JP5243292B2 - Switching power supply - Google Patents

Description

  The present invention relates to an overvoltage protection circuit in a switching power supply type LED driver.

  Many switching power supply type LED drivers detect the current flowing through the LED load and control the output. When a failure mode in which the LED load is open occurs, no current flows through the LED load, so the switching power supply determines that the LED is off and tries to increase the output voltage. At this time, if there is no protective circuit, the output voltage continues to rise, and eventually the switching transistor and other circuit elements may be destroyed.

  In order to prevent the output voltage from continuing to rise in this manner, Patent Documents 1 and 2 disclose that the circuit protection is performed by controlling the operation of the switching transistor when it is detected that the output voltage has become an overvoltage. Yes.

  FIG. 8 shows an example of a conventional switching power supply device. The switching power supply device of FIG. 8 uses two error amplifiers to control the operation of the switching transistor so that the load current or output voltage does not exceed a set value.

  Specifically, the switching power supply apparatus of FIG. 8 includes a power conversion unit 100 and a control unit 200. The power conversion unit 100 includes an input capacitor 2, a coil 3, a switching transistor 4, a diode 5, and an output capacitor 6. The control unit 200 includes a load current detection circuit 10, an output voltage detection circuit 11, an error amplifier 30, a phase compensation circuit 15, an error amplifier 31, a phase compensation circuit 16, and a PWM modulation circuit 32. Here, 1 is a DC power supply as an external power supply source, and 7 is an LED load that operates by receiving a stable current or voltage supply from a switching power supply device.

  The power conversion unit 100 operates by receiving the input voltage Vi from the DC power supply 1. The power conversion unit 100 is driven by the control unit 200 as follows, and a stable current or voltage obtained by the operation is supplied to the LED load 7.

  In the control unit 200, the load current detection circuit 10 generates a current feedback signal Ifb corresponding to the load current Io. The error amplifier 30 inverts and amplifies the difference between the current feedback signal Ifb and the reference voltage signal Vref1. The error signal Ve1 obtained from the error amplifier 30 is phase-compensated by the phase compensation circuit 15 and supplied to the PWM modulation circuit 32.

  The output voltage detection circuit 11 generates a voltage feedback signal Vfb corresponding to the output voltage Vo. The error amplifier 31 inverts and amplifies the difference between the voltage feedback signal Vfb and the reference voltage signal Vref2. The error signal Ve2 obtained from the error amplifier 31 is phase-compensated by the phase compensation circuit 16 and supplied to the PWM modulation circuit 32.

  The PWM modulation circuit 32 compares one of the error signal phase-compensated by the phase compensation circuit 15 and the error signal phase-compensated by the phase compensation circuit 16 with a triangular wave signal (not shown), and the switching transistor 4 Drive signal Vpwm is generated. Then, on / off of the switching transistor 4 is switched based on the generated drive signal Vpwm. As described above, the switching transistor 4 of the power conversion unit 100 is controlled by the control unit 200.

  When the switching power supply device is activated, the output voltage Vo gradually increases. When the output voltage Vo exceeds the threshold value of the LED load 7, the load current Io starts to flow through the LED load 7. Thereafter, the load current Io gradually increases, current control is performed so that the current feedback signal Ifb becomes equal to the reference voltage signal Vref1, and the load current Io becomes a constant value.

  When an open failure or the like occurs in the LED load 7 and the load current Io does not flow, the output voltage Vo further increases. When the overvoltage is detected, the PWM modulation circuit 32 generates the drive signal Vpwm based on the error signal phase-compensated by the phase compensation circuit 16. At this time, voltage control is performed so that the voltage feedback signal Vfb becomes equal to the reference voltage signal Vref2, and the output voltage Vo becomes a constant value, thereby preventing the output voltage Vo from rising without limitation.

  FIG. 9 shows an example in which the current feedback signal Ifb and the voltage feedback signal Vfb are supplied to one error amplifier as another conventional example. The same number is given to the same component as FIG.

  The switching power supply apparatus of FIG. 9 includes a power conversion unit 100 and a control unit 201, and the configuration of the control unit 201 is different from the switching power supply of FIG. The control unit 201 includes a load current detection circuit 10, an output voltage detection circuit 11, an error amplifier 33, a phase compensation circuit 15, and a PWM modulation circuit 34.

  The error amplifier 33 is supplied with a feedback signal having a high signal level by comparing the current feedback signal Ifb and the voltage feedback signal Vfb. The error amplifier 33 inverts and amplifies the difference between one of the feedback signals and the reference voltage signal Vref3. The error signal Ve3 obtained from the error amplifier 33 is phase-compensated by the phase compensation circuit 15 and supplied to the PWM modulation circuit 34.

