How it works?

beenthere

Joined Apr 20, 2004
15,819
If you read the data sheet for a 78xx regulator, you would know, too.

The regulator is limited to 1 amp current (that is the usual limit for TO-220 packaged regulators). In order for more regulated current to pass, an external transistor has to do the work. That is Q1. R1 makes a small voltage drop so the 78xx IC can control base current in Q1.
 

SgtWookie

Joined Jul 17, 2007
22,210
Nice explanation, Beenthere - I could practically swear you acquired your knowledge in an environment similar to mine... ;) But then again, I might swear anyway :rolleyes:
 
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