JP2016149192A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply device that enables an LED to stably emit light without flickering.SOLUTION: A switching power supply device comprises a resonance voltage detection circuit for detecting a resonance voltage, a skip number determining part for determining a skip number based on a lighting control signal, a mask signal generator for generating a mask signal as a turn-on instruction signal for instructing turn-on of a switching element at a bottom timing of the skip number based on the detection result of the resonance voltage detection circuit, and a controller IC 1 for turning on a switching element Q1 based on the mask signal. When the skip number determined by the skip number determining part is changed from N to M, the mask signal generator provides a transition period, and generates the mask signal for instructing turn-on of the switching element Q1 at a timing between the bottom timing of the skip number of N and the bottom timing of the skip number of M during the transition period.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a quasi-resonant switching power supply device.

  When a switching power supply device is used as an LED lighting device for lighting an LED, dimming can be easily performed by increasing / decreasing the current value, but when flickering occurs at that time, it is uncomfortable. Since a PWM switching power supply device can stably control even in a light load state, it is easy to suppress flickering even during dimming, but when the PWM method is performed with a single converter type that enables cost reduction, EMI (Electro Magnetic Interference) measures become difficult. Therefore, in recent years, a quasi-resonant switching power supply device has been used as an LED lighting device for EMI countermeasures (see, for example, Patent Document 1).

JP 2014-75875 A JP 2014-23208 A

  However, in the quasi-resonant switching power supply device, the on-time of the switching element is shortened and the oscillation frequency is increased at the time of dimming or a high input voltage as a light load. When the on-time of the switching element is controlled to be equal to or less than the minimum on-width, the oscillation frequency changes irregularly, resulting in a phenomenon that the LED is flickering. In addition, if a bottom skip operation is performed during dimming, an increase in frequency can be suppressed (for example, see Patent Document 2). However, since the average value of the switch current in one cycle before and after the switching point of the bottom skip operation differs, flickering still occurs.

  An object of the present invention is to solve the above-described problems of the prior art and to provide a switching power supply device that can emit light stably without flickering of an LED.

The switching power supply device according to the present invention is a switching power supply device that turns on the switching element at a bottom timing at which the resonance voltage becomes a bottom (lowest point voltage) by using a resonance phenomenon associated with turn-off of the switching element. A resonance voltage detection circuit that detects a voltage; a skip number determination unit that determines a skip number for skipping the bottom timing based on a dimming signal from the outside; and the skip based on a detection result by the resonance voltage detection circuit The skip number determination unit comprises: a signal generation unit that generates a turn-on instruction signal that instructs turn-on of the switching element at a number of bottom timings; and a control circuit that turns on the switching element based on the turn-on instruction signal. Will change the number of skips from N to M (Where N is an integer greater than or equal to 0 and M is an integer greater than or equal to 0 different from N), the signal generation unit provides a transition period, and the number of skips is N in the transition period. The turn-on instruction signal for instructing the turn-on of the switching element is generated at a timing between the bottom timing and the bottom timing when the number of skips is M.
Furthermore, in the switching power supply device according to the present invention, the signal generation unit skips the timing for instructing the turn-on of the switching element from the bottom timing with the skip number N in the turn-on instruction signal generated in the transition period. The number may gradually approach the bottom timing of M.
Furthermore, in the switching power supply device of the present invention, the skip number determination unit may determine the skip number based on the dimming signal and the input voltage.
Furthermore, in the switching power supply device of the present invention, the transition period may be set to 2 to 3 times the period of the commercial AC power supply.

  According to the present invention, by switching the bottom skip operation, it is possible to prevent an abrupt change in the switch current average value, and it is possible to emit light stably without causing the LED to flicker.

It is a circuit block diagram which shows the structure of embodiment of the switching power supply device which concerns on this invention. It is a wave form diagram of the auxiliary | assistant winding signal and BD signal which are input into the microcomputer shown in FIG. It is a block diagram which shows the structure of the microcomputer shown in FIG. It is a figure which shows the example of a skip table shown in FIG. It is a wave form diagram for demonstrating the mask signal production | generation operation | movement in the mask signal production | generation part shown in FIG.

