Hi guys, Doing a simple circuit.
V(+)------+------+
20-30V _ | ^ LED|\| +----|+\ | | >-+--out R +-|-/ | | | |/| | | +---)--+ GND | VminusThe LED is a GaP one that avalanches at ~25V* R is 100k I need V minus to be 3 or so volts below ground. (V+ to the opamp will get the usual 0.1 bypass cap and some R between it and the led.)
I thought I'd power it from a Phihong 48 volt wall wart. With a LM317HV for the 20-30 (+Vminus) side. I first drew it up with another lm317 to make the ground above Vminus. Duh... it can't sink any current. An LM337HV would work.. but it looks to "be no more".
Any ideas for making my ground? At the moment I'm thinking I could just use another opamp. (a dual opamp is easy.)
George H.
*So the LED is an AND114R, I ordered some other GaP LEDs from the same company to see if I could get them to break down. There's these AND113R's that have very similar specs. (same wavelength 700nm but a bit more light output.) I cranked 'em up to 50V... no breakdown, another supply, 100V.. no breakdown, another supply... finally at ~125 V the AND113R's avalanched. The avalanche was also photosensitive. maybe more so... But 125V is way too scary! And WTF is going on in the AND114r's?