JPH0898521A - Switching power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] The FET as a switching element should be turned on completely. A series circuit composed of a diode 15 and a capacitor 16 connected in parallel to the FET3 as a switching control circuit of a FET3 as a switching element, and a connection point between the diode 15 and the capacitor 16 of the series circuit and the gate of the FET3. The gate resistor 8 connected to the gate of the FET 3 has its collector connected to the gate of the FET 3 via the resistor 10, its emitter connected to the connection point of the capacitor 5 and the inductor 6, and the base thereof receives the detection signal from the voltage detection circuit 40. The switching control circuit 42 including the transistor 11 is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device used as an internal power supply for a circuit breaker with an earth leakage alarm.

[0002]

2. Description of the Related Art FIG. 13 is a circuit diagram showing a conventional example of this type of switching power supply device. In FIG. 13, the switching power supply device has an F as a switching element connected between a positive side DC power supply terminal P and a negative side DC power supply terminal N.
Drain / source of ET3, anode of diode 4
A series circuit including a cathode, a capacitor 5, and an inductor 6, a cathode / anode of a diode 7 connected between the cathode of the diode 4 and the negative side DC power supply terminal N, and a zener diode 12 connected in parallel with the capacitor 5. A voltage detection circuit 40 that outputs a detection signal from the connection point between the Zener diode 12 and the resistor 13, its collector to the gate of the FET 3 via the resistor 10, and its emitter to the capacitor 5 At the connection point of the inductor 6 and the inductor 6, the transistor 11 to which the detection signal from the voltage detection circuit 40 is input via the current limiting resistor 14 at its base, the gate resistor 8 connected between the drain and gate of the FET 3, and the FET 3 Anode / Caso of Zener diode 9 connected between source and gate It is composed of a load 2 is connected in parallel with the capacitor 5. Here, gate resistance 8 and resistance 1
0, current limiting resistor 14 and transistor 11 are FET3
The open / close control circuit 45 of FIG. The Zener diode 9 is a Zener diode for preventing overvoltage of the gate-source voltage of the FET 3.

The operation of this switching power supply device is as follows. When a DC voltage is applied between the positive and negative DC power supply terminals P and N, this DC voltage is input to the gate of the FET 3 via the gate resistor 8 to charge the gate-source capacitance and raise the gate voltage. Then, FET3 turns on. When the FET 3 turns on, the capacitor 5 is charged through the diode 4. The voltage of the capacitor 5 rises due to charging, and the Zener diode 1 of the voltage detection circuit 40
When the voltage of 2 is exceeded, a detection signal is output, and this detection signal is input to the base of the transistor 11 via the current limiting resistor 14 to turn on the transistor 11. When the transistor 11 is turned on, the gate voltage of the FET3 drops and FE
The charging current flows until T3 is turned off and the energy stored in the inductor 6 is completely discharged from the inductor 6 through the capacitor 5. When the voltage of the capacitor 5 drops due to energization of the load 2 connected in parallel with the capacitor 5 and falls below the voltage of the Zener diode 12, the base current of the transistor 11 is cut off and the transistor 11 is turned off. FET turns off when transistor 11 turns off
The gate voltage of 3 rises and FET3 turns on. This operation is repeated to obtain a substantially constant DC voltage between both terminals of the capacitor 5.

[0004]

In the above-mentioned switching power supply device, the FET as a switching element is operated by a voltage applied to the gate through a gate resistor connected between the positive side DC power supply terminal and the gate of this FET.
When the source capacitance is charged and the voltage exceeds a predetermined gate voltage, it turns on, but when the FET starts turning on, the resistance value between the drain and source of the FET decreases, so the voltage applied to the gate decreases. There is a problem that the FET does not turn on completely and the on loss increases. For this reason, the resistance value of the gate resistance is usually set lower than the resistance value required to supply the charging current of the drain-source capacitance of the FET to prevent the voltage applied to the gate from decreasing. ,
When the resistance value of the gate resistance is set low, the current flowing back to the power supply through this gate resistance increases when the FET is off,
This causes a problem of increased loss of gate resistance.

An object of the present invention is to provide a switching power supply device in which the FET as a switching element is completely turned on without increasing the gate loss by setting the resistance value of the gate resistance low.

[0006]

In order to achieve the above-mentioned object, a switching power supply device according to a first aspect of the present invention is an FET connected between a positive side and a negative side DC power supply terminal. A series circuit including a diode, a capacitor and an inductor, a diode connected between a connection point of the diode and the capacitor and a negative side DC power supply terminal, a voltage detection circuit connected in parallel with the capacitor, and this voltage In a switching power supply device comprising a switching control circuit for inputting a detection signal of a detection circuit and controlling switching of the FET so that the voltage of the capacitor becomes constant, the switching control circuit is connected in parallel to the FET. A series circuit including a diode and a capacitor, a connection point of the diode and the capacitor of the series circuit, and the F
A gate resistor connected between the gate of ET, a collector of which is connected through a resistor to a gate of the FET, an emitter of which is connected to a connection point of the capacitor and the inductor, and a base of which is detected by the voltage detection circuit. It is composed of a transistor to which a signal is input.

