DIY ESD gun?

[nctnico]

I may need to make a design (based on an ARM SoC) of mine less susceptible to ESD events. In order to do that I'd like to be able to test this in my own lab instead of driving up and down to an certification lab. I'm thinking about putting together something with a transformer from a backlight inverter. This interesting part is how to measure the output pulses so I have an idea on what to send into the transformer.

Has anyone already pursuid a project like this? Any suggestions?

[zapta]

I have not experience with ESD guns but it looks that charging a known capacitor with know voltage and then discharging it on your circuit will give you consistent results.

[HackedFridgeMagnet]

Maybe I don't understand the question.

Cant you just use a resistor divider into an a2d?

Or a hv probe into your oscilloscope.

http://www.home.agilent.com/en/pd-1938466-pn-N2771B/high-voltage-probe-10001-30-kv-50-mhz

I have used a pulse generator that was made from an automotive ignition coil. No feedback, no measuring but it has a spark.
... and it hurts.

[TerraHertz]

When I was working designing poker machine electronics, we had a similar problem.

The human body model is a standard, see http://en.wikipedia.org/wiki/Human-body_model
That doesn't specify a voltage. The commercial testers allow discharge voltage to be set at various levels, typically up to many KV. It's meant to simulate the charge a human can pick up in typical environments, like walking across a thick carpet in dry air.

However we didn't have to just deal with the 'human body model' ESD. Some gamblers like to see if they can crash the machines using piezo spark lighters, and other improvised sparky things. So we needed to design to the 'human bastard model'.

Here are some pics of the improvised ESD torture rig I made. There was an adjustable zero to 10KV supply, that could be configured for positive or negative output relative to ground.
That was connected to the insulated post at the corner of this device. It would charge up a 1000pF 10KV rated ceramic disk capacitor via the 4 Meg ohm resistor. From the capacitor there's an adjustable spark gap. The other side of the spark gap can be jumpered to the earth, active or neutral mains input of the equipment, or via a flying lead and an insulating rod handle, held close to parts of the machine chassis, so the spike would arc to the case.

The big yellow toroids are to block the spike from going back up the mains source. Actually they turned out to not be able to withstand the voltage, and would arc across the windings. So on the commonly used one (earth) I added another ferrite with better insulated wire wound through it.  (One lead of this yellow torrid is broken off its solder lug in the photos.)

The metal baseplate is a sort of ground plane - it's the other side of the HV disk capacitor, inductively shorted to mains ground, and could be given varying degrees of coupling to parts of the EUT chassis.

If you make something as death-trappy as this, be sure to have lots of warning signs when in use. And disconnect from mains when you're not actually using it.

Edit: Oh, I forgot to mention. We got a big sheet of galvanized iron sheet, about 3m x 3m, and used that as a reference plane for those zapping experiments. We'd mount the zapper with its 'ground' in contact with the sheet, and the poker machine standing on insulators on the metal sheet. All the better to kill it.
We did get the machine to the point where it could survive that treatment without a glitch. Mostly by having the processor in an inner metal box, with all IO fully opto-isolated. And very, very careful separation of dirty and clean ground planes.

[AndyC_772]

design to the 'human bastard model'.

 

[nctnico]

Thanks for the ideas so far (especially to TerraHertz for the long post with pictures). I just got a call and it seems my time table has been pushed forward so no more time for tinkering  I think I'll use a piezo gas lighter for now.

Edit: I went shopping and bought a gas lighter which runs on an AA battery. Inside there is a small PCB with some transistors and a HV transformer. No piezo despite the text on the packaging. I got rid of the metal shell and connected a ground wire to it. Actually it works pretty well. My old & trusty HP6002A power supply got quite upset when I started zapping the DUT.

[DaveW]

I started off using a lighter as well but found I needed a bit more voltage & power, so I bought a antistatic gun for records (http://www.amazon.co.uk/gp/product/B0033SHDSS/ref=oh_details_o06_s00_i00?ie=UTF8&psc=1)

That particular model can have a ground lead added using just a ring terminal placed under a screw inside the case, drill a small hole for the wire to get out and all done; a nice bit of kit