Simple Variable Voltage Current Power Supply Circuit Using a Single FET

Wednesday, September 24, 2014

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For many applications the requirements are not that stringent and a simple, discretely constructed regulator as described here will suffice.
The current limiting components can then be left out.
With values as shown, the output I voltage is 12V and the output current is limited to 0.5 A. For applications not requiring current limiting the circuit can supply up to 1 A.
The relation between input voltage, load resistance and regulated output voltage is shown in table 1.
This table can therefore be used to determine whether the regulation for a particular application is sufficient. The ’heart’ of the regulator, high power low-frequency transistor T1, l must be fitted onto an adequate heatsink. FET T3 operates as a current source with an output 3, maximum of 11 . . . 18 mA: this it limits the base current of T1, of course, but the alternative would have been a very low value resistor; ‘ or this would have resulted in large!
The cost of high grade, regulated power supplies has dropped with the advent of modern lCs.