-frequency oscillation function, a function of alternately driving the two power MOSFETs Q1 and Q2, and a function of setting a dead time period for turning off the two power MOSFETs Q1 and Q2. A feedforward, feedback control function and output variable function for controlling voltage, current, and power are provided.

  Referring to FIG. 11, Vg1 and Vg2 indicate drive signals for power MOSFETs Q1 and Q2 set in advance by control unit 1. A dead time period in which both are turned ON / OFF alternately and both are turned OFF is set. VQ1, IQ1 and VQ2, IQ2 indicate the drain-source voltage and drain current of the power MOSFETs Q1, Q2. When the drive signal Vg1 is High, the drain current IQ1 flows through the power MOSFET Q1, and when it is Low, the voltage VQ1 substantially equal to the DC input power source E is applied (the same applies to the power MOSFET Q2). In the dead time period, the drain-source voltages VQ1 and VQ2 have rising and falling waveforms with an arbitrary slope due to the effect of the capacitor C2, the inductor L, and the excitation inductance of the output transformer T. Further, the drain currents IQ1 and IQ2 have a series resonance current waveform set approximately by the inductor L and the resonance capacitor C1, and these combined currents are generated between the inductor L, the primary winding L11 of the output transformer T, and the resonance capacitor C1. This is the current of the series resonant circuit. VC1 represents the voltage waveform of the resonant capacitor C1, and has a waveform delayed in phase from the current of the series resonant circuit. ID3 and ID4 indicate current waveforms of the output rectifier diodes D3 and D4. The relationship between the drive frequency of the power MOSFETs Q1 and Q2 and the series resonance frequency of the inductor L and the resonance capacitor C1 is expressed as “resonance frequency> drive. By satisfying the condition of “frequency”, it is possible to set the current of one of the diodes D3 and D4 to flow after the current of one of the diodes D3 and D4 has finished flowing. Not transmitted. That is, during the period in which no current flows through the diodes D3 and D4, the secondary side of the output transformer T is considered to be unloaded, and the primary side excitation inductance L of the output transformer T is connected in series with the series resonance circuit on the primary side. As a result of the insertion and switching of the series resonance condition, inflection points are also found in the waveforms of the drain currents IQ1 and IQ2.

  In such a complex resonance type series converter, ZVS (zero voltage switching), that is, a condition setting such that a current starts to flow after the applied voltage of the switching elements Q1 and Q2 is reduced is possible, and switching loss is extremely small. Since the recovery loss of the secondary side rectifier diodes D3 and D4 can be avoided, high frequency can be achieved with high efficiency. Further, since the voltage / current waveform at the time of switching is stable and the ringing of the secondary side rectifier diodes D3 and D4 can be suppressed, the noise is also excellent.

  The above-described prior art is a so-called separately-excited switching power supply that drives the two switching elements Q1 and Q2 by setting the frequency in advance with an oscillator while having such various features. A level shifter to the switching element Q1 on the potential side is necessary, and from the viewpoint of frequency followability and loss, there is a technical problem regarding high frequency in reducing the size of the output transformer T (the current level shifter has a limit of about 500 kHz) In addition, due to cost problems, self-excited studies as shown in Patent Documents 2 to 4, for example, have been made.

  FIG. 12 is a diagram showing an example of a voltage feedback self-excited separately excited composite resonance series converter using power MOSFETs Q1 and Q2 in the same manner. It should be noted that the output transformer T1 is provided with feedback windings L13 and L12, and the feedback windings L13 and L12 are positively fed back to the gate terminals of the power MOSFETs Q1 and Q2 through the gate resistors R1 and R2, respectively. By connecting in the obtained direction, the self-excited oscillation operation is continued.

