JP6396793B2 - Switching power supply circuit - Google Patents

Description

  The present invention relates to a switching power supply circuit, and more particularly to a switching power supply circuit used for driving a light emitter such as a light emitting diode (LED).

  Patent Document 1 discloses a light emitter driving circuit using a triac dimmer as a phase control dimmer connected to an AC power source, a diode bridge as a rectifier, and an LED (Light Emitting Diode) driver IC. It is disclosed. The rectifier outputs a voltage whose magnitude changes according to the conduction angle in the triac dimmer. The driver IC has a phase angle detection terminal (VHV terminal). The driver IC monitors the voltage waveform applied to the phase angle detection terminal from the triac dimmer via the diode bridge, and outputs an output current (ILED) having a magnitude corresponding to the voltage waveform as a drive current. have. As described above, by using the LED driver IC, it is possible to perform dimming control of the LED lighting device by diverting an existing triac dimmer.

JP 2013-30461 A

  The triac dimmer has a characteristic that a voltage lower than the original voltage determined by the conduction angle is generated until the stable operation is performed after the AC power supply is turned on. Therefore, when this low voltage waveform is applied to the phase angle detection terminal, a small output current is initially output from the driver IC, and then a desired output current is generated after the triac dimmer starts a stable operation. Will be output. That is, the drive current supplied to the LED rises stepwise, and the LED is lit so that the brightness of the LED changes in two steps. Such a phenomenon may be recognized by the user as flickering of the LED.

  Accordingly, an object of the present invention is to provide a switching power supply circuit using a phase control dimmer that can prevent flickering of a light emitter when an AC power supply is on.

A switching power supply circuit according to the present invention is a switching power supply circuit that generates a drive current supplied to a light emitter, and includes a phase control dimmer connected to an AC power supply, and an output voltage of the phase control dimmer Rectifier, an operation stabilization circuit for supplying a holding current for stably operating the phase control dimmer, an input terminal conductively connected to the output terminal of the rectifier, and an input terminal applied to the input terminal A drive current control unit having a current setting terminal for setting the drive current having a magnitude corresponding to the voltage waveform, and a period from when the AC power supply is turned on until the phase control dimmer operates stably. and a delay circuit for delaying the voltage application to the input terminal such that the voltage to the input terminal is not applied Ru delaying the start of setting of the driving current by the current setting terminal, the delay circuit, the driving electric A first terminal connected to the input terminal of the control unit; a second terminal held at a ground potential; and a third terminal for controlling conduction between the first terminal and the second terminal. A first switching element, a first reference potential output from the drive current control unit at one end, a capacitive element connected at the other end to the third terminal of the first switching element, and one end at the capacitance A first resistance element connected to the other end of the element and the third terminal of the first switching element, the other end being held at a second reference potential lower than the first reference potential, and the capacitance The capacitance of the element and the resistance value of the first resistive element are selected such that charging of the capacitive element is terminated after the phase-controlled dimmer starts a stable operation. The resistance value of the resistance element is determined while the capacitor element is being charged. Potential of the third terminal of kicking the first switching element that is set to be higher than the threshold voltage of the first switching element.

As a result, the potential at one end of the first resistance element rises until the charging of the capacitive element is completed after the AC power supply is turned on, so that the first terminal and the second terminal of the first switching element are in a conductive state. In this conduction period, the ground potential is applied to the input terminal of the drive current control unit. Therefore, by selecting the capacitance of the capacitive element and the resistance value of the first resistive element so that the charging of the capacitive element is completed after the low voltage period until the phase control dimmer operates stably. In the low voltage period until the phase control dimmer operates stably, the output voltage of the rectifier is not applied to the input terminal of the drive current control unit. Therefore, the brightness of the light emitter does not change in two steps when the AC power is turned on, and flickering of the light emitter can be prevented.

  Moreover, it is preferable that the switching power supply circuit of the present invention further includes a discharge circuit that discharges the electric charge stored in the capacitive element.

  Thereby, the electric charge stored in the capacitive element can be quickly discharged.

  The switching power supply circuit of the present invention further includes a potential change terminal that changes in potential in conjunction with turning on and off of the AC power supply, and the discharge circuit is a first terminal connected to the one end of the capacitive element. A second terminal connected to the other end of the capacitive element, and a third terminal connected to the potential change terminal for controlling conduction between the first terminal and the second terminal. It is preferable that the 2nd switching element which has is included.