  The present embodiment is a quasi-resonant switching power supply device that supports dimming, and is configured by a non-insulated buck-boost method. Referring to FIG. 1, the switching power supply according to the present embodiment controls a controller IC1 including a switching element Q1 such as a MOSFET and a control circuit 11 that drives the switching element Q1, and the on-timing of the switching element Q1. And a microcomputer 2 to be provided.

  A commercial AC power supply AC is connected to the AC input terminal of the rectification circuit DB via the EMI filter F1, and an input capacitor Cin is connected between the rectification output positive terminal and the rectification output negative terminal of the rectification circuit DB. The rectification output positive terminal of the rectifier circuit DB is connected to the D / ST terminal of the controller IC1 through the filter F2. The D / ST terminal is a terminal connected to the drain of the switching element Q1. The rectified output negative terminal of the rectifier circuit DB is connected to the S / GND terminal of the controller IC1 via the reactor L1 and the resistor Rocp. The S / GND terminal is a terminal connected to the source of the switching element Q1. As a result, a closed circuit in which the switching element Q1 and the reactor L1 are connected in series is formed between both terminals of the input capacitor Cin, that is, both terminals of a DC voltage obtained by rectifying the AC voltage of the commercial AC power supply AC. When element Q1 is turned on, reactor L1 is excited. A voltage resonant capacitor Cv is connected between the D / ST terminal and the S / GND terminal of the controller IC1. Voltage resonant capacitor Cv forms a resonant circuit with reactor L1 when switching element Q1 is turned off.

  The cathode of a diode D1 is connected to the S / GND terminal of the controller IC1 via a current detection resistor Rs, and the anode of the diode D1 is a negative output to which an LED load RL composed of a plurality of LED elements is connected. It is connected to the negative terminal of the output capacitor Co, which is a terminal. The positive terminal of the output capacitor Co, which is the positive output terminal to which the LED load RL is connected, is connected to the connection point between the reactor L1 and the rectified output negative terminal of the rectifier circuit DB. The diode D1 connected to the reactor LI and the output capacitor Co function as a rectifying / smoothing circuit. As a result, a parallel circuit is formed in which the output capacitor Co and the LED load RL are connected in parallel. When the switching element Q1 is turned off, the diode D1 is turned on, and the power excited in the reactor L1 is output.

  The controller IC 1 includes a VCC terminal as a power input terminal, an OCP / BD terminal to which an overcurrent protection signal and a mask signal from the microcomputer 2 are input, a COMP terminal for feedback phase compensation, and a dimming signal. Are input, and an ISENSE terminal to which a feedback current detection signal is input.

  The OCP / BD terminal of the controller IC1 is connected to the COMMON line connected to the S / GND terminal of the controller IC1 via the resistor R1.

  A control circuit capacitor Ca is connected between the VCC terminal of the controller IC1 and the COMMON line connected to the S / GND terminal of the controller IC1. The auxiliary output terminal of the reactor L1 is connected to the anode of the diode D2 via the resistor R2, and the cathode of the diode D2 is connected to the VCC terminal of the controller IC1. Thereby, the capacitor Ca for control circuits is charged with the output of the electric power charged by the reactor L1.

  Capacitors C1, C2, and C3 are respectively connected between the COMP terminal, the VREF terminal, the ISENSE terminal, and the COMMON line of the controller IC1. The connection point between the current detection resistor Rs and the cathode of the diode D1 is connected to the ISENSE terminal of the controller IC1 through the resistor R3. The resistor R3 and the capacitor C3 function as a filter, and a current value flowing through the LED load RL is input to the ISENSE terminal as a feedback current detection signal.

  The microcomputer 2 includes an AC value input terminal, an auxiliary winding signal input terminal, a BD (bottom detect) signal input terminal, a dimming signal input terminal, and a mask signal output terminal.