An activation circuit IGN based on relaxation oscillation is added. The starter circuit IGN forms a series circuit of a resistor R3 and a capacitor C5 between both terminals of the DC input power supply E, and connects these connection points to the gate terminal of the power MOSFET Q2 via the Sidac Q3. As a result, when the potential of the capacitor C5 reaches the breakdown voltage, the Sidac Q3 is turned on, and the charge of the capacitor C5 is discharged through the Sidak Q3, the gate resistor R2, and the feedback winding L12. At this time, the gate resistor R2 is discharged. When the generated voltage drop becomes equal to or higher than the threshold voltage Vth of the gate terminal of the power MOSFET Q2, the power MOSFET Q2 is turned on for a moment, and the charge of the resonant capacitor C1 charged in advance through the resistor R4 is the primary winding of the output transformer T1. Discharge occurs through line L11 and choke coil (inductor) L. As a result of the oscillation of the discharge current of the resonant capacitor C1, a feedback voltage equal to or higher than the gate threshold voltage Vth of the power MOSFET Q1 is obtained in the feedback winding L13, and oscillation is started by a positive feedback action. In this starting circuit IGN, in order to charge the resonant capacitor C1 at the time of starting as described above, a resistor R4 that bypasses the high-side power MOSFET Q1 and a diode D5 that draws current from the resistor R3 are provided.
Japanese Patent No. 2734296 Japanese Patent No. 3371595 JP 2002-262568 A JP 2006-129548 A

FIG. 13 shows the waveform of each part at the time of startup. FIG. 13A shows the potential Vc1 of the resonance capacitor C1 constituting the composite resonance circuit. When the power is turned on, the DC capacitor is charged up to the DC input power supply voltage E with the time constant of the resistor R4 and the resonance capacitor C1. . FIG. 13B shows the potential Vc5 of the capacitor C5 constituting the starter circuit IGN. When the power is turned on, the resistor R3 and the capacitor C5 are charged with a time constant. During the charging, the potential Vc5 is reaches the breakdown voltage _{V BO} of SIDAC Q3, the charge of the capacitor C5 and the SIDAC Q3 is turned ON to discharge the potential Vc5 of the capacitor C5 drops rapidly. When the discharge current value in this case becomes equal to or less than the holding current (valley current) of the Sidac Q3, the Sidac Q3 is turned off, charging from the resistor R3 starts again from that point, and this operation is repeated until the converter is started (said Dac The voltage that turns OFF when Q3 is equal to or lower than the holding current is represented by Voff).

  Such a voltage feedback type self-excited converter may be difficult to start. This difficulty in starting is caused by the capacitor components connected to the outputs of the respective windings of the output transformer T1, and naturally no electric charge exists in these capacitor components when the power is turned on. For this reason, even when the power is turned on and a start pulse is applied from the start circuit IGN and the power MOSFET Q2 is turned on, it is absorbed by various capacitors and a sufficient feedback voltage cannot be obtained in the auxiliary winding L13. Arise. FIG. 13C shows the gate voltage Vg2 of the power MOSFET Q2 when starting is possible, and FIG. 13D shows the case where starting is not expected. Note that the most influential capacitor connected to each winding of the output transformer T1 is a smoothing capacitor C3.

  An object of the present invention is to provide a switching power supply device that can be reliably started in a voltage feedback self-excited complex resonance series converter that can realize a significant circuit simplification and cost reduction compared to other excitation types. Is to provide.

  In the switching power supply device of the present invention, a series circuit composed of first and second switching elements is connected between both terminals of the DC input power supply, and the connection point between the first and second switching elements and the DC input power supply A series resonant circuit composed of an inductor, a resonant capacitor, and a primary winding of an output transformer is connected between one terminal and the secondary side of the output transformer obtained by switching of the first and second switching elements. The induced current is rectified and smoothed by a diode and a smoothing capacitor and output, and the voltage induced in the first and second auxiliary windings of the output transformer is applied to the control terminals of the first and second switching elements. Switching power supply comprising a voltage feedback self-excited composite resonant series converter that continues switching at A starting circuit for applying a starting pulse to one control terminal of the first and second switching elements, and an amplifying means for expanding the induced voltage of the auxiliary winding corresponding to the other of the first and second switching elements And a function limiting means for stopping the function of the amplifying means after activation.

  According to the above configuration, the switching elements are turned on by applying the induced voltages of the first and second auxiliary windings to the control terminals of the first and second switching elements through the gate resistors, respectively. In a switching power supply device comprising a voltage feedback type self-excited complex resonance series converter that is continuously driven by / OFF driving, a starting circuit for applying a starting pulse to one control terminal of the first and second switching elements is provided. In addition, the other of the first and second switching elements is provided with an amplifying means for expanding the induced voltage of the corresponding auxiliary winding and a function limiting means for stopping the function of the amplifying means after activation.

