Vishay makes some nice 6-pin (4-terminal) optocouplers frotriac control; their VO3052 is rather inexpensive and their IL420 costs bout $
2 more for the same control. The difference is that the cheapie is non-zero crossing; a quick look on a scope did not show zero-crossing glitches of the triac itself (used datasheet app circuit). Perhaps the difference is microseconds or less. Which type should be used,and exactly why? Thanks."Robert Baer" schreef in bericht news:T_ednUwB8uFWKr_WnZ2dnUVZ snipped-for-privacy@posted.localnet...
Don't know the types you mentioned but last month I bought some MOC3023 and MOC3043 for less then one Euro a piece. Brands are Fairchild and Motorola according to the logos. First type without -, second type with zero crossing detection.
Zerocrossing detection is usefull when you do not need phase control. I used them for heater controls which ranged from 0-100% in steps of 0.5%, each step half a mains period. As the load was resistive, I did not need expensive filters to keep the noise from the mains. It hardly made any noise.
The one without zero crossing was used to repair an incandescent dimmer. A huge toroid coil and some capacitors were in place already to prevent the noise and disturbances spreading over the network.
So *what* type you need and *exactly* why depends on the load and you wishes and maybe some other circumstances.
petrus bitbyter
You'll need to use the non-zero-crossing ("random") type for phase control.. for static switching applictations there will often be some advantage in reducing EMI with the zero-crossing type, certainly when the load is nominally resistive.
The zero crossing type inhibits triggering of the triac until the line voltage is less than a certain value, so turn-on could be delayed as much as (approximately) 1/2 cycle of the mains (8.3msec@60Hz,
10ms@50Hz) Turn-off, as always, occurs when the current drops below the holding current (a fairly low current of the same order as the gate trigger current)."Robert Baer"
** Any triac that is triggered to be fully on continuously switches ( off and immediately back on again) at zero crossings - long as the load is essentially resistive.What a " zero crossing" trigger IC does is ensure the same thing happens in the very first half cycle too.
All triacs switch off at zero crossings too, long as the load is resistive.
..... Phil
Maybe I was looking at the datasheets sideways, but it seems to me that the IL420 is non-zero crossing as well.
From what I know about it, the zero crossing feature gets you triac turn ons closer to the voltage zero and therefore a cleaner load voltage waveforem. Less need to filter out nasty RF, etc.
-- Paul Hovnanian paul@hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel.
Thanks; the loads are inductive (relays) with one possible exception.
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