Power supply control device and switching power supply device

Abstract

Provided are a power supply control device and a switching power supply device. The power supply control device controls a switching element of the switching power supply device, which includes a transformer having a primary winding, a secondary winding, and an auxiliary winding; the switching element connected to the primary winding; and a capacitor connected to the auxiliary winding. The power supply control device has a power supply terminal connected to one end of the capacitor; a switch and a resistor connected in series between the power supply terminal and ground; a first control circuit that controls the switch; and a second control circuit that controls the switching element. The first control circuit performs control to turn on the switch when a first voltage applied to the power supply terminal exceeds a first reference voltage for a first time. The second control circuit performs control to turn off the switching element when the first voltage exceeds a second reference voltage higher than the first reference voltage.

Description

Technical Field

[0001] This invention relates to power control devices and switching power supply devices. Background Technology

[0002] Conventional switching power supply devices are known that rectify and smooth a DC voltage derived from an AC power supply by switching a switching element on and off, thereby outputting a voltage Vout. Furthermore, it is generally known that the switching of this switching element is controlled, for example, by a power control device made of an integrated circuit.

[0003] The voltage Vcc of the power supply driving such a power control device is the voltage induced in the auxiliary winding of the transformer by switching the switching elements on and off. Patent Document 1 discloses a power control device in which, when the load becomes heavier and the voltage Vcc gradually rises, and an overvoltage of the voltage Vcc is detected, the power supply terminal to which the applied voltage Vcc is connected to ground, which is a ground potential, via a virtual resistor, and the voltage Vcc is reduced by allowing current to flow through the virtual resistor.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2007-215336

[0005] The power control device disclosed in Patent Document 1 immediately flows a large current through the virtual resistor when the voltage Vcc reaches 23V, thereby reducing the voltage Vcc. Therefore, even if the switching power supply device malfunctions, it is difficult for the voltage Vcc to exceed the overvoltage protection voltage (25V), and it may be unable to perform the function of disconnecting the switching element. Summary of the Invention

[0006] One embodiment of the power control device of the present invention controls a switching element of a switching power supply device, the switching power supply device comprising: a transformer having a primary winding, a secondary winding and an auxiliary winding; the switching element connected to the primary winding; and a capacitor connected to the auxiliary winding. The power control device further comprises: a power terminal connected to one end of the capacitor; a switch and a resistor connected in series between the power terminal and ground; a first control circuit controlling the switch; and a second control circuit controlling the switching element. The first control circuit controls the switch to turn on when a first voltage applied to the power terminal continuously exceeds a first reference voltage for a first time, and the second control circuit controls the switch to turn off when the first voltage exceeds a second reference voltage higher than the first reference voltage. Attached Figure Description

[0007] Figure 1It is a diagram showing the general structure of a switching power supply device.

[0008] Figure 2 This is a diagram showing the general structure of the power control device.

[0009] Figure 3 This is a diagram representing an example from the very first moment.

[0010] Figure 4 This is a graph showing an example of the time series variation of voltage Vcc.

[0011] Label Explanation

[0012] 1: Switching power supply device; 10: AC power supply; 12: Capacitor; 40: Transformer; 50: Error amplifier; 100: Power control device; 101: First voltage detection circuit; 102: Second voltage detection circuit; 103: First reference voltage generation circuit; 104: Second reference voltage generation circuit; 105: First comparator; 106: Second comparator; 111: Timing circuit; 112: Control circuit; 113: Output circuit; 121: Third voltage detection circuit; 123: Third reference voltage generation circuit; 125: Third comparator; 200: First control circuit; 300: Second control circuit; Q11: Switching element; Q21: Switch; R21: Resistor; Vth1: First reference voltage; Vth2: Second reference voltage; Vth3: Third reference voltage. Detailed Implementation

[0013] Hereinafter, preferred embodiments of the present invention will be described using the accompanying drawings. The drawings are provided for ease of explanation. Furthermore, the embodiments described below do not unduly limit the scope of the invention as defined in the claims. Additionally, not all structures described below are necessarily essential structural elements of the present invention.

