JP2009183037A - Switching power supply circuit and vehicle equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply circuit, wherein even when overcurrent is produced continuously, ample overcurrent protection can be realized. <P>SOLUTION: The switching power supply circuit includes: a switching circuit that switches input direct-current voltage in accordance with a pulse signal and outputs switching output voltage; an output circuit that converts the switching output voltage into direct current and outputs output direct-current voltage; a control circuit that outputs a pulse signal to the switching circuit and controls the pulse width of the pulse signal so that the output direct-current voltage of the output circuit is constant at a first voltage value; an overcurrent detection circuit that detects an overcurrent produced in the output circuit; a delay circuit that, when an overcurrent is detected at the overcurrent detection circuit, stops the output of a pulse signal from the control circuit for a predetermined time; and an output voltage detection circuit that, when the output direct-current voltage of the output circuit becomes lower than a second voltage value lower than the first voltage value, continuously makes the output of a pulse signal from the control circuit stop. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a switching power supply circuit and a vehicle including the same, and more specifically to a switching power supply circuit that realizes overcurrent protection and a vehicle including the same.

  Conventionally, a technique for realizing overcurrent protection has been proposed for a switching power supply circuit (for example, Patent Document 1). Overcurrent occurs when the load suddenly changes or when the load is short-circuited. Hereinafter, a conventional switching power supply circuit employing this technique will be described in detail with reference to FIGS.

  First, a block configuration of a conventional switching power supply circuit will be described with reference to FIG. FIG. 4 is a diagram showing a block configuration of a conventional switching power supply circuit. In FIG. 4, the switching power supply circuit includes a switching circuit 1, output circuits 2 and 3, resistors 4 and 5, a control IC 6, an overcurrent detection circuit 7, and a delay circuit 8.

  The switching circuit 1 switches the DC input voltage E1 according to the pulse signal P1 input from the control IC 6, and is a switching output voltage based on the switched input voltage E1, and is input to each of the output circuits 2 and 3. Two switching output voltages are output. Specifically, the switching circuit 1 includes an input terminal 11, a switching element 12, and a converter 13. The switching element 12 is composed of an FET and switches the input voltage E1 from the input terminal 11 in accordance with a pulse signal P1 input from the control IC 6. The converter 13 converts the switched input voltage E1 into two switching output voltages that are input to the output circuits 2 and 3, respectively.

  Each of the output circuits 2 and 3 is connected to the subsequent stage of the switching circuit 1. The output circuit 2 converts the switching output voltage from the converter 13 into a DC voltage and outputs an output voltage E2. Specifically, the output circuit 2 includes a diode 21, a capacitor 22, and output terminals 23 and 24. The diode 21 rectifies the switching output voltage from the converter 13. The capacitor 22 smoothes the output of the rectified diode 21. As a result, a DC output voltage E2 is obtained between the output terminals 23 and 24. The output circuit 3 converts the switching output voltage from the converter 13 into a DC voltage and outputs an output voltage E3. Specifically, the output circuit 3 includes a diode 31, a capacitor 32, and output terminals 33 and 34. The diode 31 rectifies the switching output voltage from the converter 13. Capacitor 32 smoothes the output of rectified diode 31. As a result, a DC output voltage E3 is obtained between the output terminals 33 and 34. Each of the output voltages E2 and E3 is output as a power supply voltage to an external device (not shown).

  One end of the resistor 4 is connected to the output terminal 33 of the output circuit 3, and the other end is connected to one end of the resistor 5. The other end of the resistor 5 is grounded. The voltage of the resistor 5 is a voltage corresponding to the output voltage E3.

  The control IC 6 outputs a pulse signal P1 from the OUT terminal to the gate terminal of the switching element 12 while performing pulse width control so that the voltage of the resistor 5 input to the FB input terminal is constant at a predetermined voltage. Further, when a stop signal S2 from the delay circuit 8 described later is input to the stop signal terminal, the control IC 6 stops the output of the pulse signal P1 while the stop signal S2 is input.

  The overcurrent detection circuit 7 detects the voltage of the resistor 5. The overcurrent detection circuit 7 detects that an overcurrent has occurred in the output circuit 2 and / or the output circuit 3 when the detected voltage becomes higher than a predetermined threshold value. The overcurrent detection circuit 7 outputs an overcurrent detection signal S1 to the delay circuit 8 while the detected voltage is higher than a predetermined threshold.

