7824 Single Power Supply 25V 2A with IC 7824 and TIP2955

Advertisements

This circuit uses a PNP Power Transistor TIP2955, you can use any other according to your current and voltage requirement. Look at R2 a 10 Ohm resistor, when the current in your load to the power supply is less than 70mA the voltage across R2 is less than 10E * 70mA = 700mV right.

Click to view circuit and read more

The base emitter junction of Q1 will be biased or turned on around 700mV, less than 700mV the transistor just does nothing. When the current in your load goes over 70mA the voltage across R2 goes above 700mV and a small base current Ib flows from emitter to base of Q1 turning on the transistor. Now a collector current Ic flows from emitter to collector and then to your load supplying the excess demand. The Ic = Ib * hfe where hfe or beta is the DC gain value.

Source:
http://schematics.blogspot.com/2004/10/single-power-supply.html

This entry was posted on Wednesday, September 5th, 2007 at 10:13 pm and is filed under Power supply. You can follow any responses to this entry through the RSS 2.0 feed.