[0014] 1. Structure of a switching power supply device

[0015] Figure 1 This is a structural example of a switching power supply device 1 including a power control device 100. The switching power supply device 1 is a so-called flyback AC-DC converter. Specifically, the switching power supply device 1 stores energy by allowing current to flow through the primary winding P of the transformer 40 when the switching element Q11 is turned on. When the switching element Q11 is turned off, the energy stored in the primary winding P is output from the secondary winding S of the transformer 40 via the diode D14. The switching power supply device 1 smooths the voltage output from the diode D14 using a capacitor C14, thereby generating a DC voltage Vout.

[0016] The switching power supply device 1 includes an AC power supply 10, a transformer 40, an error amplifier 50, a power control device 100, a diode bridge Db, a switching element Q11, capacitors C11, C12, C13, C14, diodes D11, D12, D13, D14, and a resistor R11.

[0017] The AC voltage based on AC power supply 10 is the AC input voltage of switching power supply device 1. A diode bridge Db rectifies the AC voltage based on AC power supply 10. The positive terminal of diode bridge Db is connected to one end of the primary winding P in transformer 40 and one end of capacitor C11, while the negative terminal of diode bridge Db and the other end of capacitor C11 are connected to ground. For example, ground is at ground potential. Additionally, ground is connected to the terminal TGnd of power control device 100.

[0018] In addition to the primary winding P, transformer 40 also has a secondary winding S and an auxiliary winding D. The other end of the primary winding P is connected to the drain of switching element Q11. Switching element Q11 is, for example, an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), with its source connected to one end of resistor R11. The other end of resistor R11 is grounded. Therefore, the primary winding P and switching element Q11 are connected in series between the positive and negative terminals of the diode bridge Db.

[0019] The buffer circuit Snb is set between one end and the other end of the primary winding P in the transformer 40 to absorb the transient voltage generated in the primary winding P due to the switching of the switching element Q11.

[0020] One end of the secondary winding S is connected to the anode of diode D14. Capacitor C14 is connected between the cathode of diode D14 and the other end of the secondary winding S. The voltage smoothed by capacitor C14 is output as Vout. Diode D14 and capacitor C14 rectify and smooth the voltage induced in the secondary winding S, generating the DC output voltage Vout of the switching power supply device 1.

[0021] The light-emitting diode (LED) Pct and the phototransistor Pcr constitute an optocoupler. The anode of the LED Pct is connected to the cathode of the diode D14, and the cathode of the LED Pct is connected to the error amplifier 50. The error amplifier 50 causes a current corresponding to the deviation between the voltage Vout and the reference voltage of the error amplifier 50 to flow through the LED Pct.

[0022] The anode of diode D13 is connected to one end of the auxiliary winding D of transformer 40. The cathode of diode D13 is connected to terminal TVcc of power control device 100 and one end of capacitor C12. The other end of auxiliary winding D and the other end of capacitor C12 are grounded. Terminal TVcc is an example of a power supply terminal.

[0023] The voltage induced in the auxiliary winding D is rectified by diode D13 and smoothed by capacitor C12. Diode D13 and capacitor C12 rectify and smooth the voltage induced in the auxiliary winding D to generate Vcc, which is the voltage input to terminal TVcc of power control device 100. The generated voltage Vcc is the power supply voltage of power control device 100, and is an example of a first voltage.

[0024] The emitter of the phototransistor Pcr is grounded, and its collector is connected to terminal TFb of the power control device 100. Capacitor C13 is connected in parallel with the phototransistor Pcr. The collector current flowing through the phototransistor Pcr depends on the amount of light received from the light-emitting diode Pct. That is, the larger the voltage Vout, the more light emitted by the light-emitting diode Pct, and therefore the larger the collector current of the phototransistor Pcr.

[0025] The power control device 100 is configured, for example, as an integrated circuit device. Terminal TFb is pulled up to its internal power supply voltage, and a voltage Fb is generated at terminal TFb by the collector current flowing into the phototransistor Pcr. Voltage Fb varies according to the collector current of the phototransistor Pcr. That is, voltage Fb is the voltage corresponding to the deviation from voltage Vout.

[0026] The power control device 100 detects the voltage Fb and controls the switching element Q11 to reduce the deviation of the voltage Vout represented by the voltage Fb. Specifically, the power control device 100 performs PWM (Pulse Width Modulation) control based on the voltage CS and the voltage Fb applied to one end of the resistor R11, which are input from the terminal TCS, to reduce the deviation of the voltage Vout, and generates a drive signal DRV. The drive signal DRV output from the terminal TDRV is supplied to the gate of the switching element Q11.

