JPS6335176A - Switching power source - Google Patents

Abstract

PURPOSE:To prevent the damage of an element upon overload even when a supplying voltage is high, by changing the limit value of a driving current in accordance with the value of the supplying voltage for a switching transformer. CONSTITUTION:A driving current width control circuit 2 controls the width of the driving current of a switching transformer 1 in accordance with the signal of a feedback circuit 13 to stabilize an output voltage. A current limitting circuit 4 increased the driving current upon overload and outputs a signal to the driving current width control circuit 2 when the driving current has arrived at some limit value while the driving current width control circuit 2 reduces the width of the driving current to limit the value of the driving current. When a supplying voltage for the switching transformer 1 is high, the limit value of the current limitting circuit 4 becomes lower, while the limit value becomes higher when the supplying voltage is low.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to switching power supplies, especially switching transformer drive current values! It concerns one source of switching power supply that connects 4R to the fii and lSaki circuits.

[Conventional technology]

Conventionally, in this type of switching power supply, as shown in FIG. 2, a drive current width control circuit 12 controls the entire drive current width of the switching transformer 11 in response to a signal from a feedback circuit 13 to control the output voltage? Stabilize, my friend. [The current limiting circuit 14 is overloaded, and when the drive current increases and reaches a certain value, it sends a signal to the drive current width control circuit 12 to reduce the drive current width, fully control the drive current width, and control the element. Damage was completely prevented.

[Problem that the invention seeks to solve]

In the conventional switching power supply mentioned above, the drive current limit value is kept constant regardless of the supply voltage value to all switching transformers, so when the supply voltage is high, the output voltage does not drop even if there is an overload, and the temperature There is a drawback that the increase is large and the element is destroyed.

[Means for solving problems]

A switching transformer according to the present invention, a driving am current width control circuit of the switching transformer, and a current limiting circuit that limits the maximum value of the driving current;
A switching mechanism having a feedback circuit that feeds back an output voltage to the drive current width control circuit, wherein the current limiting circuit changes a limiting value according to the voltage supplied to the switching transformer. Embodiments Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

The drive current width control circuit 2 controls the drive current width of the switching transformer 1 in accordance with the signal from the feedback circuit 13, and completely stabilizes the output voltage. When the current limit circuit 4 is overloaded, the drive current increases and reaches a certain limit value, and when it reaches a certain limit value, the drive current width control circuit 2 sends all of the current δ to the drive current width control circuit 2, and the drive current width control circuit 2 reduces the flow of the sea bream. What is the drive current value? The limit value of the current limiting circuit 4 is low when the supply voltage to the limiting zero switching circuit 1 is high, and the limit value is high when the supply voltage is low. Therefore, regardless of whether the supply voltage value is high or low.

Output capacity remains constant.

[Effects of the Invention] As explained above, the present invention has the advantage that ['fej1! Changing the current limit value has the effect of preventing element damage during overload even when the supply voltage value is high.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional switching power supply.

Claims (1)

[Claims] A switching power supply comprising a switching transformer, a drive current width control circuit for the switching transformer, a current limiting circuit that limits the maximum value of the drive current, and a feedback circuit that feeds back an output voltage to the drive current width control circuit, A switching power supply characterized in that the current limiting circuit changes a limiting value according to a voltage supplied to the switching transformer.