JPH0767277B2 - Control circuit for separately-excited switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline of the Invention] According to the present invention, DC power input to an input terminal is once converted into high-frequency AC power through a transformer and a switching element, and voltage conversion and stabilization operations are performed. In the separately excited switching power supply that is converted back to DC power by the diode and smoothing capacitor, it is composed of a triangular wave generation circuit, a comparison circuit, and an oscillation / drive circuit that stabilize the output voltage and perform the oscillation / drive function of the switching operation. Control circuit, and the oscillation / drive circuit is C-
Power consumption is reduced by using a MOS type inverting circuit and using a threshold voltage of the inverting circuit to configure a comparison circuit and a simple triangular wave generation circuit that charges the capacitor with the output current of the photocoupler. It is a control circuit for a separately excited switching power supply that is small and has excellent noise resistance.

[Industrial application field]

The present invention relates to a control circuit for a separately-excited switching power supply, and more particularly to a control circuit for a separately-excited switching power supply with reduced power consumption, reduced power consumption, and excellent noise resistance.

[Conventional technology]

FIG. 5 shows the configuration of a control circuit of a conventional separately-excited switching power supply. 1A and 1B are input terminals, 2 is an input smoothing capacitor, 3 is a transformer, 4 is a switching element, 5 is a diode, and 6 is an output. Smoothing capacitors, 7 and 8 are voltage detection resistors, 9 is an amplifier, 10 is a reference voltage, 11 is a photocoupler, 12 is a comparison amplifier, 13 is a drive circuit, 14 is an oscillator, and 15 is a triangular wave generation circuit. In the figure, input terminals 1A, 1B
The DC power input to is once converted into high-frequency AC power through the transformer 3 and the switching element 4, and after being subjected to voltage conversion and stabilization operations, is converted again to DC power by the diode 5 and the output smoothing capacitor 6. . In the figure, the operation of stabilizing the output voltage and oscillating / driving is as follows.

The output voltage is detected by the resistors 7 and 8 and is input to an error amplifier composed of an amplifier 9 and a reference voltage 10 which form a control signal generating circuit to create a control signal according to the amount of fluctuation of the output voltage. It is transmitted to the control circuit on the input side via the coupler 11. On the input side, the comparator amplifier compares the triangular wave output of the triangular wave generation circuit 15 that receives the signal of the oscillator 14 and outputs the triangular wave with the signal voltage transmitted through the photocoupler 11.
Enter 12 Since the error amplifier on the output side is configured to transmit the control signal according to the fluctuation of the output voltage to the photocoupler 11, the comparison amplifier 12 compares the control signal with the triangular wave to output the output voltage. A pulse voltage whose pulse width is controlled according to the fluctuation can be output, and this pulse voltage is transmitted to the drive circuit 13 to drive the switching element 4. With this configuration, when the output voltage is about to change due to changes in the input voltage and the load, the control circuit can control the pulse width applied to the switching element to keep the output voltage constant.

[Problems to be Solved by the Invention]

The conventional pulse width control circuit requires a triangular wave generation circuit and a comparison circuit in addition to the oscillator, which has a problem that the circuit configuration is complicated and the number of parts is increased. In order to solve the problem of the large number of parts, there are switching power supply ICs that incorporate these functions, but since they are bipolar type ICs, they consume a lot of power and require high efficiency of a low power switching power supply. It had the drawback that it could not be used in the field.

Further, in the conventional example, since the output of the photocoupler is direct current, there is a problem that the comparison circuit may malfunction due to the influence of noise generated by switching.

[Means for Solving the Problems]

In order to solve the conventional problems, the present invention relates to a capacitor for charging an output signal of a photocoupler or a current obtained by amplifying the output signal, which is connected to an output side of a photocoupler for transmitting an output of a conventional control signal generation circuit. , An inverting circuit connected to the capacitor that inverts the output when the charging voltage of the capacitor exceeds the built-in threshold voltage, and a switching of the separately excited switching power supply when the output of the inverting circuit connected to the inverting circuit reverses It is a control circuit having a configuration in which an element is turned off, and an oscillation / drive circuit that discharges a capacitor during a predetermined off period of the oscillation circuit.