  Therefore, even at the start-up time when the induced voltage of the auxiliary winding becomes small, the induced voltage expanded by the amplifying means is inputted to the switching element on the side opposite to the side where the start pulse is inputted. The function limiting means restricts the amplitude of the control terminals of the first and second switching elements to a prescribed level when the steady oscillation is started, which causes destruction of the element. There is nothing. In this way, the voltage feedback type self-excited complex resonance series converter capable of greatly simplifying the circuit and reducing the cost as compared with the separately excited type can be reliably started.

Preferably, the function limiting means comprises a limiter for limiting the induced voltage of the auxiliary winding .

In a preferred embodiment, the function limiting means comprises a detection circuit that detects that steady oscillation has occurred and stops the amplification means .

  In the switching power supply device of the present invention, the start-up circuit corresponds to a control power supply, a relaxation oscillation circuit energized by the control power supply, and an induced voltage of one of the first and second auxiliary windings. An oscillation detection circuit for determining whether or not a predetermined level at which the switching element to be switched can be switched has been reached, and the relaxation oscillation in response to a determination result of the oscillation detection circuit and not reaching the predetermined level A logic circuit that applies an oscillation signal of the circuit to the corresponding switching element as a start signal and blocks the oscillation signal of the relaxation oscillation circuit from being applied to the corresponding switching element when the predetermined level is reached. Features.

  According to the above configuration, the starting circuit includes a control power source, a relaxation oscillation circuit energized by the control power source, and an induced voltage of one of the first and second auxiliary windings. An oscillation detection circuit for determining whether one of the second auxiliary windings has reached a predetermined level at which the corresponding switching element can be switched; and in response to a determination result of the oscillation detection circuit, During the period when the level has not been reached, the oscillation signal of the relaxation oscillation circuit is applied as an activation signal to the corresponding switching element, and when the level reaches the predetermined level, the oscillation signal of the relaxation oscillation circuit is not applied to the corresponding switching element. And a logic circuit to be blocked.

  Therefore, it is possible to easily set an appropriate start-up condition by setting the resistance of the relaxation oscillation circuit that generates a sawtooth wave or a rectangular wave by charging or discharging a capacitor or inductor via a resistor.

  Furthermore, in the switching power supply device of the present invention, the oscillation detection circuit stops the operation of the relaxation oscillation circuit when an induced voltage of at least one of the first and second auxiliary windings reaches the predetermined level. It is characterized by making it.

  According to the above configuration, since the operation of the relaxation oscillation circuit is stopped during steady self-excited oscillation, power saving can be achieved.

Further, in the switching power supply apparatus of the present invention, the pulse width of the pulse input to the logic circuit, said not more than the series resonant circuit half the resonance period of, and the period of the pulse is the resonant capacitor to start It is characterized by being equal to or more than the time constant to be charged in advance.

  According to the above configuration, when the start pulse is given from the relaxation oscillation circuit to the control terminal of the switching element, the timing of the start pulse is important, and if sufficient charge is not stored in the resonant capacitor, the auxiliary winding by the start pulse is used. Since the other switching element cannot be turned on by the induced voltage of the line, the selection can be made assuredly by starting as described above.

  As described above, the switching power supply device of the present invention applies the induced voltages of the first and second auxiliary windings to the control terminals of the first and second switching elements through the gate resistors, respectively. In a switching power supply device composed of a voltage feedback type self-excited complex resonance series converter which is continuously driven by ON / OFF driving of these switching elements, it is activated at one control terminal of the first and second switching elements. A start circuit for providing a pulse is provided, and the other of the first and second switching elements has an amplifying means for expanding the induced voltage of the corresponding auxiliary winding, and a function for stopping the function of the amplifying means after starting. Limiting means.

  Therefore, even at the time of start-up where the induced voltage of the auxiliary winding becomes small, the induced voltage expanded by the amplifying means is inputted to the switching element on the side opposite to the side where the start pulse is inputted. Since the function limiting means regulates the amplitude of the first and second switching elements to a specified level at the control terminal of the first and second switching elements, the element can be destroyed. There is no invitation. In this way, the voltage feedback type self-excited complex resonance series converter capable of greatly simplifying the circuit and reducing the cost as compared with the separately excited type can be reliably started.

