JP2016032409A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute an overcurrent protection function reliably regardless of the input voltage.SOLUTION: A switching power supply unit 1 includes a transformer 5, a switching element 6, a control section 7, a secondary circuit 8, a capacitor 10, a monitor circuit 20, and the like. The transformer 5 has a primary winding 5a, a secondary winding 5b and an auxiliary winding 5c. The switching element 6 is connected with the primary winding 5a. The secondary circuit 8 is connected with the secondary winding 5b. The capacitor 10 is connected in parallel with the auxiliary winding 5c. The monitor circuit 20 includes a Zener diode 21, resistors 22-24 and a transistor 25, and is configured so that the voltage at the detection terminal 7a of the control section 7 exceeds a second predetermined value, when the voltage of the capacitor 10 goes below a first predetermined value. A control section 100 suppresses switching operation of the switching element 6, when the voltage at the detection terminal 7a exceeds the second predetermined value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a switching power supply device having an overcurrent protection function.

  In a switching power supply device having an overcurrent protection function, there is a technology that suppresses overheating of a transformer or a secondary circuit by controlling a switching operation of a switching element when a short circuit of an auxiliary winding of a transformer occurs. Are known. For example, Patent Document 1 (FIG. 1, claim 1, etc.) includes a control circuit 15 that detects the current flowing through the switching element Q1 with a current detection terminal and executes an overcurrent protection function when the current exceeds a threshold value. It is shown.

JP 2012-249499 A

  However, in the configuration in which the overcurrent protection function is executed based on the current flowing through the switching element as in Patent Document 1, if the input voltage is high, the amount of current flowing through the switching element is reduced, so that a short circuit of the auxiliary winding occurs. However, the detected current does not exceed the threshold value, and the overcurrent protection function may not be executed.

  The objective of this invention is providing the switching power supply device which can perform an overcurrent protection function reliably irrespective of an input voltage.

  According to an aspect of the present invention, a transformer having a primary winding, a secondary winding and an auxiliary winding, a switching element connected to the primary winding, and a detection terminal connected to the switching element A control unit for controlling a switching operation of the switching element, and a secondary side circuit connected to the secondary winding, and supplying an alternating current to the primary winding by the switching operation of the switching element. In the switching power supply device configured to transmit the voltage induced in the secondary winding to the secondary side circuit, a capacitor connected in parallel to the auxiliary winding, and a voltage of the capacitor A monitor circuit configured to cause the voltage at the detection terminal to exceed a second predetermined value when the voltage is less than a first predetermined value, and the control unit includes: When the voltage at the detection terminal exceeds the second predetermined value by the monitor circuit when the pressure becomes less than the first predetermined value, the switching operation of the switching element is suppressed. A switching power supply is provided.

  According to the above aspect, not the configuration that executes the overcurrent protection function based on the current flowing through the switching element, but the configuration that executes the overcurrent protection function based on the rise in the voltage of the detection terminal connected to the switching element. Thus, even when the input voltage is high, there is no problem that the overcurrent protection function is not executed due to a decrease in the amount of current flowing through the switching element, and the overcurrent protection function can be executed reliably. That is, according to the above viewpoint, the overcurrent protection function can be reliably executed regardless of the input voltage.

  The monitor circuit includes a Zener diode connected in parallel to the capacitor, a transistor having a base connected to an anode of the Zener diode, and a collector connected to a connection line between the detection terminal and the switching element. When the voltage of the capacitor is equal to or higher than the first predetermined value, the Zener diode is turned on to supply current to the base of the transistor, and the transistor forms a bypass of the connection line, When the voltage of the capacitor is less than the first predetermined value, the Zener diode becomes non-conductive and does not supply current to the base of the transistor, and the transistor does not form a bypass of the connection line, The voltage of the detection terminal is configured to exceed the second predetermined value. Good.

  The switching power supply device having the above-described configuration is configured to convert an AC voltage induced at one end of the auxiliary winding into a direct current and supply the power supply voltage to the control unit, and in addition to the detection terminal and the auxiliary winding. A first resistor that is arranged between the transistor and supplies a predetermined divided voltage to the detection terminal, and the monitor circuit is connected to the collector of the transistor to form a series circuit with the transistor A series resistor connected in parallel to the first resistor; a third resistor disposed between the anode of the Zener diode and the base of the transistor; and the transistor of the transistor. A fourth resistor disposed between the base and the other end of the auxiliary winding and connected in series to the anode of the Zener diode via the third resistor. It is.

  The switching element is an FET, the drain of the FET is connected to the primary winding, the source of the FET is connected to the detection terminal, and the gate of the FET receives the output voltage of the control unit. May be.

  According to the present invention, the overcurrent protection function can be reliably executed regardless of the input voltage.

It is a block diagram which shows the switching power supply device which concerns on one Embodiment of this invention. It is a graph which shows the change of the electric current / voltage of each part when the input voltage is set to AC90V and AC264V in the Example which concerns on this invention, and a comparative example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a switching power supply device 1 according to an embodiment of the present invention includes an AC power supply 2, a bridge diode 3, an electrolytic capacitor 4, a transformer 5, a switching element 6, a control unit 7, a secondary side circuit 8, A feedback circuit 9 and the like are included.

