Switching power supply device

Abstract

The present application provides a switching power supply device, the circuit structure is simple and can accurately carry out protection for abnormality. The switching power supply device (100) has a converter (102), a control unit (9), a switching circuit (20), an isolation transformer (21), a first rectifier circuit (22), a second rectifier circuit (23) and an overheating detection circuit (29). When the switching element of the switching circuit becomes an overheating state, the overheating detection circuit detects the situation and outputs a stop signal (S4) for stopping the switching action of the switching circuit. The control unit determines the output short circuit of the converter or the low voltage condition of the output of the converter according to the comparison result of the change of the output voltage of the first rectifier circuit connected with the main winding of the isolation transformer and the change of the output voltage of the second rectifier circuit connected with the auxiliary winding of the isolation transformer, and executes the control for output short circuit protection or output low voltage protection according to the determination result.

Description

TECHNICAL FIELD

[0001] The present application relates to a switching power supply device having a DC-DC converter that steps down or steps up a direct-current voltage. BACKGROUND

[0002] For example, in an electric automobile or a hybrid automobile, a high-voltage battery for driving a traveling motor is mounted, and a power supply device for stepping down the voltage of the battery and supplying it to each part is mounted. As the power supply device, a switching power supply device having a DC-DC converter that converts a direct-current voltage into an alternating-current voltage by switching the direct-current voltage, and then converts the alternating-current voltage into a direct-current voltage of a prescribed voltage value by rectifying the alternating-current voltage is generally used.

[0003] In such a switching power supply device, a function of detecting an abnormality caused by an overcurrent or an overvoltage and protecting a circuit in the case where the abnormality occurs is provided. For example, in the switching power supply device of Patent Literature 1, an input current detection circuit, an input voltage detection circuit, and an output voltage detection circuit are provided. Further, a value of an output current is estimated from values of an input current, an input voltage, and an output voltage detected by these detection circuits, and whether a failure occurs is determined on the basis of the output current in addition to the output voltage.

[0004] In addition, in the switching power supply device of Patent Literature 2, an overcurrent protection circuit including a current detection circuit and a first opening and closing element, and an overvoltage protection circuit including a voltage detection circuit and a second opening and closing element are provided. When a current flowing in a switching element is excessively large, the first opening and closing element is turned on, and the overcurrent protection circuit forcibly turns off the switching element to stop a primary direct-current power supply circuit, thereby protecting the switching element from the overcurrent. In addition, when a secondary direct-current power supply voltage becomes a set voltage value or more, the second opening and closing element is turned on, and the overvoltage protection circuit forcibly turns off the switching element to stop the primary direct-current power supply circuit, thereby protecting the switching element from the overvoltage.

[0005] Patent Literature 1: Japanese Patent Application Laid-Open No. 2007-97368

[0006] Patent Literature 2: Japanese Patent Application Laid-Open No. H7-213051

[0007] Among the abnormalities that occur in switching power supply devices, in addition to current abnormalities (overcurrent) caused by short circuits and voltage abnormalities (output voltage drop) caused by circuit breaks / faults, there are also overheating abnormalities, such as abnormal heating of switching elements leading to high temperatures. To detect these various abnormalities and provide corresponding protection, conventional methods have involved setting up current detection circuits, voltage detection circuits, and overheat detection circuits according to the type of abnormality. The detection signals output from each detection circuit are sent to the control unit, which determines the presence and type of abnormality and executes control measures to provide protection corresponding to each abnormality. However, this requires a large number of detection circuits for various abnormality types, resulting in a complex circuit structure. Summary of the Invention

[0008] The objective of this invention is to provide a switching power supply device with a simple circuit structure that can accurately protect against malfunctions.

[0009] The switching power supply device of the present invention includes: a converter that switches an input DC voltage to convert it into a DC voltage of a predetermined value; and a control unit that controls the operation of the converter. The converter includes: a switching circuit that switches the DC voltage; a drive circuit that drives the switching circuit; a rectifier circuit that rectifies the switched AC voltage; and an insulation transformer disposed between the switching circuit and the rectifier circuit. The secondary winding of the insulation transformer consists of a main winding and an auxiliary winding. The rectifier circuit consists of a first rectifier circuit and a second rectifier circuit. The first rectifier circuit is disposed between the main winding and the output terminal of the converter, and the second rectifier circuit is connected to the auxiliary winding. Additionally, the following circuits are provided: a first voltage detection circuit that detects the output voltage of the first rectifier circuit; a second voltage detection circuit that detects the output voltage of the second rectifier circuit; an overheat detection circuit that detects the overheating state of the switching element; and a feedback circuit that provides feedback control to the drive circuit to make the output voltage of the converter reach the target value. When the temperature of the switching element exceeds a threshold, the overheat detection circuit outputs a stop signal to stop the switching circuit from operating and perform overheat protection. The control unit, based on a comparison between the voltage change detected by the first voltage detection circuit and the voltage change detected by the second voltage detection circuit, determines whether the converter output is short-circuited or the converter output is low voltage, and executes control for output short-circuit protection or output low-voltage protection based on this determination.

[0010] Thus, in a case where the switching element becomes an overheated state, the switching circuit can be stopped from switching operation by the stop signal output from the overheating detection circuit without the control section, thereby performing the overheating protection. In addition, the control section can determine that the output of the converter has a short circuit or a voltage drop by comparing the changes in the respective detection voltages of the first voltage detection circuit and the second voltage detection circuit. Therefore, no interface circuit or the like is required between the overheating detection circuit and the control section, and no overcurrent detection circuit for short circuit detection is required, thereby simplifying the circuit structure. Moreover, the protection corresponding to the type of abnormality can be accurately performed with the simple circuit structure.

[0011] In the present application, the control section performs, for example, the following processing.

[0012] A. In a case where the respective detection voltages rise after a state where the voltage detected by the first voltage detection circuit is lower than the voltage at normal time and the voltage detected by the second voltage detection circuit is lower than the voltage at normal time continues for a certain time and before a prescribed first time elapses, it is determined that the overheating protection by the overheating detection circuit is performed.

