[Moderator's note: This post was moved to start a new thread]

by the way, if I want to get a controlled voltage out V2(-70 to -120V, 3-5mA) floated on V1 (~20V), beside using isolated DC-DC and isolate op-amp for input control, any other good and cheap idea to achieve it ?




thanks

 

Let's get some terms straight. Floating usually means some form of galvanic isolation. For example, you float an oscilloscope by removing the connection between its chassis and earth ground. If you want one power supply to be stacked on top of another, that certainly is possible, but it is not floating in the traditional sense because there must be a direct connection between the two supplies to maintain the stacking. Your drawing shows this.

It also shows V2 as being positive with respect to V1, but your text ways -70 V to -120 V. A -70 V supply referenced to a +20 V supply would be making -50 V with respect to the system GND. Is this what you want, or do you want the combined output to be +90 V?

ak

 

Hmm, I want go a -70v (V2) with regards to V1( 20V)... V2 is 70V lower than V1... if V1 changed, the -70V potenial is not changed between V1 and V2...

thanks