  In the switching power supply device of the present invention, as described above, the starting circuit includes a control power supply, a relaxation oscillation circuit energized by the control power supply, and one of the first and second auxiliary windings. An oscillation detection circuit for determining whether the induced voltage has reached a predetermined level at which one of the first and second auxiliary windings can switch the corresponding switching element, and determination of the oscillation detection circuit In response to the result, an oscillation signal of the relaxation oscillation circuit is applied as an activation signal to the corresponding switching element during a period in which the predetermined level has not been reached, and when the predetermined level is reached, the oscillation signal of the relaxation oscillation circuit corresponds to And a logic circuit that blocks the switching element from being applied.

  Therefore, it is possible to easily set an appropriate starting condition by setting the resistance of the relaxation oscillation circuit that generates a sawtooth wave or a rectangular wave by charging or discharging a capacitor or an inductor via a resistor.

  Furthermore, as described above, the switching power supply device according to the present invention is configured such that the oscillation detection circuit causes the relaxation oscillation when the induced voltage of at least one of the first and second auxiliary windings reaches the predetermined level. Stop circuit operation.

  Therefore, the operation of the relaxation oscillation circuit is stopped during steady self-excited oscillation, so that power saving can be achieved.

The switching power supply device of the present invention, as described above, the pulse width of the pulse input to the logic circuit is 1/2 or less of the resonance period of the series resonance circuit and the resonance capacitor the period of the pulse More than the time constant that is charged prior to startup.

  Therefore, the activation can be surely performed.

[Embodiment 1]
FIG. 1 is a block diagram of a switching power supply device which is a voltage feedback type self-excited complex resonance series converter according to a first embodiment of the present invention. This switching power supply device is intended to reduce the loss of the switching elements Q1 and Q2, and to reduce the size and cost, and to increase the frequency of the operation. The basic configuration uses the start-up circuit IGN based on the relaxation oscillation. This is the same as the switching power supply device shown in FIG. That is, between both terminals of the DC input power supply E, a power source smoothing capacitor C0 is connected to a series circuit of switching elements Q1 and Q2 (hereinafter referred to as power MOSFET), and the power MOSFET Q1 is bypassed at startup. Thus, a resistor R4 for charging the resonant capacitor C1 is connected. A series resonance circuit of an inductor L, a primary winding L11 of the output transformer T1, and the resonance capacitor C1 is formed between a connection point of the power MOSFETs Q1 and Q2 and one end of the DC input power supply E, and A capacitor C2 is connected in parallel with one of the power MOSFETs Q1 and Q2 (FIG. 1 shows an example in which one end of the DC input power source E is connected to the low voltage side and the capacitor C2 is connected in parallel to the power MOSFET Q2). Further, diodes are connected in antiparallel to the power MOSFETs Q1 and Q2, respectively (in FIG. 1, the body diodes of the power MOSFETs Q1 and Q2 are also used and omitted).

  Further, an intermediate tap is provided in the output winding of the output transformer T1 and divided into two (L21, L22), and a full-wave rectifier circuit is formed by diodes D3 and D4 that rectify their outputs, and between the intermediate taps. A smoothing capacitor C3 and a DC load Load are connected. Further, the output transformer T1 is provided with a first auxiliary winding L12, the opposite polarity side of the primary main winding L11 is connected to the gate of the power MOSFET Q2 via the gate resistor R2, and the auxiliary winding L12 is generated. The power MOSFET Q2 is configured to be able to be self-excited with voltage. As for the gate drive circuit of the high-voltage side power MOSFET Q1, a second auxiliary winding L13 is provided in the output transformer T1, and the gate resistor R1 is connected to the same polarity side as the primary main winding L11 from the amplifier 12 and the limiter 11 described later. The power MOSFET Q1 is connected to the gate of the power MOSFET Q1 through a voltage generated in the auxiliary winding L13 so that the power MOSFET Q1 can be driven by self-excitation. Thus, the power MOSFETs Q1 and Q2 are alternately turned ON / OFF by the feedback voltages from the two auxiliary windings L13 and L12, and the self-excited oscillation is continued.

