mhelin
Well-known member
I've built a 24V LM317 supply for powering two (single stage) BA283 mic pres. It works but gets too hot to touch, the heatsink is a piece of aluminium L-profile which should be enough. So from where is the heat coming from, is the 24V difference too much? AFAIK it's not enough to kill the internal opamp (comparator) which is powered by the voltage difference (so the max. diff is the 36-37V which the same as what most opamps take). Or does the amp have some oscillation somewhere? Or the LM317?
So should I build another LM317 stage for the other channel, or use it as pre-regulator (like 48V -> 36V for the first and 36V -> 24V for the second one). Third option is to parallel the LM317 with another similar one (is it possible?)
Datasheet contains interesting ideas like tracking preregulator (8.3.4) and slow turn-on (8.3.8):
http://www.ti.com/lit/ds/symlink/lm317.pdf
As the input is already regulated I guess a regular 3055 single transistor circuit with a zener or just a resistor divider used for biasing could do the job, right?
The PSU I use is a one for Cisco IP phones from Ebay (380mA output).
http://www.ebay.co.uk/itm/Genuine-CISCO-48V-Mains-AC-DC-Adapter-Power-Supply-for-Cisco-1142N-Aironet-1140-/120994607996
So should I build another LM317 stage for the other channel, or use it as pre-regulator (like 48V -> 36V for the first and 36V -> 24V for the second one). Third option is to parallel the LM317 with another similar one (is it possible?)
Datasheet contains interesting ideas like tracking preregulator (8.3.4) and slow turn-on (8.3.8):
http://www.ti.com/lit/ds/symlink/lm317.pdf
As the input is already regulated I guess a regular 3055 single transistor circuit with a zener or just a resistor divider used for biasing could do the job, right?
The PSU I use is a one for Cisco IP phones from Ebay (380mA output).
http://www.ebay.co.uk/itm/Genuine-CISCO-48V-Mains-AC-DC-Adapter-Power-Supply-for-Cisco-1142N-Aironet-1140-/120994607996