[0013] B. In a case where a state where the voltage detected by the first voltage detection circuit is lower than the voltage at normal time and the voltage detected by the second voltage detection circuit is higher than the voltage at normal time continues for a prescribed second time, it is determined that the output of the converter has a short circuit, and the control for output short circuit protection is performed.

[0014] C. In a case where a state where the voltage detected by the first voltage detection circuit is lower than the voltage at normal time and the voltage detected by the second voltage detection circuit is lower than the voltage at normal time continues for a third time longer than the first time, it is determined that the output of the converter becomes a low voltage, and the control for output low voltage protection is performed.

[0015] In the present application, the control section can have only the functions of A and B, A and C, or B and C of the above-described A to C.

[0016] In the present application, the control section can output a permission signal in a case where the switching circuit is permitted to perform switching operation, and stop the permission signal or output an inhibition signal different from the permission signal in a case where it is determined that the output of the converter has a short circuit, thereby causing the switching circuit to stop switching operation and performing the output short circuit protection.

[0017] In the present application, the control section can stop the permission signal or output the inhibition signal in a case where the number of times that the output of the converter has a short circuit reaches a prescribed number of times.

[0018] In the present application, the control section can output a failure detection signal as the control for output low voltage protection.

[0019] The switching power supply device according to the present application has the effect of simple circuit structure and accurate protection against abnormalities. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a block diagram showing an example of the switching power supply device of the present application.

[0021] Figure 2 is a circuit diagram of a main part of Figure 1

[0022] Figure 3 is a flowchart showing the operation of the switching power supply device at the time of overheat protection.

[0023] Figure 4 is a timing chart showing the change of the winding voltages at the time of overheat protection.

[0024] Figure 5 is a flowchart showing the operation of the switching power supply device at the time of output short-circuit protection.

[0025] Figure 6 is a timing chart showing the change of the winding voltages at the time of output short-circuit protection.

[0026] Figure 7 is a flowchart showing the operation of the switching power supply device at the time of output low-voltage protection.

[0027] Figure 8 is a timing chart showing the change of the winding voltages at the time of output low-voltage protection.

[0028] Figure 9 is a table showing the relationship between the circuit state, the protection function, and the winding voltages in the switching power supply device.

[0029] Figure 10 is a circuit diagram of a main part of the switching power supply device of the comparative example.

[0030] REFERENCE NUMERALS

[0031] ​9: control unit; 20: switching circuit; 21: isolation transformer; 22: first rectifier circuit; 23: second rectifier circuit; 24: first voltage detection circuit; 25: second voltage detection circuit; 27: PWM circuit (drive circuit); 28: feedback circuit; 29: overheat detection circuit; 100: switching power supply device; 101: first converter; 102: second converter; K: temperature measuring element; La: primary winding; Lb: secondary winding (main winding); Lc: secondary winding (auxiliary winding); T5, T6: output terminals; Q3: switching element; S2: permission signal; S4: stop signal; Va: main winding voltage; Vb: auxiliary winding voltage; X: first time; Y: second time; Z: third time. DETAILED DESCRIPTION

[0032] Embodiments of the present application will be described with reference to the accompanying drawings. Hereinafter, a switching power supply device mounted on a vehicle such as a four-wheel automobile will be exemplified.

[0033] In Figure 1 The switching power supply device 100 has input terminals T1, T2, output terminals T3, T4, output terminals T5, T6, a first converter 101, and a second converter 102.

[0034] The first converter 101 is a DC-DC converter on the main side, which converts a direct current voltage Vi input to the input terminals T1, T2 into a direct current voltage V1 of a prescribed voltage value, and outputs to the output terminals T3, T4. The second converter 102 is a DC-DC converter on the auxiliary side, which converts the direct current voltage Vi input to the input terminals T1, T2 into a direct current voltage V2 of a voltage value different from the prescribed voltage value described above, and outputs to the output terminals T5, T6.

[0035] As an example, the input voltage Vi of the input terminals T1, T2 is 200 V, the output voltage V1 of the output terminals T3, T4 is 12 V, and the output voltage V2 of the output terminals T5, T6 is 10 V. That is, in the case of the present example, both the first converter 101 and the second converter 102 are DC-DC converters of the step-down type which convert a high voltage into a low voltage.

[0036] The input terminal T1 is connected to the positive electrode of a battery (omitted from the drawing) which supplies the direct current voltage Vi, and the input terminal T2 is connected to the negative electrode of the battery. The output terminals T3, T4 are connected to a load which operates with the output voltage V1 as a power supply, and a battery or the like (omitted from the drawing) which is charged by the output voltage V1. The output terminals T5, T6 are connected to a control circuit or the like (omitted from the drawing) which operates with the output voltage V2 as a power supply. The output terminal T4 and the output terminal T6 among the terminals T1 to T6 are electrically connected outside the switching power supply device 100, and grounded to a common ground terminal (omitted from the drawing).

[0037] The switching power supply device 100 further has a voltage detection circuit 6, a power supply circuit 7, a backup control circuit 8, a control section 9, and diodes Dl, D2.

[0038] The voltage detection circuit 6 is provided between the output terminal T3 and the control section 9, and detects the output voltage VI of the first converter 101. The power supply circuit 7 is provided between the backup control circuit 8 and the control section 9, and normally supplies a power supply voltage to the control section 9 based on the output voltage VI. The backup control circuit 8 is provided between the output terminal T5 and the power supply circuit 7, and supplies the output voltage V2 of the second converter 102 as a backup power supply to the power supply circuit 7 in the case where the output voltage VI of the first converter 101 disappears or drops to less than a prescribed value due to a disconnection or a failure.

[0039] The diode Dl is provided between the output terminal T3 and the power supply circuit 7, and forms a supply path for supplying the output voltage VI of the first converter 101 to the power supply circuit 7. The diode D2 is provided between the backup control circuit 8 and the power supply circuit 7, and forms a supply path for supplying the backup power supply (output voltage V2) from the backup control circuit 8 to the power supply circuit 7.