  The starting circuit IGN forms a series circuit of a resistor R3 and a capacitor C5 between both terminals of the DC input power source E, and connects these connection points to the gate terminal of the power MOSFET Q2 via the Sidac Q3. Become.

  As a result, when the potential of the capacitor C5 reaches the breakdown voltage, the Sidac Q3 is turned on, and the charge of the capacitor C5 is discharged through the Sidak Q3, the gate resistor R2, and the feedback winding L12. At this time, the gate resistor R2 is discharged. When the generated voltage drop becomes equal to or higher than the threshold voltage Vth of the power MOSFET Q2, the power MOSFET Q2 is turned on for a moment, and the charge of the resonance capacitor C1 charged in advance through the resistor R4 is changed to the primary winding L11 of the output transformer T1 and Discharge through a choke coil (inductor) L. As a result of the oscillation of the discharge current of the resonant capacitor C1, a feedback voltage equal to or higher than the threshold voltage Vth of the power MOSFET Q1 is obtained in the feedback winding L13, and oscillation is started by a positive feedback action. The above configuration is similar to the switching power supply device shown in FIG. 13 which is a voltage feedback type self-excited composite resonance series converter.

  It should be noted that in the present embodiment, when a starting pulse is applied from the starting circuit IGN to the gate of the power MOSFET Q2 as described above, a large induced voltage is obtained in the feedback winding L13 on the power MOSFET Q1 side. The amplifier 12 as an amplifying means is provided, and the limiter 11 as a function limiting means for stopping the function by the amplification after activation is provided.

  FIG. 2 is a waveform diagram for explaining the operation at the time of activation. A start pulse equal to or higher than the threshold voltage Vth of the power MOSFET Q2 as shown in FIG. 2A is given from the start circuit IGN to the gate of the power MOSFET Q2, and the power MOSFET Q2 is turned on. Thus, in the configuration shown in FIG. 12 described above, even if the voltage induced in the feedback winding L13 does not reach the threshold voltage Vth of the power MOSFET Q1 as shown in FIG. The voltage induced in the feedback winding L13a by the amplifier 12 as described above can be increased to the threshold voltage Vth or more as shown in FIG. In FIG. 2B and FIG. 2C, the start pulse is observed as a negative value, and a positive voltage is observed as a rebound of the start pulse. This rebound voltage is shown in FIG. As shown in FIG. 2, if the threshold voltage Vth of the power MOSFET Q1 is not reached, it dampens and disappears. As shown in FIG. 2C, when the rebound voltage momentarily reaches the threshold Vth, the power MOSFET Q1 is turned on momentarily. The induced voltage is increased by the positive feedback, and it starts at once. In this way, the induced voltage of the feedback winding L13 is reduced by the limiter 11 to a voltage not less than the allowable value Vmax of the power MOSFET Q2 and not less than the threshold voltage Vth, as shown in FIG. Oscillation can be continued stably within the range of VLim.

  With this configuration, in the voltage feedback self-excited composite resonance series converter that can realize a significant circuit simplification and cost reduction compared to the separate excitation type, when switching the power MOSFET Q2 by the start pulse, Even if only a small pulse is induced in the feedback winding L13 due to the influence of the discharging smoothing capacitor C3, the other power MOSFET Q1 can be reliably turned on and started.

[Embodiment 2]
FIG. 3 is a block diagram of a switching power supply device that is a voltage feedback self-excited complex resonance series converter according to a second embodiment of the present invention. This switching power supply device is similar to the switching power supply device shown in FIG. 1 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. It should be noted that although the amplifier 12 is used in the present embodiment, the induced voltage of the feedback winding L13 becomes equal to or higher than the threshold voltage Vth of the power MOSFET Q1 instead of the limiter 11 as function limiting means. A detection circuit 13 for detecting the completion of the activation and stopping the amplifier 12 is provided. A momentary overvoltage is absorbed by the Zener diodes ZD1 and ZD2 provided between the gate and source of the power MOSFET Q1.

