Soft Start For Switching Power Supply

The output voltage from the input voltage is an interesting property is appreciably lower switching power supply: It's produced by the current is smaller than the output current. However, input power (UI), of course, is higher than the output power. On the switch when low input voltage is too low, the regulator try to draw full current will need to be looked at another aspect.

Supply can not cope with it, if it fails or the fuse blows. It (On / Off by input) switch to disable the regulator reduced, so is advisable. Related capacitor is charged until. If the regulator starts to draw current, charging current overload voltage source which is not already on a level declined.

Soft Start For Switching Power Supply Circuit Diagram:

Power Supply Circuit Diagram

The circuit in the diagram provides an output voltage of 5 V and is supplied by a 24 V source. The regulator need not be disabled until the capacitor is fully charged: when the potential across the capacitor has reached a level of half or more of the input voltage, all is well. This is why the zener diode in the diagram is rated at 15 V. Many regulators produced by National Semiconductor have an integral on/off switch, and this is used in the present circuit.

The input is intended for TTL signals, and usually consists of a transistor whose base is accessible externally. This means that a higher switching voltage may be applied via a series resistor: the value of this in the present circuit is 22 kΩ. When the voltage across the capacitor reaches a level of about 17 V, transistor T1 comes on, whereupon the regulator is enabled.

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