TI 79M20C replacement

[giosif]

Hi,

I am trying to find a replacement for a suspected bad -20V voltage regulator - the logo seems to be that of TI and the marking says 79M20C.
I've searched over the net but, excepting AliExpress, I couldn't find anything similar.
Anyone has any suggestions where I could find a replacement for this, TI or non-TI?

Thanks!

[Ian.M]

79M20 regulators do seem to be somewhat rare.  For 78/79xx series regulators M in the middle codes 500mA current rating (as opposed to L for 100mA, no letter for 1A and S for 2A) so unless you need the same current limit as the original, you can substitute a 7920 regulator in a compatible package.  Otherwise use a 79M15 regulator + a 5.1V Zener in series with its GND leg, anode to the regulator.

[giosif]

Thank you for the detailed response!
Interesting suggestion with the -15V regulator + the 5.1 Zener.
One question on it, though: wouldn't the Zener need to sustain a 500mA reverse current?

[Ian.M]

No. it only has to handle the 79xx GND leg current which is typically between 1mA and 10mA over the whole load current range.  Check your specific regulator manufacturer's datasheet to confirm the GND leg current will keep the Zener at an appropriate point in it's Ir/Vr characteristic.

Another option would be a LM337, with the ADJ pin lifted so you can insert a potential divider between the output and ground to set it to -20V.  The other two pins and the tag are compatible.  However that has an even higher current limit: 1.5A

[giosif]

Ah, ok. Would that be the inbut bias current figure for the voltage regulator?

I am aware of the adjustable regulators, but I wanted to avoid that route, if possible.

[giosif]

+-18V is a more available voltage (78X18, 79X18). Will your schematics work at 18V?

Really don't know.
This is for a dead meter (Solartron 7060).

In any case, I went ahead and bought both a -15V voltage regulator + a few types of 5.1V Zener diodes, but also a 7920, in case the first combination proves a challenge.