Hi all,

Someone suggested that you can use a negative voltage to offset the dropout voltage of an LDO. I have never used this method so I was thinking of trying it out (see TR1 and TR2 in schem attached). The idea is to use (5K ohm?) trimmers to trim the outputs to zero volts, then adjust normally via VR1 and VR2 for regular use. Thoughts?

Also should I keep C9 and C10 connected to GND or their respective offset rails?

Thanks!

 

Below is the LTspice sim of a dual tracking output supply you might want to consider:

It uses an added LM337 (U3) negative regulator (can be in a small plastic package since it only outputs about 10mA) to provide a stable -1.24V reference so both outputs can go to zero volts.

Pot U5 adjusts both (tracking) plus and minus voltages, while pot U2 changes the relative output voltages, so one output can be different from the other if desired.

You can add the protective diodes and ADJ pin filtering, which are not shown here.

 

Ooooh that's a nice little gem for the ol' notebook. Thanks! I have been teaching myself more about precise analog instrumentation circuits so I am preparing a nice little dual polarity-power supply (that wont take up the whole bench like my very very old BK Precision triple output PSU).