Dual Supply for Low Power but Sensitive Circuit

[jean-paul]

Just a quick reply and some old school info: when 79xx ( the negative version ) regs are not loaded sufficiently they will exhibit strange behaviour. If you want the device to be reliable just load the negative reg with a resistor in series with a "power-on" LED to make sure enough current is drawn from the reg for it to function correctly.

 

[DigitalJunkie]

Just a quick reply and some old school info: when 79xx ( the negative version ) regs are not loaded sufficiently they will exhibit strange behaviour. If you want the device to be reliable just load the negative reg with a resistor in series with a "power-on" LED to make sure enough current is drawn from the reg for it to function correctly.

Good idea,it wouldn't hurt to put one on each regulator,just to provide a bit of a minimum load.

 

[wg_ski]

Good idea,it wouldn't hurt to put one on each regulator,just to provide a bit of a minimum load.

Actually, you need to put it on the - side only. It's a start-up problem with the negative reg if the current is drawn directly from + to -. Having a bit of extra current to gnd on the - side insures that it starts up normally.

 

[star882]

You can cascade regulators to increase the PSRR.