[0040] The control section 9 is composed of a microcomputer, and controls the respective operations of the first converter 101, the second converter 102, and the backup control circuit 8. An external signal SI is input from an external device such as a vehicle-mounted ECU (Electronic Control Unit) to the control section 9. This external signal SI is a signal that requests the second converter 102 to operate. In addition, the control section 9 outputs a permission signal S2 to the second converter 102 in response to the external signal SI. This permission signal S2 is a signal that permits the second converter 102 to perform switching operation. Further, in the case where the output voltage VI is detected by the voltage detection circuit 6 to be less than a prescribed value, the control section 9 outputs a backup command signal S3 to the backup control circuit 8. This backup command signal S3 is a signal for turning on a switching element (not shown) possessed by the backup control circuit 8.

[0041] The first converter 101 has an input filter 1, a switching circuit 2, an isolation transformer 3, a rectification circuit 4, and a smoothing circuit 5. Since the structures of these parts are well known, and the first converter 101 itself has no direct relation to the present application, detailed description of the first converter 101 is omitted. In addition, the first converter 101 of the present example is an isolation type DC-DC converter in which the input side and the output side are insulated by means of the isolation transformer 3.

[0042] The second converter 102 has a switching circuit 20, an isolation transformer 21, a first rectifying circuit 22, a second rectifying circuit 23, an isolation circuit 26, a PWM (Pulse Width Modulation) circuit 27, a feedback circuit 28, and an overheat detection circuit 29. As described above, the second converter 102 has a function of stepping down the DC voltage Vi input to the input terminals Tl, T2 and outputting it, and a function of supplying a backup power source to the power supply circuit 7 when an output abnormality occurs in the first converter 101. The second converter 102 of the present example is also an isolation type DC-DC converter in which the input side and the output side are insulated by the isolation transformer 21.

[0043] Figure 2 The specific circuits of the switching circuit 20, the isolation transformer 21, the first rectifying circuit 22, and the second rectifying circuit 23 of the second converter 102 are shown. The circuits shown here are an example, and the present application is not limited to these. Also, in the following description, the isolation circuit 26 in the block of the second converter 102 that constitutes the Figure 2 Figure 1 is omitted.

[0044] The switching circuit 20 has a switching element Q3 and a temperature measuring element K. In the present example, the switching element Q3 is a FET (Field Effect Transistor) connected between the primary winding La of the isolation transformer 21 and a ground terminal. The gate of the switching element Q3 is connected to the PWM circuit 27, and the switching element Q3 performs on-off operation in accordance with the PWM signal supplied to the gate from the PWM circuit 27. The temperature measuring element K is constituted by, for example, a thermistor, and is disposed in the vicinity of the switching element Q3 to detect the temperature of the switching element Q3. The output (detected temperature) of the temperature measuring element K is sent to the overheat detection circuit 29 described later.

[0045] The isolation transformer 21 has a primary winding La and secondary windings Lb, Lc. Of the secondary windings, the winding Lb is a main winding, and the winding Lc is an auxiliary winding. The primary winding La is connected to the switching circuit 20, the main winding Lb is connected to the first rectifying circuit 22, and the auxiliary winding Lc is connected to the second rectifying circuit 23. The primary side and the secondary side of the isolation transformer 21 are electrically insulated. The input voltage Vi applied to the primary winding La is switched to an alternating voltage (pulse voltage) by the on-off of the switching element Q3, and is transmitted from the primary winding La to the main winding Lb and the auxiliary winding Lc of the isolation transformer 21.

[0046] ​The first rectifier circuit 22 connected to the main winding Lb has a diode D3 and a capacitor Cl, and a first voltage detection circuit 24 is provided at the rear stage thereof. The diode D3 is a rectifier diode for rectifying an alternating voltage generated in the main winding Lb to a direct voltage. The capacitor Cl is an output capacitor for smoothing the direct voltage rectified by the diode D3 and outputting from output terminals T5, T6. The diode D3 is connected between one end of the main winding Lb and the output terminal T5, and the capacitor Cl is connected between the output terminals T5, T6.

[0047] The first voltage detection circuit 24 is connected in parallel to the capacitor Cl, and detects a voltage across the capacitor Cl, that is, an output voltage of the first rectifier circuit 22. This output voltage is a voltage corresponding to a voltage generated in the main winding Lb, and is therefore hereinafter referred to as "main winding voltage". This main winding voltage Va is also an output voltage V2 of the second converter 102 (Va = V2). The main winding voltage Va detected by the first voltage detection circuit 24 is sent to the control section 9.

[0048] The second rectifier circuit 23 connected to the auxiliary winding Lc has a diode D4 and a capacitor C2, and a second voltage detection circuit 25 is provided at the rear stage thereof. The diode D4 is a rectifier diode for rectifying an alternating voltage generated in the auxiliary winding Lc to a direct voltage. The capacitor C2 is a capacitor for smoothing the direct voltage rectified by the diode D4.

[0049] The second voltage detection circuit 25 is connected in parallel to the capacitor C2, and detects a voltage across the capacitor C2, that is, an output voltage of the second rectifier circuit 23. This output voltage is a voltage corresponding to a voltage generated in the auxiliary winding Lc, and is therefore hereinafter referred to as "auxiliary winding voltage". The auxiliary winding voltage Vb detected by the second voltage detection circuit 25 is sent to the control section 9. In the present example, no load is connected at the rear stage of the second rectifier circuit 23, and the second rectifier circuit 23 is provided only for detecting the auxiliary winding voltage Vb, but a load can of course be connected at the rear stage of the second rectifier circuit 23.

