JPH0636672B2 - Switching Regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has an input voltage monitoring function for backing up a memory or the like that is operating as a load when the input power supply voltage is turned on / off or a power failure occurs. Regarding switching regulators.

[Prior art]

Usually, this kind of switching regulator is
AC power of 60Hz or 400Hz is input, and the AC voltage is once rectified, smoothed and converted to DC, then DC
-It is configured to convert to the required output voltage using a DC converter. Furthermore, when supplying power to a memory etc. to such a switching regulator,
An AC input voltage detection function is added so that a voltage drop of the AC input can be detected instantaneously and a backup process for the memory etc. can be performed before the voltage supplied to the memory etc. has not yet dropped. Then, the power supply having the detection function must be insulated from the primary AC power supply in order to protect from a disaster such as electric shock. Because of this insulation
A transformer is used.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technique, while the switching transformer is a small one that operates at 20 kHz or more, the power transformer for insulating and detecting the AC input voltage operates at a low frequency such as 50 Hz. As a result, the shape and weight are relatively large, and not only the effect of downsizing as a whole is negated, but it is also expensive. Therefore, a first object of the present invention is to provide a switching regulator which can eliminate these drawbacks, downsize the input power supply voltage detecting means, and improve the economical efficiency. A second object of the present invention is to provide a switching regulator that can achieve the above first object and prevent an abnormal operation that occurs when the input AC power supply is turned on.

[Means for solving problems]

The first aspect of the present invention is to rectify an AC input to generate a DC,
In a switching regulator of the type which operates a DC-DC converter with the direct current, a third winding is provided separately from the primary and secondary windings in the voltage conversion transformer of the DC-DC converter, and the AC input is supplied separately. A first circuit that includes a circuit that rectifies and smoothes the input DC voltage, an auxiliary transformer, and a comparison circuit, and connects the primary winding of the auxiliary transformer and a transistor to the output side of the third winding.
And a second series circuit connecting a diode and a capacitor are connected in parallel, and a Zener diode is connected via a resistor to a connection point between the diode and the capacitor of the second series circuit. A circuit compares the input DC voltage with a reference voltage created by the Zener diode, and turns on a transistor of the first series circuit when the input DC voltage is higher than the reference voltage to cause the auxiliary transformer. It is characterized in that a current is supplied to the primary winding and the presence / absence of the AC input is detected from the secondary side output of the auxiliary drain.

The second of the present invention is to rectify an AC input to generate a DC,
In a switching regulator of the type which operates a DC-DC converter with the direct current, a third winding is provided separately from the primary and secondary windings in a voltage conversion transformer of the DC-DC converter, and a direct current is supplied from the AC input. A current limiting resistor is inserted in a smoothing circuit to be generated, and a circuit for rectifying and smoothing the AC input to obtain an input DC voltage, an auxiliary transformer, a comparison circuit, and a circuit for giving a reference voltage to the comparison circuit. And a first series circuit connecting the primary winding of the auxiliary transformer and a transistor and a second series circuit connecting a diode and a capacitor are connected in parallel to the output side of the third winding. Then, a thyristor is connected in parallel to the current limiting resistor, and a DC output obtained at both ends of the capacitor of the second series circuit is used as a control input of the thyristor, The comparison circuit compares the input DC voltage with the reference voltage, and turns on the first transistor when the input DC voltage is higher than the reference voltage to turn on the primary winding of the auxiliary transformer. It is characterized in that a current is supplied and the presence or absence of the AC input is detected from the secondary side output of the auxiliary transformer.