  As a result, when the AC power supply is turned off, the potential of the third terminal of the second switching element changes with the potential change of the potential change terminal, so that the first terminal and the second terminal of the second switching element are electrically connected. State. Therefore, the electric charge stored in the capacitor element is surely discharged by entering the conductive state. Therefore, since it is ensured that the electric charge stored in the capacitive element is discharged quickly after the AC power supply is turned off, the power is turned on again in a relatively short time after the AC power supply is turned off. Even in this case, the output voltage of the rectifier is not applied to the input terminal of the drive current control unit during the low voltage period until the phase control dimmer operates stably.

  Furthermore, the switching power supply circuit of the present invention includes a second resistance element disposed between the potential change terminal and the third terminal of the second switching element, and a second resistance element connected in series with the second resistance element. A third resistance element, wherein the third terminal of the second switching element is conductively connected between the second resistance element and the third resistance element, and the drive current control unit includes: It is preferable that the output of the drive current from the output terminal is stopped when the potential of the potential change terminal becomes equal to or lower than a third reference potential.

  Thereby, the timing at which the first terminal and the second terminal of the second switching element become conductive can be adjusted by the voltage division ratio according to the resistance value between the second resistance element and the third resistance element. Therefore, the discharge timing of the capacitive element can be immediately after the AC power supply is turned off and the drive current control unit stops outputting the drive current.

  During the low voltage period until the phase control dimmer operates stably, the output voltage of the rectifier is not applied to the input terminal of the drive current control unit. Therefore, the brightness of the light emitter does not change in two steps when the AC power is turned on, and flickering of the light emitter can be prevented.

1 is a circuit diagram of a switching power supply circuit according to an embodiment of the present invention. 2 is a graph showing an operation sequence of the switching power supply circuit shown in FIG. 1.

  A switching power supply circuit according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, a switching power supply circuit 1 according to the present embodiment drives an LED module 2, and is a phase control type regulator connected to an AC power supply (for example, 90 to 220 V commercial AC power supply) 3. A triac dimmer 11 that is an optical device and a diode bridge DB1 that is a rectifier that rectifies the output voltage of the triac dimmer 11 are included. The LED module 2 includes a plurality of LED elements connected in series or in parallel.

  FIG. 2 shows a waveform of the power supply voltage Vac of the AC power supply 3. The power supply voltage Vac, which is an AC signal, fluctuates at a very short period on the scale shown in FIG. The TRIAC dimmer 11 that is an AC signal having the same frequency as the power supply voltage Vac does not operate stably during a period from time t1 to time t2 when the power supply voltage Vac is turned on (V1 generation period). Therefore, in the V1 generation period, the output waveform Vin of the triac dimmer 11 has a relatively small height V1. Then, the triac dimmer 11 starts a stable operation at time t2, and thereafter, the output waveform Vin becomes a voltage waveform having an original size determined by the conduction angle.

  The switching power supply circuit 1 according to the present embodiment further includes a driver IC 12, an operation stabilization circuit 13, a power supply circuit 14, a switching circuit 15, a delay circuit 16, and a discharge circuit 17.

  The driver IC 12 has 14 pins (terminals). Pin 1 is a power supply terminal (Vcc), pin 2 is a terminal that determines the timing of current flow for stable operation of the triac dimmer 11, and pin 3 is a current for stable operation of the triac dimmer 11. Terminal 4 is a terminal for monitoring the current flowing in the circuit and the operation of pin 3 is turned on and off. Pin 5 is a ground terminal (GND) of driver IC 12. Pin 6 is a diode bridge DB1 from triac dimmer 11 The phase angle detection terminal (VHV) to which the output voltage is applied via the high-voltage side output terminal (+), and the 7th pin is a terminal for smoothing the dimming operation (brightness change of LED).

  The magnitude of the voltage applied to the phase angle detection terminal is such that the resistance elements R3 and R4 connected in series between the high-voltage side output terminal (+) and the low-voltage side output terminal (−) of the diode bridge DB1. It is determined by the partial pressure ratio. In FIG. 2, a voltage Vx indicates a voltage at a position between the resistance element R3 and the resistance element R4. The voltage Vx is a DC voltage whose output value changes in synchronization with the output waveform Vin of the triac dimmer 11. The potential of the low voltage side output terminal (−) is the ground potential.

  The 8th pin is a terminal for switching between non-insulated / insulated circuit systems, and the 11th pin changes the detection voltage inside the driver IC 12 in accordance with the voltage waveform applied to the 6th pin. A terminal for setting a large output current (ILED), a 12th pin for driving a switching FET Q3 (described later) included in the switching circuit 15, a 13th pin for monitoring a choke coil current, 14 The number pin is a reference voltage terminal (Vdd) that supplies a first reference potential of 3.3 V, for example. In the present embodiment, the driver IC 12 corresponds to a drive current control unit.