[0050] Returning to Figure 1 The standby control circuit 8 operates in accordance with a standby instruction signal S3 output from the control section 9. When the output voltage Vl of the first converter 101 is detected by the voltage detection circuit 6 to be lost or dropped, the control section 9 outputs the standby instruction signal S3. In accordance with this signal, a transistor (not shown) of the standby control circuit 8 is turned on, and a supply path is formed in which the output voltage V2 of the second converter 102 is supplied as a standby power source to the power supply circuit 7.

[0051] The insulation circuit 26 is a circuit for electrically insulating and transferring the permission signal S2 output from the control section 9 to the PWM circuit 27, and is constituted by an isolator.

[0052] The PWM circuit 27 receives the permission signal S2 from the isolation circuit 26, generates a PWM signal with a predetermined duty cycle, and outputs it to the switching circuit 20. As described above, this PWM signal is provided to the switching element Q3 ( Figure 2 The gate of the second converter 102 is connected to the PWM circuit 27. 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 to make the output voltage V2 reach the target value. That is, feedback control is performed in the following manner: when the output voltage V2 is higher than the target value, the duty cycle of the PWM signal is reduced; when the output voltage V2 is lower than the target value, the duty cycle of the PWM signal is increased. The PWM circuit 27 is an example of the "drive circuit" of the present invention.

[0053] The overheat detection circuit 29 detects the overheat by using a temperature sensing element K ( Figure 2 The overheating detection circuit 29 detects an overheating condition by comparing the detected temperature of the switching element Q3 with a predetermined threshold. Specifically, if the detected temperature of the temperature sensing element K does not exceed the threshold, the overheating detection circuit 29 does not detect an overheating condition in the switching element Q3; if the detected temperature of the temperature sensing element K exceeds the threshold, the overheating detection circuit 29 detects an overheating condition in the switching element Q3. When an overheating condition is detected, the overheating detection circuit 29 outputs a stop signal S4 to the PWM circuit 27 via the insulation circuit 26. This stop signal S4 is used to stop the switching action of the switching circuit 20 to provide overheat protection for the switching element Q3.

[0054] Next, the operation of the switching power supply device 100 with the above structure will be explained. The operation of each of the following three cases will be explained in detail: overheat protection, output short-circuit protection, and output undervoltage protection.

[0055] (1) Overheat protection

[0056] Overheat protection is a protective function required to prevent thermal damage to the switching element Q3 when it abnormally overheats and reaches a high temperature. (Refer to...) Figure 3 The flowchart illustrates the operation of the overheat protection.

[0057] exist Figure 3 In the circuit, when the switching element Q3 malfunctions (A1), the element heats up and its temperature gradually rises (A2). When the temperature of the switching element Q3 detected by the temperature sensing element K exceeds the threshold, the overheat detection circuit 29 detects the overheating and outputs a stop signal S4 (A3). This stop signal S4 is provided to the PWM circuit 27 via the insulation circuit 26. The PWM circuit 27 receives the stop signal S4 and stops outputting the PWM signal (A4). As a result, the switching element Q3 becomes open, and therefore the switching circuit 20 stops its switching operation (A5).

[0058] When the switching operation of the switching circuit 20 is stopped, the voltage applied to the primary winding La of the isolation transformer 21 is no longer applied, and as a result, the output voltages of the first rectifying circuit 22 and the second rectifying circuit 23, i.e., the main winding voltage Va and the auxiliary winding voltage Vb, are decreased (A6). The main winding voltage Va and the auxiliary winding voltage Vb are detected by the first voltage detecting circuit 24 and the second voltage detecting circuit 25, respectively, and each detection result is sent to the control section 9. Then, when each winding voltage Va, Vb is decreased to less than the threshold value, the control section 9 detects this situation and starts the timer (A7).

[0059] On the other hand, in the switching circuit 20, since the switching operation is stopped, the temperature of the switching element Q3 is gradually decreased (A8). Therefore, the detected temperature of the temperature measuring element K is also decreased. Then, when the overheat detecting circuit 29 detects that the temperature of the switching element Q3 is decreased to less than the threshold value, the output of the stop signal S4 is stopped (A9). Therefore, the stop signal S4 is no longer supplied to the PWM circuit 27, and the PWM circuit 27 resumes the output of the PWM signal (A10). Thus, the switching element Q3 performs the on-off operation again, and the switching operation of the switching circuit 20 is resumed (Al l), and as a result, each winding voltage Va, Vb is gradually increased (A12). Then, when each winding voltage Va, Vb is increased to more than the threshold value, the control section 9 detects this situation and stops the timer (A13).

[0060] Figure 4 is a timing chart showing the changes of the main winding voltage Va and the auxiliary winding voltage Vb at the time of overheat protection. In Figure 4 , in order to easily understand Figure 3 the steps Al to A13 correspond to which time (or period), these steps are also described.

[0061] In Figure 4 , Vm and Vn represent the main winding voltage Va and the auxiliary winding voltage Vb at the normal time (in the steps Al to A13 described later), respectively. Figure 6 and Figure 8The same applies to the auxiliary winding voltage Vb.) At the time t1, an abnormality occurs, the temperature of the switching element Q3 rises, and when the overheat detection circuit 29 detects overheating at the time t2, the switching operation of the switching circuit 20 is stopped as described above. Therefore, both the main winding voltage Va and the auxiliary winding voltage Vb gradually decrease from the normal voltages Vm, Vn. Then, at the time t3 at which the main winding voltage Va becomes less than the threshold value Va (Va < Va) and the auxiliary winding voltage Vb becomes less than the threshold value Vb (Vb < Vb), the control section 9 starts the timer. Also, here, the threshold value Va and the threshold value Vb are in the relationship Va > Vb, but can be Va = Vb or Va < Vb (in the case of the auxiliary winding voltage Vb, the threshold value Vb is set to be smaller than the threshold value Va in the case of the main winding voltage Va, as described above). Figure 6 and Figure 8 The same applies to the auxiliary winding voltage Vb.)

