To Generate 12 V from 100-200V Supply

[tahoka]

I want to make a circuit which generates 12 volt when input is 100 volts DC minimum and the o/p should remain constant 12V for maximum input of 200 Volts.
Using 7812 how do i step down the input voltage within permissible values.
Please need urgent help.

[Al_The_Man]

200v is too high for the 7812, How much current is the 12v intent supplying?
I recently had to supply 12v electronic circuit on a 240vdc generator and I used a 1N4742 12v zener with a 7.5k 20w resistor and a 100µf cap across the zener.
The value of the resistor will depend on the max current you wish to draw.
This has been running continuously for several months now.
Al.

[Mariss Freimanis]

If less than 20mA is needed use an n-channel MOSFET preregulator in front of your 78L12. Drain to +200V, 100K resistor from drain to gate, source to 78L12 input and a 6V zener anode to 78L12 output, cathode to MOSFET gate. A reverse biased base to emitter junction of any small-signal bipolar transistor makes for a dandy 6.2V zener.

If more than 20mA is needed, a buck type switching regulator is the only choice.

Mariss

[tahoka]

thank you for your help.