JP7198163B2 - switching power supply - Google Patents

Description

The present invention relates to a switching power supply device having a DC-DC converter for stepping down or stepping up a DC voltage.

For example, an electric vehicle or a hybrid car is equipped with a high-voltage battery for driving a driving motor, and a power supply device for stepping down the voltage of the battery and supplying it to each part. As this power supply, a switching power supply equipped with a DC-DC converter that switches a DC voltage to convert it to an AC voltage, rectifies the AC voltage, and converts it to a DC voltage of a predetermined voltage value is generally used. there is Such a switching power supply device is described in Patent Document 1 and Patent Document 2, for example.

The switching power supply device of Patent Literature 1 has a protection function that keeps the operation stopped when there is an abnormality in the output voltage, and a reset function that cancels the operation stop holding. A reset signal is output from the reset signal generator when a predetermined time elapses after the protection function is activated in the event of an abnormality. When the switch controlled by this reset signal is turned on, the capacitor that serves as the power supply for the control IC that controls the DC-DC converter is discharged, the power supply voltage for the control IC drops, and the operation stop holding is released.

In the switching power supply device of Patent Document 2, after the switching operation is forcibly stopped by a latch signal output when an abnormality is detected, when restarting the control circuit of the switching element, the capacitor for supplying power to the control circuit is removed. The restart time is shortened by preliminarily discharging the charge through the discharge circuit.

The capacitor discharge circuit in Patent Documents 1 and 2 is a dedicated circuit provided only for discharging the charge of the capacitor. Further, in the switching power supply, as will be described in detail later, when the time until the DC-DC converter is restarted is short, due to the charge of the output capacitor provided on the secondary side of the transformer, Overvoltage may occur in the output of the converter, but Patent Documents 1 and 2 do not mention countermeasures against this problem.

JP 2018-174633 A JP 2014-64376 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching power supply device capable of suppressing the occurrence of overvoltage when the converter is restarted without providing a dedicated discharge circuit.

A switching power supply device according to the present invention includes an input terminal to which a DC voltage is input, a first converter for converting the DC voltage input to the input terminal into a DC voltage having a predetermined voltage value, and a DC voltage input to the input terminal. a second converter for converting a voltage into a DC voltage having a voltage value different from the predetermined voltage value; a first output terminal for outputting the DC voltage converted by the first converter; and a DC voltage converted by the second converter. a second output terminal to be output, a control unit that operates using the output voltage of the first converter as a power source and drives the second converter based on a first signal that is given from the outside, and when the output voltage of the first converter disappears Alternatively, a backup control circuit is provided for supplying the output voltage of the second converter to the control unit to back up the power supply of the control unit when the voltage drops. The second converter includes a switching circuit that switches the DC voltage input to the input terminal, and a rectifier circuit that rectifies the voltage switched by the switching circuit. The second signal output by the control unit based on the first signal operates the switching circuit, and the third signal output by the control unit when the output voltage of the first converter disappears or drops causes the backup control circuit to operate. . The control unit prohibits the output of the second signal even if the first signal is input again for a certain period of time from the time when the first signal is no longer input, and outputs the third signal. is in operation. Then, the electric charge of the capacitor provided in the rectifier circuit is discharged via the backup control circuit before a certain period of time elapses.

With this arrangement, even if the time from when the first signal is stopped to when it is input again is short, the second converter does not restart for a certain period of time during which the second signal is not output. Since the charge is discharged through the backup control circuit, the second converter will not overvoltage when restarted. In addition, since the existing backup control circuit is used to discharge the electric charge of the capacitor, there is no need to provide a dedicated discharge circuit, and an inexpensive switching power supply can be realized by suppressing an increase in the number of parts.

In the present invention, the controller may output the second signal and stop outputting the third signal when the first signal is input after the predetermined time has passed.

In the present invention, even if a drive circuit that drives the switching circuit based on the second signal from the control section and a feedback circuit that performs feedback control on the drive circuit according to the output voltage of the second converter are further provided. good. In this case, by prohibiting the output of the second signal for the certain period of time, the drive circuit and the switching circuit are put into a non-operating state, the second converter stops operating, and under this state, the capacitor Charge is discharged through the backup control circuit.