[0062] After that, both the main winding voltage Va and the auxiliary winding voltage Vb continue to decrease, and at the time t4, each voltage Va, Vb becomes approximately zero (Va « 0, Vb « 0). However, since the switching element Q3 is no longer energized after the switching operation is stopped at the time t2, the temperature of the element continues to decrease, and therefore, when the overheat detection circuit 29 no longer outputs the stop signal S4 at the time t5 at which the temperature is below the threshold value, the switching circuit 20 resumes the switching operation. Therefore, both the main winding voltage Va and the auxiliary winding voltage Vb start to rise. Then, at the time t6 at which the main winding voltage Va becomes equal to or greater than the threshold value Va (Va > Va) and the auxiliary winding voltage Vb becomes equal to or greater than the threshold value Vb (Vb > Vb), the control section 9 stops the timer. After that, each winding voltage Va, Vb continues to rise, and when it becomes the normal voltage Vm, Vn at the time t7, the circuit returns to the normal state.

[0063] Here, the time X from the start of the timer at the time t3 to the stop of the timer at the time t6 is, for example, 400 s. The value of X is set in such a manner that the temperature of the switching element Q3 decreases within the time X to resume the switching operation (time t5), that is, to recover from the abnormal state. The time X corresponds to the "first time" in the present application.

[0064] Thus, in the case of the overheat protection, when the switching element Q3 becomes in the overheated state, the overheat detection circuit 29 detects this and outputs the stop signal S4 for stopping the switching operation to the PWM circuit 27, whereby the overheat detection circuit 29 directly stops the operation of the switching circuit 20 without passing through the control section 9. Also, from the start of the stop of the switching operation, the switching operation is resumed within a certain time X, and each winding voltage Va, Vb rises, and therefore, the control section 9 determines that the overheat protection by the overheat detection circuit 29 is performed by detecting this.

[0065] (2) Output short protection

[0066] The output short-circuit protection is a protection function required to prevent burnout of circuit components and the like due to overcurrent in the case where a short-circuit occurs between the output terminals T5, T6. The operation of the output short-circuit protection will be described with reference to the flowchart of Fig. 10. Figure 5

[0067] In Figure 5 , when a short-circuit occurs between the output terminals T5, T6 (Bl), the output voltage V2 of the 2nd converter 102 drops (B2). Therefore, the feedback circuit 28 performs feedback control on the PWM circuit 27 to increase the duty (B3). As a result, the PWM circuit 27 outputs a PWM signal of the maximum duty (B4). However, since the output terminals T5, T6 are in a short-circuit state, even if the switching circuit 20 performs switching operation at the maximum duty, the output voltage of the 1st rectifier circuit 22, i.e., the main winding voltage Va does not rise but continues to drop (B5). On the other hand, the output voltage of the 2nd rectifier circuit 23, i.e., the auxiliary winding voltage Vb is not affected by the short-circuit between the output terminals T5, T6, and therefore, by switching operation of the switching circuit 20 at the maximum duty, the output voltage of the 2nd rectifier circuit 23, i.e., the auxiliary winding voltage Vb continues to rise (B5). During this period, each voltage detection circuit 24, 25 continuously detects each winding voltage Va, Vb.

[0068] Further, when the control section 9 detects that the main winding voltage Va drops to be less than the threshold value and the auxiliary winding voltage Vb rises to exceed the threshold value based on the outputs of each voltage detection circuit 24, 25, the control section 9 starts the timer (B6). Then, at the time when a certain time elapses, the control section 9 determines an output short-circuit, and stops the timer (B7), and also stops the output permission signal S2 (B8). Thus, the PWM circuit 27 becomes in a non-operational state, and the switching circuit 20 stops switching operation (B9).

[0069] Figure 6 is a timing chart showing the changes of the main winding voltage Va and the auxiliary winding voltage Vb at the time of the output short-circuit protection. In Figure 6 , in order to easily understand which time (or period) the steps Bl to B9 of Fig. 10 correspond to, these steps are also described together. Figure 5

[0070] In Figure 6 ​​In the process, when an output short circuit occurs at time t1', the main winding voltage Va decreases from its normal voltage Vm, and the auxiliary winding voltage Vb increases from its normal voltage Vn. Then, at time t2', when the main winding voltage Va falls below the threshold Vα and the auxiliary winding voltage Vb exceeds the threshold Vγ, the control unit 9 starts the timer. Then, at time t3', the main winding voltage Va becomes approximately zero, and the auxiliary winding voltage Vb reaches its maximum voltage. When time t4', a certain time Y has elapsed since the timer started, the control unit 9 determines that there is an output short circuit and stops the timer. Furthermore, the control unit 9 stops outputting the permission signal S2, and the switching circuit 20 also stops its switching operation.

[0071] When the switching operation stops at time t4', the auxiliary winding voltage Vb decreases, but due to the continued short circuit, the main winding voltage Va remains unchanged (Va≈0). Furthermore, by time t5', the auxiliary winding voltage Vb also becomes approximately zero (Vb≈0). Then, when the short circuit is released at time t6', the switching operation restarts, and both the main winding voltage Va and the auxiliary winding voltage Vb begin to rise.

[0072] Here, the time Y from when the timer starts at time t2' to when the timer stops at time t4' is, for example, 200ms, set to be much smaller than... Figure 4 The value of time X (400s) (in) Figure 6 For convenience, Y is lengthened, but in reality, Y << X. This is because it is necessary to detect the output short circuit as early as possible so that the switching action can be stopped quickly to protect the circuit components from overcurrent. Time Y is equivalent to the "second time" in this invention.

[0073] Thus, in the event of an output short circuit, the main winding voltage Va decreases, while the auxiliary winding voltage Vb increases. Therefore, the control unit 9 detects these voltage changes and determines that an output short circuit has occurred. Furthermore, the control unit 9 stops outputting the permission signal S2, thereby stopping the switching circuit 20 from operating.

[0074] (3) Output low voltage protection

[0075] Output low voltage protection is a protection function required to detect faults when power is no longer supplied to the output side due to open-circuit faults in switching element Q3 or PWM circuit 27. (Refer to...) Figure 7 The flowchart illustrates the operation of the output low voltage protection.