In the switching power supply device according to the second aspect of the present invention, the switching control circuit has a gate resistance connected between the positive power supply terminal and the gate of the FET, and its collector has a resistance. A first transistor connected in parallel to the capacitor, and a transistor whose emitter is connected to the gate of the FET via the capacitor and the inductor, and whose base receives a detection signal from the voltage detection circuit. A series circuit including a resistor, a capacitor and a second resistor, the connection point of the first resistor and the capacitor being connected to the gate of the FET through the resistor and the diode, and the series circuit connected in parallel to the first resistor and the capacitor And a transistor that opens and closes contrary to the transistor.

Further, in the invention described in claim 2, as in the invention described in claim 3, the collector is F through a resistor.
It is convenient to insert a Zener diode between the resistor and the collector of the transistor, whose emitter is connected to the gate of ET between the capacitor and the inductor, and whose base receives the detection signal from the voltage detection circuit. is there.
Furthermore, in each of the above-mentioned inventions, it is preferable to interpose a resistor between the voltage detection circuit and the capacitor as in the invention described in claim 4.

[0009]

According to the first aspect of the invention, the FET as the switching element starts the ON operation, and even if the resistance between the drain and the source of the FET is reduced, the gate of the FET is connected in parallel with the FET. Since the electric charge charged in the capacitor of the series circuit including the diode and the capacitor is applied through the gate resistance, the voltage applied to the gate does not decrease, and the FET is completely turned on. Therefore, as in the conventional example, the resistance value of the gate resistance is set to FE.
It is not necessary to set the resistance lower than the resistance value required to supply the charging current for the gate-source capacitance of T.

According to the second aspect of the present invention, when the FET starts the ON operation and the resistance between the drain and the source of the FET decreases, the first resistor, the capacitor and the second resistor connected in parallel to the capacitor. The voltage charged in the capacitor of the series circuit consisting of is connected to the gate of the FET through the resistor between the collector of the capacitor and the inductor and the detection signal from the voltage detection circuit is input to the gate of the transistor. Since it is applied to the gate of the FET by the turning-off operation of the transistor that opens and closes contrary to the above, the voltage applied to the gate of the FET does not drop as in the invention described in claim 1.

According to a third aspect of the invention, in the second aspect of the invention, the collector is connected to the gate of the FET through a resistor, the emitter is connected between the capacitor and the inductor, and the base is connected to the voltage detection circuit. Since a Zener diode is inserted between the collector of the transistor to which the detection signal of is input and the resistor, when this transistor is turned on, the collector voltage drops by the voltage of this Zener diode. The off operation of the transistor that performs the opening / closing operation becomes more reliable.

According to a fourth aspect of the present invention, a resistor is inserted between the voltage detecting circuit and the capacitor in each of the above-mentioned inventions. By inserting this resistor, the voltage of the capacitor is included in the voltage detecting circuit. Since the sum of the voltage drop of the resistor through which the charging current of this capacitor flows is input, the detection signal of the voltage detection circuit becomes larger.

[0013]

1 is a circuit diagram showing an embodiment of a switching power supply device of the first invention. The embodiment shown in FIG.
3 is different from that of the embodiment shown in FIG.
The gate resistor 8 is connected between the cathode of the diode 15 and the capacitor 16 and the gate of the FET 3 by connecting a series circuit composed of the anode / cathode and the capacitor 16 of the diode 15 and the capacitor 1.
6, the transistor 11, the gate resistor 8, the resistor 10 and the current limiting resistor 14 constitute the switching control circuit 42.

In this embodiment, when a DC voltage is applied between the positive and negative DC power supply terminals P and N, this DC voltage is applied to the capacitor 16 via the diode 15 to charge the capacitor 16, and at the same time, the diode 16 is charged. 15 is applied to the gate of the FET 3 via the gate resistor 8 and the gate-source capacitance is charged to increase the gate voltage.
FET3 turns on. In this case, even if the FET3 starts the ON operation and the resistance between the drain and the source of the FET3 is lowered, the charge charged in the capacitor 16 is applied to the gate of the FET3 through the gate resistor 8, so that it is applied to the gate. The voltage never drops, and the FET 3 is completely turned on. Therefore, unlike the conventional example shown in FIG. 13, it is not necessary to set the resistance value of the gate resistance lower than the resistance value required to supply the charging current of the gate-source capacitance of the FET 3, and the gate loss is not increased. Absent. When the operation starts, the capacitor 16 is charged when the voltage of the capacitor 5 rises and the FET 3 is turned off, and is held until the FET 3 is turned on in the next cycle.