In the present invention, the backup control circuit includes a first switching element that forms a supply path for supplying the output voltage of the second converter to the control section, and a third signal from the control section that turns on the first switching element. and a second switching element that turns on the . In this case, the discharge path of the capacitor is formed by the first switching element and the second switching element.

The first switching element is a first transistor provided between the second output terminal and the control section, and the second switching element is a second switching element provided between the base of the first transistor and the ground. A transistor, the discharge path of the capacitor may be from the emitter of the first transistor to ground through the collector and emitter of the second transistor.

According to the switching power supply device of the present invention, it is possible to suppress the occurrence of overvoltage when restarting the converter without providing a dedicated discharge circuit.

1 is a block diagram showing a switching power supply device according to the present invention; FIG. 2 is a circuit diagram of a main part of FIG. 1; FIG. 3 is a diagram showing discharge paths in the circuit of FIG. 2; FIG. 3 is a time chart for explaining the operation of the circuit of FIG. 2; It is a circuit diagram for explaining a conventional problem. It is a time chart for explaining a conventional problem.

An embodiment of the present invention will be described with reference to the drawings. In the following, a switching power supply device mounted on a vehicle such as a four-wheeled motor vehicle will be taken as an example.

In FIG. 1, the switching power supply device 100 includes input terminals T1 and T2, output terminals T3 and T4, output terminals T5 and T6, a first converter 101 and a second converter .

The first converter 101 is a DC-DC converter on the main side, converts the DC voltage Vi input to the input terminals T1 and T2 into a DC voltage V1 having a predetermined voltage value, and outputs the DC voltage V1 to the output terminals T3 and T4. The second converter 102 is a DC-DC converter on the sub side, and converts the DC voltage Vi input to the input terminals T1 and T2 into a DC voltage V2 having a voltage value different from the predetermined voltage value, and outputs the voltage at the output terminal T5, Output to T6. The output terminals T3 and T4 correspond to the "first output terminal" in the invention, and the output terminals T5 and T6 correspond to the "second output terminal" in the invention.

As an example, the input voltage Vi of the input terminals T1 and T2 is 200V, the output voltage V1 of the output terminals T3 and T4 is 12V, and the output voltage V2 of the output terminals T5 and T6 is 10V. That is, in the case of this example, both the first converter 101 and the second converter 102 are step-down DC-DC converters that convert a high voltage to a low voltage.

The input terminal T1 is connected to the positive terminal of a battery (not shown) that supplies a DC voltage Vi, and the input terminal T2 is connected to the negative terminal of the battery. The output terminals T3 and T4 are connected to a load powered by the output voltage V1, a battery charged by the output voltage V1, and the like (not shown). A control circuit or the like that operates using the output voltage V2 as a power source is connected to the output terminals T5 and T6 (not shown). Out of the terminals T1 to T6, the output terminal T4 and the output terminal T6 are electrically connected outside the switching power supply device 100 and grounded to a common ground (not shown).

The switching power supply device 100 further includes a voltage detection circuit 6, an internal power supply circuit 7, a backup control circuit 8, a control section 9, and diodes D1 to D3.

The voltage detection circuit 6 is provided between the output terminal T3 and the control section 9 and detects the output voltage V1 of the first converter 101 . The internal power supply circuit 7 is provided between the backup control circuit 8 and the control section 9, and normally supplies power supply voltage to the control section 9 based on the output voltage V1. The backup control circuit 8 is provided between the output terminal T5 and the internal power supply circuit 7. When the output voltage V1 of the first converter 101 disappears or drops below the threshold value due to disconnection or failure (abnormal ), the output voltage V2 of the second converter 102 is supplied to the internal power supply circuit 7 as a backup power supply for the control section 9 .

Diode D1 is provided between output terminal T3 and internal power supply circuit 7, and forms a supply path for supplying output voltage V1 of first converter 101 to internal power supply circuit 7 during normal operation. The diode D2 is provided between the backup control circuit 8 and the internal power supply circuit 7, and supplies backup power (output voltage V2) from the backup control circuit 8 to the internal power supply circuit 7 when the output voltage V1 is abnormal. Form a supply channel for A diode D3 is provided between the output terminal T5 and the backup control circuit 8 and forms a supply path for supplying the output voltage V2 of the second converter 102 to the backup control circuit 8. FIG. Diode D3 may be omitted.