  The auxiliary output terminal of the reactor L1 is connected to the ground terminal via a resistor R2, a resistor R4, and a resistor R5. The connection point between the resistor R4 and the resistor R5 is connected to the auxiliary winding signal input terminal of the microcomputer 2, and the diode D3 is connected in parallel with the resistor R5 to prevent a negative potential from being input to the microcomputer. doing. The auxiliary output terminal of the reactor L1 is connected to the power supply voltage VDD of the microcomputer 2 via a resistor R2, a capacitor C4, a resistor R6, and a resistor R7. The diode D5 and the emitter / base of the transistor Q2 are connected between both terminals of the resistor R7, and the collector of the transistor Q2 is connected to the ground terminal via the resistor R8. A connection point between the collector of the transistor Q2 and the resistor R8 is connected to the BD signal input terminal of the microcomputer 2. As a result, the auxiliary winding signal shown in FIG. 2A is input to the auxiliary winding signal input terminal of the microcomputer 2 after being shaped into the auxiliary winding signal shown in FIG. Further, the BD signal shown in FIG. 2C is generated and inputted to the BD signal input terminal of the microcomputer 2 from the auxiliary winding voltage shown in FIG. The BD signal is a signal for detecting a resonance voltage, and the capacitor C4, the transistor Q2, the resistors R6 to R8, and the like function as a resonance voltage detection circuit that detects the resonance voltage. In the BD signal, the values of the capacitor C4 and the resistors R6 to R8 constituting the resonance voltage detection circuit are set so that the falling edge is the bottom (the lowest point voltage) of the resonance voltage generated when the switching element Q1 is turned off. Is set.

  The auxiliary output terminal of the reactor L1 includes a resistor R2, a diode D4 whose cathode is connected to the resistor R2, a resistor R9 connected to the anode of the diode D4, and a Zener diode ZD1 whose anode is connected to the resistor R9. The resistor R10 connected to the cathode of the Zener diode ZD1 and the resistor R11 are connected to the power supply voltage VDD of the microcomputer 2. The connection point between the anode of the Zener diode ZD1 and the resistor R9 is connected to the ground terminal via the capacitor C5, and the connection point between the resistor R10 and the resistor R11 is connected to the AC value input terminal of the microcomputer 2. Thereby, the AC value according to the input voltage, that is, the AC voltage of the commercial AC power supply AC, is input to the AC value input terminal of the microcomputer 2.

  A dimming signal input from the outside as a PWM signal is input to the dimming signal processing unit. The dimming signal processing unit includes a dimming signal generation circuit that smoothes the PWM signal. The dimming signal smoothed by the dimming signal generation circuit is transmitted to the VREF terminal of the controller IC1 and the dimming signal of the microcomputer 2. It is input to the optical signal input terminal.

  The mask signal output terminal of the microcomputer 2 is connected to the OCP / BD terminal of the controller IC1 through a diode D6 whose anode is connected to the mask signal output terminal and a resistor R12 connected to the cathode of the diode D6. As a result, the mask signal output from the mask signal output terminal of the microcomputer 2 is input to the OCP / BD terminal of the controller IC1. The mask signal is a turn-on instruction signal that notifies the timing of turning on the switching element Q1 at the fall, and the control circuit 11 of the controller IC1 turns on the switching element Q1 by detecting the fall of the mask signal. The timing for turning off the switching element Q1 is determined based on the dimming signal input to the VREF terminal and the feedback current detection signal input to the ISENSE terminal. The control circuit 11 of the controller IC1 turns off the switching element Q1 based on the comparison result between the feedback current detection signal and the dimming signal.

  The microcomputer 2 is an information processing unit such as a microcomputer having a nonvolatile storage area such as a ROM (Read Only Memory), a volatile storage area such as a RAM (Random Access Memory), and the like. A control program for performing operation control is stored in the nonvolatile storage area. The microcomputer 2 reads out the control program stored in the non-volatile storage area and develops the control program in the volatile storage area, thereby, as shown in FIG. 3, a skip number determination unit 21 and a mask signal generation unit 22. Function as. Further, a skip table 23 is stored in the nonvolatile storage area of the microcomputer 2.

