JPS5915257Y2 - switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator, and more particularly to an improvement of a switching regulator having a smoothing capacitor in its input circuit.

In this type of switching regulator, as shown in Figure 1, the power supply voltage from an AC 100cm power supply 1 is rectified and smoothed by an input circuit 2 having a rectifier circuit RE and a smoothing capacitor C1, and becomes an operating voltage 1. It is added to a series circuit of the primary winding n1 of the transformer 3 and the transistor 4, which is a switching element.

When the transistor 4 is turned on, a primary current 11 flows, and when the transistor 4 is turned off, the energy stored in the iron core of the transformer 3 is released as a secondary current 12 due to i□.

The secondary current 12 is rectified and smoothed by the rectification and smoothing circuit 5, and is supplied to the load 6 as an output voltage Vo.

The on/off state of the transistor 4 is controlled by the control circuit 7 so that Vo remains constant.

In a switching regulator with such a configuration, the smoothing capacitor C1 of the input circuit 2 stores enough energy to maintain the output voltage Vo at approximately 100% for a while during a power outage of the power supply 1, and the output holding time ts is C1
The larger the capacity, the longer it can be made.

On the other hand, if C1 has a large capacity, the rush current generated at the moment the power supply 1 is turned on also increases.

If the inrush current becomes large, there is a risk of destroying the element.

Therefore, conventionally, when increasing the capacitance of a smoothing capacitor in order to lengthen the output holding time, it was necessary to limit the rush current using a relay, thyristor, etc., and the complexity of the circuit was unavoidable.

By the way, in a switching regulator having a transformer, a spike voltage is generated due to the leakage inductance of the transformer, so as shown in FIG. A back electromotive force absorption circuit 8 is provided.

The present invention realizes a switching regulator with a simple configuration that uses a back electromotive force absorption circuit and can lengthen the output holding time without increasing inrush current.

That is, as shown in the embodiment of FIG. 2, the present invention connects a series circuit of a diode D2 and a backup capacitor C3 in parallel to the smoothing capacitor C1, and connects the resistor R1 of the back electromotive force absorption circuit 8 to the diode D2. When the power supply 1 is normal, the capacitor C3 is charged with a back electromotive force.
In the event of a power outage, the charging voltage Vc of C3 is supplied to the series circuit of transformer 3 and transistor 4 via diode D2.

Therefore, in the present invention, the output holding time ts corresponds to the sum of the capacitances of the smoothing capacitor C1 and the backup capacitor C3, and can be made longer than in the case of only C1.

If the capacitance of C3 is selected to be equal to the capacitance of C1, the output holding time can be doubled.

On the other hand, since the capacitance of C3 does not affect the inrush current, it is the same as the case of only C1.

In the above description, an on-off type switching regulator is exemplified, but an on-on type switching regulator may be used.

Moreover, although the case where the output voltage vO is given to the control circuit 7 is illustrated, the transformer 3 is further provided with a secondary winding, and the output voltage 'V
A voltage proportional to p may be obtained and this voltage may be applied to the control circuit 7.

Further, in the above description, the case where an AC power source is used as the power source is exemplified and explained, but the same can be applied to the case where a DC power source is used.

As explained above, the present invention provides a switching regulator that can lengthen the output holding time without increasing the rush current with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of a conventional switching regulator, and FIG. 2 is a connection diagram showing an embodiment of the switching regulator of the present invention. DESCRIPTION OF SYMBOLS 1... Power supply, 2... Input circuit, 3... Transformer, 4... Switching transistor, 8... Back electromotive force absorption circuit, C1... Smoothing capacitor, C3...
・Backup container.

Claims (1)

[Scope of utility model registration request] A switching regulator is configured to apply voltage from a power supply to a series circuit of a transformer and a switching element via a rectifier circuit and a smoothing capacitor, and a series circuit of a diode and a backup capacitor connected in parallel to the smoothing capacitor. , a means for applying the back electromotive force of the transformer through a diode and a resistor is provided at the midpoint of this series circuit, and in the event of a power outage, the voltage stored in the backup capacitor is connected to the transformer and the switching element in series through the diode. A switching regulator characterized in that the output is maintained by applying it to the circuit.