The control unit 9 is composed of a microcomputer and controls each operation of the first converter 101 , the second converter 102 and the backup control circuit 8 . An output request signal S1 is input to the control unit 9 as an external signal from an external device such as an in-vehicle ECU (electronic control unit). This signal S1 is a signal requesting the operation of the second converter 102 and corresponds to the "first signal" in the present invention. Control unit 9 also receives output request signal S 1 and outputs output permission signal S 2 to second converter 102 . This signal S2 is a signal that permits the operation of the second converter 102, and corresponds to the "second signal" in the present invention. Furthermore, the control unit 9 outputs a backup command signal S3 to the backup control circuit 8 when the voltage detection circuit 6 detects that the output voltage V1 has disappeared or decreased. This signal S3 is a signal for turning on a switching element (described later) provided in the backup control circuit 8, and corresponds to a "third signal" in the present invention.

The first converter 101 has an input filter 1 , a switching circuit 2 , an isolation transformer 3 , a rectifying circuit 4 and a smoothing circuit 5 . Since the configuration of each of these parts is known and the first converter 101 itself is not directly related to the present invention, detailed description of the first converter 101 is omitted. The first converter 101 of this example is an insulation type DC-DC converter in which the input side and the output side are insulated by the insulation transformer 3 .

The second converter 102 includes a switching circuit 20 , an isolation transformer 21 , a main winding side rectification circuit 22 , an auxiliary winding side rectification circuit 23 , an isolation circuit 26 , a PWM (Pulse Width Modulation) circuit 27 , and a feedback circuit 28 . I have. As described above, the second converter 102 has the function of stepping down the DC voltage Vi input to the input terminals T1 and T2 and outputting it, and the function of supplying backup power to the control unit 9 when the output of the first converter 101 is abnormal. and The second converter 102 of this example is also an insulation type DC-DC converter in which the input side and the output side are insulated by the insulation transformer 21 . In FIG. 1, a circuit after the rectifier circuit 23 on the auxiliary winding side is omitted.

FIG. 2 shows specific circuits of the switching circuit 20, the isolation transformer 21, and the rectifying circuit 22 on the main winding side in the second converter 102. As shown in FIG. 2 also shows a specific circuit of the backup control circuit 8. As shown in FIG. The circuits shown here are examples, and the present invention is not limited to these. 2, the rectifying circuit 23 and the insulating circuit 26 on the auxiliary winding side among the blocks constituting the second converter 102 in FIG. 1 are omitted.

The switching circuit 20 has a switching element Q3. In this example, the switching element Q3 is an FET (Field Effect Transistor) and is connected between the primary winding La of the isolation transformer 21 and the ground. The gate of the switching element Q3 is connected to the PWM circuit 27, and the PWM signal given to the gate from the PWM circuit 27 causes the switching element Q3 to turn on and off.

The isolation transformer 21 has a primary winding La and secondary windings Lb and Lc. Of the secondary windings, winding Lb is the main winding and winding Lc is the auxiliary winding. Since the auxiliary winding Lc is not directly related to the present invention, the circuit after the winding is omitted. The primary side and secondary side of the isolation transformer 21 are electrically insulated. An input voltage Vi applied to the primary winding La is switched by turning on and off the switching element Q3 to become an AC voltage (pulse voltage), which is transmitted to the secondary windings Lb and Lc of the insulating transformer 21 .

A rectifier circuit 22 provided after the secondary winding Lb has a diode D4 and a capacitor C1. The diode D4 is a rectifying diode for rectifying the AC voltage generated in the secondary winding Lb into a DC voltage. The capacitor C1 is an output capacitor for smoothing the DC voltage rectified by the diode D4 and outputting it from the output terminals T5 and T6. Diode D4 is connected between one end of secondary winding Lb and output terminal T5, and capacitor C1 is connected between output terminals T5 and T6.