  In the skip table 23, the number of skips corresponding to the input voltage and the dimming rate is set. The number of skips indicates the number of times that the bottom timing at which the resonance voltage becomes the bottom (the lowest point voltage) is skipped, that is, ignored. In the present embodiment, as shown in FIG. 4, the first table 23a is referred to when the input voltage is less than 132V and the number of skips is set according to the dimming rate, and the input voltage is 132V or more and 176V. The second table 23b that is referred to when the input voltage is 176 V or more is referred to when the input voltage is 176 V or more, and is referred to when the number of skips is set according to the dimming rate. The third table 23c is stored as a skip table 23 in the nonvolatile storage area. In the first table 23a, the dimming rate is 66% or more and the skip number is 0, the dimming rate is 33% or more and less than 66%, the skip number is 1, and the dimming rate is less than 33% and the skip number is 2. Each is set. In the second table 23b, the number of skips is 0 when the dimming rate is 70% or more, the number of skips is 1 when the dimming rate is 40% or more and less than 70%, and the number of skips is 2 when the dimming rate is less than 40%. Respectively. In the third table 23c, the number of skips is 0 when the dimming rate is 80% or more, the number of skips is 1 when the dimming rate is 50% or more and less than 80%, and the number of skips is 2 when the dimming rate is less than 50%. Each is set. The dimming rate indicates that the higher the percentage, the brighter. According to the first table 23a, the second table 23b, and the third table 23c, the percentage of the dimming rate is small, that is, as the dimming is reduced, the number of skips tends to increase. Even if the dimming rate is the same percentage, the number of skips tends to increase as the AC value increases. For example, when the dimming rate is 68%, the number of skips is 0 when the input voltage is less than 132V, the number of skips is 1 when the input voltage is 132V or more and less than 176V, and the number of skips is 1 when the input voltage is 176V or more. Respectively.

  The skip number determination unit 21 recognizes the input voltage of the commercial AC power supply AC based on the AC value input to the AC value input terminal, and adjusts the dimming rate based on the dimming signal input to the dimming signal input terminal. Recognize Then, the skip number determination unit 21 specifies the skip number corresponding to the input voltage and the dimming rate by referring to the skip table 23 and notifies the mask signal generation unit 22 of it.

  When the skip number notified from the skip number determination unit 21 is N, the mask signal generation unit 22 becomes Hi level at the rising timing of the auxiliary winding signal input to the auxiliary winding signal input terminal, and the BD signal input terminal After skipping the falling timing of the BD signal input to N times N times, a mask signal that becomes a low level at the (N + 1) th falling timing is generated, and the generated mask signal is output from the mask signal output terminal. . However, N is an integer of 0 or more.

  FIG. 5A shows an example of a mask signal when N = 0 is notified as the skip number. The mask signal generator 22 sets the mask signal to Hi level at the timing t1 when the auxiliary winding signal rises. Then, the mask signal generation unit 22 sets the mask signal to the Hi level, and then skips the falling edge of the BD signal input to the BD signal input terminal, and the time when the BD signal falls (0 + 1 = 1) times The mask signal is set to the low level at the timing t2. Thus, the mask signal becomes a turn-on instruction signal that instructs the turn-on of the switching element Q1 at the bottom timing when the skip number is 0, and the bottom that turns on the switching element Q1 at the bottom timing when the resonance voltage becomes the bottom (lowest point voltage). Switching operation is performed, and switching loss can be reduced.

  FIG. 5B shows an example of a mask signal when N = 1 is notified as the skip number. The mask signal generator 22 sets the mask signal to Hi level at the timing t1 when the auxiliary winding signal rises. Then, after setting the mask signal to the Hi level, the mask signal generation unit 22 skips the timing at the time t2 when the BD signal falls for the first time, and the timing at the time t3 when the BD signal falls for the (1 + 1 = 2) th time. Then, the mask signal is set to the low level. As a result, the mask signal becomes a turn-on instruction signal for instructing the turn-on of the switching element Q1 at the bottom timing when the skip number is 1, skipping the first bottom timing when the resonance voltage becomes the bottom (lowest point voltage), A bottom skip operation for turning on the switching element Q1 is performed at the bottom timing. By the bottom skip operation, the time until the switching element Q1 is turned on can be extended, and both suppression of frequency increase and reduction of switching loss can be achieved.

