# would this work?

Discussion in 'Electronic Basics' started by Dan, Feb 3, 2004.

1. ### DanGuest

hi,
I need to regulate a dc voltage to +24V.

Would this work? the ICs are LM2937IMP-12 from National
Input voltage say 25-30 volts but coming from an unregulated power supply.

____
| |
o------------o------|2937|-----o-------------------------o
| |____| |
--- | ---
--- | ---
| | |
'--------+--------'
|
| ____
| | |
+---------------|2937|---------¬
--- |____| |
--- | ---
| | ---
| | |
| | |
| | |
| | |
o---------------------o-----------------+------------o---o
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

thanks,
Daniele Malleo

2. ### Beau SchwabeGuest

I have done this before with stacking two 5V regulators from a 12V
power source to supply a +5/-5 without any problems, however I would
preload the regulators with a voltage divider. Especially the lower

1K 1K
24V output(top regulator) <----/\/\----o----/\/\----> GND
|
12V output(bottom regulator) <---------o

-Beau Schwabe

3. ### John PopelishGuest

You are onto an idea that can work, but you don't have the connections
quite right. Both regulators need to have the unregulated voltage
applied to their inputs, but the output of one has to be connected to
the reference terminal (the one normally grounded) to elevate its
reference to 12 volts. You should also load the 12 volt output to
ground with a resistor to make sure it always has some minimum load
(see the data sheet). Be warned that this method may screw up the
current limit and have other problems during start up and shut down
when voltages may be momentarily reversed. Finding a single 24 volt
regulator (or an adjustable that can be set to 24 volts) is probably
simpler. Low drop out regulators are harder to set up as adjustable
units because of the variable current that passes through the
reference pin as output load current changes.