reading external high voltages

[doec]

Hi all,
I need help to read two external voltage (about 150V DC) and their difference (ranging from 1 to 5V) from inside an IC (0.35u CMOS process).
In order to not to damage internal circuitry, I would like to make an indirect reading. Do you have some advice?
Thank you,
doec

 

[barry]

I guess the obvious answer would be to use a voltage divider. When you say 'indirect' do you mean you want an external ADC? I'm not sure what you're looking for. What difference does the process matter?

 

[leo_o2]

I agree on voltage divider. Simply way is a divider with two resistors. However, the high frequency characteristic will not be good.

 

[doec]

I had already taken into account the voltage divider.
I wanted to see if any solutions with zener diodes or other proposals could work well for me.
The process has been specified only to emphasize that I can't go directly inside the circuit with the high voltage.
Thank you for your response,
doec

 

[nandhu015]

what about a step down transformer which indeed provide isolation and stepdown

 

[Raza]

what about a step down transformer which indeed provide isolation and stepdown

He is asking to read DC volts, and as I know transformers do not work on DC. If I am wrong please alert me.