# Circuit help: switching a load only at peak of AC mains

Discussion in 'Electronic Basics' started by JB, Sep 17, 2013.

1. ### JBGuest

I have a series of measurements to make of the inrush current of a range of
LED drivers and electronic ballasts. Is there a simple way of ensuring that
the load is always switched on at the peak of the mains cycle? I'll probably
use a substantial relay or thyristor to do the actual switching. This is for
a single phase 230V 50Hz supply.
I have done zero crossing triggers for switching loads but never peak! My
Google mojo seems to have deserted me on this one. Any help much
appreciated.
JB

2. ### Phil AllisonGuest

"JB"
** Well, a zero crossing detector followed by a 5 m/S delay will do it.

I know someone with exactly the same task as yours and he used a PIC
programmed to get both zero and peak switching of a triac - which he also
bypassed with a hefty relay operated simultaneously to eliminate glitches
associated with some of the loads encountered.

.... Phil

3. ### petrus bitbyterGuest

Can it be that difficult to make a 90 degrees shifted sine and switch on the
zero crossing of it?

petrus bitbyter

4. ### George CorneliusGuest

Timing it is easy. But if it is part of a regulation scheme the thyristor
will also have be capable of being turned off while carrying full current.
What's the term for this - commutation?

Or is this a problem of designing a solid state relay that remains on for
one or more cycles, one where it is allowed for the thyristor to turn off
on its own at the next zero crossing following the arrival of the "off"
signal?

George

5. ### Daniel PittsGuest

Can you just give it the right voltage as a DC pulse to perform your
measurements? That seems like an easier task to me.

6. ### Daniel PittsGuest

Can you just give it the right voltage as a DC pulse to perform your
measurements? That seems like an easier task to me.

7. ### Phil AllisonGuest

"Daniel is the Pitts"

** So stupid, it's actually funny.

.... Phil

8. ### petrus bitbyterGuest

The OP only asks for switching on so far. There are dozens of SSRs for sale
designed for switching on at zero crossing. So you use the shifted sine to
switch on the not-shifted. As for switching off GTO devices can be
considered. Common SSRs switch off at the zero crossing of the load current.

petrus bitbyter

9. ### Phil AllisonGuest

"petrus bitbyter"
** The loads being considered are essentially off line switchers (
PS ) - so the current draw falls to near zero just after each AC voltage
peak, requiring the SSR to be re-triggered every half cycle at the next
peak.

Or, just drive the LED on continually until you want the SSR it to
commutate off.

..... Phil

10. ### Daniel PittsGuest

Why don't you enlighten rather than belittle?
You are? Well, I'll try not to laugh at you.

If the OP needs to make a measurement of the inrush current on the LED
drivers and ballasts, why not simulate the conditions the easiest way
possible?

11. ### Phil AllisonGuest

"Daniel Pitts" = "Daniel is the Pitts"

** No-one can teach a pig to sing.

And you are another PITA fucking troll.

Piss off.

12. ### Daniel PittsGuest

Lol, I think you were looking in a mirror and saw the troll.

*plonk*

13. ### Phil AllisonGuest

"Daniel Pitts" = "Daniel is the Pitts"

** **** you - pig brain.

14. ### Jasen BettsGuest

use a dimmer and adjust it while observing?