JPH0755043B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a switching power supply device.

(B) Outline of the Invention The present invention provides a switching power supply device which includes a switching element connected in series with a primary winding of a switching transformer and which adjusts an output voltage by changing an ON / OFF time ratio of the switching element. A voltage detector that operates when the output voltage deviates from the allowable range is provided, and when the voltage detector operates, the elements that have a holding function, such as thyristors, are turned on to stop the operation of the switching element, and the input voltage In order to quickly restore the operation of the switching element in the event of a momentary power failure, by providing a comparator to detect that the input voltage drop has been applied and a reverse voltage is applied to the holding function element when an input voltage drop is detected. Is.

(C) Conventional Technology FIG. 2 shows a configuration diagram of a conventional switching power supply device. Power supplied from an AC power supply 1 is rectified by a rectifier 2 and smoothed by a capacitor 3, and then a FET or the like. It is supplied to the primary winding 51 of the switching transformer 5 connected in series with the switching element 4. The pulse current generated in the secondary winding 52 of the transformer 5 when the switching element 4 is turned on and off is smoothed by the filter 6 including the diodes 61, 62, the reactor 63 and the capacitor 64, and is supplied to the load 7. It The ON / OFF ratio of the switching element 4 is controlled in order to keep the voltage E ₀ supplied to the load 7 constant. As this control means, the constant voltage control circuit 8 detects the load voltage E ₀ , the gate output width of the pulse width control circuit 9 is controlled according to the change of the voltage E ₀ , and the switching element is output by the pulse output from this control circuit 9. 4 is on / off controlled. Note that
10 is an excitation energy absorption circuit, which is a resistor 101, a diode 10
2 and a capacitor 103, a switching element 4
Absorbs the excitation energy of the transformer 5 when the switch is turned off. 20
Is an auxiliary power supply for the pulse control circuit 9, which is composed of a resistor 21, a Zener diode 22 and a transistor 23, and lowers the voltage of the capacitor 3 and supplies it to the pulse width control circuit 9. Further, the pulse width control circuit 9 is composed of a monolithic IC 91, a resistor 92, etc., and controls the pulse width of the signal output according to the signal from the constant voltage control circuit 8 and at the same time the potential V _{D of the} point _D.
The range of the pulse width is determined by this, and the pulse signal to the switching element 4 is not output at all when V _D becomes 3 V or more, for example.

In the switching power supply device as shown in FIG.
In general, a means for stopping the operation of the switching element 4 when the supply voltage E ₀ to the load 7 deviates from the allowable range is often adopted. In the case of FIG. 2 as well, the supply voltage E to the load 7
_{When 0} is outside the predetermined voltage allowable range,
The voltage detection unit 81 incorporated in the constant voltage control circuit 8 operates,
A current flows through the diode 96-1 / 2 of the photothyristor.
The current flowing through the diode turns on the photothyristor 96-2 / 2 of the switch unit 95, and the voltage V _C at the point _C
(= 5V) is supplied to the resistor 92 via the resistor 97. At this time, the resistance 97 should be adjusted so that the voltage V _D
If the resistance values of 92 and 92 are selected, the generation of the pulse from the monolithic IC 91 is stopped by the turn-on of the photothyristor, and the operation of the switch element 4 is stopped.

Since the thyristor 96-2 / 2 of the photothyristor has a holding function, the turn-on state is maintained even when the current does not flow to the diode 96-1 / 2. Therefore, in order to turn off the photothyristor and return it to the operable state, the voltage of the capacitor 3 drops, the voltage V _C at the point _C also drops, and the current flowing through the photothyristor must fall below the holding current. I won't.

(D) Problems to be Solved by the Invention The use of a thyristor having a holding function in the switch portion 95 has the following problems. The case where the constant voltage control circuit 8 has a built-in undervoltage detection function that operates when the load voltage E ₀ drops below the allowable value will be described below with reference to FIG.

As shown now FIG. 3 waveform b, the AC power supply 1 is a power failure at time t _1, as the operation mode when the power returns at time t ₄ after a short time, the voltage V _A at point A As shown by the waveform b, the switching operation continues due to the charge accumulated in the capacitor 3 even after a power failure, but the potential drops with time, and constant voltage control becomes impossible, and at time t ₂ , the undervoltage detection function is activated. The photothyristor 96 is turned on (waveform E), the voltage V _{D at} point _D rises (waveform D), and the switching operation also stops. Therefore, the voltage E ₀ applied to the load 7 also disappears (waveform C).

At this time, when the AC power supply recovers at time t ₄ before the current i flowing through the photothyristor decreases below the holding current,
The photothyristor continues to maintain its turn-on state, and the switching operation of the switch element 4 remains stopped even if the AC power supply becomes normal. In order to restart the photothyristor, the photothyristor is artificially turned off ( There is a problem that the AC power supply must be cut off during the time when it becomes less than the holding current.

Therefore, an object of the present invention is to provide a device for immediately stopping the photothyristor when power is restored.

