JPH0241658A - Switching power-supply reverse-current preventive circuit - Google Patents

Abstract

PURPOSE:To reduce a loss by connecting a non-inverting buffer and an inverting buffer in parallel with the control-signal output terminal of a control circuit and installing a transistor for preventing reverse currents. CONSTITUTION:A switching power supply is composed of a smoothing circuit 2, a switching transistor 3, a transformer 4, a transistor(Tr) 5 for preventing reverse currents, a control circuit 7, etc. A non-inverting buffer 8 and an inverting buffer 9 are connected in parallel with the output terminal of a control signal output from the control circuit 7, and each of these buffers 8, 9 is bonded with the input sides of Trs 12-13 through resistors 10-11. The output side of the Tr 12 is connected between one end of a reference power supply 6 and the gate of the Tr 5 for preventing reverse currents through a resistor 14. The output side of the Tr 13 is also bonded similarly. Consequently, the control signal is input to the gate of the Tr 3 from the control circuit 7 and the Tr 3 is interrupted while the Tr 12 is switched on through the non-inverting buffer 8, and the Tr 5 is electrified. The Tr 13 remains interrupted at that time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply backflow prevention circuit for preventing backflow of energy from an energy storage capacitor of a switching power supply to a transformer.

[Prior Art] There is an energy backflow prevention circuit provided in a conventional switching power supply as shown in FIG. While the switching transistor 3 connected to the input power source 1 via the smoothing circuit 2 is cut off, the backflow prevention transistor 5 is turned on by the voltage transformer 4, and the voltage is transferred to the secondary side via the transformer lance 4. The transmitted energy is transmitted to the energy Jj jt2 capacitor 15, while the voltage is transformed while the switching transistor 3 is conducting.
The configuration is such that energy is transmitted to the lance 4, the backflow prevention transistor 5 is cut off by the transformer 4, and energy is prevented from flowing back from the energy storage capacitor 15. In addition, 7 in the figure is a control circuit,
In order to control the current flowing to the gate of the switching transistor 3 and drive it on/off, an inverting buffer 19, J
1 anti-inverting buffer 20 resistors 21, 22, transistor 2
It is connected to the circuit consisting of 3.24. Also, in the figure, 16
is a coil, 17 is a smoothing capacitor, 26 is a reference power supply,
27 is a resistance.

[Problems to be Solved] - The conventional switching power supply backflow prevention circuit 11 described above has a transformer 4 that controls the backflow prevention transistor 5.
Since the output voltage of the converter changes rapidly depending on the switching input power supply voltage, there is a drawback that the input power supply pressure range cannot be widened.

Furthermore, if a diode is inserted in place of the reverse current prevention transistor 5, the input power supply voltage range can be made wider compared to the case where the reverse current prevention transistor 5 is inserted, but the reverse recovery time of the diode The disadvantage is that the loss increases because the process is slow.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a switching power supply backflow prevention circuit that has low loss and has a wide input voltage range.

[Means for Solving the Problems] In order to achieve the first object, the switching transistor, a voltage transformer that transforms and outputs the input voltage, and a switching transistor and a transformer that transforms and outputs the input voltage, and a switching transistor that transforms and outputs the switching transistor. a control circuit for turning off;
A switching source including a capacitor that stores energy output from the transformer includes a backflow prevention transistor whose output side is connected between one end of the output side of the transformer and the capacitor; The input side of this 41 anti-inverting buffer is connected to the reference power supply connected between the 41 anti-inverting buffer and the control Cu output terminal of the control circuit, and the reference power supply connected between the control circuit and the backflow prevention transistor. a transistor connected between one end of the reference power supply and the gate of the backflow prevention transistor, and an input side connected to the inverting buffer;
Base the output side on the above! The structure includes a transistor connected between the other end of the first power supply and the gate of the backflow prevention transistor.

[Example] Next, an embodiment of the present invention will be described with reference to the drawings.

In addition, below, the common code|symbol is attached|subjected to the part common to the conventional art, and the overlapping description is abbreviate|omitted.

FIG. 1 is a basic circuit diagram of the present invention, in which a non-inverting buffer 8 and an inverting buffer (inverter) 9 are connected in parallel to the output terminal of the control signal output from the control circuit 7. are connected to the input sides of transistors 12 and 13 via resistors 10 and 11, respectively. The output side of the transistor 12 connected to the non-inverting buffer 8 is connected between one end of the reference power supply 6 and the gate of the backflow prevention transistor 5 via a resistor 14.

Further, the output side of the transistor 13 connected to the inversion buffer 9 is connected between the gate of the backflow prevention transistor 5, one end of the output side of the backflow prevention transistor 5, and the other end of the reference power supply 6. The other end of the output side of the backflow prevention transistor 5 is connected to one end of the output side of the transformer 4, and the other end of the output side of the transformer 4 is grounded.

According to this basic circuit configuration, a control signal is manually inputted from the control circuit 7 to the gate of the switching transistor 3, and at the same time when the switching transistor 3 is cut off, the control signal input to the gate of the switching transistor 3 and the inverted control signal are sent to the control circuit. 7 and passed through the non-inverting buffer 8, the transistor 12 becomes conductive.
A current is passed from the reference power source 6 to the backflow prevention transistor 5 through the resistor 14, and the backflow prevention transistor 5 is turned on.

At this time, since the inverting buffer 9 inverts the control signal output from the control circuit 7, current is not passed through the gate of the transistor 13, and the transistor 13 remains cut off.

On the other hand, the control signal input from the control circuit 7 to the gate of the switching transistor 3 is inverted, and the switching transistor 3 becomes conductive, and at the same time, the control signal input from the control circuit 7 to the inverting buffer 9 is also inverted, and the signal from the inverting buffer 9 is inverted. As a result, the transistor 13 becomes conductive, and the charge stored in the gate of the reverse current prevention transistor 5 is rapidly discharged.