[0076] exist Figure 7When an abnormality occurs due to a failure of the switching element Q3 or the PWM circuit 27, etc. (Cl), power is no longer transmitted from the primary side to the secondary side of the isolation transformer 21, and thus both the main winding voltage Va and the auxiliary winding voltage Vb decrease (C2). Further, when the control portion 9 detects that both the winding voltages Va, Vb have decreased to less than the threshold values based on the outputs of the voltage detection circuits 24, 25, the control portion 9 starts the timer (C3). Then, when a certain time elapses, the control portion 9 determines that the output is low voltage, and stops the timer (C4), and also outputs a failure detection signal (C5). This failure detection signal is sent to a not-shown vehicle-mounted ECU, in which an alarm or display, etc. processing is performed.

[0077] Figure 8 Fig. 9 is a timing chart showing the changes in the main winding voltage Va and the auxiliary winding voltage Vb at the time of output low voltage protection. In Figure 8 In the above-described embodiment, in order to easily understand Figure 7 Steps Cl to C5 of Fig. 9 correspond to which time (or period), and these steps are also described together.

[0078] In Figure 8 When an abnormality occurs at time tl" and power is no longer transmitted to the output side, both the main winding voltage Va and the auxiliary winding voltage Vb gradually decrease from the normal voltages Vm, Vn. Further, at time t2" when the main winding voltage Va becomes less than the threshold value Va (Va < Va) and the auxiliary winding voltage Vb becomes less than the threshold value Vb (Vb < Vb), the control portion 9 starts the timer.

[0079] After that, both the main winding voltage Va and the auxiliary winding voltage Vb continue to decrease, and at time t3", each of the voltages Va, Vb becomes approximately zero (Va « 0, Vb « 0). Further, when the time t4" at which a certain time Z has elapsed from the start of the timer is reached, the control portion 9 determines that the output is low voltage, and stops the timer, and also outputs a failure detection signal. Then, when the time elapses and the failure of the switching element Q3, etc. is resolved at time t5", the switching operation is restarted, and both the main winding voltage Va and the auxiliary winding voltage Vb change to increase.

[0080] Here, the time Z from the start of the timer at time t2" to the stop of the timer at time t4" is set to a time longer than the time X (Y < X < Z). This is because, in the case of the overheat protection of the switching element Q3, after the switching operation is stopped, the temperature of the switching element Q3 naturally decreases, and the switching operation is automatically restarted, and thus it is not necessary to set the time X to a long time, in contrast to the case of the output low voltage protection. Figure 4 Figure 4 Figure 8 ​​In the event of an output low voltage protection condition, the switching action will not restart until the fault is cleared. Therefore, a relatively long time Z is required to determine the output low voltage. Time Z is equivalent to the "third time" in this invention.

[0081] Therefore, when comparing overheat protection and output undervoltage protection, the similarity between the two is that both the main winding voltage Va and the auxiliary winding voltage Vb drop due to the abnormality. However, the difference is that in the case of overheat protection, the switching action restarts (recovers) within a certain time X. In contrast, in the case of output undervoltage protection, the switching action does not restart (does not recover) within a certain time Z.

[0082] Thus, when the output is under low voltage protection, both the main winding voltage Va and the auxiliary winding voltage Vb drop. This state lasts for a certain period of time. Therefore, the control unit 9 determines that the output has become low voltage by detecting these voltage changes and outputs a fault detection signal.

[0083] Figure 9 The circuit states, protection functions, and the relationship between winding voltages in the switching power supply device 100 are shown. If the circuit is in a normal state, both the main winding voltage Va and the auxiliary winding voltage Vb remain high. Figure 4 (Vm, Vn) Under normal conditions. When the switching element Q3 overheats, the overheat protection function (1) activates, the switching action stops, and the voltages Va and Vb of each winding drop, but will automatically recover within a certain period of time (restarting the switching action). In addition, when a short circuit occurs between the output terminals T5 and T6, the main winding voltage Va drops, but the auxiliary winding voltage Vb rises, and the output short circuit protection function (2) activates, stopping the switching action. In this case, it will not automatically recover within a certain period of time. In addition, when the output voltage V2 drops, both the main winding voltage Va and the auxiliary winding voltage Vb drop, and the output low voltage protection function (3) activates to detect the fault. In this case, it will not automatically recover within a certain period of time either.

[0084] from Figure 9 It can be seen that the overheat protection function (1) and the output short circuit protection function (2) can be distinguished by the different changes in the auxiliary winding voltage Vb. In addition, the output short circuit protection function (2) and the output low voltage protection function (3) can also be distinguished by the different changes in the auxiliary winding voltage Vb. On the other hand, the overheat protection function (1) and the output low voltage protection function (3) cannot be distinguished solely by the voltages Va and Vb of each winding, but they can be distinguished by whether there is automatic recovery within a certain period of time.

[0085] Figure 10 A comparative example of the present invention is shown. In the figures, the counterparts to... Figure 2Identical parts are labeled with the same number. Figure 10 In addition to Figure 2 In addition to the structure, it also includes an interface circuit 30 disposed between the overheat detection circuit 29 and the control unit 9, and an overcurrent detection circuit 31 disposed between the first rectifier circuit 22 and the output terminal T5. The interface circuit 30 is a circuit used to electrically isolate the output signal of the overheat detection circuit 29 and input it to the control unit 9. The overcurrent detection circuit 31 is a circuit that detects the overcurrent flowing in the event of a short circuit between the output terminals T5 and T6. The output of the overcurrent detection circuit 31 is input to the control unit 9.

