Join Date: Aug 2010
Location: Surrounded by glass, no really my room is full of tubes
interesting three terminal high voltage device
I figured it was possible to build something resembling the internals of an LM317 for regulating voltages up to about 400V
See the attached schematic for what i've breadboarded, ive used a LM385-1.2 reference because it allows operation down to 10uA keeping adjust pin current relatively low. The opamp is a MC34071 because its rail to rail, feeding into a LH0002 buffer to isolate the opamp from the capacative load. The MC34071 is rated for about 10.000pF of capacative load, however this buffer allows swapping to better opamps that might not be capable of driving capacative loads.
The device uses an 10V auxillary voltage in its current configuration, this has the benefit of keeping minimum output current requirements low, so the output divider resistors can be larger in value. the downside is of course increased complexity.
I havent used any output capacitance in my prototype, however with the transistor current limiter as drawn oscillation occurs when the current limit is reached. My question is: Would an RC damper on the input of the LH0002 solve this, or should i add some capacitance on the output and try again?