  The pulse signal P1 and the overcurrent detection signal S1 are input to the delay circuit 8. The delay circuit 8 performs a predetermined operation when both the pulse signal P1 and the overcurrent detection signal S1 are input. Thereafter, the delay circuit 8 outputs the stop signal S2 to the stop signal terminal of the control IC 6 and simultaneously starts measuring the delay time. The stop signal S2 is continuously output until the end of the delay time measurement. Specifically, delay circuit 8 includes a bipolar transistor and a capacitor connected to the base terminal of the bipolar transistor. When both the pulse signal P1 and the overcurrent detection signal S1 are input, charging to the capacitor starts as the predetermined operation described above. Thereafter, when the voltage of the capacitor becomes higher than the base voltage of the bipolar transistor, the collector terminal and the emitter terminal of the bipolar transistor are short-circuited, and the stop signal S2 is generated. At the same time, discharge from the capacitor starts and measurement of the delay time starts. Thereafter, when the voltage of the capacitor becomes lower than the base voltage due to discharge, the collector terminal and the emitter terminal of the bipolar transistor are opened, the output of the stop signal S2 is stopped, and the measurement of the delay time is finished.

  Next, the operation of the conventional switching power supply circuit will be described with reference to FIGS. FIG. 5 is a time chart for explaining the operation of the conventional switching power supply circuit. T 1 is a delay time set in the delay circuit 8. In FIG. 5, it is assumed that overcurrent has occurred at time t1, and overcurrent continues to occur even after time t7 has elapsed.

  At time t1, the overcurrent detection circuit 7 detects the occurrence of overcurrent, and outputs an overcurrent detection signal S1 to the delay circuit 8. At time t2, the pulse signal P1 is also input to the delay circuit 8, and the condition for starting the measurement of the delay time T1 is satisfied. The delay circuit 8 starts measuring the delay time T1 at the same time as outputting the stop signal S2 to the stop signal terminal of the control IC 6 at time t3 after performing a predetermined operation. At time t3, the control IC 6 stops outputting the pulse signal P1.

  At time t4 when the delay time T1 has elapsed from time t3, the delay circuit 8 stops outputting the stop signal S2. As a result, the control IC 6 outputs the pulse signal P1 again at time t4. Here, in the example of FIG. 5, the overcurrent detection signal S <b> 1 is continuously output to the delay circuit 8. That is, overcurrent continues to occur. Therefore, at time t4, both the pulse signal P1 and the overcurrent detection signal S1 are input to the delay circuit 8, and the condition for starting the measurement of the delay time T1 is satisfied again. After performing the predetermined operation again, the delay circuit 8 outputs the stop signal S2 to the stop signal terminal of the control IC 6 at the time t5 and simultaneously starts measuring the delay time T1. At time t5, the control IC 6 stops outputting the pulse signal P1 again.

  At time t6 when the delay time T1 has elapsed from time t5, the delay circuit 8 stops outputting the stop signal S2. Thereby, the control IC 6 outputs the pulse signal P1 again at time t6. Here, since the overcurrent detection signal S1 is continuously output to the delay circuit 8, the condition for starting the measurement of the delay time T1 in the delay circuit 8 is satisfied at time t6. After performing the predetermined operation again, the delay circuit 8 outputs the stop signal S2 to the stop signal terminal of the control IC 6 at time t7, and simultaneously starts measuring the delay time T1. At time t7, the control IC 6 stops outputting the pulse signal P1 again.

As described above, when an overcurrent occurs, the conventional switching power supply circuit stops outputting the pulse signal P1 in the time interval (t3 to t4, t5 to t6) corresponding to the delay time T1. As a result, the frequency of the pulse signal P1 is substantially lowered, so that the voltages of the output voltages E2 and E3 output from the output circuits 2 and 3 can be lowered, and overcurrent protection is realized. ing.
JP-A-5-336745

  However, in the above-described conventional switching power supply circuit, when the overcurrent continues, the output voltages E2 and E3 decrease, but the outputs themselves from the output circuits 2 and 3 continue. . For this reason, the above-described conventional switching power supply circuit has problems such as overheating of elements in the switching power supply circuit and elements in the external devices connected to the output circuits 2 and 3. Thus, in the conventional switching power supply circuit, when the overcurrent is continuously generated, sufficient overcurrent protection cannot be realized.

