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[SOLVED] Pros & cons of fixed resistor variable VDC bench supply/Op Amp voltage followers?

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d123

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Hi!
Any opinions on the pros and cons/virtues and defects of making a simple DC bench power supply using fixed resistors and a standard linear voltage regulator, with a MOSFET around the regulator to handle the current side of the output, to obtain set voltage outputs ranging from +5 to +15V?
Also - Are general purpose Op Amps used as voltage followers, with a MOSFET to handle the current side of the output, a good way of maintaining a reasonably stable output voltage (to power what obviously would be unknown loads/circuits)?
I'm happy to be re-directed to threads that have escaped my attention which have already answered either question, thanks.
 

crutschow

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Re: Pros & cons of fixed resistor variable VDC bench supply/Op Amp voltage followers?

An op amp plus a power transistor can certainly be used for a bench supply but IC linear regulators, like the common LM317, are simpler to use and typically have a built-in voltage reference, current limit, and over-temperature protection, so that would be my first choice.

The LM317 can have a continuously adjustable voltage output using a pot, or fixed outputs using fixed resistors selected by a rotary switch in the voltage sense (ADJ) loop. (A good option might be to have the switch select a pot for an adjustable output and select fixed resistors for say 3.3V, 5V, and 15V.)

You only need to add a power transistor around an LM317 if you need more than 1.5A, which is usually more than adequate for typical electronic projects.

One important factor when building a linear regulator is the power dissipated in the series linear regulator element, which equals the output current times the difference between the input and output voltages.
This can require a fairly large heat-sink for large currents and low output voltages.
For higher power levels you might consider a fan cooled heat-sink such as those used for PC CPUs.
 
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