T&L Publications

Can anyone point me to a circuit for the above? I want to get switching mode efficiency, but also variable output voltage. Thanks.

Hi there,


Check out National Semiconductors 'Simple Switcher" line of switching
regulators. These are normally used with two fixed resistors, but if
you make the 'top' resistor a variable pot you get an adjustable output.

I've done this already and it seems to work pretty well.
You just need to size the inductor for your required max ripple
at all output voltages. Note however that you probably should NOT
make the 'bottom' resistor variable, but keep that fixed.

I don't know if you are hoping to build the circuit yourself...
If you are just looking for a variable switching regulator, DimensionEngineering makes two: the AnyVolt Micro Universal DC-DC Converter, which can regulate up or down, and can source 0.5A, and the 10W Step down adjustable switching regulator, which can regulate only to a lower voltage, and can source 1A.
Both are pin-compatible with the 78xx family of linear regulators, and adjust by a built-in screw pot.

Thanks for the pointers. I'm just getting back into hobby building after many years away. Built a 317 based variable bench suppy many years ago and thought it would be a useful 'return' project to do something similar, but with based on modern approaches.

Thanks again for the links, I'm sure I'll have many more questions as I get back up to current practice.