  The PWM modulation circuit 34 generates a drive signal Vpwm for the switching transistor 4 based on the error signal phase-compensated by the phase compensation circuit 15. Then, on / off of the switching transistor 4 is switched based on the generated drive signal Vpwm.

  When the current feedback signal Ifb is supplied to the error amplifier 33, current control is performed by the current feedback signal Ifb from the load current detection circuit 10 so that the load current Io becomes a constant value.

  When the output voltage Vo rises due to an open failure in the LED load 7 or the like, the voltage feedback signal Vfb is supplied to the error amplifier 33, and the output voltage Vo is a constant value by the voltage feedback signal Vfb from the output voltage detection circuit 11. The voltage is controlled so that

JP2006-085993 JP2001-190067

  In the conventional switching power supply as shown in FIG. 8, an error signal is generated from the current feedback signal Ifb and the voltage feedback signal Vfb by two error amplifiers. Therefore, an increase in circuit scale is a problem.

  In the conventional switching power supply as shown in FIG. 9, the current feedback signal Ifb and the voltage feedback signal Vfb are compared with the reference signal Vref3 by one error amplifier. The error amplifier 23 is normally connected to a phase compensation circuit 15 optimized for load current control. Therefore, when an overvoltage is detected, in other words, when the LED load 7 is switched to a state in which the voltage is controlled, a response is delayed and an overshoot of the output voltage Vo occurs.

  Accordingly, an object of the present invention is to suppress an increase in circuit scale and suppress an overshoot of an output voltage when an overvoltage is detected.

  In order to solve the above problems, the present invention provides a load current detection circuit that generates a current feedback signal according to a load current, an output voltage detection circuit that generates a voltage feedback signal according to an output voltage, and the current feedback signal or the In a step-up switching power supply device having an error amplifier that generates an error signal based on a voltage feedback signal and a phase compensation circuit that performs phase compensation of the error signal, either the current feedback signal or the voltage feedback signal A first switch circuit that selects one of the two and supplies the error amplifier; a second switch circuit that changes a connection configuration of the phase compensation circuit; and the load current and the output voltage, 1 switch circuit and a switch control circuit that switches the connection of the second switch circuit at the same time, and the output voltage of the switch control circuit is less than a predetermined voltage. Or when the load current is larger than a predetermined current, the current feedback signal is supplied to the error amplifier, the load current is equal to or lower than the predetermined current, and the output voltage reaches the predetermined voltage, The connection of the first switch circuit is switched so that a voltage feedback signal is supplied to the error amplifier.

  According to the present invention, even when an error signal for performing current control and voltage control is generated using one error amplifier, high-speed and stable operation when an overvoltage occurs is possible. In addition, since the circuit for switching between current control and voltage control is composed of a small logic circuit and a switch, an increase in circuit scale can be suppressed.

Step-up switching power supply device according to first embodiment of the present invention Specific examples of the first and second phase compensation circuits in the first embodiment Other specific examples of the first and second phase compensation circuits in the first embodiment Operational waveform of step-up switching power supply device of the present invention Step-up switching power supply device according to second embodiment of the present invention Specific Example of Phase Compensation Circuit in Second Embodiment Another specific example of the phase compensation circuit in the second embodiment Conventional step-up switching power supply. Conventional step-up switching power supply.

  Embodiments of the present invention will be described below.

  FIG. 1 shows a switching power supply apparatus according to a first embodiment of the present invention. The switching power supply device shown in FIG. 1 includes a power conversion unit 100 and a control unit 101. The power conversion unit 100 includes an input capacitor 2, a coil 3, a switching transistor 4, a diode 5, and an output capacitor 6. The control unit 101 also includes a load current detection circuit 10, an output voltage detection circuit 11, a first switch circuit 12, an error amplifier 13, a second switch circuit 14, a first phase compensation circuit 15, and a second phase compensation. A circuit 16, a PWM modulation circuit 17, and a switch control circuit 18 are included.

  The power converter 100 is supplied with the input voltage Vi from the DC power source 1. The power conversion unit 100 is driven and controlled by the control unit 101, and power is supplied to the LED load 7.

  Inside the controller 101, the load current detection circuit 10 generates a current feedback signal Ifb corresponding to the load current Io. The output voltage detection circuit 11 generates a voltage feedback signal Vfb corresponding to the output voltage Vo.

