JP5772278B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device that can improve the start-up circuit and realize low power consumption at low cost during standby.

  FIG. 6 is a circuit diagram showing a configuration of a conventional flyback type switching power supply device. FIG. 7 is a circuit diagram showing an internal configuration of the control unit 50a. FIG. 8 is a circuit diagram showing an internal configuration of the activation circuit 57. The operation of the switching power supply device will be described with reference to FIGS.

  First, the sine wave voltage output from the AC power source 1 is rectified by the bridge rectifier 2 and output to the drain terminal of the switching element 5 through the capacitor 3 and the primary winding P of the transformer 4. On the other hand, the starter circuit 57 in the control unit 50a is charged by supplying a current to the backup capacitor 12 of the auxiliary power supply circuit by the constant current source 80 until the voltage at the Vcc terminal exceeds 16.5V because the switch 81 is on. To do. When the voltage at the Vcc terminal exceeds 16.5 V and the internal power supply 51 starts to operate and starts supplying power to the control unit 50a, the starting circuit 57 turns off the switch 81 and stops supplying the starting current.

  When the voltage of the Vcc terminal exceeds 16.5V and the operation of the control unit 50a starts, the switching element 5 starts the switching operation. For this reason, energy is supplied to each winding of the transformer 4, and a current flows through the secondary winding S and the auxiliary winding D.

  The current flowing through the secondary winding S is rectified and smoothed by the rectifying diode 6 and the output capacitor 7 to become DC power, and is output from Vout to an external load.

  By repeating the switching operation of the switching element 5, the output voltage of Vout gradually increases, and when the reference voltage set by the error amplifier 8 is reached, the current flowing through the photodiode of the photocoupler 9 a increases. Then, since the current flowing through the phototransistor of the photocoupler 9b increases, the voltage at the FB terminal decreases due to the voltage drop of the resistor 60a. Thereby, the control part 50a controls the switching element 5, and stabilizes the output voltage of Vout. During the period when the switching operation of the switching element 5 is stopped, the voltage VFB at the FB terminal increases as the current from the resistor 60 a charges the capacitor 10.

  The current flowing through the auxiliary winding D is rectified and smoothed by the diode 11 and the backup capacitor 12, and is used as an auxiliary power source for the control unit 50a to supply power to the Vcc terminal. As described above, once the Vcc terminal reaches the start-up voltage (16.5 V), the switch 81 in the start-up circuit 57 is turned off, so that power supply to the Vcc terminal after start-up is performed by this auxiliary power supply circuit. . Since the polarity of the auxiliary winding D is the same as that of the secondary winding S, the voltage of Vcc is proportional to the output voltage of Vout.

  When the load connected to Vout becomes a light load, the current flowing through the photodiode of the photocoupler 9a increases according to the error of the Vout voltage with respect to the reference voltage set by the error amplifier 8. Then, since the current flowing through the phototransistor of the photocoupler 9b increases, the voltage at the FB terminal decreases due to the voltage drop of the resistor 60a. As a result, the flip-flop 56 is reset by the control unit 50a, and the switching element 5 is controlled to be turned on / off via the AND circuit 65, the inverter 67, the buffers 68 and 69, and the switching elements 70 and 71. When the load is further reduced, the BST comparator 55 outputs an H level to the OR circuit 64 to stop the on / off control of the switching element 5 or increase the off duty time, that is, intermittent control is performed.

  While the voltage at the FB terminal decreases and the oscillation of the switching element 5 stops, the current flowing through the photodiode of the photocoupler 9a decreases, and accordingly, the current flowing through the phototransistor of the photocoupler 9b decreases. Thereby, the capacitor 10 is charged from the resistor 60a, and the voltage of the FB terminal rises. The switching power supply device repeats the above operation, and controls the voltage by intermittent control that lengthens the OFF time of the switching element at light load. Here, the auxiliary winding D of the transformer 4 charges the backup capacitor 12 during the operation of the switching element 5 to increase the Vcc voltage.