  The operation stabilization circuit 13 includes a field effect transistor (FET) Q1 and two resistors R1 and R2. The operation stabilizing circuit 13 is connected between the high voltage side output terminal (+) and the low voltage side output terminal (−) of the diode bridge DB1. If the current flowing through the FET Q1 and the two resistors R1 and R2 detected by the third pin of the driver IC 12 is 20 mA or more, the second pin (the gate terminal of the FET Q1) of the driver IC 12 is LOW, and if it is less than 20 mA, the driver IC 12 No. 2 pin is HI. With this operation, a holding current for stably operating the triac dimmer 11 can be always supplied. Note that the values of the two resistors R1 and R2 are such values that the triac dimmer 11 operates stably.

  The power supply circuit 14 includes an FET Q2, two resistors R5 and R6, and a Zener diode D2. When the AC power supply 3 is turned on and the input voltage to the power supply circuit 14 becomes equal to or higher than the breakdown voltage of the Zener diode D2, the FET Q2 is turned on. Therefore, assuming that the voltage drop between the gate and source of the FET Q2 can be ignored, a voltage substantially equal to the breakdown voltage of the Zener diode D2 is generated at the source terminal of the FET Q2. Since the voltage at the source terminal is clamped by the Zener diode D2, a constant stable voltage (for example, 13.5V) can always be applied to the first pin (Vcc) of the driver IC 12. That is, the source terminal of the FET Q2 is a potential change terminal whose potential changes in conjunction with the on / off of the AC power supply 3. When the AC power supply 3 is turned off and the potential of the source terminal of the FET Q2 and the potential of the first pin of the driver IC 12 is equal to or lower than the off-threshold potential (third reference potential) of 6.5 V, for example, the driver IC 12 Stop output.

  The switching circuit 15 includes an FET Q3. The gate terminal of the FET Q3 is connected to the 12th pin of the driver IC 12. The source terminal of the FET Q3 is connected to the 11th pin of the driver IC 12. The drain terminal of the FET Q3 is connected to the LED module 2. The FET Q3 outputs a constant output voltage and output current by repeatedly turning on and off at a switching frequency based on a signal supplied from the 12th pin of the driver IC 12.

  The delay circuit 16 includes an NPN transistor Q5 that is a switching element (first switching element), a capacitor C4 (corresponding to the “capacitance element” of the present invention), and a resistance element R17 (“first resistance element” of the present invention). Equivalent). The collector terminal of the transistor Q5 is connected to the 6th pin of the driver IC 12. The emitter terminal of the transistor Q5 is connected to the low-voltage side output terminal (−) of the diode bridge DB1. The base terminal of the transistor Q5 is a terminal for controlling conduction between the collector terminal and the emitter terminal. One end of the capacitor C4 is connected to the 14th pin of the driver IC 12, that is, the reference voltage terminal (Vdd), so that the first reference potential is applied. The other end of the capacitor C4 is connected to the base terminal of the transistor Q5. One end of the resistor element R17 is connected to the other end of the capacitor C4 and the base terminal of the transistor Q5. The other end of the resistance element R17 is held at the second reference potential which is the ground potential in the present embodiment. Specifically, the other end of the resistance element R17 is connected to the low voltage side output terminal (−) of the diode bridge DB1.

  The discharge circuit 17 discharges the electric charge stored in the capacitor C4. The discharge circuit 17 is a PNP transistor Q4, which is a switching element (second switching element), a diode D4, and a resistance element R8 (“second” of the present invention). And the resistance element R9 (corresponding to the “third resistance element” of the present invention) The emitter terminal of the transistor Q4 is connected to one end of the capacitor C4. Is connected to the other end of the capacitor C4, and the base terminal of the transistor Q4 is a terminal for controlling conduction between the collector terminal and the emitter terminal, and is connected to the anode terminal of the diode D4. One end of the resistance element R8 is connected to the source terminal of the FET Q2. The resistance element R9 is the resistance element R8. One end of the resistor element R8 is connected to the other end of the resistor element R8 so as to be connected in series, and the other end of the resistor element R9 is connected to the low-voltage side output terminal (−) of the diode bridge DB1. The cathode terminal is connected between the resistance element R8 and the resistance element R9, that is, the base terminal of the transistor Q4 is connected to the source terminal of the FET Q2 via the diode D4 and the resistance element R8.