  Therefore, an object of the present invention is to provide a switching power supply circuit capable of realizing sufficient overcurrent protection even when an overcurrent is continuously generated.

  The present invention has been made to solve the above-described problems, and a switching power supply circuit according to the present invention switches a DC input voltage according to an input pulse signal, and a switching output voltage based on the switched DC input voltage. A switching circuit that outputs DC, an output circuit that converts the switching output voltage output from the switching circuit to DC and outputs a DC output voltage, and outputs a pulse signal to the switching circuit and a DC output that is output from the output circuit A control circuit that controls the pulse width of the pulse signal so that the voltage is constant at the first voltage value, an overcurrent detection circuit that detects an overcurrent generated in the output circuit based on the current flowing through the switching circuit, Outputs a pulse signal from the control circuit when an overcurrent is detected in the current detection circuit A delay circuit that stops for a predetermined time and a DC output voltage output from the output circuit are detected, and when the detected DC output voltage is lower than a second voltage value lower than the first voltage value, An output voltage detection circuit for continuously stopping the output of the pulse signal.

  According to such a configuration, when the DC output voltage becomes lower than the second voltage value, the output of the pulse signal from the control circuit is continuously stopped. Here, when the overcurrent is continuously generated, the process in which the output of the pulse signal is stopped for a predetermined time in the delay circuit is repeated, and the DC output voltage starts to decrease from the first voltage value. The voltage itself is output. On the other hand, when the DC output voltage becomes lower than the second voltage value, the DC output voltage itself can be stopped by continuously stopping the output of the pulse signal. As a result, when overcurrent is continuously generated, problems such as element overheating can be solved, and sufficient overcurrent protection can be realized. On the other hand, when the DC output voltage does not become lower than the second voltage value, that is, when the overcurrent does not continuously occur, the DC output voltage from the output circuit can be automatically returned to the first voltage value.

  Preferably, when an overcurrent is detected in the overcurrent detection circuit, the delay circuit short-circuits between the emitter terminal and the collector terminal, thereby controlling a transistor that grounds the output terminal of the control circuit that outputs the pulse signal, When the output terminal of the circuit is grounded, the capacitor that starts charging and the emitter terminal and the collector terminal of the transistor are opened after a lapse of a predetermined time when the voltage of the capacitor becomes higher than the third voltage value by charging. And a comparator for releasing the grounding of the output terminal of the control circuit.

  With such a configuration, a constant delay time can always be generated regardless of the temperature characteristics of the base voltage of the transistor.

  The present invention is also directed to a vehicle. The vehicle according to the present invention includes the switching power supply circuit and a device that inputs a DC output voltage output from an output circuit of the switching power supply circuit as a power supply voltage. Prepare.

  The present invention can provide a switching power supply circuit capable of realizing sufficient overcurrent protection even when an overcurrent is continuously generated.

  A switching power supply circuit according to an embodiment of the present invention will be described below with reference to FIGS.

  First, a block configuration of a switching power supply circuit according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a block configuration of a switching power supply circuit according to an embodiment of the present invention. In FIG. 1, the switching power supply circuit includes a switching circuit 1a, output circuits 2 and 3, resistors 4 and 5, a control IC 6a, an overcurrent detection circuit 7a, a delay circuit 8a, a resistor 9, and an output voltage detection circuit 10. Note that among the circuits illustrated in FIG. 1, the same circuits as those illustrated in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted here.

  The switching circuit 1a further includes a resistor 14 with respect to the switching circuit 1 shown in FIG. One end of the resistor 14 is connected to the source terminal of the switching element 12, and the other end is grounded. In normal times, the gate voltage Vge of the switching element 12 becomes the pulse signal P1 itself from the control IC 6a, and the switching element 12 performs a switching operation according to the pulse signal P1. On the other hand, when the stop signal S2 is output from the delay circuit 8a, the gate voltage Vge is maintained at the low level (L level), and the switching element 12 stops the switching operation and opens between the drain terminal and the source terminal. To do. The configuration and operation other than these are the same as those of the switching circuit 1 shown in FIG.

