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
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 regulator in your schematic. 1K 1K 24V output(top regulator) <----/\/\----o----/\/\----> GND | 12V output(bottom regulator) <---------o -Beau Schwabe
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.