FIG. 2 is a circuit diagram showing another embodiment of the switching power supply device of the first invention. The difference between the embodiment shown in FIG. 2 and the embodiment shown in FIG.
The point is that the voltage detection circuit 41 is provided instead of 0. The voltage detection circuit 41 includes a resistor 30 connected in parallel with the capacitor 5.
And a series circuit composed of the cathode and anode of the Zener diode 12, and a series circuit composed of the emitter / collector of the transistor 28, the resistor 26 and the resistor 27 connected in parallel to the series circuit, and the base of the transistor 28. Is connected to the resistor 30 and the cathode of the Zener diode 12 via the resistor 29, and the resistor 26
A detection signal is output from the connection point of the resistor 27 and the resistor 27. The detection signal from the voltage detection circuit 41 is input to the base of the transistor 11 of the switching control circuit 42. In this case, since the resistors 26 and 27 of the voltage detection circuit 41 also function as current limiting resistors, the current limiting resistor 1 in FIG.
4 is not necessary.

The voltage detection circuit 41 is one in which the current flowing through the Zener diode 12 is amplified by the transistor 28, and the embodiment shown in FIG. 2 has an improved output voltage accuracy as compared with the embodiment shown in FIG. To do. FIG. 3 is a circuit diagram showing an embodiment of the switching power supply device of the second invention. The embodiment shown in FIG. 3 is different from the conventional example shown in FIG. 13 in that the resistor 19 (first resistor), the capacitor 18 and the resistor 20 (second resistor) connected in parallel to the capacitor 5 in the circuit shown in FIG. A series circuit composed of a resistor), a resistor 24 connected between the cathode of the diode 4 and the collector of the transistor 11, and an anode of the diode 23.
A series circuit composed of a cathode, a series circuit composed of a cathode / anode of a diode 21 and a resistor 22 connected between the gate of the FET 3 and the connection point b of the resistor 19 and the capacitor 18, and its collector connected to the anode of the diode 4. The emitter is a connection point a between the capacitor 18 and the resistor 20.
Is provided with a transistor 17 whose base is connected to the anode of the diode 23, and a gate resistor 8, a resistor 10,
The open / close control circuit 43 is composed of the transistor 11, the current limiting resistor 14, the resistor 19, the capacitor 18, the resistor 20, the transistor 17, the resistor 24, and the diode 23.

In this embodiment, the transistor 11 is on and the transistor 17 is off when the switching power supply operates and the voltage of the capacitor 5 rises and the FET 3 is off. When the transistor 17 is turned off, the capacitor 18 is charged through the resistors 19 and 20. When the voltage of the capacitor 5 drops and the transistor 11 turns off, the transistor 17 turns on and the voltage at the connection point a between the capacitor 18 and the resistor 20 rises to the voltage of the capacitor 5, so the resistor 19 and the capacitor 18
As for the voltage at the connection point b, the charging voltage of the capacitor 18 further increases. The voltage of this capacitor 18 is the resistance 2
2. Since the voltage is applied to the gate of the FET 3 via the diode 21, the voltage applied to the gate does not decrease, and the FET 3 is completely turned on. Other operations are similar to those of the conventional example shown in FIG.

FIG. 4 is a circuit diagram showing another embodiment of the switching power supply device of the second invention. 4 differs from the embodiment shown in FIG. 3 in that the voltage detection circuit 4
The point is that the voltage detection circuit 41 is provided instead of 0. The action and effect are similar to those of the embodiment shown in FIG. 5 and 6 are circuit diagrams showing further different embodiments of the switching power supply device of the second invention. 5 and 6 are different from the embodiments shown in FIGS. 3 and 4 in that the cathode / anode of the Zener diode 25 is interposed between the resistor 10 of the switching control circuit 43 and the collector of the transistor 11. It is a point that the switching control circuit 44 is inserted.

By inserting the Zener diode 25, the collector voltage of the transistor 11 is reduced by the voltage of the Zener diode, so that the diode 23 is easily turned on and the transistor 17 is turned on when the transistor 17 is turned on.
The off operation of is more reliable. Others are shown in FIG. 3 and FIG.
The same as the embodiment shown in FIG. 7 and 8 are circuit diagrams showing still another embodiment of the switching power supply device of the first invention, and FIGS. 9 to 12 are circuit diagrams showing still another embodiment of the switching power supply device of the second invention. The embodiments shown in FIGS. 7 to 12 differ from the embodiments shown in FIGS. 1 to 6 in that a resistor 31 is interposed between the voltage detection circuit 40 or 41 and the capacitor 5, respectively.