  The control IC 6a controls the pulse signal P1 from the OUT terminal to the gate terminal of the switching element 12 through the resistor 9 while performing pulse width control so that the voltage of the resistor 5 input to the FB input terminal becomes constant at a predetermined voltage. Is output. Further, when a stop signal S3 from an output voltage detection circuit 10 described later is input to the stop signal terminal, the control IC 6a stops outputting the pulse signal P1 while the stop signal S3 is input.

  The overcurrent detection circuit 7 a detects the voltage of the resistor 14. The overcurrent detection circuit 7a detects that an overcurrent has occurred in the output circuit 2 and / or the output circuit 3 when the detected voltage becomes higher than a predetermined threshold. The overcurrent detection circuit 7a outputs an overcurrent detection signal S1 to the delay circuit 8a while the detected voltage is higher than a predetermined threshold.

  The overcurrent detection signal S1 is input to the delay circuit 8a. The delay circuit 8a performs a predetermined operation when the overcurrent detection signal S1 is input. Thereafter, the delay circuit 8a outputs the stop signal S2 and starts measuring the delay time at the same time. The stop signal S2 is continuously output until the end of the delay time measurement. The predetermined operation of the delay circuit 8a will be described later.

  The output voltage detection circuit 10 detects the voltage of the resistor 5 that is a voltage corresponding to the output voltage E3. When the detected voltage becomes lower than a predetermined threshold, the output voltage detection circuit 10 performs a predetermined operation, and then outputs a stop signal S3 to the stop signal terminal of the control IC 6a. The predetermined operation of the output voltage detection circuit 10 will be described later.

  Next, the operation of the switching power supply circuit according to the embodiment of the present invention will be described with reference to FIG. 1 and FIG. FIG. 2 is a diagram showing a time chart for explaining the operation of the switching power supply circuit according to the embodiment of the present invention. T1 is a delay time set in the delay circuit 8a. In FIG. 2, it is assumed that an overcurrent has occurred in the output circuit 2 and / or the output circuit 3 at time t1, and that the overcurrent continues to occur after time t11 has elapsed. In FIG. 2, it is assumed that the voltage E5 of the resistor 5 becomes lower than a predetermined threshold set in the output voltage detection circuit 10 at time t9.

  At time t1, the stop signal S2 is not output from the delay circuit 8a. Therefore, the gate voltage Vge becomes the pulse signal P1 itself from the control IC 6a, and changes from the L level to the high level (H level). Here, in the example of FIG. 2, an overcurrent has occurred at time t1. Therefore, when the drain terminal and the source terminal of the switching element 12 are short-circuited at time t1, a voltage higher than a predetermined threshold set in the overcurrent detection circuit 7a is applied to the resistor 14. become. Therefore, at time t1, overcurrent detection circuit 7a detects the occurrence of overcurrent and outputs overcurrent detection signal S1 to delay circuit 8a.

  The delay circuit 8a outputs the stop signal S2 at the time t2 after performing a predetermined operation, and simultaneously starts measuring the delay time. At the same time, the gate voltage Vge becomes L level, and the switching element 12 stops the switching operation and opens between the drain terminal and the source terminal. When the drain terminal and the source terminal are opened, no voltage is applied to the resistor 14, so the overcurrent detection circuit 7a stops outputting the overcurrent detection signal S1 at time t2.

  At time t3 when the delay time T1 has elapsed from time t2, the delay circuit 8a stops outputting the stop signal S2. Thereby, the gate voltage Vge becomes the pulse signal P1 itself from the control IC 6a. Here, in the example of FIG. 2, overcurrent is continuously generated. Therefore, when the drain terminal and the source terminal of the switching element 12 are short-circuited at time t4, a voltage higher than a predetermined threshold set in the overcurrent detection circuit 7a is applied to the resistor 14. become. Therefore, at time t4, the overcurrent detection circuit 7a outputs the overcurrent detection signal S1 to the delay circuit 8a again. The delay circuit 8a outputs a stop signal S2 at the time t5 after performing a predetermined operation, and simultaneously starts measuring the delay time. At the same time, the gate voltage Vge becomes L level, and the output of the overcurrent detection signal S1 from the overcurrent detection circuit 7a is also stopped.

  At time t6 when the delay time T1 has elapsed from time t5, the delay circuit 8a stops outputting the stop signal S2. In the example of FIG. 2, since the overcurrent is continuously generated, the overcurrent detection circuit 7a outputs the overcurrent detection signal S1 to the delay circuit 8a again at time t7. The delay circuit 8a outputs the stop signal S2 at the time t8 after performing a predetermined operation, and simultaneously starts measuring the delay time. At the same time, the gate voltage Vge becomes L level, and the output of the overcurrent detection signal S1 from the overcurrent detection circuit 7a is also stopped.