  FIG. 4 is an electric circuit diagram showing a specific configuration example of the amplifier 12 and the detection circuit 13. In the amplifier 12, a weakly induced voltage generated at the time of start-up generated in the feedback winding L13 is supplied to the base of the npn transistor Q11 at the first stage via the resistor R11, and the transistor Q11 is turned on, so that the control power supply Vcc The base current of the second stage pnp transistor Q12 flows through the diode D11 and the resistor R12, and the transistor Q12 is turned ON, so that the control power supply Vcc passes through the transistor Q12 and the diode D12 to the gate of the power MOSFET Q1. An amplified start-up voltage is provided.

  On the other hand, in the detection circuit 13, when oscillation is started after startup, a DC voltage is generated in the capacitor C 11 via the diode D 13 and the resistor R 13. When this voltage reaches the Zener voltage of the Zener diode ZD 3, As a result of turning on the transistor Q13 via R18 and the Zener diode ZD3, the base-emitter of the transistor Q11 is short-circuited, so that the amplifier 12 including the transistors Q11, Q12, etc. is stopped. The diode D14 is for preventing reverse voltage. With such a configuration, the configuration described with reference to FIG. 3 can be realized relatively easily, the same operation as in FIG. 2 described above can be realized, and the operation can be reliably started.

  FIG. 5 is a circuit diagram of the configuration shown in FIG. 4 in order to prevent the amplified start pulse applied to the gate of the power MOSFET Q1 during start-up from being absorbed by the gate resistor R1 and the feedback winding L13 in series with the gate resistor R1. A capacitor C12 is provided, and a diode D15 provided in parallel with the capacitor C12 prevents the influence of the capacitor C12 after activation. With such a configuration, startup is more reliable.

  FIG. 6 shows that, in the amplifier 12a, instead of amplification to a predetermined level (Vcc- (VD12 + VQ12), where VD12 is the ON voltage of the diode D12 and VQ12 is the ON voltage of the transistor Q12) by the transistors Q11 and Q12, Amplification to an arbitrary level is performed by the operational amplifier OP. The weak induced voltage generated in the feedback winding L13 at the time of start-up is input to the + terminal of the operational amplifier OP via the protective resistor R13, the speed-up capacitor C13, and the discharge resistor R14, and the + terminal has a divided voltage. A resistor R15 and a reverse voltage preventing diode D14 are also connected. The output of the operational amplifier OP is given to the gate of the power MOSFET Q1 through the diode D12, and is divided by the feedback resistor R17 and the resistor R16 and fed back to the negative terminal of the operational amplifier OP.

  After startup, in the same manner as described above, in the detection circuit 13, the feedback voltage obtained in the feedback winding L13 is rectified and smoothed by the diode D13, the resistor R13, and the capacitor C11, and the DC voltage of the capacitor C11 becomes the zener diode ZD3. When the Zener voltage is reached, the transistor Q13 is turned ON to short-circuit the + terminal of the operational amplifier OP, and the amplification operation is stopped. As described above, the capacitor C12 prevents the starting pulse from being consumed by the gate resistor R1, and the Zener diode ZD3 in parallel with the capacitor C12 prevents the influence of the capacitor C12 after starting. When a comparator is used in place of the operational amplifier OP, a voltage obtained by dividing the control power supply Vcc by resistors R17 and R16 is applied as a reference potential to the negative terminal of the comparator, and the rest is substantially the same as in FIG. It becomes the composition of.

[Embodiment 3]
FIG. 7 is a block diagram of a switching power supply device which is a voltage feedback self-excited complex resonance series converter according to a third embodiment of the present invention, and FIG. 8 is a block diagram showing a specific configuration thereof. This switching power supply device is similar to the switching power supply device shown in FIG. 3 and FIG. 4 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. Referring to FIG. 7, it should be noted that in the present embodiment, the same relaxation oscillation is used, but the startup circuit 21 is used instead of the startup circuit IGN.

  The startup circuit 21 is provided between the gate and source of the power MOSFET Q2, and generally includes an internal power supply Vcc for startup, a relaxation oscillation circuit 22, an oscillation detection circuit 23, a logic gate circuit 24, and an output circuit 25. Is done. Then, when the activation pulse is applied from the relaxation oscillation circuit 22 to the gate of the power MOSFET Q2 via the logic gate circuit 24 and steady oscillation is detected by the oscillation detection circuit 23, the logic gate circuit 24 blocks the output of the activation pulse. The oscillation is continued with the feedback voltage generated in the auxiliary winding L12. The output circuit 25 is composed of a power amplifier or a buffer circuit, and its output is given to the gate of the power MOSFET Q2 via a diode D21.