  The current feedback signal Ifb and the voltage feedback signal Vfb are supplied to the error amplifier 13 via the first switch circuit 12. The error amplifier 13 inverts and amplifies the difference between the feedback signal of either the current feedback signal Ifb or the voltage feedback signal Vfb and the reference voltage signal Vref. Which feedback signal is supplied to the error amplifier 13 can be selected by switching the connection of the first switch circuit 12.

  A first phase compensation circuit 15 and a second phase compensation circuit 16 are connected to the output terminal of the error amplifier 13 via a second switch circuit 14. The error signal Ve obtained from the error amplifier 13 is phase-compensated by one of the phase compensation circuits selected by the second switch circuit 14 and supplied to the PWM modulation circuit 17.

  A specific example of the first phase compensation circuit 15 and the second phase compensation circuit 16 is shown in FIG. In FIG. 2, the resistor 20 and the capacitor 21 constitute the first phase compensation circuit 15 in FIG. 1, and the resistor 20 and the capacitor 22 constitute the second phase compensation circuit 16.

  The resistor 20 is connected between the output terminal and the inverting input terminal of the error amplifier 13, that is, the feedback unit. The capacitor 21 and the capacitor 22 are respectively connected in parallel with the resistor 20 via the second switch circuit 14. The second switch circuit 14 selects one of the capacitor 21 and the capacitor 22.

  When the second switch circuit 14 selects the capacitor 21, the phase compensation of the error signal Ve is performed by the first phase compensation circuit 15 including the resistor 20 and the capacitor 21. When the second switch circuit 14 selects the capacitor 22, the phase compensation of the error signal Ve is performed by the second phase compensation circuit 16 including the resistor 20 and the capacitor 22.

  Thus, by switching the connection of the second switch circuit 14, the phase compensation circuit that performs phase compensation of the error signal Ve is switched. That is, the phase compensation of the error signal Ve can be selectively performed by phase compensation circuits having different constants.

  FIG. 3 shows another specific example of the first phase compensation circuit 15 and the second phase compensation circuit 16. 2, the resistor 20 and the capacitor 21 constitute the first phase compensation circuit 15 in FIG. 1, and the resistor 20 and the capacitor 22 constitute the second phase compensation circuit 16.

  One terminal of the resistor 20 is connected to the output terminal of the error amplifier 13. The capacitor 21 and the capacitor 22 are connected in parallel between the other terminal of the resistor 20 and GND through the second switch circuit 14. The operation of the second switch circuit 14 is the same as that described in FIG.

  As shown in FIG. 3, the first phase compensation circuit 15 and the second phase compensation circuit 16 are not feedback units of the error amplifier 13, but the second switch circuit 14 is connected between the output terminal of the error amplifier 13 and GND. You may connect via.

  In addition to the configurations shown in these two specific examples, the second switch circuit 14 may change the resistance value of the phase compensation circuit or change both the resistance value and the capacitance value. As long as the second switch circuit 14 changes the constant of the phase compensation circuit that performs phase compensation of the error signal Ve, the connection form of the phase compensation circuit and the second switch circuit 14 is not limited.

  As described above, the error signal Ve is phase-compensated by one of the phase compensation circuits and supplied to the PWM modulation circuit 17. The PWM modulation circuit 17 compares the error signal phase-compensated by one of the phase compensation circuits with a triangular wave signal (not shown), and generates the drive signal Vpwm for the switching transistor 4. Then, on / off of the switching transistor 4 is switched based on the generated drive signal Vpwm.

  Energy is stored in the coil 3 from the DC power source 1 during the period when the switching transistor 4 is turned on. The input capacitor 2 reduces the ripple and noise of the input voltage Vi. The current flowing through the LED load 7 in this cycle is supplied from the output capacitor 6. When the switching transistor 4 is turned off, the energy stored in the coil 3 is supplied to the LED load 7 and the output capacitor 6 through the diode 5.

  The switch control circuit 18 generates a signal for switching the connection between the first switch circuit 12 and the second switch circuit 14 in accordance with the load current Io and the output voltage Vo.

  For example, the switch control circuit 18 supplies the current feedback signal Ifb to the error amplifier 13 and outputs the first phase compensation when the output voltage Vo is less than a predetermined voltage or when the load current is larger than the predetermined current. The connection of the first and second switch circuits is switched so that the circuit 15 is selected. Further, when the load current Io becomes equal to or lower than the predetermined current and the output voltage Vo reaches the predetermined voltage, the voltage feedback signal Vfb is supplied to the error amplifier 13 and the second phase compensation circuit 16 is selected. The connection of the first and second switch circuits is switched.

  SW1 and SW2 in the first switch circuit 12 are controlled by the switch control circuit 18 so as to complementarily turn on and off. Similarly, SW3 and SW4 in the second switch circuit 14 are turned on and off in a complementary manner. Further, SW1 and SW3 are controlled to be turned on or off at the same time, and SW2 and SW4 are also turned on or off at the same time.

