Micro-EDM spark generator

Thread Starter

hrs

Joined Jun 13, 2014
414
Hi,

I want to make a micro-EDM spark generator, if doable.

Preliminary specs:
Strike voltage ~100V. Maybe +/- 10V adjustable with jumper or pot.
2kHz to 10kHz pulse frequency, programmable from MCU.
Current limit 2A to 8A, programmable from MCU. 10% tolerance (random number. It doesn't need to be super accurate).
25V ~ 35V output voltage, controlled by moving electrode in or out.

Implementation specific stuff:
Power supply from a 300VA transformer 220VAC to 42VDC rectified.
Strike voltage using step-up transformer or some other means?
Current limited LM25085 or some other buck converter.

Work piece needs to be on the high side, electrode on the low side.
Earth ground to high side and enclodure? Make high side common? I also need 5V for the MCU.

The application note uses an LM321 to sense current. Is that acceptable here somehow or should that be an inamp instead?
Can we use the internal comparator(ADJ, ISEN) to set the current limit from the MCU?

Attached is a picture with the general idea. It's taken from an LM25085 app note with some of my additions in red. Surely there's a ton of things wrong with it and missing circuitry for propper sensing and setting etc, but do you think that this is a direction that could work?

LM25085 datasheet
https://www.ti.com/lit/ds/symlink/lm25085.pdf
LM25085 current controlled application note
https://www.ti.com/lit/an/snva486a/snva486a.pdf
 

Attachments

Thread Starter

hrs

Joined Jun 13, 2014
414
I haven't seen that particular one but it looks like an RC type but I'll give it a read.
What I would like to explore is something with more control over the spark.
 

Thread Starter

hrs

Joined Jun 13, 2014
414
Would this work to set a current limit? Also, if you want to sense at the load and not at the high side, do you then need a 42V inamp?
[edit] Image attached.
 

Attachments

Top