JPH0365049A - Switching power supply circuit - Google Patents

Abstract

PURPOSE:To attain inexpensiveness with simplification by detecting DC input voltage with a switching control performed in accordance with this detected voltage. CONSTITUTION:In a switching power supply circuit, an AC input 1 is rectified by a rectifying bridge 2 and smoothed by an electrolytic capacitor 3 with DC voltage generated. This DC voltage is on-off controlled by a switching transistor 6 to generate a high frequency and input to a primary winding of a pulse transformer 5. While a secondary winding output of this transformer is rectified and smoothed by a rectifier 7 and an electrolytic capacitor 8 with DC output voltage generated. In a switching control circuit 4, both end voltage values of the electrolytic capacitor 3 are detected with an on-time of the switching transistor 6 controlled. As a result, output voltage is held to a fixed value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a stabilized power supply circuit, and particularly to a switching type power supply circuit.

[Conventional technology]

Conventionally, in this type of switching power supply circuit, the output voltage has been stabilized by detecting the output voltage value on the secondary side and feeding it back to the control circuit on the negative side.

[Problem to be solved by the invention]

The above-described conventional switching power supply circuit has the disadvantage that it is expensive because it requires an insulating element such as a photocoupler because it feeds back from the secondary circuit to the primary circuit.

[Means to solve the problem]

The switching power supply circuit of the present invention detects the DC voltage value input to the primary winding of the pulse transformer, and changes the ON time or switching frequency of the transistor for kneeling the primary winding of the pulse transformer in accordance with this voltage value. I'm letting you do it.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention.

AC power 1 is rectified by a rectifier bridge 2 and smoothed by an electrolytic capacitor 3 to become a DC voltage. By turning on and off the switching transistor 6, this DC voltage becomes a high frequency and is input to the primary winding of the pulse transformer 5. The secondary winding output of the pulse transformer 5 becomes a DC output voltage through a rectifier 7 and an electrolytic capacitor 8.

Here, the switching control circuit 4 has a function of detecting the DC voltage value across the electrolytic capacitor 3 and controlling the ON time of the switching transistor 6. When this DC voltage value is high, the ON time is shortened and the DC voltage is O when the voltage value is low
Increase N time. Therefore, the output voltage can be kept constant despite fluctuations in the AC input voltage.

〔Effect of the invention〕

As explained above, the present invention detects the DC voltage value input to the primary winding of a pulse transformer and controls switching in accordance with the voltage value, thereby stabilizing the output voltage easily and inexpensively. There is an effect that can be achieved.

... Pulse transformer, 6... Switching transistor, 7... Rectifier.

Claims (1)

[Claims] A switching power supply characterized by detecting a DC voltage value input to a primary winding of a pulse transformer and changing the ON time or switching frequency of a transistor for driving the primary winding of the pulse transformer in accordance with this voltage value. circuit.