  However, when the control of the switching element 5 is stopped, the backup capacitor 12 is discharged, so that the Vcc voltage decreases. For this reason, in the prior art, when the load is light and the switching element 5 is off, the BST comparator 55 outputs an H level signal and outputs the H level signal to turn on the switch 81. The power supply voltage of the control unit 50a at the time of light load is stably secured by supplying the current from the starting circuit 57 to the backup capacitor 12 for charging and increasing the Vcc terminal voltage.

  On the other hand, due to the recent increase in eco-consciousness as a social background, there is an urgent need to reduce power consumption during remote control standby.

  In Patent Document 1, a current is supplied to the control circuit through the start circuit during intermittent oscillation so that the control circuit does not stop operating. This is because the auxiliary winding voltage, which is poorly coupled, is likely to decrease during a light load such as standby, and the VCC winding voltage decreases while oscillation is stopped because intermittent oscillation is performed during standby. In this way, a countermeasure for stopping the operation of the control circuit is taken.

JP 2010-35299 A

  However, in Patent Document 1, there is a problem that power consumption increases because the power source of the control circuit is obtained from the drain of the switching element 5. This is a loss that cannot be ignored because the drain voltage is high although the current of the control circuit is as small as several hundred μA. In the prior art, since the auxiliary winding D is provided in the transformer 4, the transformer is expensive and large.

  An object of the present invention is to provide a switching power supply apparatus that can significantly reduce loss without providing an auxiliary winding.

In order to solve the above problems, the present invention has a switching element connected to a primary winding of a transformer, and a control circuit turns on the switching element when a voltage is input to the primary side of the transformer. A switching power supply device that rectifies and smoothes a voltage induced in the secondary winding of the transformer by performing off / off control and outputs the voltage to a load, the capacitor supplying power to the control circuit, and starting the control circuit An activation circuit that supplies current to the capacitor when the switching element is off, and a bottom detection circuit that detects that the main electrode voltage of the switching element is at the bottom, and the activation circuit includes: when said bottom detection circuit detects the bottom, one shot outputs a one-shot pulse signal in response to a signal from the bottom detection circuit It includes a pulse circuit, the one-shot pulse circuit outputs a pulse signal of a time that is inversely proportional to the charging voltage of the capacitor, according to the time width of the pulse signal and supplies a current to the capacitor from the activation circuit It is characterized by that.

According to the present invention, when the switching element is turned off and the bottom detection circuit detects that the main electrode voltage of the switching element has become the bottom, the one-shot pulse circuit responds to the signal from the bottom detection circuit. A signal is output, a pulse signal having a time inversely proportional to the charging voltage of the capacitor is output, and a current is supplied from the starting circuit to the capacitor according to the time width of the pulse signal, so that the capacitor is charged. As a result, the Vcc line can be charged only when the drain voltage when the switching element is turned off is low in free vibration, so that the loss can be greatly reduced as compared with the conventional circuit without providing an auxiliary winding.

It is a circuit diagram which shows the structure of the control circuit of the switching power supply apparatus which concerns on Example 1 of this invention. It is a figure which shows the operation | movement waveform of each part of the switching power supply device which concerns on Example 1. FIG. It is a circuit diagram which shows the structure of the principal part of the control circuit of the switching power supply which concerns on Example 2 of this invention. It is a circuit diagram which shows the structure of the one shot pulse circuit in the control circuit in the switching power supply device concerning Example 3 of this invention. It is a figure which shows the relationship between the power supply voltage of the one-shot pulse circuit of the switching power supply device concerning Example 3 of this invention, and a one-shot pulse width. It is a circuit diagram which shows the structure of the conventional flyback type switching power supply device. It is a circuit diagram which shows the structure inside the control circuit in the conventional switching power supply device. It is a circuit diagram which shows the structure inside the starting circuit in the conventional switching power supply device.

  Embodiments of a switching power supply apparatus according to the present invention will be described below in detail with reference to the drawings.

Example 1
1 is a circuit diagram showing a configuration of a control circuit of a switching power supply apparatus according to Embodiment 1 of the present invention. The configuration of the control circuit shown in FIG. 1 is the same as that of the conventional circuit shown in FIG. 6 except for the configuration of the control circuit shown in FIG. To do.

  First, the starting circuit 57 includes a constant current source circuit 80 and a switch 81a. The constant current source circuit 80 includes a high voltage switch 82, resistors 83 and 85, a transistor 84, a diode 86, and a comparator 54.