  Next, the basic operation of the switching power supply circuit 1 according to this embodiment will be described. Here, first, the operation of the switching power supply circuit equivalent to the conventional one without the delay circuit 16 and the discharge circuit 17 will be described. When the AC power supply 3 is turned on at time t1, the FET Q2 is turned on and the potential of the power supply terminal (Vcc) of the driver IC 12 rises. Further, a small voltage corresponding to V1 is input to the sixth pin (VHV) of the driver IC 12 from time t1. When the power supply terminal (Vcc) becomes the on-threshold voltage (13.5 V) or higher, the driver IC 12 starts operating, and the potential of the reference voltage terminal (Vdd) increases. The driver IC 12 starts the switching operation at the time when the reference voltage terminal (Vdd) becomes 2.8 V or more, that is, at the time tx when the predetermined time T has elapsed from the time t1, and the output current (ILED) set by the 11th pin is It flows to the LED module 2 as a drive current. As a result, the capacitor C2 is charged, and the LED module 2 is lit with a relatively small luminance. Assuming that the V1 generation period ends at time t2, a normal voltage is input to the sixth pin of the driver IC 12 from time t2. Then, the LED module 2 is lit at a higher luminance at a time ty when a predetermined time T has elapsed from the time t2. That is, the brightness of the LED module 2 changes in two stages. When the triac dimmer 11 is operated after the LED module 2 is turned on, the voltage waveform input to the 6th pin changes. As a result, the magnitude of the output current (ILED) output from the 11th pin changes, and the light emission intensity of the LED module 2 changes accordingly.

  On the other hand, since the switching power supply circuit 1 according to the present embodiment includes the delay circuit 16 and the discharge circuit 17, it operates as follows. At time t1, the AC power supply 3 is turned on, the driver IC 12 starts operating, and the potential of the reference voltage terminal (Vdd) rises. A DC voltage having a first reference potential is output from the reference voltage terminal (Vdd). As a result, the capacitor C4 is charged based on a time constant determined by the capacitance of the capacitor C4 and the resistance value of the resistance element R17. The resistance value of the resistance element R17 is set so that the potential of the base terminal of the transistor Q5 during the charging is higher than the threshold voltage of the transistor Q5. Therefore, during the charging, the transistor Q5 is turned on and the collector terminal and the emitter terminal are conducted. As a result, the phase angle detection terminal (VHV) of the driver IC 12 is held at the ground potential from time t1.

  In the present embodiment, the capacitance of the capacitor C4 and the resistance value of the resistance element R17 are selected so that charging of the capacitor C4 ends after the V1 generation period until the triac dimmer 11 stably operates ends. Has been. Specifically, as shown in FIG. 2, the charging of the capacitor C4 ends at a time t3 when a little time has elapsed from the time t2 that is the end time of the V1 generation period. When the charging of the capacitor C4 is completed, the potential of the base terminal of the transistor Q5 becomes lower than the threshold voltage of the transistor Q5, so that the transistor Q5 is turned off, and a resistance element is connected to the phase angle detection terminal (VHV) of the driver IC12. A predetermined potential determined by the voltage division ratio between R3 and resistance element R4 is applied. The 11th pin of the driver IC 12 sets an output current (ILED) having a magnitude corresponding to the voltage waveform applied to the phase angle detection terminal from the time t4 when the predetermined time T has elapsed from the time t3 as the drive current. As a result, the capacitor C2 is charged, and the LED module 2 is lit with high brightness. The output current (ILED) is not output until time t4. Thus, in the present embodiment, the output voltage of the diode bridge DB1 is not applied to the phase angle detection terminal (VHV) of the driver IC 12 during the V1 generation period when the triac dimmer 11 is not operating stably. . As a result, the brightness of the LED module 2 does not change in two steps when the AC power supply 3 is turned on, and flickering of the LED module 2 can be prevented.

  When the AC power supply 3 is turned off after the LED module 2 starts to emit light, the FET Q2 is turned off. Then, the potential of the source terminal of the FET Q2 and the first pin of the driver IC 12 is lowered to be equal to or lower than the off-threshold potential (third reference potential), and as described above, the driver IC 12 stops outputting the drive current. Further, the potential at the source terminal of the FET Q2 decreases, so that the voltage between the base and the emitter of the transistor Q4 exceeds the threshold voltage of 0.7V. As a result, the transistor Q4 is turned on and the charge stored in the capacitor C4 is discharged. As described above, in the present embodiment, the provision of the discharge circuit 17 ensures that the charge stored in the capacitor C4 is discharged quickly after the AC power supply 3 is turned off. Therefore, even when the AC power supply 3 is turned off and turned on again in a relatively short time, the output of the diode bridge DB1 is output during a low voltage period until the triac dimmer 11 operates stably. No voltage is applied to the 6th pin.