The backup control circuit 8 has a first transistor Q1, a second transistor Q2, and a resistor R1. The first transistor Q<b>1 is provided between the output terminal T<b>5 and the control section 9 and forms a supply path for supplying the output voltage V<b>2 of the second converter 102 to the control section 9 . The second transistor Q2 is provided between the base of the first transistor Q1 and the ground, and is turned on by a backup command signal S3 from the control section 9 to turn on the first transistor Q1. A resistor R1 is a base resistor connected to the base of the first transistor Q1. The first transistor Q1 corresponds to the "first switching element" of the invention, and the second transistor Q2 corresponds to the "second switching element" of the invention.

The emitter of the first transistor Q1 is connected to the output terminal T5 via the diode D3. A collector of the first transistor Q1 is connected to the internal power supply circuit 7 (FIG. 1) through a diode D2. The base of the first transistor Q1 is connected to the collector of the second transistor Q2 through the resistor R1. The base of the second transistor Q2 is connected to the control section 9, and the emitter of the second transistor Q2 is grounded. A discharge path for the capacitor C1 is formed by the first transistor Q1 and the second transistor Q2. This will be explained in detail later.

Returning to FIG. 1, the isolation circuit 26 is a circuit that electrically isolates the output enable signal S2 output from the control section 9 and transmits it to the PWM circuit 27, and is composed of an isolator.

The PWM circuit 27 receives the output permission signal S2 from the isolation circuit 26, generates a PWM signal having a predetermined duty, and outputs it to the switching circuit 20. FIG. This PWM signal is applied to the gate of switching element Q3 (FIG. 2) as described above. The feedback circuit 28 compares the output voltage V2 of the second converter 102 with a target value, and performs feedback control on the PWM circuit 27 so that the output voltage V2 matches the target value. That is, feedback control is performed so that the duty of the PWM signal is reduced when the output voltage V2 is higher than the target value, and the duty of the PWM signal is increased when the output voltage V2 is lower than the target value.

Next, in the switching power supply device 100 having the above configuration, problems associated with restarting the second converter 102 and solutions thereof will be described.

First, based on FIGS. 5 and 6, a problem associated with restarting the second converter 102 will be described. In the time chart of FIG. 6, (a) is the output voltage V2 of the second converter 102, (b) is the output request signal S1 input to the control unit 9 from the outside, and (c) is the output output from the control unit 9. The permission signal S2, (d) represents the backup command signal S3 output from the control section 9. FIG. t1 to t4 represent times. "H" (High) of the signals S1 to S3 represents a state in which the signal is output, and "L" (Low) represents a state in which the signal is not output.

Between times t1 and t2, the output request signal S1 is "H", and in response to this, the output permission signal S2 is also "H". In this section, the PWM circuit 27 is driven by the output permission signal S2 output from the control section 9, and the second converter 102 is in an operating state.

At time t2, when the output request signal S1 becomes "L", the output enable signal S2 also becomes "L". That is, the output permission signal S2 is no longer output from the control unit 9, and the second converter 102 is put into a non-operating state. After this non-operating state continues for the time W1, at time t3, when the output request signal S1 becomes "H" again, the output permission signal S2 also becomes "H" accordingly. Therefore, the output permission signal S2 output from the control unit 9 causes the second converter 102 to enter the operating state again. That is, the second converter 102 is restarted at time t3.

Here, if the time W1 until the restart of the second converter 102 is short, at the time of restart (time t3), the overvoltage Z as shown in FIG. . This is because the time W1 is so short that the charge in the capacitor C1 of the rectifier circuit 22 cannot be completely discharged during this time. The details will be described below.

FIG. 5 shows the circuit state at the restart of second converter 102 (time t3). When restarting, the PWM circuit 27 is supplied with the output enable signal S2 of "H", so that the PWM circuit 27 turns the switching element Q3 of the switching circuit 20 on and off. As a result, the second converter 102 enters an operating state. On the other hand, when the output permission signal S2 is no longer output (time t2), the backup command signal S3 remains at "L" as shown in FIG. It does not change even at startup (time t3). Therefore, during the time t2-t3 (time W1), the backup command signal S3 is not output, so both the first transistor Q1 and the second transistor Q2 of the backup control circuit 8 are turned off as shown in FIG. there is Therefore, if the time W1 until the restart of the second converter 102 is short, the charge in the capacitor C1 is not discharged and the voltage across the capacitor C1 maintains a high state, which becomes the overvoltage Z at restart. appears (Fig. 6(a)).