[0027] In addition, Figure 1 In this configuration, the switching element Q11 is separate from the power control device 100, but it can also be integrated into the power control device 100.

[0028] Diodes D11 and D12 perform full-wave rectification of the AC voltage from AC power supply 10, generating a full-wave rectified voltage VH. The full-wave rectified voltage VH is input to terminal TVH of power control device 100.

[0029] If capacitor C12 is not fully charged, the voltage Vcc will be low, and the power control device 100 may fail to operate properly. Therefore, the power control device 100 can control the charging of capacitor C12 by applying a full-wave rectified voltage VH to terminal TVH. For example, if the voltage induced in the auxiliary winding D is low immediately after the AC power supply 10 is turned on, capacitor C12 may not be fully charged, and the voltage Vcc may be low.

[0030] 2. Structure of the power control device

[0031] Reference Figure 2 ,right Figure 1 The general structure of the terminals TDRV, TVcc, TFb, TCS, and TGnd of the power control device 100 shown will be described.

[0032] The power control device 100 includes a first control circuit 200, a second control circuit 300, a switch Q21, and a resistor R21. The power supply terminal of the power control device 100 is terminal TVcc, and the ground terminal is terminal TGnd.

[0033] The first control circuit 200 includes a first voltage detection circuit 101, a first reference voltage generation circuit 103, a first comparator 105, a timing circuit 111, a third voltage detection circuit 121, a third reference voltage generation circuit 123, and a third comparator 125. The first control circuit 200 is a circuit that controls the switch Q21.

[0034] The first voltage detection circuit 101 is connected to the terminal TVcc and detects the voltage Vcc, which is the power supply voltage of the power control device 100. The detected voltage Vcc is input to the positive input terminal of the first comparator 105. On the other hand, the first reference voltage Vth1 generated by the first reference voltage generation circuit 103 is input to the negative input terminal of the first comparator 105. For example, the first reference voltage generation circuit 103 may be a structure that divides the voltage VH input to the terminal TVH (not shown) with multiple resistors to generate the first reference voltage Vth1. Alternatively, the first reference voltage generation circuit 103 may be a structure that generates the first reference voltage Vth1 by stepping down the voltage VH using a step-down circuit.

[0035] The first comparator 105 outputs a low-level signal to the timing circuit 111 when Vcc < Vth1, and a high-level signal to the timing circuit 111 when Vcc > Vth1. The signal input from the first comparator 105 to the timing circuit 111 is designated as input signal A. Furthermore, the signal output from the timing circuit 111 to switch Q21 is designated as output signal B.

[0036] The third voltage detection circuit 121 is connected to the terminal TVcc and detects the voltage Vcc, which is the power supply voltage of the power control device 100. The detected voltage Vcc is input to the negative input terminal of the third comparator 125. On the other hand, the third reference voltage Vth3 generated by the third reference voltage generation circuit 123 is input to the positive input terminal of the third comparator 125.

[0037] When Vcc > Vth3, the third comparator 125 outputs a low-level signal to the timing circuit 111; when Vcc < Vth3, it outputs a high-level signal to the timing circuit 111. The signal input from the third comparator 125 to the timing circuit 111 is designated as the input signal C.

[0038] When both the input signal A and the output signal B are at level L, switch Q21 is in the off state. On the other hand, when the input signal A switches from level L to level H, if the input signal A remains at level H for a predetermined first time, the timing circuit 111 switches the output signal B from level L to level H, and switch Q21 switches from off to on.

[0039] As described below, when switch Q21 switches from open to closed, voltage Vcc decreases. When voltage Vcc decreases and falls below the third reference voltage Vth3, the output signal of the third comparator 125 switches from L level to H level. That is, the input signal C of timing circuit 111 switches from L level to H level, and timing circuit 111 switches its output signal B from H level to L level, thus switching switch Q21 from closed to open.

[0040] For example, the timing circuit 111 can also be configured to receive a periodic pulse signal generated by an oscillator (not shown) and be able to set a first time based on the pulse signal. In this configuration, the timing circuit 111 can, for example, set the first time based on the number of input pulses.

[0041] Switch Q21 can also be an N-channel MOSFET, for example. The output signal B of timing circuit 111 is input to the gate of switch Q21. When the output signal B is at a high level (H), switch Q21 is turned on, and terminal TVcc is grounded through resistor R21. When the output signal B is at a low level (L), switch Q21 is turned off, and terminal TVcc is not connected to ground.