That is, in the conventional control circuit, according to the present invention, the oscillation circuit is configured by a C-MOS type inverting circuit, the comparison circuit is configured by using the threshold voltage of the inverting circuit, and the capacitor is used as the output current of the photocoupler. Its main feature is that it uses a simple triangular wave generation circuit that charges with.

[Action]

 The present invention has the following differences from the conventional control circuit.

In the prior art, a triangular wave generation circuit is used to generate a constant triangular wave for input to the comparison circuit, whereas in the present invention, the triangular wave generation circuit is composed of a photocoupler and a capacitor, and the charging voltage when charging the capacitor is a triangular wave. In addition to being used, it also has a control signal transmission function that changes the slope of the charging voltage according to the signal from the output side.

Oscillation circuit is a C-MOS type inverting circuit with low power consumption I
Configuration using C (A bipolar oscillator circuit was used in the prior art.) In the conventional technology, a constant triangular wave voltage and a fluctuating control signal from the output side are input to a comparison circuit to generate a pulse. While the width control is performed, in the present invention, the C-MO is used as the inverting circuit.
Using an S-type inverting circuit IC, the threshold voltage and the charging voltage of the capacitor, which is a control signal from the output side, are compared and input to the oscillation / driving circuit for pulse width control.

According to the present invention, the configuration of the control circuit can be simplified, the loss of the control circuit is small, and the separately excited switching power supply excellent in noise resistance can be configured. This will be described below with reference to the drawings.

〔Example〕

FIG. 1 is a diagram showing a first embodiment of the present invention, in which 16 is a capacitor, 17 is an inverting circuit, and 18 is an oscillating / driving circuit. The same reference numerals as those in FIG. 5 indicate the same parts. Input terminal 1A, 1
When a DC voltage is applied between B, it is converted into a high frequency AC by the transformer 3 and the switching element 4, and after voltage conversion and stabilization is performed, it is rectified and smoothed again by the diode 5 and the capacitor 6, and the DC voltage is changed. Is output. The DC output voltage is detected by the resistors 7 and 8, and its variation is error-amplified by the amplifier 9 and the reference voltage 10 and is transmitted to the input side by the photocoupler 11. Now, assuming that the switching element 4 is in the ON state, the switching operation will be described below.

The DC output of this photocoupler 11 causes the capacitor 16
Is charged, and when its charging voltage rises and exceeds a certain value, the output of the inverting circuit 17 is inverted to a low level. The oscillating / driving circuit 18 receives the inverted signal and drives the switching element 4 off. This oscillator / drive circuit 18
The switching element 4 is turned on again at a predetermined oscillation period, and the same operation is repeated thereafter. The operation of the oscillation / drive circuit 18 will be described later.

Thus, according to this configuration, the oscillation / drive circuit 18
It is possible to control the timing of switching the switching element 4 from ON to OFF by a signal from the photocoupler 11 while repeating the ON operation of the switching element 4 at a constant cycle. That is, when the output side control circuit is configured so that the output current of the photocoupler 11 increases when the output voltage becomes higher than the rated value, the time at which the voltage of the capacitor 16 reaches the threshold voltage of the inverting circuit 17 at this time. Since it becomes shorter and the timing of inverting the output of the inverting circuit 17 becomes earlier, the ON period of the switching element 4 becomes shorter, the rise of the output voltage is suppressed, and the output voltage is stabilized.

As described above, according to the present invention, there is an effect that the triangular wave generating circuit and the comparison circuit, which have been conventionally required for controlling the pulse width, can be easily configured by using the capacitor and the inverting circuit.

In addition, as is apparent from the above description, the output current of the photocoupler is charged in the capacitor and has a low impedance with respect to high frequency noise, so that the noise resistance characteristic is improved compared to the conventional configuration. can get.