[Conventional example]

Here, in order to facilitate understanding of the present invention, a conventional example will be given and described with reference to the circuit diagram of FIG. In the figure,
The AC input obtained from the AC power supply 1-1 is rectified by the diode 1-2, smoothed by the capacitor 1-3, and converted into DC. This DC power is applied to the series circuit of the primary side of the transformer 1-5 and the transistor 1-4.
A pulse wave control voltage of 20 kHz or more is applied to the bases of the transistors 1-4, and an intermittent current is caused to flow between the collector and emitter to induce a voltage-converted output from the secondary side winding of the transformer 1-5. , 1-6 diode and 1-
It is converted into direct current by the capacitor 7 and is led to the output side. In this method, the output voltage is monitored to control the width of the pulse wave added to the base of the transistor,
A control circuit is added to obtain a constant output voltage,
Since it is not directly related to the present invention, its explanation is omitted.

With such a configuration, even if the input power supply 1-1 fails, the output V _out drops after the input power supply 1-1 due to the accumulated charges of the capacitor 1-3. That is, transformer 1-5
Since the above pulse current continues to flow for several ms to about 100 ms after a power failure, it is impossible to detect a power failure in an early time. Therefore, 50Hz or 60Hz, such as 1-8,
Alternatively, a low-frequency transformer operating at 400 Hz or the like is provided, the secondary side output is made DC by the diode 1-9 and the capacitor 1-10, and the applied AC input is detected as the DC output V _PF . It was designed to be monitored. Since the capacitor 1-10 requires a much smaller capacity than the capacitor 1-3 as a capacity required for the detection circuit, the discharge is performed quickly. as a result,
V _PF drops faster than V _out after the AC power supply 1-1 fails.

However, in this conventional example, the transformer 1-8 has 50
Since it operates at a low frequency such as Hz, it becomes a large transformer. On the other hand, since the transformer 1-5 operates at 20 kHz or higher, it can be made compact even if it has a power capacity of several tens of watts or several hundreds of watts. Therefore, relatively low power (1 W or less)
The transformer 1-8 for processing power and the transformer 1-5 for processing electric power of several tens of W or more may be about the same size, and the effect of the power supply device, which is a miniaturized switching regulator itself, may be canceled. become.

Example of Invention

A first embodiment according to the present invention will be described with reference to the circuit diagram of FIG. In this figure, from the input power source to V
The operation for obtaining _out is the same as that of the conventional example shown in FIG. 3, and therefore its explanation is omitted. The 2-5 transformer found in the DC-DC converter circuit is provided with another winding of 2-5a, the primary side of the 2-8 auxiliary transformer and the series circuit of the 2-9 transistor, and 2-10. The series circuit of the diode and the capacitor 2-11 is connected in parallel. Then, the output of the input AC power supply is rectified by the diode 2-12, smoothed by the capacitor 2-13, and then divided into low values by the resistors 2-14 and 2-15. This voltage is applied to the comparator circuit 2-18 and compared with the reference voltage created by the resistor 2-16 connected across capacitor 2-11 and the zener diode 2-17. As a result, when the divided input voltage is higher than the reference voltage, the transistor 2-9
Turn on. At that time, a current according to the operating frequency of the DC-DC converter circuit flows through the primary side of the auxiliary transformer 2-8, and the diode of 2-19 and 2-20 from the secondary side.
V _PF is obtained through the capacitor of

According to this example, the transformer 2-8 is much smaller than the transformer 1-8 in FIG. For example, 35
mm × 30mm × 30mm transformer is 15mm × 10mm × 7mm
Therefore, the volume can be reduced to about 1/30.
In addition, since other parts can be used, only small parts can be used, resulting in overall small size and low cost. In addition, capacitor 2
Since a small capacity of −13 can be used, there is no time delay when the power input is turned off.

FIG. 2 shows a circuit diagram of the second embodiment according to the present invention. Differences in this example from the embodiment of FIG. 1 will be described below. In Fig. 2, the resistor 3-1 is inserted in the rectifying current smoothing circuit on the input side, and when the input AC voltage rises sharply from "0" V when the input switch is turned on, it becomes steep in the electrolytic capacitor 3-2. This is useful for limiting the current so that a large inrush current does not flow. Then, the voltage across the capacitor 3-2 becomes high, and DC-DC
When the output voltage of the converter circuit becomes high and the voltage across the capacitor 3-5 becomes sufficiently high, the gate of the thyristor 3-3 connected in parallel to the resistor 3-1 becomes 3-
It is turned on through the limiting resistor 6 and the normal operation is started.