[0042] The second control circuit 300 includes a second voltage detection circuit 102, a second reference voltage generation circuit 104, a second comparator 106, a control circuit 112, and an output circuit 113. The second control circuit 300 is a circuit that controls the switching element Q11.

[0043] The second voltage detection circuit 102 is connected to the terminal TVcc and detects the voltage Vcc, which is the power supply voltage of the power control device 100. The detected voltage Vcc is input to the positive input terminal of the second comparator 106. On the other hand, the second reference voltage Vth2 generated by the second reference voltage generation circuit 104 is input to the negative input terminal of the second comparator 106.

[0044] When Vcc < Vth2, the second comparator 106 outputs an L-level signal to the control circuit 112, and when Vcc > Vth2, it outputs an H-level signal to the control circuit 112.

[0045] Control circuit 112 generates a control signal for controlling switching element Q11 and outputs it to output circuit 113. When a signal of level L is input from the second comparator 106, control circuit 112 generates a control signal to switch switching element Q11 on and off. The generated control signal is supplied to switching element Q11 via output circuit 113. Output circuit 113 functions, for example, as a timing buffer for adjusting the output of the control signal. In this case, energy is supplied to transformer 40, and the switching power supply device 1 outputs voltage Vout.

[0046] Additionally, control circuit 112 receives the voltage CS applied to one end of resistor R11 from terminal TCS, and the voltage Fb, which varies according to the collector current of phototransistor Pcr, from terminal TFb. The collector current of phototransistor Pcr flows according to the amount of light emitted by light-emitting diode Pct. The amount of light emitted by light-emitting diode Pct corresponds to the deviation between voltage Vout and the reference voltage of error amplifier 50.

[0047] Based on the voltages CS and Fb, the control circuit 112 performs PWM control to reduce the deviation of the voltage Vout, generating a drive signal DRV. The drive signal DRV output from the terminal TDRV is supplied to the switching element Q11.

[0048] On the other hand, when a signal of level H is input from the second comparator 106, the control circuit 112 generates a control signal that turns off the switching element Q11. The generated control signal is supplied to the switching element Q11 via the output circuit 113. In this case, the supply of energy to the transformer 40 stops, and the switching power supply device 1 stops. Therefore, the voltage Vout decreases, and the voltage Vcc also decreases accordingly.

[0049] 3. Control of the switch by the first control circuit

[0050] Reference Figure 2 and Figure 3The control of the first control circuit 200 will be described. The voltage Vcc rises slowly and continuously after the power supply device 1 is turned on. The first voltage detection circuit 101 detects the voltage Vcc input from the terminal TVcc, and the voltage Vcc detected by the first voltage detection circuit 101 is compared with the first reference voltage Vth1 generated by the first reference voltage generation circuit 103 through the first comparator 105.

[0051] Similarly, the third voltage detection circuit 121 detects the voltage Vcc input from the terminal TVcc, and the voltage Vcc detected by the third voltage detection circuit 121 is compared with the third reference voltage Vth3 generated by the third reference voltage generation circuit 123 through the third comparator 125. In addition, the voltage Vcc detected by the first voltage detection circuit 101 and the third voltage detection circuit 121 is an example of the first voltage.

[0052] When Vcc < Vth1, that is, when the voltage Vcc is lower than the first reference voltage Vth1, the output of the first comparator 105 is at level L. If the output signal B of the timing circuit 111 is also at level L, then the switch Q21 is open. That is, the first control circuit 200 does not control the voltage Vcc, and the voltage Vcc does not change.

[0053] If the state of Vcc > Vth1 persists for a first time, that is, if the voltage Vcc exceeds the first reference voltage Vth1 for a first time, the first control circuit 200 controls the voltage Vcc to decrease. In this case, the output signal of the first comparator 105, that is, the input signal A of the timing circuit 111, remains at level H for a first time, so the output signal B switches from level L to level H. Therefore, switch Q21 switches from open to closed.

[0054] With switch Q21 turned on, terminal TVcc and ground are connected via resistor R21. Therefore, current flows from terminal TVcc towards ground through resistor R21. Because a voltage drop occurs in resistor R21, the voltage Vcc decreases. Furthermore, switch Q21 is an example of a switch, and resistor R21 is an example of a resistor.