Next, a solution to the above problems according to the present invention will be described with reference to FIGS. 3 and 4. FIG.

In the present invention, as shown in FIG. 4(c), from the time when the output request signal S1 is no longer input to the control unit 9 (time t2), during a certain time W2 (W2>W1), at time t3, Even if the output request signal S1 is input to the control unit 9, the output permission signal S2 is maintained at "L". That is, during this period, the control section 9 prohibits the output of the output permission signal S2. Further, as shown in FIG. 4(d), the backup command signal S3 is "H" for a certain period of time W2. That is, during this time, the control section 9 outputs the backup command signal S3.

FIG. 3 shows the circuit state at time W2 (time t2 to t4) in FIG. During this time, the output permission signal S2 is "L" and the PWM circuit 27 is not supplied with the output permission signal S2, so that the PWM circuit 27 does not operate. Therefore, the switching element Q3 of the switching circuit 20 is turned off, and the second converter 102 stops operating. On the other hand, during the time W2, the backup command signal S3 becomes "H" and the backup command signal S3 is given from the control section 9 to the backup control circuit 8, so that the first transistor Q1 and the second transistor Q1 of the backup control circuit 8 Both transistors Q2 are turned on.

By turning on the two transistors Q1 and Q2, a discharge path for the charge accumulated in the capacitor C1 is formed as indicated by the thick arrow in FIG. Specifically, the capacitor C1 is discharged through the path of capacitor C1→diode D3→emitter of first transistor Q1→base resistor R1→collector of second transistor Q2→emitter of second transistor Q2→ground.

In this case, by appropriately selecting the time constant of the discharge path, the discharge of the capacitor C1 can be completed within the time W2 in FIG. can be done. Further, even if the output request signal S1 becomes "H" at time t3, the second converter 102 does not restart at this time, so the overvoltage as shown in FIG. Z never occurs.

After that, when the output request signal S1 is "H" when the time W2 has passed (time t4), that is, when the output request signal S1 is input to the control unit 9, the control unit 9 The output permission signal S2 is output again as shown in FIG. 4(c), and the output of the backup command signal S3 is stopped as shown in FIG. 4(d). The second converter 102 is restarted at time t4 as shown in FIG. 4A by the output permission signal S2 output from the control unit 9. At this point, as described above, the discharge of the capacitor C1 has been completed, so no overvoltage occurs in the output of the second converter 102 . At time t4, the output of the backup command signal S3 from the control unit 9 is stopped, so that the transistors Q1 and Q2 of the backup control circuit 8 are switched from on to off.

As described above, in the above-described embodiment, even if the output request signal S1 is input again for a certain period of time W2 from the time when the output request signal S1 is no longer input to the control unit 9 (time t2), the control The unit 9 prohibits the output of the output permission signal S2, and outputs the backup command signal S3 to put the backup control circuit 8 into the operating state. Then, the capacitor C1 provided in the rectifier circuit 22 is discharged through the backup control circuit 8 before the predetermined time W2 elapses.

Therefore, even if the time W1 from when the output request signal S1 is stopped to when it is input again is short, the second converter 102 does not restart during the predetermined time W2 during which the output permission signal S2 is not output. Then, the charge in the capacitor C1 is discharged through the backup control circuit 8. As a result, the second converter 102 does not generate overvoltage at the time of restart (time t4).

The transistors Q1 and Q2 of the backup control circuit 8 are originally for supplying the output voltage V2 of the second converter 102 to the control section 9 as a backup power supply. Transistors Q1 and Q2 are used together as a discharge path for capacitor C1. Therefore, there is no need to provide a dedicated discharge circuit in addition to the backup control circuit 8, and an inexpensive switching power supply device 100 can be realized while suppressing an increase in the number of parts.

In addition to the embodiments described above, the present invention can adopt various embodiments such as those described below.

In the above embodiment, as shown in FIG. 4(d), the period during which the backup command signal S3 is output is the same as the period W2 during which the output permission signal S2 is stopped. The period may be shorter than W2 and longer than W1. Alternatively, the backup command signal S3 may be output only during W1.