  Further, when the skip number determined by the skip number determination unit 21 is changed from N to M, the mask signal generation unit 22 provides a transition period. In the transition period, the bottom timing when the skip number before the change is N And a turn-on instruction signal for instructing the turn-on of the switching element at a timing between the changed skip number and the bottom timing of M. However, M is an integer of 0 or more different from N.

  For example, when the number of skips notified from the skip number determination unit 21 is increased from N to M, the mask signal generation unit 22 provides a transition period. In this transition period, the mask signal generation unit 22 becomes Hi level at the rising timing of the auxiliary winding signal input to the auxiliary winding signal input terminal, and the (N + 1) th time of the BD signal input to the BD signal input terminal. A mask signal that is at a low level is generated at a timing delayed by the delay time Tdeley from the falling edge, and the generated mask signal is output from the mask signal output terminal. The transition period is set to 2 to 3 times the cycle of the commercial AC power supply AC, and is set to several tens of ms (a time constant that is 2 to 3 times the COMP terminal constant). The delay time Tdeley is set in a range of 0 to A times the resonance period Tres (where A is an increase number from N to M), and is gradually extended in the transition period. Thereby, in the mask signal, the timing for instructing the turn-on of the switching element Q1 is the bottom timing when the number of skips before the change is N, that is, the bottom timing when the number of skips after the change is M from the (N + 1) th bottom timing, That is, it gradually approaches the (M + 1) -th bottom timing, and switching of the bottom skip operation can prevent an abrupt change in the average value of the switch current, and allows the LED to emit light stably without flickering. Can do. Note that the delay time Tdeley may be extended linearly, or in the case of digital control, the resolution may be increased to extend stepwise.

  When the number of skips notified from the skip number determination unit 21 is decreased from N to M, the mask signal generation unit 22 provides a transition period in the same manner as when the skip number is increased. In this transition period, the mask signal generation unit 22 becomes Hi level at the rising timing of the auxiliary winding signal input to the auxiliary winding signal input terminal, and the (M + 1) th time of the BD signal input to the BD signal input terminal. A mask signal that is at a low level is generated at a timing delayed by the delay time Tdeley from the falling edge of the signal, and the generated mask signal is output from the mask signal output terminal. The delay time Tdeley is set in a range of 0 to B times the resonance period Tres, and is gradually shortened in the transition period (where B is a decrease number from N to M). Thereby, in the mask signal, the timing for instructing the turn-on of the switching element Q1 is the bottom timing when the number of skips before the change is N, that is, the bottom timing when the number of skips after the change is M from the (N + 1) th bottom timing, That is, it gradually approaches the (M + 1) -th bottom timing, and switching of the bottom skip operation can prevent an abrupt change in the average value of the switch current, and allows the LED to emit light stably without flickering. Can do. Note that the delay time Tdeley may be linearly shortened, or in the case of digital control, the resolution may be increased to be shortened step by step.

  FIG. 5C shows an example of a mask signal in a transition period when the number of skips is increased from N = 0 to M = 1 or the number of skips is decreased from N = 1 to M = 0. . The mask signal generator 22 sets the mask signal to Hi level at the timing t1 when the auxiliary winding signal rises. Then, after setting the mask signal to the Hi level, the mask signal generating unit 22 sets the mask signal to the Low level at the timing of time t4 that is delayed by the delay time Tdeley from the first fall of the BD signal (time t2). As shown in FIG. 5C, the switching operation during the transition period is not a bottom switching operation in which the switching element Q1 is turned on at the bottom (minimum voltage) of the resonance voltage, but a hardware in which the switching element Q1 is turned on regardless of the resonance voltage. Since the bottom switching operation is performed, the switching loss temporarily increases. However, it is a time of several tens of milliseconds, and the switching element Q1 is not permanently overheated.

  In the present embodiment, the buck-boost method has been described as an example, but the present invention can be applied to various chopper methods and flyback methods other than the buck-boost method. The microcomputer 2 may be configured by an analog circuit, but it is preferable to program-control the timing at which the switching element Q1 is turned on by the microcomputer 2 in order to respond more flexibly to various LED lamps.