[0055] When the voltage Vcc drops below the third reference voltage Vth3, i.e., when Vcc < Vth3, the output signal of the third comparator 125, i.e., the input signal C of the timing circuit 111, switches from L level to H level. Simultaneously, the output signal B of the timing circuit 111 switches from H level to L level. Therefore, switch Q21 switches from ON to OFF, and no current flows through resistor R21. Since no current flows through resistor R21, no voltage drop is generated in resistor R21, and the control based on the first control to reduce the voltage Vcc stops.

[0056] After the control based on the first control to reduce voltage Vcc stops, voltage Vcc continues to rise slowly. If the voltage Vcc rises above the first reference voltage Vth1 for a first time, the control based on the first control circuit 200 to reduce voltage Vcc is performed again. If voltage Vcc is lower than the third reference voltage Vth3, the control based on the first control circuit 200 to reduce voltage Vcc stops. Voltage Vcc is controlled by the first control circuit 200 to be between the third reference voltage Vth3 and the first reference voltage Vth1. For example, the first reference voltage Vth1 is 48V, and the third reference voltage is 45V.

[0057] Figure 3 This is a diagram illustrating an example of the first time point. The horizontal axis represents time. As shown, the time from time t0 to time t1 is defined as the first time point T1. The CLK signal is shown as an example of a reference signal. Input signal A is the input signal of timing circuit 111, which is at level L when Vcc < Vth1 and at level H when Vcc > Vth1.

[0058] When the voltage Vcc rises above the first reference voltage Vth1, i.e., when Vcc > Vth1, the output of the first comparator 105, i.e., the input signal A of the timing circuit 111, switches from L level to H level. The time when the CLK signal first rises after this switching of input signal A is set as t0. If the input signal A remains at H level from time t0 to time t1, the output signal B of the timing circuit 111 switches from L level to H level. By switching the output signal B to H level, switch Q21 switches from off to on.

[0059] For example, such as Figure 3 As shown, when the first time T1 is set to the time from time t0 to time t1, the first time T1 becomes the time equivalent to 4 cycles of the CLK signal. For example, when the frequency of the CLK signal is 1kHz, the first time is 4 milliseconds. Furthermore, the first time T1 can be changed to a time equivalent to any number of cycles of the CLK signal, and by changing the frequency of the CLK signal, the first time T1 can be set to any value.

[0060] As described above, the first control circuit 200 of this embodiment controls the switch Q21 to turn on when the voltage Vcc exceeds the first reference voltage Vth1 for a first time. Therefore, it can suppress the influence of very short-term pseudo-overvoltages such as noise and reduce the voltage Vcc. On the other hand, if the voltage Vcc is lower than the third reference voltage Vth3, the first control circuit 200 controls the switch Q21 to turn off and stops the control of reducing the voltage Vcc. Therefore, it reduces the possibility of reducing the voltage Vcc until the power control device 100 stops operating. In addition, the first time can be set arbitrarily, for example, it can be set according to the environment in which the switching power supply device 1 is used.

[0061] 4. Control of the switching elements by the second control circuit

[0062] return Figure 2 The control of the second control circuit 300 will be described below. When the voltage Vcc exceeds the second reference voltage Vth2, which is higher than the first reference voltage Vth1, the second control circuit 300 controls the disconnection of the switching element Q11. For example, the first reference voltage Vth1 is 48V and the second reference voltage is 49V.

[0063] The second control circuit 300 detects the voltage Vcc input from the terminal TVcc via the second voltage detection circuit 102. The detected voltage Vcc is compared with the second reference voltage Vth2 generated by the second reference voltage generation circuit 104 via the second comparator 106. Here, the voltage Vcc detected by the second voltage detection circuit 102 is an example of the first voltage.

[0064] When Vcc < Vth2, that is, when the voltage Vcc is lower than the second reference voltage Vth2, the second control circuit 300 does not control the switching element Q11 to turn off. In this case, the second comparator 106 outputs an L-level signal to the control circuit 112. In this case, the control circuit 112, as described above, performs PWM control based on the voltage CS input from terminal TCS and the voltage Fb input from terminal TFb, in a manner that minimizes the deviation of voltage Vout, and generates a drive signal DRV. The drive signal DRV is supplied to the switching element Q11, and the switching power supply device 1 outputs voltage Vout.