  In the example of FIG. 2, the voltage E5 of the resistor 5 starts to decrease from time t1 and becomes lower than a predetermined threshold set in the output voltage detection circuit 10 at time t9. Therefore, the output voltage detection circuit 10 outputs the stop signal S3 to the stop signal terminal of the control IC 6a at time t10 after performing a predetermined operation. For this reason, the control IC 6a continuously stops the output of the pulse signal P1 after time t10. When the output of the pulse signal P1 is continuously stopped, the gate voltage Vge always becomes L level, so that the voltage E5 of the resistor 5 rapidly decreases to 0V. Note that the delay circuit 8a stops outputting the stop signal S2 at the time t11 when the delay time T1 has elapsed from the time t8.

  As described above, in the switching power supply circuit according to the present embodiment, when the overcurrent is continuously generated, the output from each of the output circuits 2 and 3 is stopped by continuously stopping the output of the pulse signal P1. Stop itself. As a result, problems such as overheating of elements in the switching power supply circuit and elements in external devices connected to the output circuits 2 and 3 can be solved. As a result, sufficient overcurrent protection can be realized.

  On the other hand, in the switching power supply circuit according to the present embodiment, when the occurrence time of the overcurrent is short and the voltage E5 of the resistor 5 does not become lower than the predetermined threshold value, the time interval (t2 to t2) corresponding to the delay time T1 is conventionally provided. Only at t3, t5 to t6), the output of the pulse signal P1 is stopped. That is, if the occurrence time of the overcurrent is short, the switching operation of the switching power supply circuit is only temporarily stopped, and the output voltage from the output circuit can be automatically restored to a desired voltage. For example, there are the following merits for automatically returning. If the switching power supply circuit is to be activated rapidly, an overcurrent with a short generation time is likely to occur. For this reason, it is usually necessary to lengthen the startup time. However, the switching power supply circuit according to the present embodiment can be started up while protecting an overcurrent having a short generation time. For this reason, in the switching power supply circuit according to the present embodiment, the startup time can be shortened.

  Next, a specific circuit configuration of the switching power supply circuit according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing a specific circuit configuration of the switching power supply circuit according to the embodiment of the present invention.

  In FIG. 3, the overcurrent detection circuit 7a includes an operational amplifier 71 and resistors 72 to 74, and the delay circuit 8a includes resistors 81 to 85, a diode 86, a capacitor 87, an operational amplifier 88, and a bipolar transistor 89, and an output voltage detection circuit. 10 includes resistors 101 to 108, an operational amplifier 109, a diode 110, a capacitor 111, and an operational amplifier 112.

  In the overcurrent detection circuit 7a, the inverting input terminal of the operational amplifier 71 is connected to one end of the resistor 14, and the non-inverting input terminal is connected to one end of the resistor 72, one end of the resistor 73, and one end of the resistor 74, respectively. Connected. The other end of the resistor 72 is connected to the Vcc terminal of the control IC 6a. The other end of the resistor 73 is grounded. The output terminal of the operational amplifier 71 is connected to the other end of the resistor 74, one end of the resistor 81, one end of the resistor 82, and the cathode terminal of the diode 86.

  In the delay circuit 8a, the other end of the resistor 81 is connected to the Vcc terminal of the control IC 6a. The other end of the resistor 82 is connected to the anode terminal of the diode 86, one end of the capacitor 87, and the non-inverting input terminal of the operational amplifier 88. The other end of the capacitor 87 is grounded. An inverting input terminal of the operational amplifier 88 is connected to one end of the resistor 83 and one end of the resistor 84. The other end of the resistor 83 is connected to the Vcc terminal of the control IC 6a. The other end of the resistor 84 is grounded. The output terminal of the operational amplifier 88 is connected to one end of the resistor 85. The other end of resistor 85 is connected to the base terminal of bipolar transistor 89. The bipolar transistor 89 has an emitter terminal connected to the gate terminal of the switching element 12 and one end of the resistor 9, and a collector terminal grounded.