  When SW1 and SW3 are turned on and SW2 and SW4 are turned off, the current feedback signal Ifb is supplied to the error amplifier 13, and the first phase compensation circuit 15 is selected. At this time, current control is performed so that the current feedback signal Ifb from the load current detection circuit 10 becomes equal to the reference voltage signal Vref, and the load current Io becomes a constant value.

  When SW2 and SW4 are turned on and SW1 and SW3 are turned off, the voltage feedback signal Vfb is supplied to the error amplifier 13 and the second phase compensation circuit 16 is selected. At this time, voltage control is performed so that the voltage feedback signal Vfb from the load voltage detection circuit 11 becomes equal to the reference voltage signal Vref, and the output voltage Vo becomes a constant value.

  Thus, the first phase compensation circuit 15 is selected when the LED load 7 is current-controlled, and the second phase compensation circuit 16 is selected when the LED load 7 is voltage-controlled. Each phase compensation circuit has a constant optimized for each control operation.

  Since the switch circuits 12 and 14 and the switch control circuit 18 for switching the control operation state of the LED load 7 can be configured by small logic circuits and switches, an increase in circuit scale can be suppressed.

  Next, a specific operation example will be described using the operation waveform diagram of FIG. In FIG. 4, the vertical axis represents voltage or current, and the horizontal axis represents time.

  The switch control circuit 18 switches SW2 and SW4 on when the load current Io is equal to or less than the LED lighting detection value Idet and the output voltage Vo reaches the overvoltage detection voltage Vdet. In other states, SW1 and SW3 are configured to be on.

  At time t1, when the switching power supply device is activated, the output voltage Vo starts to increase. At this startup, the load current Io is less than the LED lighting detection value Idet, but since the output voltage Vo is less than the overvoltage detection voltage Vdet, SW1 and SW3 are turned on, SW2 and SW4 are turned off, and the LED load 7 is Current controlled. When the output voltage Vo exceeds the threshold value of the LED load 7, the load current Io starts to flow. Then, the current feedback signal Ifb is controlled to be equal to the reference voltage signal Vref, and when the steady state is reached, a constant current (load control current Ic) is supplied to the LED load 7.

  Assume that the LED load 7 is opened at time t2 after the steady state is reached. Then, since no current flows to the LED load 7, the PWM modulation circuit 17 drives the switching transistor 4 to further increase the output voltage Vo.

  The output voltage Vo rises with time and reaches the overvoltage detection voltage Vdet at time t3. Then, SW2 and SW4 are turned on, SW1 and SW3 are turned off, and the LED load 7 is voltage-controlled. The voltage feedback signal Vfb is controlled to be equal to the reference voltage signal Vref, and the output voltage Vo is controlled to a constant voltage (overvoltage protection control voltage Vc). At this time, the phase compensation circuit that performs phase compensation of the error signal Ve is switched to the second phase compensation circuit 16 having a constant optimized for voltage control, so that overshoot of the output voltage Vo when an overvoltage occurs is suppressed. It becomes possible.

  Thus, when it is detected that an overvoltage has occurred, the feedback signal supplied to the error amplifier 13 is switched from the current feedback signal Ifb to the voltage feedback signal Vfb, and the LED load 7 is voltage-controlled. At the same time, the phase compensation circuit connected to the output side of the error amplifier 13 is switched to one optimized for voltage control. As a result, even when an error signal for performing current control and voltage control is generated using one error amplifier, overshoot of the output voltage Vo when an overvoltage occurs can be suppressed, and high-speed and stable operation is possible. It becomes. Since the switch control circuit 18 is composed of a small logic circuit, the increase in circuit scale is small.

  FIG. 5 shows a second embodiment of the switching power supply device according to the present invention. The basic configuration is the same as that of the first embodiment, and only the configuration of the phase compensation circuit and the second switch circuit 14 is different. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The switching power supply apparatus of FIG. 5 is obtained by omitting the SW 4 and the second phase compensation circuit 16 in the second switch circuit 14 in the first embodiment. The second switch circuit 14 is characterized by selecting or deselecting the phase compensation circuit 15 for performing phase compensation of the error signal Ve.

  Here, FIG. 6 shows a specific example of the phase compensation circuit in the second embodiment. In FIG. 6, a resistor 20 and a capacitor 21 constitute the phase compensation circuit 15 in FIG. The phase compensation circuit 15 is connected to the feedback unit of the error amplifier 13 via the second switch circuit 14.