[0065] The second control circuit 300 can also control the switching element Q11 to disconnect if the state of Vcc > Vth2 continues for a second time, that is, if the voltage Vcc exceeds the second reference voltage Vth2 for a second time. In this case, the second comparator 106 outputs a signal of level H to the control circuit 112. If the output signal of the second comparator 106 remains at level H for a second time, the control circuit 112 generates a control signal to disconnect the switching element Q11 regardless of the voltage CS input from terminal TCS or the voltage Fb input from terminal TFb. The generated control signal is supplied to the switching element Q11 via the output circuit 113, and the switching element Q11 disconnects.

[0066] When the switching element Q11 is turned off, the energy supply to the transformer 40 stops, and the switching power supply device 1 stops. Therefore, the voltage Vout drops, and the voltage Vcc also drops accordingly. Furthermore, the second time is a time that can be set by incorporating a buffer or similar element in the control circuit 112.

[0067] As described above, the second control circuit 300 of this embodiment controls the switching element Q11 to be disconnected. For example, if the voltage Vcc rises sharply due to a malfunction of the switching power supply device 1, and the voltage Vcc exceeds the second reference voltage Vth2 without a first time interval after exceeding the first reference voltage Vth1, the first control circuit 200 does not control the switch Q21, but the second control circuit 300 controls the switching element Q11 to be disconnected. Since the second control circuit 300 controls the switching element Q11 to be disconnected, the voltages Vout and Vcc can be reduced. Therefore, for example, the possibility of the device (not shown) supplied with voltage Vout, the power control device 100, malfunctioning due to a malfunction of the switching power supply device 1 is reduced.

[0068] Furthermore, the second control circuit 300 of this embodiment controls the switching element Q11 to be disconnected when the voltage Vcc exceeds the second reference voltage Vth2 for a second duration. Therefore, it can suppress the influence of pseudo-overvoltages that are very short-lived, such as noise, and reduce the voltages Vout and Vcc. In addition, the second duration can be set arbitrarily, for example, it can be set according to the environment in which the switching power supply device 1 is used.

[0069] Furthermore, the second time is shorter than the first time; conversely, it is preferable that the first time is longer than the second time. For example, the first time could be approximately 4 milliseconds, and the second time approximately tens of microseconds. In this case, even if the voltage Vcc rises sharply due to a malfunction of the switching power supply device 1, since the voltage Vcc exceeds the second reference voltage Vth2 after the second time, before the first time in which switch Q21 is in the off state, the second control circuit 300 can reliably control the switching element Q11 to be turned off.

[0070] 5. Time series variation of voltage Vcc

[0071] Figure 4 This is a diagram illustrating an example of voltage Vcc control. The vertical axis represents voltage, and the horizontal axis represents time. The start-up time of the switching power supply device 1 is set to 0. The first comparative example Vcc1 represents an example of the change in the time series of voltage Vcc in the power control device 100 of this embodiment, and the second comparative example Vcc2 represents an example of the change in the time series of voltage Vcc in a conventional power control device. Furthermore, 48V is approximately the reference for the first reference voltage Vth1, 49V is approximately the reference for the second reference voltage Vth2, and 45V is approximately the reference for the third reference voltage Vth3.

[0072] like Figure 4 As shown, from time 0 to time t1, the first comparison example Vcc1 and the second comparison example Vcc2 continuously increase from 0V. Specifically, both the first comparison example Vcc1 and the second comparison example Vcc2 exceed 48V at time t0 and then slowly increase until time t1. The second comparison example Vcc2 also slowly continues to increase after time t1, exceeding 49V. That is, in the existing power control device, the voltage Vcc continuously increases, exceeding the second reference voltage Vth2.

[0073] On the other hand, in the first comparative example Vcc1, during the period from time t0 to time t1, i.e., the first time T1, the state exceeding 48V persists, therefore the first control circuit 200 controls the switch Q21 to turn on. Specifically, at time t0, the input signal A from the first comparator 105 to the timing circuit 111 switches from L level to H level, and at time t1 after the first time T1, the output signal B of the timing circuit 111 switches from L level to H level.

[0074] At time t1, switch Q21 is turned on, and current flows through resistor R21, causing the first comparator Vcc1 to begin to decrease. The first comparator Vcc1 continues to decrease, falling below 45V at time t2. At time t2, the input signal C from the third comparator 125 to the timing circuit 111 switches from low level to high level, and the timing circuit 111 switches its output signal B from high level to low level, thus turning switch Q21 from on to off.