FIG. 2 shows a second embodiment of the present invention, in which 19 is a transistor, which is configured to amplify the output of the photocoupler 11. The same reference numerals as those in FIG. 1 indicate the same parts.
In general, a high-speed switching type photocoupler having a response speed of about 1 μsec or less has a low current transfer ratio of about 15%, and conversely, a photocoupler having a high current transfer ratio has a drawback that the switching speed becomes slow. Therefore, if a photocoupler with a high switching speed is used, it is necessary to increase the bias current of the control circuit on the output side to supply a large current to the photocoupler, which increases the rating of the photocoupler and the loss of the control circuit. There was a problem of increase. Further, if a photocoupler with a slow switching speed is used, the charge speed of the capacitor that repeats charging and discharging at high speed cannot be accurately controlled while the switching device 4 is turned on and off, although the photocoupler is a current-driven type. Since the operation may become unstable, there is a problem that it cannot be used for applications where the driving frequency of the switching element is high.

In the second embodiment, since the high-speed transistor is used for amplification, it becomes possible to use a high-speed switching type photocoupler, and the photocoupler need only transfer a DC signal to the base of the transistor. Since it is not affected by the change in the charging current due to the charging / discharging of the capacitor 16, a low speed photocoupler can be applied. As a result, there is an effect that a stable, low-loss and high-speed control circuit can be configured.

FIG. 3 is a third embodiment of the present invention and specifically shows the circuit connection of the oscillation / drive circuit 18. 201 ~ 2
05 is an inverting circuit, 21 is a capacitor, 22 and 23 are resistors, and 24 and 25 are diodes. The same reference numerals as those in FIG. 2 indicate the same parts. 17,201 to 205 are C-MOS type inverting circuits (6 circuits)
It is possible to use a commercial product built in a single IC package. An oscillating circuit is configured by the inverting circuits 201 to 203, the capacitor 21, and the resistor 22, the oscillation cycle is determined by the capacitor 21 and the resistor 22, and pulse width control for controlling the ON period of the switching element 4 is performed by the inverting circuits 17, 204 and 205. .

Now, assume that the switching element 4 is turned on. The DC output of the photocoupler 11 allows the capacitor
16 starts charging and its charging voltage rises. The charging voltage of the capacitor 16 is a constant value, that is, the inverting circuit 17
When the threshold value is exceeded, the output of the inverting circuit 17 is inverted to the low level. Then, the output of the inverting circuit 205 is inverted to a high level, and the output of the inverting circuit 204 is inverted to a low level to drive the switching element 4 off. At this point, the output of the inverting circuit 202 of the oscillation circuit is still maintained at the high level, so that the capacitor 16 continues to be charged and the output of the inverting circuit 17 is maintained at the low level. When the oscillation circuit finishes the predetermined ON period and the OFF period, that is, when the output of the inverting circuit 202 becomes a low level, the charge accumulated in the capacitor 16 starts discharging through the diode 25,
When the charging voltage of the capacitor 16 drops below a certain value, that is, the threshold value of the inverting circuit 17, the inverting circuit 17 inverts and its output returns to a high level. However, since the output of the inverting circuit 202 of the oscillation circuit is maintained at a low level,
Since the output of the inverting circuit 17 has a current flowing through the resistor 23 and the diode 24, the input of the inverting circuit 205 is maintained at a low level, and as a result, the switching element 4 continues to be in the off state. During the off period of this oscillator circuit, the charge of the capacitor 16 is discharged through the diode 25. When the output of the inverting circuit 202 of the oscillating circuit becomes high level after the lapse of a predetermined off period, the current flowing through the resistor 23 and the diode 24 disappears, so that the input of the inverting circuit 205 becomes high level. Therefore, the output of the inverting circuit 205 is inverted to the low level, and the output of the inverting circuit 204 is inverted to the high level by this output, and the switching element 4 is driven on. At the same time, the capacitor 16 starts charging. Note that the diodes 24 and 25 are for preventing current from flowing into the inverting circuit 205 and the capacitor 16 when the output of the inverting circuit 202 is at a high level, and 23 is a current limiting resistor. As described above, according to the third embodiment, the oscillation / driving circuit can be configured by simply adding a few resistors and capacitors to the C-MOS type inverting circuit IC, so that the circuit can be greatly simplified. At the same time, the power consumption of the C-MOS type IC is extremely small,
Compared with the case of using the conventional switching regulator control IC, there is an effect that the loss can be reduced.