  The resistor 20 is connected to the feedback section of the error amplifier 13 via the second switch circuit 14. The capacitor 21 is connected in parallel with the resistor 20. When SW3 in the second switch circuit 14 is turned on, the phase compensation circuit 15 is connected to the error amplifier 13. The configuration is such that the phase compensation circuit 15 is disconnected from the error amplifier 13 when SW3 in the second switch circuit 14 is turned off.

  FIG. 7 shows another specific example of the phase compensation circuit in the second embodiment. As in FIG. 6, the resistor 20 and the capacitor 21 constitute the phase compensation circuit 15 in FIG. The phase compensation circuit 15 is connected between the output terminal of the error amplifier 13 and GND via the second switch circuit 14.

  One terminal of the resistor 20 is connected to the output terminal of the error amplifier 13. The capacitor 21 is connected in parallel between the other terminal of the resistor 20 and GND via the second switch circuit 14. As described with reference to FIG. 6, when SW3 in the second switch circuit 14 is turned on, the phase compensation circuit 15 is connected to the error amplifier 13. The configuration is such that the phase compensation circuit 15 is disconnected from the error amplifier 13 when SW3 in the second switch circuit 14 is turned off.

  In the second embodiment, when the current feedback signal Ifb is supplied to the error amplifier 13 and the LED load 7 is current-controlled, SW3 in the second switch circuit 14 is turned on. When the voltage feedback signal Vfb is supplied to the error amplifier 13 and the LED load 7 is voltage-controlled, SW3 in the second switch circuit 14 is turned off, and the phase compensation circuit 15 is disconnected from the error amplifier 13.

  When the LED load 7 is current-controlled, the control unit 101 can be stably operated by connecting the phase compensation circuit 15 to the error amplifier 13 and performing phase compensation of the error signal Ve. When overvoltage is detected, that is, when the LED load 7 is voltage-controlled, the control unit 101 can be made to respond at high speed by disconnecting the phase compensation circuit 15 and the overshoot of the output voltage Vo can be suppressed.

  As long as the second switch circuit 14 switches between connecting and disconnecting the phase compensation circuit 15 to the error amplifier 13, the connection form of the phase compensation circuit and the second switch circuit 14 is not limited.

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Input capacitor 3 Coil 4 Switching transistor 5 Diode 6 Output capacitor 7 LED load 10 Load current detection circuit 11 Output voltage detection circuit 12 First switch circuit 13 Error amplifier 14 Second switch circuit 15 First phase compensation Circuit 16 Second phase compensation circuit 17 PWM modulation circuit 18 Switch control circuit 20 Phase compensation resistor 21 Phase compensation capacitor 22 Phase compensation capacitor 100 Power conversion unit 101 Control unit

Claims (7)

A load current detection circuit that generates a current feedback signal according to the load current;
An output voltage detection circuit for generating a voltage feedback signal according to the output voltage;
An error amplifier that generates an error signal based on the current feedback signal or the voltage feedback signal;
In a step-up switching power supply device having a phase compensation circuit that performs phase compensation of the error signal,
A first switch circuit for selecting one of the current feedback signal and the voltage feedback signal and supplying the selected one to the error amplifier;
A second switch circuit for changing the connection configuration of the phase compensation circuit;
A switch control circuit for simultaneously switching the connection of the first switch circuit and the second switch circuit according to the load current and the output voltage;
The switch control circuit supplies the current feedback signal to the error amplifier when the output voltage is less than a predetermined voltage, or when the load current is larger than a predetermined current, and the load current becomes a predetermined current or less, In addition, when the output voltage reaches the predetermined voltage, the connection of the first switch circuit is switched so as to supply the voltage feedback signal to the error amplifier. The phase compensation circuit comprises first and second phase compensation circuits;
2. The step-up switching power supply device according to claim 1, wherein the second switch circuit selects one of the first and second phase compensation circuits.   3. The step-up switching power supply device according to claim 2, wherein the first and second phase compensation circuits are connected to a feedback unit of the error amplifier via the second switch circuit.   3. The step-up switching power supply according to claim 2, wherein the first and second phase compensation circuits are connected between an output terminal of the error amplifier and GND via the second switch circuit. apparatus.   2. The step-up switching power supply device according to claim 1, wherein the second switch circuit connects or disconnects the phase compensation circuit to the error amplifier.   6. The step-up switching power supply device according to claim 5, wherein the phase compensation circuit is connected to a feedback unit of the error amplifier via the second switch circuit.   6. The step-up switching power supply device according to claim 5, wherein the phase compensation circuit is connected between the output terminal of the error amplifier and GND via the second switch circuit.

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