Another step up circuit request:

[dkace]

Hi,
If someone follows my posts, he will find out that I have several posts on steping up from 5V to 350V etc.
Now I have this urgent problem:
Suppose I have DC current of 5V. I want to step up to 5000V and 4mA.
Can someone give specific instractions, step-by-step ( I mean ICs, design considerations etc) how to go from dc to AC, then transform it to 5000V and make it 4mA?
Thanks,
D.

 

[IanP]

First stage will be a square wave generator. It can be based on 555 IC. As you need 20W (5000V * 4mA) of power it will be unable to drive next stage by itself.
So you need a transistor (can be BLT or FET) to drive a HV transformer which will convert 5V square wave on primary to 5000 on secondary. Here you can use an off-the shelf TV HV transformer.
The 555 generator's frequency has to be somewhere around 15kHz ..

 

[dkace]

Thanks IanP, your post was very helpfull.
I have another question now. You suggest a 555 for the waveform. I agree that this is the easiest selection of a squarewave generator. Now, if I want minimum frequency drift I think that 555 is not so good, as it dependend on the external RC circuitry witch has a 5 to 10% tolerance.
In a previous post
(h**p://&highlight=)
I was asking if that circuit could work as an astable multivibrator instead of a 555. In fact it is a circuit I copied from a real board and it is actually working- I could never make it work in simulation.
My question is : Instead of using the 555 ( which I may finally do ) Is it possible to use a schmidt trigger and have reliable results at the end?
D.

 

[IanP]

You can use an opamp in Schmidt-trigger configuration (**broken link removed**) or single Schmidt-Trigger gate with a resistor between output and input and a capacitor between input and 0V. Both options will generate a square wave but the easiest is still 555 ..