  In the output voltage detection circuit 10, the inverting input terminal of the operational amplifier 109 is connected to one end of the resistor 5, and the non-inverting input terminal is connected to one end of the resistor 101, one end of the resistor 102, and one end of the resistor 103, respectively. Connected. The other end of the resistor 101 is connected to the Vcc terminal of the control IC 6a. The other end of the resistor 102 is grounded. The output terminal of the operational amplifier 109 is connected to the other end of the resistor 103, one end of the resistor 104, one end of the resistor 105, and the cathode terminal of the diode 110. The other end of the resistor 104 is connected to the Vcc terminal of the control IC 6a. The other end of the resistor 105 is connected to the anode terminal of the diode 110, one end of the capacitor 111, and the inverting input terminal of the operational amplifier 112. The other end of the capacitor 111 is grounded. The non-inverting input terminal of the operational amplifier 112 is connected to one end of the resistor 106 and one end of the resistor 107. The other end of the resistor 106 is connected to the Vcc terminal of the control IC 6a. The other end of the resistor 107 is grounded. The output terminal of the operational amplifier 112 is connected to one end of the resistor 108 and the stop signal terminal of the control IC 6a. The other end of the resistor 108 is connected to the Vcc terminal of the control IC 6a.

  Next, the operation of the circuit configuration shown in FIG. 3 will be described with reference to FIG. 2 again. In the overcurrent detection circuit 7a, the operational amplifier 71 operates as a comparator. The ratio between the resistance value of the resistor 72 and the resistance value of the resistor 73 is determined so that a voltage that is a predetermined threshold value is applied to the resistor 73. Therefore, the operational amplifier 71 changes the output voltage SE1 from the H level to the L level when the voltage of the resistor 14 becomes higher than the voltage of the resistor 73 at time t1. The overcurrent detection signal S1 according to the present embodiment is a signal that enters a stop state when the output voltage SE1 is at an H level and enters an output state when the output voltage SE1 is at an L level. Simultaneously with the change of the output voltage SE1 to the L level, as a predetermined operation of the overcurrent detection circuit 7a, rapid discharge of the capacitor 87 of the delay circuit 8a is started. This discharge is performed via the diode 86.

  In the delay circuit 8a, the operational amplifier 88 operates as a comparator. The operational amplifier 88 changes the output voltage from the H level to the L level at time t2 when the voltage of the capacitor 87 becomes lower than the voltage of the resistor 84 due to discharging. As a result, the emitter terminal and the collector terminal of the bipolar transistor 89 are short-circuited, and the emitter voltage SE2 changes from H level to L level. The stop signal S2 according to the present embodiment is a signal that enters a stop state when the emitter voltage SE2 is at an H level and enters an output state when the emitter voltage SE2 is at an L level. In addition, because of this short circuit state, the OUT terminal of the control IC 6a is grounded and the pulse signal P1 is not input to the gate terminal of the switching element 12, so that the gate voltage Vge becomes L level at time t2. When the gate voltage Vge becomes L level, the drain terminal and the source terminal of the switching element 12 are opened, and the voltage of the resistor 14 becomes 0V. Therefore, the operational amplifier 71 of the overcurrent detection circuit 7a changes the output voltage SE1 from the L level to the H level at time t2. At the same time as the output voltage SE1 changes to the H level, charging of the capacitor 87 of the delay circuit 8a is started. This operation corresponds to the start of measurement of the delay time T1. This charging is performed via the resistors 81 and 82.

  At time t3 when the voltage of the capacitor 87 becomes higher than the voltage of the resistor 84 due to charging, the measurement of the delay time T1 ends, and the operational amplifier 88 changes the output voltage from the L level to the H level. As a result, the emitter terminal and the collector terminal of the bipolar transistor 89 are opened, and the emitter voltage SE2 changes from the L level to the H level. Further, in this open state, the pulse signal P1 from the control IC 6a is input to the gate terminal of the switching element 12, so that the gate voltage Vge becomes H level at time t4. When the gate voltage Vge becomes H level, the drain terminal and the source terminal of the switching element 12 are short-circuited, and a voltage is applied to the resistor 14. Here, since the overcurrent is continuously generated in the example of FIG. 2, the voltage of the resistor 14 becomes higher than the voltage of the resistor 73. Therefore, the operational amplifier 71 changes the output voltage SE1 from the H level to the L level at time t4. At the same time when the output voltage SE1 changes to the L level, the capacitor 87 of the delay circuit 8a starts rapid discharge as a predetermined operation of the overcurrent detection circuit 7a.

