DC - DC Volage regulator

[scbaumli]

I'm looking to find a way to go from 0-650 VDC to 0-120VDC, 20mA. I wish that when the input voltage is 0-120 then the output voltage is te same and anything over that stays at 120VDC. Right now I have resistors in series along with the loads in series, which works, but then the load won't come on until I reach 300VDC minimum and would like for the load to turn on at about 50VDC.
What could I do in this situation?
Your help in this matter is greatly appreciated!

 

[jbartos]

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