[0086] After adopting Figure 10 In that configuration, the control unit 9 determines the output low voltage based on the output of the first voltage detection circuit 24 (main winding voltage) and the output of the second voltage detection circuit 25 (auxiliary winding voltage). This is consistent with... Figure 2 The situation is not much different. However, regarding overheat protection, in Figure 2 In the middle, when the switching element Q3 overheats, the overheat detection circuit 29 outputs a stop signal, causing the switch to stop operating. Conversely, in Figure 10 In the process, the control unit 9 determines whether the switching element Q3 is overheated based on the output signal of the overheat detection circuit 29. If overheating is detected, it stops outputting the permission signal S2, thereby stopping the switching operation. Additionally, in Figure 2 In the middle, the control unit 9 determines whether there is an output short circuit based on the output of the first voltage detection circuit 24 (main winding voltage Va) and the output of the second voltage detection circuit 25 (main winding voltage Vb). Conversely, in Figure 10 In the middle, the control unit 9 determines whether there is an output short circuit based on the output signal of the overcurrent detection circuit 31.

[0087] from Figure 2 and Figure 10 A comparison shows that, in Figure 10 In this case, because an interface circuit 30 and an overcurrent detection circuit 31 are provided, it is compatible with... Figure 2 In comparison, the circuit structure becomes more complex. On the other hand, in Figure 2 In the event of overheating, the overheat detection circuit 29 outputs a stop signal S4, causing the switch to stop operating. Therefore, it is not necessary to... Figure 10 The interface circuit 30, in addition, since the presence or absence of an output short circuit can be determined based on the outputs of the first voltage detection circuit 24 and the second voltage detection circuit 25, is not required. Figure 10 The overcurrent detection circuit 31. Furthermore, in Figure 10 In this case, the control unit 9 determines whether the switching element Q3 is overheating, thus increasing the load on the control unit 9. Figure 2In this case, since it is not necessary to determine whether there is overheating in the control unit 9, the load on the control unit 9 is reduced.

[0088] As explained above, according to the switching power supply device 100 of this embodiment, when the switching element Q3 becomes overheated, the switching operation of the switching circuit 20 can be stopped without going through the control unit 9 by using the stop signal S4 output from the overheat detection circuit 29. Furthermore, the control unit 9 can determine whether a short circuit or voltage drop has occurred at the output of the second converter 102 by comparing the changes in the detection voltage (main winding voltage Va) of the first voltage detection circuit 24 and the detection voltage (auxiliary winding voltage Vb) of the second voltage detection circuit 25. Therefore, an interface circuit 30 is not required between the overheat detection circuit 29 and the control unit 9. Figure 10 Furthermore, an overcurrent detection circuit 31 for detecting output short circuits is not required. Figure 10 This simplifies the circuit structure and reduces the load on the control unit 9. Furthermore, although the circuit structure is simple, it... Figure 9 As shown, it can accurately perform protection corresponding to the type of anomaly.

[0089] In addition to the embodiments described above, various other embodiments can also be adopted in this invention.

[0090] In the above embodiments, various protection functions in the second converter 102 have been described, but they can also be provided in the first converter 101. Figure 1 and Figure 2 The same structure can also be provided in both converters 101 and 102. In addition, the present invention is not limited to the switching power supply device 100 having the first converter 101 and the second converter 102, but can also be applied to switching power supply devices having only one converter or switching power supply devices having three or more converters.

[0091] In the above embodiments, with having Figure 9 The present invention is exemplified by a switching power supply device 100 having all functions (1) to (3), but is not limited thereto. For example, the present invention can also be applied to switching power supply devices having only overheat protection function (1) and output short-circuit protection function (2), or switching power supply devices having only overheat protection function (1) and output low voltage protection function (3). In addition, the present invention can also be applied to switching power supply devices having only output short-circuit protection function (2) and output low voltage protection function (3). In this case, the overheat detection circuit 29 and the temperature sensing element K are not required.

[0092] In the above embodiments, Figure 5In the operation of the output short-circuit protection, when the output short-circuit is detected (determined), the output permission signal S2 is stopped immediately, and the switching operation is stopped (B7 to B9). Alternatively, the control section 9 can count the number of times of detection of the short-circuit, and when the number of times reaches a predetermined number N (N≥2), the control section 9 stops the output of the permission signal S2, and stops the switching operation.

[0093] In the above embodiment, the control section 9 stops the switching operation by stopping the output of the permission signal S2 at the time of the output short-circuit. Alternatively, the control section 9 can stop the switching operation by outputting an inhibition signal different from the permission signal S2 at the time of the output short-circuit.

[0094] In the above embodiment, the switching operation is stopped by supplying the stop signal S4 output from the overheat detection circuit 29 to the PWM circuit 27. Alternatively, the switching operation can be stopped by supplying the stop signal S4 to the switching circuit 20. Similarly, the permission signal S2 (or the inhibition signal) output from the control section 9 can be supplied to the switching circuit 20.

[0095] In the above embodiment, the example in which both the first converter 101 and the second converter 102 are DC-DC converters of the step-down type is described. Alternatively, each of the converters 101 and 102 can be a DC-DC converter of the step-up type. Further alternatively, one of the converters 101 and 102 can be a DC-DC converter of the step-down type, and the other can be a DC-DC converter of the step-up type.

[0096] In the above embodiment, the example in which both the first converter 101 and the second converter 102 are DC-DC converters of the isolated type is described. Alternatively, each of the converters 101 and 102 can be a DC-DC converter of the non-isolated type.

[0097] In the above embodiment, the PWM circuit 27 is described as an example of the drive circuit that drives the switching circuit 20. Alternatively, a drive circuit that drives the switching circuit 20 by a method other than PWM can be provided.

[0098] In the above embodiment, the switching power supply device 100 mounted on a vehicle is described as an example. The switching power supply device of the present application can be applied to uses other than in vehicles.