  Referring to FIG. 8, the relaxation oscillation circuit 22 is an astable multivibrator including a timer IC realized by an LMC555 manufactured by National Semiconductor, and includes resistors R21, R22 connected to the internal power supply Vcc, and The frequency and ON duty can be set easily and in detail from the voltage at each connection point of the series circuit by the resonance capacitor C21. The output of the relaxation oscillation circuit 22 is inverted by a logic gate circuit (NOT) 26 and input to a two-input logic gate circuit (AND) 24. The other input of the logic gate circuit 24 has a feedback winding. An inverted signal of the output obtained by integrating the feedback voltage from one end of L12 by the integrating circuit constituted by the resistor R23, the diode D22 and the capacitor C22 of the oscillation detecting circuit 23 is input. A discharging resistor R24 is connected in parallel to the integrating capacitor C22. The output of the logic gate circuit 24 is supplied from the output circuit 25 to the gate of the power MOSFET Q2 via the diode D21.

  FIG. 9 is a diagram showing operation waveforms of the startup circuit 21 configured as described above. (A)-(e) respond | corresponds to each part ae of FIG. 8, respectively. (A) shows the output signal of the relaxation oscillation circuit 22, and the inverted signal shown in (b) is given to one input of the logic gate circuit 24. Until startup, the power MOSFETs Q1 and Q2 are not switched. Therefore, there is no feedback voltage from the feedback winding L12 shown in (c), and the output from the oscillation detection circuit 23 shown in (d) is also at a low level. Thus, the other input of the logic gate circuit 24 is at a high level. Accordingly, the output from the output circuit 25 shown in (e) is the inverted signal of the output signal of the relaxation oscillation circuit 22 shown in (b).

  On the other hand, when self-excited oscillation is started by the start pulse from the relaxation oscillation circuit 22, the feedback voltage shown in (c) is obtained from the feedback winding L12, and the capacitor C22 constituting the integration circuit has (d ) Is generated, the output of the oscillation detection circuit 23 is at a high level. As a result, the logic gate circuit 24 is blocked by the other input, and the start pulse disappears at the same time as the start, and thereafter, the self-excited oscillation by the feedback voltage is switched.

In FIG. 9, the pulse width of the inverted signal of the output of the relaxation oscillation circuit 22 (pulse input to the logic gate circuit 24) is ½ or less of the resonance period of the series resonance circuit, and the pulse period is a resonance capacitor. C1 is selected to be greater than or equal to the time constant that is charged prior to activation. Here, when giving a starting pulse to the gate of the power MOSFET Q2, the timing of the starting pulse is important, and if sufficient charge is not stored in the resonant capacitor C1, the other voltage is induced in the auxiliary winding L13 by the starting pulse. Since the power MOSFET Q1 cannot be turned on, by selecting as described above, reliable activation can be performed.

  By configuring in this way, after starting up, steady oscillation is continued by the feedback voltage from the feedback winding L12 without being influenced by the starting circuit (timer IC) 21, and when oscillation stops, it starts up quickly. It is possible to get into action. With such a configuration, the period and width of the activation pulse can be easily set by the CR constant of the relaxation oscillation circuit 22, and appropriate activation conditions can be easily set. Further, the voltage of the start pulse can be selected by the internal power supply Vcc.