In the above embodiment, both the first converter 101 and the second converter 102 are step-down DC-DC converters, but the converters 101 and 102 may be step-up DC-DC converters. Further, one of the converters 101 and 102 may be a step-down DC-DC converter and the other may be a step-up DC-DC converter.

In the above embodiment, both the first converter 101 and the second converter 102 are isolated DC-DC converters, but the converters 101 and 102 may be non-isolated DC-DC converters. .

In the above embodiment, the voltage detection circuit 6 and the internal power supply circuit 7 are provided separately from the control unit 9 as shown in FIG. good.

In the above-described embodiment, the PWM circuit 27 is used as an example of the drive circuit that drives the switching circuit 20. However, a drive circuit that drives the switching circuit 20 by a method other than PWM may be provided.

In the above embodiment, the transistors Q1 and Q2 are used as switching elements provided in the backup control circuit 8, but FETs, relays, and the like may be used instead of the transistors.

In the above embodiment, the switching power supply device 100 mounted on a vehicle was taken as an example, but the switching power supply device of the present invention can also be applied to applications other than on-vehicle use.

8 backup control circuit 9 control unit 20 switching circuit 22 rectifier circuit 27 PWM circuit (drive circuit)
28 feedback circuit 100 switching power supply device 101 first converter 102 second converter T1, T2 input terminals T3, T4 output terminals (first output terminals)
T5, T6 output terminals (second output terminals)
Q1 first transistor (first switching element)
Q2 second transistor (second switching element)
C1 Capacitor S1 Output request signal (first signal)
S2 Output enable signal (second signal)
S3 Backup command signal (third signal)

Claims (5)

an input terminal to which a DC voltage is input;
a first converter that converts the DC voltage input to the input terminal into a DC voltage having a predetermined voltage value;
a second converter that converts the DC voltage input to the input terminal into a DC voltage having a voltage value different from the predetermined voltage value;
a first output terminal for outputting the DC voltage converted by the first converter;
a second output terminal for outputting the DC voltage converted by the second converter;
a control unit that operates using the output voltage of the first converter as a power source and drives the second converter based on a first signal that is provided from the outside;
a backup control circuit that supplies the output voltage of the second converter to the control unit to back up the power supply of the control unit when the output voltage of the first converter disappears or drops,
The second converter includes a switching circuit that switches the DC voltage input to the input terminal, and a rectifier circuit that rectifies the voltage switched by the switching circuit,
A second signal output by the control unit based on the first signal causes the switching circuit to operate, and a third signal output by the control unit when the output voltage of the first converter disappears or decreases causes the In a switching power supply device in which a backup control circuit operates,
The control unit prohibits the output of the second signal and outputs the third signal even if the first signal is input again for a predetermined time after the input of the first signal is stopped. thereby setting the backup control circuit to an operating state,
A switching power supply device according to claim 1, wherein a capacitor provided in said rectifier circuit is discharged through said backup control circuit before said fixed time elapses. The switching power supply device according to claim 1,
The control unit outputs the second signal and stops outputting the third signal when the first signal is input when the predetermined time has passed. switching power supply. In the switching power supply device according to claim 1 or claim 2,
a drive circuit that drives the switching circuit based on the second signal from the control unit;
a feedback circuit that performs feedback control on the drive circuit according to the output voltage of the second converter,
By prohibiting the output of the second signal for the predetermined time, the driving circuit and the switching circuit are put into a non-operating state, the second converter stops operating, and under this state, the A switching power supply device, wherein the charge of a capacitor is discharged via the backup control circuit. In the switching power supply device according to any one of claims 1 to 3,
The backup control circuit is
a first switching element forming a supply path for supplying the output voltage of the second converter to the control unit;
a second switching element that is turned on by the third signal from the control unit to turn on the first switching element,
A switching power supply device, wherein a discharge path of the capacitor is formed by the first switching element and the second switching element. In the switching power supply device according to claim 4,
the first switching element is a first transistor provided between the second output terminal and the control unit;
the second switching element is a second transistor provided between the base of the first transistor and ground;
A switching power supply device, wherein the discharge path extends from the emitter of the first transistor to the ground via the collector and emitter of the second transistor.

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