  The Vcc terminal of the control circuit 50 is input from the drain terminal of the switching element 5 through the starting circuit 57 and the StartUP terminal.

  The control unit 50 deletes the OR circuit 53 from the control unit 50a of the prior art, a bottom detection circuit including the comparator 20, the reference voltage 25, the capacitors 26 and 27, the diode 28, and the DC bias circuit 29, and the AND circuit 21. Further, an inverter 22, a one-shot trigger circuit 23, and an OR circuit 24 are further provided.

  The bottom detection circuit detects the bottom point of the free oscillation of the drain voltage that occurs during the OFF period of the switching element 5. The non-inverting input terminal of the comparator 20 is connected to one terminal of capacitors 26 and 27, the cathode of the diode 28, and the like. The DC voltage from the DC bias circuit 29 is superimposed on the DC bias circuit 29. The DC bias circuit 29 includes a DC power supply 30 and a series circuit of a resistor 31 and a resistor 32 connected to both ends of the DC power supply 30.

  The other end of the capacitor 27, the anode of the diode 28, the negative electrode of the DC power supply 30, and one end of the resistor 32 are connected to the ground GND.

  The other end of the capacitor 26 is connected to the StartUP terminal of the control circuit 50, and the StartUP terminal is connected to the drain terminal of the switching element 5.

  The inverting input terminal of the comparator 20 is connected to the positive electrode of the reference voltage 25, and the negative electrode of the reference voltage 25 is connected to the ground GND.

  The output terminal of the comparator 20 is connected to one input terminal of the OR circuit 24, and the other input terminal of the OR circuit 24 is connected to the output terminal of the AND circuit 65. An output terminal of the OR circuit 24 is connected to one input terminal of the AND circuit 21 through a one-shot trigger circuit 23 and an inverter 22. The output terminal of the comparator 54 is connected to the other input terminal of the AND circuit 21. The output terminal of the AND circuit 21 is connected to the gate terminal of the switch 81a, and the drain terminal of the switch 81a is connected to the on / off control terminal of the constant current source circuit 80.

  FIG. 2 is a diagram illustrating operation waveforms of respective units of the switching power supply device according to the first embodiment. In FIG. 2, the voltage waveform between the drain and source of the switching element 5 is Vds, the non-inverting input terminal voltage of the comparator 20 (comparator input (+)), the output terminal voltage of the comparator 55 (comparator output), and the one-shot trigger circuit 23 The bottom signal, which is the output of, and the drive signal, which is the gate drive signal of the switching element 5, are shown.

  In FIG. 2, the comparator input (+) of the comparator 20 has a waveform that correlates with the drain-source voltage waveform Vds of the switching element 5 and that is advanced in phase with respect to the voltage waveform Vds. The voltage of the comparator input (+) is obtained by causing the differential current of the capacitor 26 to flow through the resistor 31 and the resistor 32 via the capacitor 26 connected to the drain terminal of the switching element 5 via the StartUP terminal of the control unit 50. It is obtained by converting to a voltage and superimposing a DC voltage bias from the DC bias circuit 29. The capacitor 27 is connected as a filter that removes noise components.

  The comparator 20 compares the voltage of the comparator input (+) with the reference voltage 25 (Vref in FIG. 2) connected to the inverting input terminal. At time t1, when the voltage waveform Vds between the drain and source of the switching element 5 reaches the bottom, an H level signal is output from the output of the comparator 20.

  The one-shot trigger circuit 23 outputs a signal having a predetermined pulse width, that is, a bottom signal to the inverter 22 at the timing of the rising edge of the output signal of the comparator 20. The inverter 22 inverts the bottom signal and outputs it to the AND circuit 21.

  Here, when the output of the AND circuit 21 is at the H level, the switch 81a is turned on to turn off the constant current source circuit 80. Therefore, when the output of the AND circuit 21 is at the L level, the switch 81a is turned off and the constant current source circuit 80 is turned on, and the backup capacitor 12 is charged via the constant current source circuit 80 and the Vcc terminal. .

