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
** 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.
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?
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.
** 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.
On Thu, 19 Sep 2013 04:13:48 -0500, John Fields Gave us:
I recently finished my 2 year "Last Great Desktop PC" build of what I consider to be my last PC.
The gold series power supply was turned off at the hard switch, so I could change a couple of SATA cable locations and add a drive.
When I turned the supply back on at the hard switch (still no PC rails enabled) the only rail that is supposed to come up is the +5 volt standby rail. But when I turned it on, I heard it audibly pop. I am familiar with this sound, as I used to design and manufacture HV power supplies in my recent past, and I knew that the switch was closed when the AC line was at its peak. I thought 'That didn't sound good... I hope everything is OK.'
Well, much to my dismay, the system would not start. I immediately suspected the supply, and removing the main connector on the MOBO and placing it on a PC Supply Tester thingy I bought a couple years ago and it was showing one of the 12Volt rails down. So I set up an RMA with the maker, and explain things, and they send me a new supply before I even get them the old one back. Hooking the new supply up to the tester shows the same problem. Then, I notice that I had not ALSO connected the VGA connector to this tester. When I do that, both supplies show good.
They want me to send it to them anyway, so I do, But I also state that if the supply is OK that likely means that the problem is the mobo. Sure enough, the new PS does not start the system, and the mobo still shows the same error. So they RMA that item. They sent me the replacement so I only need to put that back in.
Talk about a PITA though! Not the service they gave. just the logistical facts of it all. I had to ship things from work. I had to take apart a machine that started out working, and now I have to re-assemble it again. I sure hope they did not somehow zap the CPU. That alone was $600. That comes out to $100 for each core. Their supply design should not do that though, and the pulse could only have come down through the +5V standby rail as far as I can see.
The MOBO or the supply has some things which should have been incorporated into their design to quell any such behavior. Power supplies should not surge on the odd high line, high peak start scenario. Anyway, they didn't clamp that inrush, apparently.