As described above, the present embodiment is a switching power supply device that turns on the switching element Q1 at the bottom timing when the resonance voltage becomes the bottom using the resonance phenomenon accompanying the turn-off of the switching element Q1, and detects the resonance voltage. A resonance voltage detection circuit (capacitor C4, transistor Q2, resistors R6 to R8, etc.), a skip number determination unit 21 that determines the number of skips to skip the bottom timing based on a dimming signal from the outside, and a resonance voltage Based on the detection result by the detection circuit, a mask signal generation unit 22 that generates a mask signal as a turn-on instruction signal that instructs the turn-on of the switching element at the bottom timing of the number of skips, and a controller that turns on the switching element Q1 based on the mask signal IC1 When the number of skips determined by the number determination unit 21 is changed from N to M, the mask signal generation unit 22 provides a transition period. In the transition period, the number of skips before the change is changed to the bottom timing of N. A mask signal for instructing the turn-on of the switching element Q1 is generated at a timing between the later skip count and the M bottom timing.
With this configuration, in the control method that achieves both stable frequency control and switching loss reduction by bottom skip operation, it is possible to prevent a sudden change in the switch current average value by switching the bottom skip operation. The LED can emit light stably without flickering.

Further, in the present embodiment, the mask signal generation unit 22 uses the mask signal generated during the transition period to change the timing for instructing the turn-on of the switching element Q1 from the bottom timing where the number of skips before the change is N to the number of skips of M. Gradually approach the bottom timing.
With this configuration, the switching current average value can be gradually changed by switching the bottom skip operation, and therefore, flickering of the LED can be reliably prevented.

Further, in the present embodiment, the skip number determination unit 21 determines the skip number based on the dimming signal and the input voltage.
With this configuration, it is possible to set an appropriate number of skips according to the input voltage.

Furthermore, in this embodiment, the transition period is set to 2 to 3 times the cycle of the commercial AC power supply AC.
With this configuration, it is possible to reliably prevent LED flickering even in a single converter system with a power factor correction function having a relatively slow control speed.

  As mentioned above, although this invention was demonstrated by specific embodiment, the said embodiment is an example and it cannot be overemphasized that it can change and implement in the range which does not deviate from the meaning of this invention.

1 Controller IC
2 microcomputer 11 control circuit 21 skip number determination unit 22 mask signal generation unit 23 skip table 23a first table 23b second table 23c third tables C1 to C5 capacitor Ca capacitor for control circuit Cin input capacitor Co output capacitor Cv voltage resonance capacitor D1 ~ D6 Diode L1 Reactor Rs, Rocp, R1 ~ R12 Resistor Q1 Switching element Q2 Transistor ZD1 Zener diode

Claims (4)

A switching power supply device that turns on the switching element at a bottom timing when the resonance voltage becomes a bottom, using a resonance phenomenon associated with turn-off of the switching element,
A resonance voltage detection circuit for detecting the resonance voltage;
A skip number determination unit that determines the skip number for skipping the bottom timing based on a dimming signal from the outside;
Based on a detection result by the resonance voltage detection circuit, a signal generation unit that generates a turn-on instruction signal that instructs to turn on the switching element at the bottom timing of the skip number;
A control circuit for turning on the switching element based on the turn-on instruction signal,
When the skip number is changed from N to M by the skip number determination unit (where N is an integer greater than or equal to 0 and M is an integer greater than or equal to 0 different from N), the signal generation unit is In the transition period, the turn-on instruction signal for instructing the turn-on of the switching element is generated at a timing between the bottom timing with the skip number N and the bottom timing with the skip number M. A switching power supply device characterized in that:   In the turn-on instruction signal generated during the transition period, the signal generation unit gradually changes the timing for instructing the turn-on of the switching element from the bottom timing when the skip number is N to the bottom timing when the skip number is M. The switching power supply device according to claim 1, wherein   The switching power supply device according to claim 1, wherein the skip number determination unit determines the skip number based on the dimming signal and an input voltage.   The switching power supply according to any one of claims 1 to 3, wherein the transition period is set to 2 to 3 times a period of a commercial AC power supply.

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