I built this:-
Works as expected but for thermal runaway at 20mA... I used a medium power PNP that can dissipate 600mW (ish)..
24 * .02mA = 480mW so I wasn't surprised with the thermal drift.... I have since replaced the PNP with a high power darlington, but at 20mA there is still some thermal drift... What would stabilize the PNP??? A heat sink didn't work.. The slightest temperature change seems to matter a great deal... The 5.6V out of the LM337 is solid!! Running at 12v is perfectly okay...
Works as expected but for thermal runaway at 20mA... I used a medium power PNP that can dissipate 600mW (ish)..
24 * .02mA = 480mW so I wasn't surprised with the thermal drift.... I have since replaced the PNP with a high power darlington, but at 20mA there is still some thermal drift... What would stabilize the PNP??? A heat sink didn't work.. The slightest temperature change seems to matter a great deal... The 5.6V out of the LM337 is solid!! Running at 12v is perfectly okay...