  The operational amplifier 88 of the delay circuit 8a changes the output voltage from the H level to the L level at time t5 when the voltage of the capacitor 87 becomes lower than the voltage of the resistor 84 due to discharging. As a result, the emitter terminal and the collector terminal of the bipolar transistor 89 are short-circuited, and the emitter voltage SE2 changes from H level to L level. Further, because of this short circuit state, the pulse signal P1 from the control IC 6a is not input to the gate terminal of the switching element 12, so that the gate voltage Vge becomes L level at time t5. When the gate voltage Vge becomes L level, the drain terminal and the source terminal of the switching element 12 are opened, and the voltage of the resistor 14 becomes 0V. Therefore, the operational amplifier 71 of the overcurrent detection circuit 7a changes the output voltage SE1 from the L level to the H level at time t5. At the same time when the output voltage SE1 changes to the H level, charging of the capacitor 87 of the delay circuit 8a is started, and measurement of the delay time T1 is started. Since the operation performed from time t6 to time t8 is the same as the operation performed from time t3 to time t5, description thereof is omitted.

  In the output voltage detection circuit 10, the operational amplifier 109 operates as a comparator. The ratio between the resistance value of the resistor 101 and the resistance value of the resistor 102 is determined so that a voltage that becomes a predetermined threshold value is applied to the resistor 102. Therefore, the operational amplifier 109 changes the output voltage from the L level to the H level when the voltage E5 of the resistor 5 becomes lower than the voltage of the resistor 102 at time t9. At the same time when the output voltage changes to the H level, charging of the capacitor 111 is started as a predetermined operation of the output voltage detection circuit 10. This charging is performed via the resistors 104 and 105. The operational amplifier 112 operates as a comparator. The operational amplifier 112 changes the output voltage SE3 from the H level to the L level at time t10 when the voltage of the capacitor 111 becomes higher than the voltage of the resistor 107 by charging. The stop signal S3 according to the present embodiment is a signal that enters a stop state when the output voltage SE3 is at an H level and enters an output state when the output voltage SE3 is at an L level. When the output voltage SE3 changes to L level, the control IC 6a stops outputting the pulse signal P1. At the same time, since the gate voltage Vge is always at the L level, the voltage E5 of the resistor 5 rapidly decreases to 0V. After time t10, the voltage E5 of the resistor 5 is always 0V, so that the output voltage SE3 maintains the L level. In order to reset the output voltage detection circuit 10 by changing the output voltage SE3 from the L level to the H level, the power supply of the control IC 6a is turned off to temporarily stop the supply of Vcc to the output voltage detection circuit 10.

  Note that the base voltage of the bipolar transistor 89 (the bias voltage between the base terminal and the emitter terminal) has characteristics that vary greatly depending on the temperature. Specifically, the base voltage increases at a low temperature and decreases at a high temperature.

  In the conventional delay circuit 8 described above, the delay time T1 is generated using a capacitor connected to the base terminal of the bipolar transistor. For this reason, the above-described conventional delay circuit 8 has a problem that the delay time T1 is shortened when the temperature is low, the delay time T1 is long when the temperature is high, and the delay time T1 is not stable. Further, when the delay time T1 is shortened and the overcurrent is continuously generated, the substantial frequency of the pulse signal P1 does not decrease so much, and the output output from each of the output circuits 2 and 3 The voltages E2 and E3 do not decrease so much. Therefore, the above-described conventional switching power supply circuit has a problem that the possibility of overheating increases when the temperature becomes low when overcurrent is continuously generated. This is a particular problem when the switching power supply circuit is used to supply power to an external device installed in an environment that is prone to extremely low temperatures such as a vehicle.

  On the other hand, in the delay circuit 8 a according to the present embodiment, the delay time T <b> 1 is generated using the comparator connected to the base terminal of the bipolar transistor 89 as described above. Therefore, in the delay circuit 8a according to the present embodiment, a constant delay time T1 can always be generated regardless of the temperature characteristics of the base voltage of the bipolar transistor 89.