  As described above, according to the switching power supply device of the first embodiment, the control circuit 50 turns off the switch 81a of the start-up circuit 57 for a certain time only near the bottom point of the drain voltage of the switching element 5 when the switching element 5 is turned off. Then, the backup capacitor 12 connected to the Vcc terminal is charged, and at other times, the Vcc voltage is given by the voltage of the backup capacitor 12.

  As a result, when the switching element 5 is turned off, the Vcc line can be charged only when the drain voltage of the switching element 5 is at the bottom with low free vibration. Loss can be greatly reduced.

  On the other hand, medium-sized and large-sized LCD-TVs sold to general consumers in Japan generally have a power of 0.1 W or less when the screen is turned off (remote control standby). This limit value includes microcomputer power for standby by the remote controller, etc., and when it is not present, the power consumption during no load as a switching power supply must be further reduced to 0.02 W to 0.05 W or less. This limit is expected to fall further due to the promotion of ecology policies and heightened consumer eco-consciousness.

  On the other hand, the power consumption reduction effect of Example 1 is as follows. For example, when all the controller ICs are supplied from the starting circuit 57 without providing the auxiliary winding D, the voltage (VCC) supplied to the control circuit 50 for switching power supply is 15V, and the control circuit 50 for switching power supply Is about 300 μA, this current is supplied from the starting circuit 57. From FIG. 2, the drain-source voltage Vds is about 560 V at the highest voltage and about 100 V at the lowest voltage (bottom), so the voltage Vds is reduced to about 1/6 by using the bottom voltage. Can do.

  The loss of the startup circuit of the conventional circuit is (560-15) V × 300 μA = 0.1635 W as the worst condition. The loss of the startup circuit of the first embodiment is (100−15) V × 300 μA = 0.0255 W because the voltage is the bottom portion of the drain voltage. Therefore, according to the switching power supply device of the first embodiment, it is possible to achieve market-required remote control low standby power.

(Example 2)
FIG. 3 is a circuit diagram illustrating a configuration of a main part of a control circuit of the switching power supply device according to the second embodiment of the present invention. The control circuit shown in FIG. 3 is characterized in that an OR circuit 34 and a comparator 35 are further provided in the control circuit 50 shown in FIG. The comparator 35 has a non-inverting input terminal connected to the cathode of the diode 86 and the non-inverting input terminal of the comparator 54, an inverting input terminal connected to the reference voltage 36, and an output terminal connected to one input terminal of the OR circuit 34. Is done.

  The OR circuit 34 outputs a logical sum of the output of the comparator 35 and the output of the inverter 22 to the AND circuit 21.

  According to the switching power supply device of the second embodiment having such a configuration, the power supply is activated by the comparator 16.5V / 10V. Since no bottom-on signal is input when the power is turned on, the high-voltage switch 82 is turned on regardless of the bottom-on signal to charge the Vcc terminal to 16.5V.

After that, the reference voltage of the comparator 54 is switched to 10 V, the power-good signal is output, the oscillation operation is started, the normal operation is started, the amplitude of the voltage waveform Vds is increased, and the bottom detection circuit shown in FIG. Can be detected. At the same time, predetermined load power is supplied to the secondary side of the transformer 4 and normal operation is performed.
At this time, when the Vcc voltage applied to the non-inverting input terminal of the comparator 35 is equal to or higher than the reference voltage 36 (for example, 12 V), the comparator 35 outputs the H level to the OR circuit 34, so that the switch 81a is turned on. Then, the starting circuit 57 is stopped.

On the other hand, when the Vcc voltage becomes equal to or lower than the reference voltage 36 (12V) and the bottom-on signal is input from the inverter 22, the output of the OR circuit 34 becomes L level. Circuit 57 is turned on. For this reason, the Vcc terminal is charged. When the Vcc terminal is charged by 12V or more by this charging, the starting circuit 57 is turned off.
As a result, during normal operation, the Vcc terminal is maintained at about 12 V while the start-up circuit 57 is bottom-on operated.

  Thus, during normal operation and intermittent operation, an appropriate voltage can be supplied to the Vcc terminal voltage with a low loss by the bottom-on signal.

