Increasing Regulator
Current
Notes:
Although the 78xx series of
voltage regulators are available with different current outputs, you can boost the
available current output with this circuit. A power transistor is used to
supply extra current to the load the regulator, maintaining a constant
voltage. Currents up to 650mA will flow through the regulator, above this
value and the power transistor will start to conduct, supplying the extra
current to the load. This should
be on an adequate heat sink
as it is likely to get rather hot. Suppose you use a 12v regulator, 7812. The input
voltage should be a few volts higher to allow for voltage drops. Assume 20
volts. Lets also assume
that the load will draw
5amps. The power dissipation in the transistor will be Vce
* Ic or (20-12)*8=40watt. It may
keep you warm in the Winter, but you will need a large
heatsink with good thermal dissipation. If you
want to increase the output current with a negative regulator, such as the 79xx
series, then the circuit is similar, but an NPN type power
transistor is used instead.
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