At this time, the transistor 12 remains cut off, and current from the reference power supply 6 is not conducted.

Therefore, according to this circuit, since the on-resistance of the backflow prevention transistor 5 used in the backflow prevention circuit is extremely small, it is possible to reduce the loss, and the potential difference between the input side and the gate of the backflow prevention transistor 5 is When conductive, the voltage becomes approximately equal to the voltage of the reference power supply 6. As a result, the potential difference between the input side and the gate of the backflow prevention transistor 5 becomes almost zero when the transistor 13 is conductive.
It is possible to widen the voltage fluctuation range of the input power source 1 without being limited by the voltage of the input power source 1.

FIG. 2 is a circuit diagram of an embodiment in which the circuit shown in FIG. 1 is adapted to a switching power supply.

In the figure, the power supply circuit is input power supply 1. 'f-slip circuit 2, which is cut off by a switching transistor 3. Then, the voltage is transformed by the transformer 4, and the energy is stored in the energy storage capacitor 15 through the backflow prevention transistor 5. When the switching transistor 3 is made conductive, the energy stored in the energy storage capacitor 15 is transferred to the load through the coil 16. It is configured as a switching power supply that outputs a voltage across the resistor 18.

The control circuit 7 takes in this output voltage, divides it internally, detects it, compares it with a reference voltage, amplifies the error voltage, and outputs it as a control signal. This control signal is transmitted through the transistor 12, the transistor 12, and the
13, 23° and 24, and conducts or cuts them off.

Here, the output side of the transistor 12 connected to the non-inverting buffer 8 is connected between the reference power supply 6, the resistor 14 and the gate of the backflow prevention transistor 5, and the transistor 13 connected to the inverting buffer 9 The output side of is connected between the other end of the reference power supply 6 and the gate of the backflow prevention transistor 5.

Also, a transistor 23 connected to the inverting buffer 19
The output side of the transistor 24 connected to the reference power supply 26, the resistor 25, and the gate of the switching transistor is connected to the reference power supply 26, and the output side of the transistor 24 connected to the non-inverting buffer 20 is connected to the reference power supply 26.
It is connected between the other end and the gate of the switching transistor 3.

According to this configuration, the control circuit 7 detects the output voltage, compares it with the voltage of the reference power supply 6, and outputs a corresponding control signal. That is, the transistor 23 is made conductive by the signal passed through the inverting buffer 19, and the gate current of the reference power supply 26 is passed through the switching transistor 3 to make the switching transistor 3 conductive. The signal makes the transistor 13 conductive, cuts off the backflow prevention transistor 5, and discharges the charge stored in the energy storage capacitor 15 via the coil 16.

On the other hand, the signal passed through the non-inverting buffer 20 makes the transistor 24 conductive, shutting off the switching transistor 3, and discharging the charge stored in the gate, and at the same time, the signal passing through the non-inverting buffer 8 makes the transistor
2 is made conductive, and the backflow prevention transistor 5 is made conductive.

That is, through this on/off control, the switching period of the switching transistor 3 is controlled, and at the same time, the backflow prevention transistor 5 is switched. At this time, the voltage that controls the backflow prevention transistor 5 is
It can be kept constant, and in this case, turn-on and turn-off can be made faster, reducing loss.

[Effects of the Invention] As explained above, the present invention connects a non-inverting buffer and an inverting buffer in parallel to the control signal output terminal of a control circuit, and connects the output side of a transistor whose input side is connected to the non-inverting buffer. Connect between the - end of the reference power supply and the gate of the reverse current prevention transistor, and connect the output side of the transistor whose input side is connected to the inverting buffer between the other end of the reference power supply and the gate of the reverse current prevention transistor. Since it is connected,
The backflow prevention transistor can be controlled without being limited by the input power supply voltage, making it possible to widen the fluctuation range of the input power supply voltage, and reducing loss by using the reverseflow prevention transistor in the backflow prevention circuit. There is an effect that it can be done.

[Brief explanation of the drawing]

Fig. 1 is a basic circuit diagram of one embodiment of the present invention, and Fig. 2 is a basic circuit diagram of an embodiment of the present invention.
A circuit diagram of an embodiment of a switching iL source to which the circuit shown in the figure is applied, and FIG. 3 is a circuit diagram of a conventional switching power supply. Input power supply 2: F slip circuit 3 Niswitching transistor 4: Transformer transformer 5: Transistor for backflow prevention 1 6, 26: Reference power supply 7 control circuits 8.20
: Non-inverting buffer 9.19: Inverting buffer 10.11, 14, 21, 22, 25: Resistor 12.13
, 23, 24: Transistor 15: Energy storage capacitor 16: Coil 17: Smoothing capacitor 18: Load resistance

Claims (1)

[Scope of Claims] A switching power supply including a switching transistor, a transformer that transforms and outputs an input voltage, a control circuit that turns on and off the switching transistor, and a capacitor that stores energy output from the transformer. A backflow prevention transistor whose output side is connected between one end of the output side of the transformer and the capacitor, a reference power supply connected between the transformer and the backflow prevention transistor, and a control circuit comprising: a non-inverting buffer and an inverting buffer connected in parallel to a control signal output terminal; a transistor having an input side connected to the non-inverting buffer and an output side connected between one end of the reference power supply and the gate of the backflow prevention transistor; . A switching power supply backflow prevention circuit comprising a transistor having an input side connected to the inversion buffer and an output side connected between the other end of the reference power supply and the gate of the backflow prevention transistor.