  The transformer 5 has a primary winding 5a, a secondary winding 5b, and an auxiliary winding 5c. A switching element 6 is connected to the primary winding 5a. A secondary circuit 8 is connected to the secondary winding 5b.

  The switching element 6 is an FET, the drain of the FET is connected to the primary winding 5a, the source of the FET is connected to the detection terminal 7a of the control unit 7, and the gate of the FET is connected to the output terminal 7b of the control unit 7. The output voltage of the control unit 7 is received.

  The controller 7 controls the switching operation of the switching element 6.

  Here, the operation of the switching power supply device 1 will be described.

  The alternating current input from the alternating current power source 2 is rectified by the bridge diode 3, smoothed by the electrolytic capacitor 4, and then converted into alternating current again by the switching operation of the switching element 6, and supplied to the primary winding 5a. The alternating current supplied to the primary winding 5 a is transformed by the transformer 5, induced in the secondary winding 5 b, and transmitted to the secondary side circuit 8. Although not shown, the alternating current transmitted to the secondary circuit 8 is rectified by a diode in the secondary circuit 8, smoothed by an electrolytic capacitor, and then output to a load. The secondary output voltage is fed back to the control unit 7 via the feedback circuit 9, and the switching operation is controlled by the control unit 7 so that the output voltage is kept constant.

  The switching power supply device 1 further includes a capacitor 10, a monitor circuit 20, and the like.

  The capacitor 10 is an electrolytic capacitor, and is connected in parallel to the auxiliary winding 5c via a diode 12 connected to one end of the auxiliary winding 5c. The AC voltage induced in the auxiliary winding 5c is rectified by the diode 12, smoothed by the capacitor 10, and supplied to the control unit 7 via the power supply terminal 7c. Further, an electrolytic capacitor 14 is connected in parallel to the auxiliary winding 5c via a diode 13. The AC voltage induced in the auxiliary winding 5c is rectified by the diode 13, smoothed by the electrolytic capacitor 14, and the power source The voltage is supplied to the control unit 7 via the terminal 7c. As described above, the control unit 7 is driven by the power supply voltage obtained by converting the alternating voltage induced at one end of the auxiliary winding 5c into a direct current.

  Monitor circuit 20 includes a Zener diode 21, resistors 22 to 24, and a transistor 25.

  The zener diode 21 is connected in parallel to the capacitor 10 together with the resistors 23 and 24. The resistors 23 and 24 are connected in series to the anode of the Zener diode 21, and the base of the transistor 25 is connected between the resistors 23 and 24. In other words, the resistor 23 is disposed between the anode of the Zener diode 21 and the base of the transistor 25. The resistor 24 is disposed between the connection point between the resistor 23 and the base of the transistor 25 and the other end of the auxiliary winding 5 c, and is connected in series to the anode of the Zener diode 21 via the resistor 23.

  One end of the resistor 22 is connected to the detection terminal 7a and the resistor 11 for voltage division. The other end of the resistor 22 is connected to the collector of the transistor 25. A series circuit including the resistor 22 and the transistor 25 is connected to the resistor 11 in parallel.

  The transistor 25 has a base connected to the anode of the Zener diode 21 via the resistor 23, a collector connected to the connection line between the detection terminal 7 a and the source of the switching element 6 via the resistor 22, and an emitter auxiliary winding. It is connected to the other end (ground) of the line 5c. An appropriate resistor is interposed in the connection line.

  Here, when the voltage of the capacitor 10 is equal to or higher than the first predetermined value, the Zener diode 21 supplies a current to the base of the transistor 25 by causing a current to flow from the cathode to the anode (that is, in a conductive state). As a result, the transistor 25 is turned on, a bypass of the connection line is formed, and the detection terminal 7a is grounded to the other end of the auxiliary winding 5c via the transistor 25 in the conductive state. Thereby, the voltage rise of the detection terminal 7a is suppressed.

  On the other hand, when the voltage of the capacitor 10 is less than the first predetermined value, the Zener diode 21 does not supply current from the cathode to the anode (that is, becomes non-conductive) and does not supply current to the base of the transistor 25. In this case, the transistor 25 is turned off, the bypass of the connection line is not formed, and the voltage at the detection terminal 7a increases.

  As described above, the monitor circuit 20 is configured such that the voltage of the detection terminal 7a exceeds the second predetermined value when the voltage of the capacitor 10 becomes less than the first predetermined value.

  For example, when the short-circuit of the auxiliary winding 5c occurs, the capacitor 10 continues to discharge, so that the voltage of the capacitor 10 decreases and the voltage of the capacitor 10 becomes less than the first predetermined value. Then, in the monitor circuit 20, since the Zener diode 21 does not supply current to the transistor 25, the transistor 25 is turned off, the voltage of the detection terminal 7a increases, and the voltage of the detection terminal 7a exceeds the second predetermined value. When the voltage at the detection terminal 7a exceeds the second predetermined value, the control unit 100 suppresses (for example, stops) the switching operation of the switching element 6. Thereby, overheating of the transformer 5 and the secondary side circuit 8 is suppressed.