[0075] At time t2, switch Q21 switches from on to off, and current no longer flows through resistor R21, causing the first comparison voltage Vcc1 to rise slowly again. Thus, the first comparison voltage Vcc1 is controlled to be approximately between 45V and 48V. That is, the power control device 100 of this embodiment controls the voltage Vcc to be between the third reference voltage Vth3 and the first reference voltage Vth1.

[0076] Furthermore, the third reference voltage Vth3 is preferably 90% or more of the second reference voltage Vth2. In this case, the difference between the second reference voltage Vth2 and the third reference voltage Vth3 is small, and the voltage Vcc does not need to drop to a voltage lower than the third reference voltage Vth3, so the resistance value of resistor R21 can be set to be larger. As a result, the current flowing from terminal TVcc to ground through resistor R21 is smaller. Therefore, even if the voltage Vout starts to rise due to a malfunction of the switching power supply device 1 when switch Q21 is on, the voltage Vcc rises above the second reference voltage Vth2 because the current flowing from terminal TVcc to ground through resistor R21 is small. Therefore, when the voltage Vout starts to rise, the second control circuit 300 can reliably disconnect the switching element Q11 to reduce the voltage Vout and voltage Vcc. In addition, since the current flowing through resistor R21 is small when switch Q21 is on, the power consumption of the first control circuit 200 can be suppressed.

[0077] 6. Effects

[0078] As described above, the power control device 100 in this embodiment includes a first control circuit 200. The first control circuit 200 controls the switch Q21 to be turned on when the voltage Vcc continuously exceeds the first reference voltage Vth1 for a first time. Therefore, it can suppress the influence of very short-term pseudo-overvoltages such as noise and reduce the voltage Vcc. On the other hand, if the voltage Vcc is lower than the third reference voltage Vth3, the first control circuit 200 controls the switch Q21 to be turned off and stops the control of reducing the voltage Vcc. Therefore, it reduces the possibility that the voltage Vcc will continue to decrease until the power control device 100 stops operating. In addition, the first time can be set arbitrarily. For example, the first time can be set according to the environment in which the switching power supply device 1 is used.

[0079] Furthermore, the power control device 100 in this embodiment includes a second control circuit 300, which controls the switching element Q11 to be turned off. For example, if the voltage Vcc rises sharply due to a malfunction of the switching power supply device 1, and the voltage Vcc exceeds the second reference voltage Vth2 within a period of time after exceeding the first reference voltage Vth1, the second control circuit 300 controls the switching element Q11 to be turned off before the first control circuit 200 controls the switching circuit Q21 to be turned on. As a result, the voltages Vout and Vcc can be reduced, thus preventing a prolonged overvoltage state.

[0080] Furthermore, in this embodiment, the second control circuit 300 controls the switching element Q11 to turn off when the voltage Vcc exceeds the second reference voltage Vth2 for a second duration. Therefore, it can suppress the effects of very short-term pseudo-overvoltages such as noise, and reduce the voltages Vout and Vcc. Additionally, the second duration can be arbitrarily set; for example, it can be set according to the environment in which the switching power supply device 1 is used.

[0081] The embodiments and variations have been described above, but the present invention is not limited to these embodiments and can be implemented in various ways without departing from its spirit. For example, the embodiments described above can also be appropriately combined.

[0082] This invention includes structures that are substantially the same as those described in the embodiments (e.g., structures with the same function, method, and result, or structures with the same purpose and effect). Furthermore, this invention includes structures in which non-essential parts of the structures described in the embodiments have been replaced. Additionally, this invention includes structures capable of achieving the same effect or purpose as the structures described in the embodiments. Furthermore, this invention includes structures in which known techniques have been incorporated into the structures described in the embodiments.

[0083] The following content is derived based on the above implementation methods and variations.

[0084] One embodiment of the power control device is as follows: the switching power supply includes: a transformer having a primary winding, a secondary winding, and an auxiliary winding; a switching element connected to the primary winding; and a capacitor connected to the auxiliary winding; the power control device controls the switching element of the switching power supply, the power control device comprising: a power terminal connected to one end of the capacitor; a switch and a resistor connected in series between the power terminal and ground; a first control circuit for controlling the switch; and a second control circuit for controlling the switching element; the first control circuit controls the switch to turn on when a first voltage applied to the power terminal continuously exceeds a first reference voltage for a first time; and the second control circuit controls the switch to turn off when the first voltage exceeds a second reference voltage higher than the first reference voltage.