Claims

1. A switching power supply device, comprising: A converter that switches an input DC voltage to convert it into a DC voltage of a specified value; and The control unit controls the operation of the converter. The converter includes: A switching circuit having a switching element, which switches the input DC voltage by turning the switching element on and off; A driving circuit that drives the switching circuit; A rectifier circuit that rectifies the voltage converted to AC by the switching circuit; as well as An insulated transformer, disposed between the switching circuit and the rectifier circuit, has a primary winding connected to the switching circuit and a secondary winding connected to the rectifier circuit. Its features are, The secondary winding of the insulated transformer consists of a primary winding and an auxiliary winding. The rectifier circuit consists of a first rectifier circuit and a second rectifier circuit. The first rectifier circuit is disposed between the main winding and the output terminal of the converter, and the second rectifier circuit is connected to the auxiliary winding. The switching power supply device also has: The first voltage detection circuit detects the output voltage of the first rectifier circuit; The second voltage detection circuit detects the output voltage of the second rectifier circuit; An overheat detection circuit that detects the overheating state of the switching element; and A feedback circuit provides feedback control to the drive circuit to ensure that the converter's output voltage reaches the target value. When the temperature of the switching element exceeds a threshold, the overheat detection circuit outputs a stop signal to stop the switching circuit from operating and to provide overheat protection. The control unit determines whether the converter output is short-circuited or the converter output is low based on a comparison between the voltage change detected by the first voltage detection circuit and the voltage change detected by the second voltage detection circuit. If the converter output is determined to be short-circuited, control for output short-circuit protection is executed; if the converter output is determined to be low, control for output low-voltage protection is executed.

2. The switching power supply device according to claim 1, characterized in that, If, after a certain period of time, both the voltage detected by the first voltage detection circuit and the voltage detected by the second voltage detection circuit are lower than normal, and before a predetermined first time has elapsed, the voltages detected by both the first and second voltage detection circuits rise, the control unit determines that overheat protection has been activated by the overheat detection circuit. If the voltage detected by the first voltage detection circuit is lower than the normal voltage and the voltage detected by the second voltage detection circuit is higher than the normal voltage for a predetermined second time period, the control unit determines that a short circuit has occurred at the output of the converter and executes control for output short circuit protection. If the voltage detected by the first voltage detection circuit is lower than the normal voltage and the voltage detected by the second voltage detection circuit is lower than the normal voltage for a third time longer than the first time, the control unit determines that the output of the converter has become low voltage and performs control for output low voltage protection.

3. The switching power supply device according to claim 1, characterized in that, If, after a certain period of time, both the voltage detected by the first voltage detection circuit and the voltage detected by the second voltage detection circuit are lower than normal, and before a predetermined first time has elapsed, the voltages detected by both the first and second voltage detection circuits rise, the control unit determines that overheat protection has been activated by the overheat detection circuit. If the voltage detected by the first voltage detection circuit is lower than the normal voltage and the voltage detected by the second voltage detection circuit is higher than the normal voltage for a predetermined second time, the control unit determines that a short circuit has occurred at the output of the converter and executes control for output short circuit protection.

4. The switching power supply device according to claim 1, characterized in that, If, after a certain period of time, both the voltage detected by the first voltage detection circuit and the voltage detected by the second voltage detection circuit are lower than normal, and before a predetermined first time has elapsed, the voltages detected by both the first and second voltage detection circuits rise, the control unit determines that overheat protection has been activated by the overheat detection circuit. If the voltage detected by the first voltage detection circuit is lower than the normal voltage and the voltage detected by the second voltage detection circuit is lower than the normal voltage for a third time longer than the first time, the control unit determines that the output of the converter has become low voltage and performs control for output low voltage protection.

5. A switching power supply device, comprising: A converter that switches an input DC voltage to convert it into a DC voltage of a specified value; and The control unit controls the operation of the converter. The converter includes: A switching circuit having a switching element, which switches the input DC voltage by turning the switching element on and off; A driving circuit that drives the switching circuit; A rectifier circuit that rectifies the voltage converted to AC by the switching circuit; as well as An insulated transformer, disposed between the switching circuit and the rectifier circuit, has a primary winding connected to the switching circuit and a secondary winding connected to the rectifier circuit. Its features are, The secondary winding of the insulated transformer consists of a primary winding and an auxiliary winding. The rectifier circuit consists of a first rectifier circuit and a second rectifier circuit. The first rectifier circuit is disposed between the main winding and the output terminal of the converter, and the second rectifier circuit is connected to the auxiliary winding. The switching power supply device also has: The first voltage detection circuit detects the output voltage of the first rectifier circuit; The second voltage detection circuit detects the output voltage of the second rectifier circuit; as well as A feedback circuit provides feedback control to the drive circuit to ensure that the converter's output voltage reaches the target value. The control unit determines whether the converter output is short-circuited or the converter output is low based on a comparison between the voltage change detected by the first voltage detection circuit and the voltage change detected by the second voltage detection circuit. If the converter output is determined to be short-circuited, control for output short-circuit protection is executed; if the converter output is determined to be low, control for output low-voltage protection is executed.

6. The switching power supply device according to claim 5, characterized in that, If the voltage detected by the first voltage detection circuit is lower than the normal voltage and the voltage detected by the second voltage detection circuit is higher than the normal voltage for a predetermined period of time, the control unit determines that a short circuit has occurred at the output of the converter and executes control for output short circuit protection. If the voltage detected by the first voltage detection circuit is lower than the normal voltage and the voltage detected by the second voltage detection circuit is lower than the normal voltage for a period of time longer than the predetermined time, the control unit determines that the output of the converter has become low voltage and performs control for output low voltage protection.

7. The switching power supply device according to any one of claims 1 to 3, 5, and 6, characterized in that, When the control unit permits the switching circuit to perform a switching action, it outputs a permission signal. When it determines that a short circuit has occurred at the output of the converter, it stops the permission signal or outputs a prohibition signal different from the permission signal, thereby causing the switching circuit to stop its switching action and perform output short circuit protection.

8. The switching power supply device according to claim 7, characterized in that, If the number of times the converter's output is short-circuited reaches a predetermined number, the control unit stops the permission signal or outputs the prohibition signal.

9. The switching power supply device according to any one of claims 1, 2, 4 to 6, characterized in that, The control unit outputs a fault detection signal as a control for the output low voltage protection.

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