  The timing at which the transistor Q4 is turned on is determined by the voltage dividing ratio of the resistance values of the two resistance elements R8 and R9. Therefore, the timing at which the transistor Q4 is turned on can be adjusted by changing the voltage dividing ratio. Therefore, in the present embodiment, the discharge timing of the capacitor C4 can be set immediately after the AC power supply 3 is turned off and the driver IC 12 stops outputting the drive current.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various design changes can be made to the above-described embodiments as long as they are described in the claims. It is possible to apply. For example, a phase control dimmer other than a triac dimmer may be used, or a rectifier other than a diode bridge may be used. A switching element other than a transistor can also be used. The emitter terminal of the transistor Q5, which is the first switching element, may be held at the ground potential other than the low-voltage side output terminal (−) of the diode bridge.

  Furthermore, the first reference potential may be applied to the first terminal of the capacitor C4 by being connected to a terminal other than the driver IC 12. The other end of the first resistance element R17 may be held other than the ground potential as long as it is held at a potential lower than the first reference potential. The other end of the first resistance element R17 is lower than the threshold voltage of the transistor Q5, and one end of the first resistance element R17 is held at a potential higher than the threshold voltage of the transistor Q5 by charging the capacitor C4. Preferably it is. Further, as the discharge circuit, a circuit having a configuration other than that exemplified in the above-described embodiment may be used. Further, the potential change terminal may be other than the source terminal of the FET Q2 as long as the potential changes in conjunction with the on / off of the AC power supply. Further, a light emitter other than the LED module may be used. In the above-described embodiment, the driver IC 12 configures the drive current control unit. However, the drive current control unit may be configured without using the driver IC.

1 switching power supply circuit 2 LED module 3 AC power supply 12 driver IC
13 Operation Stabilization Circuit 14 Power Supply Circuit 15 Switching Circuit 16 Delay Circuit 17 Discharge Circuit

Claims (4)

A switching power supply circuit for generating a drive current supplied to a light emitter,
A phase control dimmer connected to an AC power source;
A rectifier for rectifying the output voltage of the phase control dimmer;
An operation stabilizing circuit for supplying a holding current for stably operating the phase control dimmer;
A drive current control unit having an input terminal conductively connected to the output terminal of the rectifier, and a current setting terminal for setting the drive current of a magnitude according to a voltage waveform applied to the input terminal;
The drive by the current setting terminal by delaying the voltage application to the input terminal so that the voltage is not applied to the input terminal during a period from when the AC power supply is turned on until the phase control dimmer operates stably. and a delay circuit Ru delaying the start of setting of the current,
The delay circuit is
A first terminal connected to the input terminal of the drive current control unit; a second terminal held at a ground potential; and a third for controlling conduction between the first terminal and the second terminal. A first switching element having a terminal;
A first reference potential output from the drive current control unit at one end, and a capacitive element connected at the other end to the third terminal of the first switching element;
One end is connected to the other end of the capacitive element and the third terminal of the first switching element, and the other end has a first resistance element held at a second reference potential lower than the first reference potential. And
The capacitance of the capacitive element and the resistance value of the first resistive element are selected such that charging of the capacitive element ends after the phase-controlled dimmer starts stable operation,
The resistance value of the first resistance element is set such that the potential of the third terminal of the first switching element is higher than the threshold voltage of the first switching element during charging of the capacitive element. Switching power supply circuit characterized. The switching power supply circuit according to claim 1 , further comprising a discharge circuit that discharges the electric charge stored in the capacitive element. It further comprises a potential change terminal that changes its potential in conjunction with turning on and off the AC power supply
The discharge circuit is
A first terminal connected to the one end of the capacitive element; a second terminal connected to the other end of the capacitive element; and the first terminal and the second terminal electrically connected to the potential change terminal. The switching power supply circuit according to claim 2 , further comprising: a second switching element having a third terminal for controlling conduction between the first and second terminals. A second resistance element disposed between the potential change terminal and the third terminal of the second switching element;
A third resistance element connected in series with the second resistance element;
The third terminal of the second switching element is conductively connected between the second resistance element and the third resistance element;
4. The switching power supply circuit according to claim 3 , wherein the drive current control unit stops outputting the drive current when the potential of the potential change terminal becomes equal to or lower than a third reference potential. 5.

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