The inverting circuit is constructed by using the inverting circuit IC, and as shown in FIG. 4, the NAND gate 2 of the low-loss C-MOS NAND gate IC is used.
There is also a method to configure using 07-209, according to
Since the resistor 23, which is required in the third embodiment shown in FIG. 3, is no longer necessary, the loss can be further reduced. NA
The connection of the ND gates 208 and 209 indicates that the same operation as the inverting circuit 204 is performed.

The configuration of FIG. 4 increases the number of ICs by one as compared with the configuration of FIG. 3, but has an effect of reducing loss by several tens of mW. Therefore, it is appropriate to selectively use the configurations shown in FIGS. 3 and 4 selectively according to requirements.

〔The invention's effect〕

As described above, according to the present invention, the control circuit of the pulse width control separately excited switching power supply is configured by using the C-MOS type inverting circuit IC, the capacitor, etc. There is an advantage that a separately excited switching power supply that is simple and has little loss in the control circuit and excellent noise resistance can be configured. Therefore, the efficiency of the power supply can be significantly increased by using the small-capacity output separately-excited switching power supply in which the control circuit loss accounts for a large proportion of the entire power supply loss. In addition, this control circuit has a low loss and a small number of parts, so a hybrid IC
The effect is large when applied to miniaturization of separately excited switching power supply.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG.
FIG. 3 is a circuit diagram showing second and third embodiments of the present invention, FIG. 4 is an embodiment of an oscillation / driving circuit, and FIG. 5 is a control circuit of a conventional separately excited switching power supply. 1A, 1B ... Input terminals, 2, 6 ... Input and output smoothing capacitors, 3 ... Transformer, 4 ... Switching element, 5, 24, 25 ...
Diodes, 7,8 ... Resistors for voltage detection, 9 ... Amplifiers, 10 ...
Reference voltage, 11 ... Photo coupler, 12 ... Comparison amplifier, 13 ...
Drive circuit, 14 ... Oscillator, 15 ... Triangular wave generation circuit, 16, 21 ...
Capacitors, 17,201 to 205 ... Inversion circuits, 18 ... Oscillation / driving circuits, 19 ... Transistors, 22,23 ... Resistors

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tsutomu Ogata 3-9-11 Enmamachi, Musashino-shi, Tokyo Inside Nippon Telegraph and Telephone Corporation Musashino Electro-Communications Research Laboratory (72) Inventor Kazuya Suzuki 1 Takada, Toshima-ku, Tokyo No. 18-1 Origin of Western Electric Company (56) Reference JP-A-58-133165 (JP, A)

Claims (1)

[Claims] 1. A separately-excited switching power supply, which uses a switching element and a transformer to control the pulse width of the switching element to perform voltage conversion and output stabilization, wherein the output of the first C-MOS type inverting circuit is The second C-MOS type inverting circuit is connected to the input of the second C-MOS type inverting circuit, and the output of the second C-MOS type inverting circuit is connected to the input of the third C-MOS type inverting circuit. The output of the inverting circuit is connected to the input of the first C-MOS type inverting circuit via a resistor, and the output of the second C-MOS type inverting circuit is connected to the first capacitor via the first capacitor. Connected to the input of the C-MOS type inverting circuit, the output of the second C-MOS type inverting circuit is used as the output of the oscillating circuit, and the output of the separately-excited switching power supply is detected to obtain a reference voltage. A control signal generator that creates a control signal according to the amount of fluctuation of the output compared with Circuit, a photocoupler for receiving the output of the control signal generating circuit, a second capacitor charged by an output signal current of the photocoupler, and a connection between one end of the second capacitor and an output side of the photocoupler A fourth C-MOS type inverting circuit connected to the circuit section for inverting the output when the charging voltage of the second capacitor exceeds the built-in threshold voltage, the output of the oscillating circuit and the fourth C A drive circuit for connecting the output of the MOS type inversion circuit to the input of the NAND operation circuit and driving the output of the NAND operation circuit through the fifth C-MOS type inversion circuit to drive the switching element; Means for discharging the second capacitor while the output is off, and controlling the pulse width of the switching element, the control circuit for the separately excited switching power supply.