(E) Means for Solving the Problems In the present invention, a switching element connected in series with the primary winding of a switching transformer is provided on the output side of a DC power supply, and the on / off time ratio of the switching element is changed. In the case of adjusting the output voltage by adjusting the output voltage, a voltage detector is provided in the constant voltage control circuit for adjusting the output voltage, and it is turned on by the operation signal of this detector, and it is held like a thyristor for stopping the switching element. A switch part including a functional element is provided. A comparison unit is provided that compares the DC power supply voltage with a predetermined value that is set in advance, and outputs an output when the DC power supply voltage falls below a predetermined value.

(F) Function The voltage detector detects that the load voltage has dropped and turns on the thyristor to stop the switching element. After the thyristor turns on, when the voltage further decreases, the comparator section outputs to turn off the thyristor. Therefore, when the power is restored, the operation of the switching element is immediately started.

(G) Embodiment FIG. 1 shows an embodiment of the present invention, in which the same reference numerals as those in FIG. 2 indicate the same parts, and a description thereof will be omitted.
That is, in the present invention, the difference from FIG. 2 is that the comparison unit 190 is provided. The comparison unit 190 is a comparator
195, A of the DC power supply unit consisting of the rectifier 2 and the condenser 3
Resistors 191 and 192 for dividing the point voltage V _A and inputting it to one terminal of the comparator 195, and Zener diode 194 and resistors 193 and 196 and diode for inputting the voltage of a predetermined value V _A11 to the other terminal of the comparator 195. 197 and its output is applied to point D. The comparison section
190 is a predetermined value V _A11 determined by the Zener diode 194.
When the voltage divided by the resistors 191 and 192 becomes lower, it is turned off.

Next, the operation will be described.

In the normal state, the switching element 4 is on / off controlled via the constant voltage control circuit 8 and the pulse width control circuit 9,
Since the process of outputting the constant voltage to the load 7 is the same as that of FIG. 2 described above, the description thereof is omitted, and the operation of the present invention when a short-time power failure occurs will be described below with reference to the waveforms i, b and f of FIG. This will be explained using

Now, at time t ₁ , the AC power supply fails (waveform a) and the voltage at point A
When V _A drops (waveform B) and reaches time t ₂ , the voltage detection unit 81 operates to turn on the photothyristor 96 (waveform H) and raise the voltage V _D at point _D as shown by the waveform G. As a result, the monolithic IC 91 stops the operation of the switching element 4, so that the voltage E ₀ applied to the load 7 becomes zero. When the voltage V _A gradually drops and reaches V _A11 at the time t ₃ , the resistances 191, 192 and 192 are generated from the voltage set by the zener diode 194 in the comparison section.
Therefore, the voltage divided by
5 is inverted and turned off (waveform re). Comparator 1
By turning off 95, the voltage V _{B at} point B changes to resistor 196, diode 19
It is applied to the point D of the resistor 92 through 7. At this time, the resistance 9
By previously setting the voltage applied to 2 to be higher than the voltage V _C (= 5 V) at the point C, the current i flowing through the photothyristor 96 at the same time when the comparator 195 is turned off decreases to zero. Then the thyristor 96 is turned off. However, since the voltage V _D at the point _D is continuously supplied from the point B through the resistor 196 and the diode 197, the potential is high and the IC 91 keeps the pulse stopped state. At time t ₄ , the AC power is restored, and at time t ₅ , the voltage V A at point _{A rises} above V _A11 and reaches the operating voltage of the comparator 195, this comparator is turned on and the voltage at point D drops. The switching element restarts its operation. Note that the comparator
If the voltage V _A10 at the point A where the 195 operates is selected, the comparator 195 operates at time t ₃ ′ before the undervoltage detection unit 81 and the photothyristor 96 operate, and the switching element is stopped. Even if the photothyristor 96 is turned on, since the voltage V _D at the point D is raised to V _C or more, this thyristor does not maintain the turn-on state.

(H) Effects of the Invention As described above, according to the present invention, even if an element having a holding function such as a thyristor is used as an element used for detecting that the DC power supply voltage is insufficient and stopping the switching element. Since the element is immediately turned off to wait for the power recovery, the switching element immediately starts the operation at the time of the power recovery, so that the non-voltage time of the load at the moment of the momentary power failure is shortened.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a circuit configuration diagram of a conventional switching power supply device, and FIG. 3 is a waveform diagram for explanation. 1 is an AC power supply, 2 is a rectifier, 3 is a capacitor, 4 is a switching element, 5 is a switching transformer, 8 is a constant voltage control circuit, 9 is a pulse width control circuit, 81 is a voltage detection unit, 19
0 is the comparison section.

Claims (1)

[Claims] 1. A series circuit of a primary winding of a switching transformer and a switching element is connected to the output side of a DC power source,
The output voltage on the secondary side of the switching transformer is detected by a constant voltage control circuit, and the conduction ratio of the switching element is controlled via a pulse width control circuit according to the detected voltage. The voltage control circuit is provided with a voltage detection unit for detecting that the output voltage is out of the allowable range, and the pulse width control circuit is turned on by an operation signal of the voltage detection unit to stop the operation of the switching element. With a switch section consisting of a holding function element, and having a comparator for comparing the voltage of the output side of the DC power supply and the value of the auxiliary power supply of the pulse width control circuit set by a Zener diode, the output side When the voltage becomes lower than the value set by the Zener diode, a comparator for applying a reverse voltage to the switch is provided. Itching power supply.