06-04-2012, 11:59 PM
Using an LM317, you might find that a silicon diode between ADJ and ground gets you to 2V. Well, if you had one that dropped 0.75V at 5mA. The 5mA is set by the recommended 240 ohm resistor between OUT and ADJ, but can be varied considerably, and you might be lucky enough to have a sensible diode that has a slightly higher than normal Vf at modest currents...
Personally, I'd be wary about a single LM317T - presumably the valves will take somewhat more during the first few seconds of operation? Heat sinking might be a pain as well. The die in an LM317T isn't able to run as hot as a power transistor. All of this paragraph is building up to reinforcing Joe's last two words on the subject
Tempting to add an SCR crowbar if those valves are valuable/rare.
All the best,
Mark
Personally, I'd be wary about a single LM317T - presumably the valves will take somewhat more during the first few seconds of operation? Heat sinking might be a pain as well. The die in an LM317T isn't able to run as hot as a power transistor. All of this paragraph is building up to reinforcing Joe's last two words on the subject
Tempting to add an SCR crowbar if those valves are valuable/rare.
All the best,
Mark
