High voltage limiting , clamping , cut off

[jayc73]

Hi all ,
Looking for some advice on how to limit dc high voltage.

I have some small ic's which are good for 30kv dc.
How would I go about adding a limiting device to protect the circuitry from over voltage ?

Most of the time the ic will be working within 25kv to 28kv but , there may be instances which could exceed 30kv.
I'm looking for some way to protect the circuitry just in case .
Thanks ,
Jay.

 

[betwixt]

More details about these ICs and your application please.

That is an awful lot of voltage for any IC to work with/from so I suspect your answer lies with bullet proofing protection circuit around them. How that can be achieved depends on how the circuit works.

Brian.

 

[D.A.(Tony)Stewart]

I have used 30kV regulated with R dividers from an LM358. What is your concern?

 

[jayc73]

Basically its a voltage divider.
25kv to28 kv dc input - 30kv diode , 30kv 470pf cap , string of resistors and varistor - dropping voltage to 25 to 28v dc output.

Im unsure if the diode and capacitor will take more than 30kv and what is hooked up to the 25 to 28v output is rated to 30v dc maximum.

Jay

 

[jiripolivka]

Handling high voltages around sensitive circuits is difficult. To protect from overvoltage, spark gaps are used. They can be adjusted to break at a specified voltage but they must be enclosed in air-tight enclosures, to avoid moisture and air pressure variations.
Vacuum-enclosed resistors in voltage dividers allow to design good voltage regulators. Again, use a good design that counts with air pressure variation, moisture and dust.

 

[D.A.(Tony)Stewart]

Consider how a scope probe acts as 10:1 divider with R1C1:R2C to get flat response and do the same for 1000:1 divider with equal RC, except C is leakage capacitance of PU conformal coating across R string for moisture protection. Then for small shunt R2, add equivalent C2, which prevents transient feedthru by flat response.

Consider ESL in RC divider network if arc transient occurs at source. (?)

For dust elimination on surface, it must be sealed otherwise air gap cutout on PCB for creepage for each TH Res. in series.

But for Low and high cost Laser printers, there are at least 4 HV outputs at low current some with ramp control to 1% regulation. Look at regulator boards to see how it is done using resonant sine invertor with no EMI and low cost HV feedback all for <20$ in parts

 

[jayc73]

Thanks for the explinations guys but electronics is still very new to me.
To be honest , I don't quite understand some of the terminology used.

Can you please simplify things a little more.
Thanks,
Jay.

 

[D.A.(Tony)Stewart]

Cheap 1/4W 10M resistors are rated for 500V.
Thus you would need alot for 30kV series divider with a R shunt at end.

Otherwise 1kV or higher resistors cost more.

The RC divider concept s described here like scope probes.

I was suggesting a conformal coat of silicone protection would also be like the capacitors. Then the shunt R uses a larger cap to match and get a square wave response but say 1000:1 to 10 k:1 ratio as required.

It can be made small and neat.