Need help with DC to DC converter to produce -70V

[nitish111]

Hi there,

I am working on bipolar current source using improved Howland Current source which can sink up to 15 mA with supply voltage of +70 V to -70 V or more. I was able to generate +70 V with required current parameter. I need help with -70 V. I am looking for a off the shelf components with required  specs for negative rail. I found LT3462 which could generate up to -40 V. I am a beginner so any intuitions and suggestions are highly appreciated.

[Zero999]

What's the input voltage to the whole circuit?

[nitish111]

Input voltage is 5 V DC