how to generate +5V\2ma from a -90V\1A floating dc\dc ...?

[bulerias]

hi,
as wrriten on the subject,i have a dc\dc that supplies -90V,and i need to
supply also +5V\2mA,on the same ground.
i thought on linear regulator,to save space & money...but how should i connect the ground between the -90 and the +5V...? (THEY MUST BE ON THE SAME GROUND !!!)...?
THANKS
Bull

can someone upload a circuit...?
(i know its a big request)

 

[padspcb]

Use a transformer !

Well i think the simplest way is by using a transformer.
U may use a Viper series per example running on 150KHz to drive
the primary.
Also it may be auto regulated by the supply winding or by an optocoupler tied to the output.
At such "high" frequencies, the transformer is realy small, and even an e20 can do the job (10w)
Get more info on ST site, i think the Viper22 is realy cute:
The VIPer12A / 22A is an integrated PWM + MOSFET diffused in the same chip thanks to VIPower technology and is able to address low power applications delivering up to 12W in a wide range of condition (85-265VAC).
**broken link removed**

 

[techie]

Following is a method to generate a -ve supply from a +ive. With some changes, it can generate a positive supply from a negative one. I think just reversing diode & cap polarity and putting -12v in place of GND and GND in place of +V will generate a +V for you.
You obviously need an oscillator source. But it can be either had from any existing clock avaialable in the system or by making an oscillator out of invertors.