  As described above, according to the present embodiment, the overcurrent protection function is not executed based on the current flowing through the switching element 6, but based on the rise in the voltage of the detection terminal 7a connected to the switching element 6. By adopting the configuration for executing the overcurrent protection function, even when the input voltage is high, the problem that the overcurrent protection function is not executed due to a decrease in the amount of current flowing through the switching element 6 does not occur. Can be executed reliably. That is, according to the present embodiment, the overcurrent protection function can be reliably executed regardless of the input voltage.

  In the example according to the present invention (the same device as the switching power supply device 1 according to the above embodiment) and the comparative example (the device obtained by removing the monitor circuit 20 from the switching power supply device 1 according to the above embodiment), the input voltage is AC 90V. , The change in current / voltage of each part was measured when AC264V was used. The measurement results are shown in FIG.

In FIG. 2, “I _5a ” indicates a current flowing through the primary winding 5a. “V _OUT ” indicates a secondary output voltage. “Vc ₀₀₅ ” indicates the voltage of the electrolytic capacitor 14. “Vc ₀₀₄ ” indicates the voltage of the capacitor 10. The horizontal axis indicates time.

  As can be seen from FIG. 2, when the input voltage is 90V AC, there is no difference in the current / voltage waveforms of the respective parts in the example and the comparative example, and the overcurrent protection function is executed when the auxiliary winding 5c is short-circuited. And the switching operation was stopped. On the other hand, when the input voltage is AC 264 V, there is a difference in the current / voltage waveform of each part in the example and the comparative example, and the switching operation is stopped in the example. In the comparative example, the current flowing through the switching element is The overcurrent protection function was not executed without exceeding the threshold value (that is, the switching operation was not stopped and intermittent oscillation was maintained).

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various design changes can be made as long as they are described in the claims.

-A switching element is not limited to FET, You may consist of IGBT etc.
The control unit is not limited to stopping the switching operation when the voltage at the detection terminal exceeds the second predetermined value, and may limit the current by suppressing the switching operation and lowering the output voltage. .

DESCRIPTION OF SYMBOLS 1 Switching power supply device 2 AC power supply 3 Rectifier diode 4 Smoothing capacitor 5 Transformer 5a Primary winding 5b Secondary winding 5c Auxiliary winding 6 Switching element 7 Control part 7a Detection terminal 7b Output terminal 7c Power supply terminal 8 Secondary side circuit 9 Feedback Circuit 10 Capacitor 11 Resistance (first resistance)
20 Monitor circuit 21 Zener diode 22 Resistance (second resistance)
23 Resistance (3rd resistance)
24 resistance (4th resistance)
25 transistors

Claims (4)

A transformer having a primary winding, a secondary winding and an auxiliary winding;
A switching element connected to the primary winding;
A control unit having a detection terminal connected to the switching element and controlling a switching operation of the switching element;
A secondary circuit connected to the secondary winding;
With
In the switching power supply device configured to supply alternating current to the primary winding by the switching operation of the switching element and to transmit a voltage induced in the secondary winding to the secondary side circuit,
A capacitor connected in parallel to the auxiliary winding;
A monitor circuit configured such that when the voltage of the capacitor becomes less than a first predetermined value, the voltage of the detection terminal exceeds a second predetermined value;
Further comprising
The control unit performs the switching operation of the switching element when the voltage of the detection terminal exceeds the second predetermined value by the monitor circuit when the voltage of the capacitor becomes less than the first predetermined value. A switching power supply device characterized by being suppressed. The monitor circuit is
A Zener diode connected in parallel to the capacitor;
A transistor having a base connected to an anode of the Zener diode and a collector connected to a connection line between the detection terminal and the switching element;
Including
When the voltage of the capacitor is equal to or higher than the first predetermined value, the Zener diode is turned on to supply current to the base of the transistor, and the transistor forms a bypass of the connection line;
When the voltage of the capacitor is less than the first predetermined value, the Zener diode becomes non-conductive and does not supply current to the base of the transistor, and the transistor does not form a bypass of the connection line, The switching power supply device according to claim 1, wherein a voltage of the detection terminal is configured to exceed the second predetermined value. The alternating voltage induced at one end of the auxiliary winding is converted into a direct current to supply a power supply voltage to the control unit, and is arranged between the detection terminal and the other end of the auxiliary winding. A first resistor for supplying a predetermined divided voltage to the detection terminal;
The monitor circuit is
A second resistor connected to the collector of the transistor to form a series circuit with the transistor, the series circuit being connected in parallel to the first resistor;
A third resistor disposed between the anode of the Zener diode and the base of the transistor;
A fourth resistor disposed between the base of the transistor and the other end of the auxiliary winding and connected in series to the anode of the Zener diode via the third resistor;
The switching power supply according to claim 2, further comprising:   The switching element is an FET, the drain of the FET is connected to the primary winding, the source of the FET is connected to the detection terminal, and the gate of the FET receives the output voltage of the control unit. The switching power supply device according to any one of claims 1 to 3, wherein the switching power supply device is provided.

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