As described above, in this example, the series circuit connecting the diode 3-4 and the capacitor 3-5 is a thyristor 3-3.
Therefore, the reference voltage applied to the comparator circuit 3-7 is fixedly supplied by the battery 3-8.

〔The invention's effect〕

As is clear from the above description, according to the present invention, by operating the transformer used for the input AC voltage detecting means in the switching cycle of the regulator circuit,
Compared with the conventional one, it is more compact and more economical, and at the same time, it is possible to prevent abnormal operation that occurs when the input AC power supply is turned on.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment according to the present invention, FIG. 2 is a circuit diagram showing a configuration of a second embodiment according to the present invention, and FIG. 3 is a configuration example of a conventional switching regulator. It is a circuit diagram shown. In this figure, 1-1 is an AC power source, 1-2, 1-6,
1-9 is a diode, 1-3, 1-7 and 1-10 are capacitors, 1-4 is a transistor, 1-5 is a high frequency transformer, 1-8 is a low frequency transformer, and 2-1 is an alternating current. Power supply, 2-2, 2-6, 2-10, 2-12, 2-19 are diodes, 2-3, 2-7, 2-11, 13 and 2
-20 is a capacitor, 2-4 and 2-9 are transistors,
2-5 is a transformer for high frequency, 2-8 is an auxiliary transformer,
2-14 to 2-16 are resistors, 2-17 are Zener diodes, 2-18 are comparison circuits, 3-1 and 3-6 are resistors, and 3
-2, 3-5 are capacitors, 3-3 are thyristors, 3-
4 is a diode, 3-7 is a comparison circuit, and 3-8 is a battery.

Claims (2)

[Claims] 1. A switching regulator of the type in which an AC input is rectified to generate a direct current and a DC-DC converter is operated by the direct current, wherein a primary and secondary winding are provided in a voltage conversion transformer of the DC-DC converter. Separately, a third winding is provided, and separately, a circuit for rectifying and smoothing the AC input to obtain an input DC voltage, an auxiliary transformer,
A first series circuit connecting the primary winding of the auxiliary transformer and a transistor, and a second series circuit connecting a diode and a capacitor in parallel to the output side of the third winding. And a zener diode is connected to the connection point between the diode and the capacitor of the second series circuit via a resistor, and the comparison circuit connects the input DC voltage and the reference voltage generated by the zener diode. In comparison, when the input DC voltage is higher than the reference voltage, turning on the transistor of the first series circuit causes a current to be supplied to the primary winding of the auxiliary transformer,
A switching regulator, which detects the presence / absence of the AC input from the secondary side output of the auxiliary transformer. 2. A switching regulator of the type in which an AC input is rectified to generate a direct current, and a DC-DC converter is operated by the direct current, wherein a primary and secondary winding are provided in a voltage conversion transformer of the DC-DC converter. Separately, a third winding is provided, a current limiting resistor is inserted in a smoothing circuit for generating direct current from the alternating current input, and separately, a circuit for rectifying and smoothing the alternating current input to obtain an input direct current voltage, and an auxiliary A transformer, a comparison circuit, and a circuit for applying a reference voltage to the comparison circuit, and a first series circuit connecting the primary winding of the auxiliary transformer and the transistor to the output side of the third winding, A second series circuit connecting the diode and the capacitor is connected in parallel, and a thyristor is connected in parallel to the current limiting resistor to obtain a capacitor across the second series circuit. The input DC voltage is used as a control input of the thyristor, the comparison circuit compares the input DC voltage with the reference voltage, and turns on the first transistor when the input DC voltage is higher than the reference voltage. By so doing, a current is supplied to the primary winding of the auxiliary transformer, and the presence or absence of the AC input is detected from the secondary side output of the auxiliary transformer.