Circuit Design Help

[golfmonke]

Well I found the datasheet for a quality SSR, not the cheap junk i'm using, but i'll start there.

Says maximum turn on/turn off time is 100us

**broken link removed**

 

[rjenkinsgb]

The switching time of one make of the one you show (SSR-40DD) is rated as being up to ten milliseconds.
**broken link removed**

I'd allow somewhat over 10mS from switching one off to switching the other on, just to be safe.

 

[golfmonke]

Well, then that's not gonna work, hmmm, guess i'm gonna be buying the more expensive ones

 

[golfmonke]

Could I use some mosfet gate driver ic's to reduce my dead time down into the ns range?

I've been looking through mouser, can't seem to find one that will handle 8A, 30V and have ns fall/rise time.

 

[alec_t]

Built-in dead-time of mosfet gate driver ic's of which I'm aware is typically ~1uS. Big power FETs might need more than that.

 

[golfmonke]

https://www.ti.com/product/UCC5390

I did find this one, that appears like it might work.

Maybe I'm not looking at the right type, or reading the spec sheet correctly....

Low us dead time should be good enough... of course I won't know till I can test a working circuit....

Low us values would be much better than 10ms.

I'm going to test the 10ms as well, even that may be good enough, but would like to get the signal as close as possible.

What's most important is consistency, it needs to do the same thing every time, even if the exact signal isn't duplicated 100% and the device still operates close to normally of course.

 

[alec_t]

Maybe if you told us what the switched supplies are going to be used for we could offer more relevant help?

 

[golfmonke]

Maybe if you told us what the switched supplies are going to be used for we could offer more relevant help?

I've already received and continue to receive very relevant help! Including how to properly measure my circuit without shorting it with my multimeter, lol.

ronsimpson posted a very detailed circuit (post #4), and I appreciate that. However , while I could probably hook it up and get it working, I wouldn't really understand it, and if I needed to troubleshoot or tweak it, i'd be out of luck, given my level of electronics knowledge. (piss poor)

So, i'm looking for some higher level components to create the circuit. So far it seems I can use some higher quality SSR's and reduce my time between signals down to about 100us.

Now i'm trying to see if I can reduce that even further by using some mosfet gate driver ic's, which so far seem like they may reduce the dead time down to the low XXus level. That may not do much, but doesn't seem that expensive to give it a shot. I'm trying to drive a mechanical device i'm assuming that difference won't mean much. But the difference between the 10ms and the 100us SSR dead times probably will have a huge effect.

I have some of these N channel mosfets on hand.

https://www.mouser.com/datasheet/2/308/rfp30n06le-1195941.pdf

and some of these P channel mosfets on hand.

https://www.sparkfun.com/datasheets/Components/General/FQP27P06.pdf

(also have some beefy heatsinks that I can use to cool them)

which seem to indicate ~100ns to ~400ns turnon/off time.

Now trying to drive them with some higher level components. It's my current understanding, those devices would be mosfet gate driver ic's. Trying to find out if that is correct/and if any even exist for my amp and dead time needs (a lot less than the 100us that I can achieve by just using higher quality SSR's)

Don't want to blindly waste time/money on things that won't even produce the circuit/signal that much better than just using some higher quality SSR's with 100us dead time.

... what the switched supplies are going to be used for ....

Maybe i'm not describing it properly, but I hooked up a scope to a fully functional device and found the signal i'm trying to reproduce. It alternates between +30v and -5V, it is -5V for .8ms followed (what seems like immediately... but I only get a good signal on limited time/division settings due to my crappy oscilloscope) by +30V for .2ms, then 0V for ~79ms and it repeats.