By inserting the resistor 31, the voltage of the capacitor 5 and the sum of the voltage drop of the resistor 31 through which the charging current of the capacitor 5 flows are input to the voltage detecting circuit 40 or 41. The detection signal becomes large, and the on / off operation of the FET 3 becomes more reliable.

[0021]

As described above, in the switching power supply device according to the first and second aspects of the present invention, since the FET as a switching element is completely turned on, the FET is turned on like the conventional example. For completeness, it is not necessary to set the resistance value of the gate resistance of the FET lower than the resistance value required to supply the charging current of the drain-source capacitance of the FET, and the gate loss caused by setting the gate resistance value low. Is prevented and the efficiency is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching power supply device of a first invention.

FIG. 2 is a circuit diagram showing another embodiment of the switching power supply device of the first invention.

FIG. 3 is a circuit diagram showing an embodiment of a switching power supply device of the second invention.

FIG. 4 is a circuit diagram showing another embodiment of the switching power supply device of the second invention.

FIG. 5 is a circuit diagram showing still another embodiment of the switching power supply device of the second invention.

FIG. 6 is a circuit diagram showing still another embodiment of the switching power supply device of the second invention.

FIG. 7 is a circuit diagram showing still another embodiment of the switching power supply device of the second invention.

FIG. 8 is a circuit diagram showing still another embodiment of the switching power supply device of the second invention.

FIG. 9 is a circuit diagram showing a further different embodiment of the switching power supply device of the first invention.

FIG. 10 is a circuit diagram showing still another embodiment of the switching power supply device of the first invention.

FIG. 11 is a circuit diagram showing a further different embodiment of the switching power supply device of the second invention.

FIG. 12 is a circuit diagram showing still another embodiment of the switching power supply device of the second invention.

FIG. 13 is a circuit diagram showing an example of a conventional switching power supply device.

[Explanation of symbols]

 3 FET 4 Diode 5 Capacitor 6 Inductor 7 Diode 8 Gate Resistance 10 Resistance 11 Transistor 15 Diode 16 Capacitor 17 Transistor 18 Capacitor 19 First Resistor 20 Second Resistor 21 Diode 22 Resistor 23 Diode 25 Zener Diode 31 Resistor 40 Voltage Detection Circuit 41 voltage detection circuit 42 switching control circuit 43 switching control circuit 44 switching control circuit

Claims (4)

[Claims] 1. A series circuit comprising an FET, a diode, a capacitor and an inductor connected between a positive side and a negative side DC power supply terminal, and a connection point between the diode and the capacitor and a negative side DC power supply terminal. A diode connected to the capacitor, a voltage detection circuit connected in parallel to the capacitor, and a detection signal of the voltage detection circuit are input, and an opening / closing control circuit that controls opening / closing of the FET so that the voltage of the capacitor becomes constant. And a series circuit including a diode and a capacitor connected in parallel to the FET, and a connection point between the diode and the capacitor of the series circuit and the gate of the FET. With the connected gate resistance,
The collector of the FET is connected to the gate of the FET through a resistor, the emitter of the FET is connected to the connection point of the capacitor and the inductor, and the base of the FET is a transistor to which the detection signal from the voltage detection circuit is input. Switching power supply. 2. A series circuit composed of an FET, a diode, a capacitor and an inductor connected between a positive side and a negative side DC power supply terminal, and a connection point between the diode and the capacitor and a negative side DC power supply terminal. A diode connected to the capacitor, a voltage detection circuit connected in parallel to the capacitor, and a detection signal of the voltage detection circuit are input, and an opening / closing control circuit that controls opening / closing of the FET so that the voltage of the capacitor becomes constant. In a switching power supply device including:
A gate resistor connected to the gate of T, a collector of which is connected through a resistor to the gate of the FET, an emitter of which is connected to the capacitor and the inductor, and a base of which is detected by the voltage detection circuit. It is composed of a transistor to which a signal is input, a first resistor connected in parallel with the capacitor, a capacitor and a second resistor, and the connection point between the first resistor and the capacitor is a gate of the FET via the resistor and the diode. A switching power supply device comprising a series circuit connected to the first resistor and a transistor connected in parallel with the first resistor and a capacitor to perform an opening / closing operation contrary to the transistor. 3. The switching power supply device according to claim 2, wherein the collector is connected through a resistor to the gate of the FET, the emitter is connected between the capacitor and the inductor, and the detection signal from the voltage detection circuit is connected to the base. A switching power supply device, wherein a Zener diode is inserted between the collector of an input transistor and the resistor. 4. The switching power supply device according to claim 1, wherein a resistor is inserted between the voltage detection circuit and the capacitor.