  Further, the control circuit 50 monitors the voltage at the Vcc terminal and stops charging the backup capacitor 12 when the voltage at the Vcc terminal is equal to or higher than the reference voltage, so that the backup capacitor 12 is charged more than necessary. It is possible to achieve high efficiency. Furthermore, since a high voltage is not charged to the Vcc terminal, it is possible to avoid element breakdown and increase in circuit current.

  When the power is turned off, the drain terminal voltage of the switching element 5 drops to 0V, so that the Vcc terminal cannot be charged, and the operation is safely stopped when the Vcc terminal becomes 10V or less by the comparator.

(Example 3)
FIG. 4 is a circuit diagram showing a configuration of a one-shot pulse circuit of a control circuit in the switching power supply apparatus according to Embodiment 3 of the present invention. Instead of the one-shot trigger circuit 23 of the first embodiment shown in FIG. 1, the third embodiment shown in FIG. 4 uses a one-shot pulse circuit. The other configuration shown in FIG. 4 is the same as the configuration shown in FIG.

  In the one-shot pulse circuit, the positive electrode of the power supply Vcc is connected to the collector of the N-type transistor Qn1 via the resistor Rt. The emitter of the transistor Qn1 is connected to the emitter of the P-type transistor Qp2, one end of the capacitor Ct, and the input terminal of the inverter INV1. The collector of the transistor Qp2 is connected to the other end of the capacitor Ct. The bases of the transistors Qn1 and Qp2 are connected to one input terminal of the AND circuit AND1, and the bottom signal is input. The output of the inverter INV1 is connected to the other input terminal of the AND circuit AND1.

  Next, the operation of the one-shot pulse circuit will be described. First, when the bottom signal is input, the H level is input to one input terminal of the AND circuit AND1, and the H level signal of the inverter INV1 is input to the other input terminal of the AND circuit AND1. The output of AND1 outputs H level.

  When the bottom signal is input, the transistor Qn1 is turned on and charging of the capacitor Ct is started via the resistor Rt. When the voltage of the capacitor Ct reaches the input threshold voltage of the inverter INV1, the L level is output to the AND circuit AND1 via the inverter INV1, and the output of the AND circuit AND1 becomes the L level output.

  Here, since the resistor Rt is connected to the Vcc voltage, the charging time of the capacitor Ct becomes faster in proportion to the Vcc voltage. That is, the output pulse width of the AND circuit AND1 becomes narrower as the Vcc voltage increases, as shown in FIG. Thereby, when the Vcc voltage is high, the charging time is shortened, so that loss can be reduced without increasing the Vcc voltage more than necessary.

21, AND1 AND circuit 22, IND1 inverter 23 1 shot trigger circuit 24, 34 OR circuit
25 Reference voltage 26, 27, Ct Capacitor 28 Diode 29 DC bias circuit 50 Control circuit 20, 35, 54, 55 Comparator 57 Start-up circuit 81a Switch Rt Resistance Qn1 N-type transistor Qp2 P-type transistor

Claims (2)

A switching element connected to the primary winding of the transformer, and when a voltage is input to the primary side of the transformer, the control circuit controls the switching element to turn on / off the secondary winding of the transformer. A switching power supply device that rectifies and smoothes a voltage induced in a line and outputs it to a load,
A capacitor for supplying power to the control circuit;
An activation circuit for supplying current to the capacitor when the control circuit is activated and when the switching element is off;
A bottom detection circuit for detecting that the main electrode voltage of the switching element has become the bottom ,
The activation circuit includes a one-shot pulse circuit that outputs a one-shot pulse signal according to a signal from the bottom detection circuit when the bottom detection circuit detects the bottom,
The one-shot pulse circuit outputs a pulse signal having a time inversely proportional to a charging voltage of the capacitor, and supplies a current from the starting circuit to the capacitor according to a time width of the pulse signal. Switching power supply. A determination circuit for determining whether a voltage value supplied to the control circuit by the capacitor is equal to or lower than a predetermined voltage value;
The activation circuit supplies a current to the capacitor when the bottom detection circuit detects the bottom and the determination circuit determines that the voltage value supplied to the control circuit is equal to or lower than a predetermined voltage value. The switching power supply device according to claim 1.

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