[0085] According to this power control device, if the first voltage exceeds the first reference voltage for a first time, the first control circuit controls the reduction of the first voltage. Therefore, it can suppress the influence of very short-term pseudo-overvoltages such as noise and reduce the first voltage. Furthermore, even if the first voltage rises sharply due to a malfunction of the switching power supply device, if the first voltage exceeds a second reference voltage higher than the first reference voltage during the first time period before the switch is in the off state, the second control circuit can reliably control the switching element to be turned off.

[0086] In another embodiment of the power control device, the first control circuit may disconnect the switch when the first voltage is lower than a third reference voltage that is lower than the first reference voltage.

[0087] According to the power control device, if the first voltage is lower than the third reference voltage, the first control circuit stops controlling the reduction of the first voltage. Therefore, there is no possibility that the power control device will not operate if the first voltage drops excessively.

[0088] Alternatively, the power control device may be configured such that the third reference voltage is more than 90% of the second reference voltage.

[0089] According to this power control device, when the first voltage is lower than the third reference voltage when the switch is on, the switch is in the off state. That is, since it is not necessary for the first voltage to be lower than the third reference voltage, the resistance value of the resistor can be increased to some extent, thereby reducing the current flowing from the power terminal to ground through the resistor. Therefore, even if the output voltage starts to rise due to a malfunction of the switching power supply device, etc., when the switch is on, based on the energy stored in the secondary winding of the transformer, the first voltage rises above the second reference voltage because the current flowing from the power terminal to ground through the resistor is small. Therefore, when the output voltage of the switching power supply device starts to rise, the switching element can be reliably disconnected by the second control circuit.

[0090] Furthermore, according to this power control device, the current flowing through the resistor is small when the switch is on, thus suppressing power consumption.

[0091] In another embodiment of the power control device, the second control circuit may control the switching element to disconnect when the first voltage exceeds the second reference voltage for a second period of time.

[0092] According to this power control device, by setting a second time, the effects of very short-duration pseudo-overvoltages, such as noise, can be suppressed, and the first voltage can be reduced.

[0093] Another configuration of the power control device is that the first time is longer than the second time.

[0094] According to this power control device, even if the first voltage rises sharply due to a fault in the switching power supply device, the first voltage exceeds the second reference voltage after a second time during the first time period before the switch is in the open state. Therefore, the second control circuit can reliably control the switching element to be turned off.

[0095] One embodiment of a switching power supply device includes: one embodiment of the power control device; the transformer; the switching element; and the capacitor.

[0096] According to this switching power supply device, the first control circuit controls the reduction of the first voltage when the first voltage exceeds the first reference voltage for a first time. Therefore, it can suppress, for example, the effects of very short-lived pseudo-overvoltages such as noise, and reduce the first voltage. Furthermore, even if the first voltage rises sharply due to a malfunction of the switching power supply device, and the first voltage exceeds a second reference voltage higher than the first reference voltage during the first time period before the switch is in the off state, the second control circuit can reliably control the switching element to be turned off.

Claims

1. A power supply control device for controlling the switching elements of a switching power supply device, the switching power supply device comprising: A transformer has a primary winding, a secondary winding, and an auxiliary winding; The switching element is connected to the primary winding; as well as A capacitor, which is connected to the auxiliary winding, The power control device includes: A power supply terminal, which is connected to one end of the capacitor; A switch and a resistor are connected in series between the power supply terminal and ground. A first control circuit controls the switch; as well as The second control circuit controls the switching element. The first control circuit controls the switch to be turned on if the first voltage applied to the power supply terminal exceeds the first reference voltage for a first time. The second control circuit controls the switching element to disconnect when the first voltage exceeds a second reference voltage that is higher than the first reference voltage for a second duration. The first time is longer than the second time.

2. The power control device according to claim 1, wherein, The first control circuit controls the switch to be turned off when the first voltage is lower than a third reference voltage that is lower than the first reference voltage.

3. The power control device according to claim 2, wherein, The third reference voltage is more than 90% of the second reference voltage.

4. A switching power supply device, comprising: The power control device according to any one of claims 1 to 3; The transformer; The switching element; as well as The capacitor.

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