Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1432
| Posted: 02:11pm 21 Oct 2017 |
HI Warp, I only just saw your recent reply (above)
I approach the current limit problem differently.
I am OK with high current that lasts for a few cycles.
I know and have seen very high current during the load switch-on events.
These peaks exist for fractions of a 50Hz half cycle. I am OK with these too.
I let the DC supply fuse/CB do their job.
I let the fact that I have 3 x 210 Amp mosfets look after transients that
are about 200A max (thanks to ESR of the transformer primary, choke, Rds-on etc)
mean it will survive. Exact or correct numbers are not my speciality.
My rationale is:
do I want to interrupt things during the very high peak current incident?
If so, how and will it cause more issues? I think I don’t want to go there.
My view is let it go and choose mosfets good for large peak current.
Also try to mitigate the parasitics.
And let short term problems pass.
This ends up requiring huge over sized H bridge inverter designs feeding loads that
rarely exceed 1500W. I’m aware this is a brute force method but I am a lazy hacker.
You are an electronic/electrical designer.
So the way I use the EGS002 boards is to disable all current feedback and disconnect
the gate drive shutdown pins from the rest of the board (by cutting the trace).
I control on/off via the Tfb pin only.
I’m happy with this.
When first playing with the ESG002 based inverter board I looked at the two current limit sub systems. One was used to interrupt gate drive via output of a comparitor taking the fast changing DC current. Another circuit was using a low pass filtered sample of the DC current and again stopping PWM output, this time via the EG8010 only.
During testing on the bench, using small AC loads up to 500W, and adjusting the high current limits, I nearly had the toroid jumping up and down on the table top from the sudden disabling, then reenabling of gate drive.
It just didn’t seem right.
These sudden power impulses appeared to me to be something to avoid.
Again I say, we will get large current impulses from motor start up, switch-on of lighting, switch-on of SMPS driven appliances, etc.
The last thing I want to do is interfere right when the current is as it’s maximum.
wronger than a phone book full of wrong phone numbers