1 is a block diagram of a switching power supply device that is a voltage feedback self-excited composite resonance series converter according to a first embodiment of the present invention. It is an operation | movement waveform diagram at the time of starting of the said switching power supply device. It is a block diagram of the switching power supply device which is a voltage feedback type self-excited composite resonance series converter according to a second embodiment of the present invention. FIG. 4 is an electric circuit diagram showing a specific configuration example of an amplifier and a detection circuit in the switching power supply device shown in FIG. 3. FIG. 4 is an electric circuit diagram illustrating another specific configuration example of an amplifier and a detection circuit in the switching power supply device illustrated in FIG. 3. FIG. 5 is an electric circuit diagram showing still another specific configuration example of an amplifier and a detection circuit in the switching power supply device shown in FIG. 3. It is a block diagram of the switching power supply device which is a voltage feedback type self-excited composite resonance series converter according to a third embodiment of the present invention. It is a block diagram which shows the specific structure of the switching power supply device shown in FIG. FIG. 9 is an operation waveform diagram of a startup circuit in the switching power supply device shown in FIGS. 7 and 8. It is a block diagram which shows the basic composition of a separately excited composite resonance series converter. FIG. 11 is an operation waveform diagram of FIG. 10. It is a block diagram which shows the example of the conventional voltage feedback type self-excitation compound resonance series converter. FIG. 13 is an operation waveform diagram of FIG. 12.

Explanation of symbols

11 Limiter 12 Amplifier 13 Detection Circuit 21 Start-up Circuit 22 Relaxation Oscillation Circuit 23 Oscillation Detection Circuits 24 and 26 Logic Gate Circuit 25 Output Circuit C0 Capacitor (For Power Supply Smoothing)
C1 resonant capacitor C2 capacitor (for dead time)
C3 Smoothing capacitors C5, C11, C12; C21, C22 capacitors C13 Speed-up capacitors D1-D5; D11-D15; D21, D22 Diode E DC input power supply IGN Start-up circuit L Inductor L11 Primary winding L12; L13 Auxiliary winding Load DC load OP operational amplifier Q1, Q2 Power MOSFET
Q3 Sidak Q4, Q5; Q11-Q13 Transistors R1, R2 Gate resistance R4 Resistance (for starting)
R3, R11, R12, R16, R17, R18; R21 to R24 Resistor R22 Discharge resistor T1 Output transformer Vcc Internal power supply ZD1, ZD2, ZD3 Zener diode R13 Protection resistor R14 Discharge resistor R15 Voltage dividing resistor R17 Feedback resistor

Claims (6)

A series circuit composed of first and second switching elements is connected between both terminals of the DC input power supply, and between the connection point of the first and second switching elements and one terminal of the DC input power supply, A series resonant circuit comprising an inductor, a resonant capacitor and a primary winding of an output transformer is connected, and a secondary induced current of the output transformer obtained by switching of the first and second switching elements is generated by a diode and a smoothing capacitor. Rectification / smoothing is output, and the voltage induced in the first and second auxiliary windings of the output transformer is applied to the control terminals of the first and second switching elements to continue switching. In a switching power supply comprising a voltage feedback type self-excited composite resonant series converter,
An activation circuit for applying an activation pulse to one control terminal of the first and second switching elements;
Amplifying means for enlarging the induced voltage of the auxiliary winding corresponding to the other of the first and second switching elements;
A switching power supply device comprising: function limiting means for stopping the function of the amplifying means after activation. 2. The switching power supply device according to claim 1, wherein the function limiting means is a limiter for limiting an induced voltage of the auxiliary winding . 2. The switching power supply device according to claim 1, wherein the function limiting means is a detection circuit that detects that the oscillation is steady and stops the amplification means . The starting circuit is
Control power,
A relaxation oscillation circuit energized by the control power supply;
An oscillation detection circuit for determining whether an induced voltage of one of the first and second auxiliary windings has reached a predetermined level at which a corresponding switching element can be switched;
In response to the determination result of the oscillation detection circuit, the oscillation signal of the relaxation oscillation circuit is given as an activation signal to the corresponding switching element during a period when the predetermined level is not reached, and when the predetermined level is reached, the relaxation oscillation 4. The switching power supply device according to claim 1, further comprising a logic circuit that blocks an oscillation signal of the circuit from being applied to a corresponding switching element. 5. 5. The switching according to claim 4 , wherein the oscillation detection circuit stops the operation of the relaxation oscillation circuit when one induced voltage of the first and second auxiliary windings reaches the predetermined level. Power supply. Pulse width of the pulse to be inputted to the logic circuit, the equal to or less than half of the resonance period of the series resonant circuit, and the period of the pulse is the time constant over which the resonant capacitor is charged prior to the start 6. The switching power supply device according to claim 4 or 5, wherein

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