  As described above, when the overcurrent continues to occur, the switching power supply circuit according to the present embodiment stops the output itself from each of the output circuits 2 and 3, and the overcurrent is generated only for a short time. In this case, the output from each of the output circuits 2 and 3 is automatically restored. As a result, according to the present embodiment, it is possible to provide a highly convenient switching power supply circuit while realizing sufficient overcurrent protection.

  In the switching power supply circuit according to this embodiment, the delay time T1 is generated using a comparator connected to the base terminal of the bipolar transistor 89. For this reason, in the switching power supply circuit according to the present embodiment, a constant delay time T1 can always be generated regardless of the temperature characteristics of the base voltage of the bipolar transistor 89.

  In the above description, the output voltage detection circuit 10 detects the voltage E5 of the resistor 5 corresponding to the output voltage E3 of the output circuit 3, and detects the overcurrent generated in the output circuit 2 and / or the output circuit 3. However, it is not limited to this. For example, the output voltage detection circuit 10 may detect a voltage corresponding to the output voltage E2 of the output circuit 2. In this case, one end of the resistor 4 is connected to the output terminal 23 of the output circuit 2. Further, for example, the output voltage detection circuit 10 may detect both a voltage according to the output voltage E2 of the output circuit 2 and a voltage according to the output voltage E3 of the output circuit 3. In this case, in FIG. 1, first and second resistors are further provided, one end of the first resistor is connected to the output terminal 23 of the output circuit 2, and the other end of the first resistor is connected to the second resistor. Connect to one end and ground the other end of the second resistor. Then, the output voltage detection circuit 10 detects the voltage of the resistor 5 and the voltage of the second resistor.

  The switching power supply circuit according to the present invention can realize sufficient overcurrent protection even when an overcurrent is continuously generated, and is a switching that supplies power to an external device installed in a vehicle or the like. It is also useful as a power supply circuit.

The figure which shows the block configuration of the switching power supply circuit which concerns on embodiment of this invention The figure which shows the time chart for demonstrating operation | movement of the switching power supply circuit which concerns on embodiment of this invention The figure which shows the specific circuit structure of the switching power supply circuit which concerns on embodiment of this invention The figure which shows the block configuration of the conventional switching power supply circuit The figure which shows the time chart for demonstrating operation | movement of the conventional switching power supply circuit

Explanation of symbols

1, 1a Switching circuit 2, 3 Output circuit 4, 5, 9, 14, 72-74, 81-85, 101-108 Resistor 6, 6a Control IC
7, 7a Overcurrent detection circuit 8, 8a Delay circuit 10 Output voltage detection circuit 11 Input terminal 12 Switching element 13 Converter 21, 31, 86, 110 Diode 22, 32, 87, 111 Capacitor 23, 24, 33, 34 Output terminal 71, 88, 109, 112 Operational amplifier 89 Bipolar transistor

Claims (3)

A switching circuit that switches a DC input voltage according to an input pulse signal and outputs a switching output voltage based on the switched DC input voltage;
An output circuit that converts the switching output voltage output from the switching circuit into a direct current and outputs a direct current output voltage;
A control circuit that outputs the pulse signal to the switching circuit and controls a pulse width of the pulse signal so that a DC output voltage output from the output circuit is constant at a first voltage value;
An overcurrent detection circuit for detecting an overcurrent generated in the output circuit based on a current flowing through the switching circuit;
A delay circuit that stops the output of the pulse signal from the control circuit for a predetermined time when an overcurrent is detected in the overcurrent detection circuit;
When a DC output voltage output from the output circuit is detected and the detected DC output voltage is lower than a second voltage value lower than the first voltage value, an output of the pulse signal from the control circuit is performed. A switching power supply circuit comprising: an output voltage detection circuit that is continuously stopped. The delay circuit is
When an overcurrent is detected in the overcurrent detection circuit, a transistor that grounds an output terminal of the control circuit from which the pulse signal is output by short-circuiting between an emitter terminal and a collector terminal;
When the output terminal of the control circuit is grounded, a capacitor for starting charging,
A comparator that releases the ground of the output terminal of the control circuit by opening the emitter terminal and the collector terminal of the transistor after the predetermined time has elapsed when the voltage of the capacitor has become higher than the third voltage value by charging. The switching power supply circuit according to claim 1, comprising: The switching power supply circuit according to claim 1 or 2,
A vehicle comprising: a device that inputs a DC output voltage output from an output circuit of the switching power supply circuit as a power supply voltage.

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