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From: Robert Baer on 11 Dec 2009 16:22
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.
From: Spehro Pefhany on 11 Dec 2009 17:47
On Fri, 11 Dec 2009 13:22:54 -0800, Robert Baer
<robertbaer(a)localnet.com> wrote:

> 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.

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(a)60Hz,
10ms(a)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).

From: petrus bitbyter on 11 Dec 2009 17:44

"Robert Baer" <robertbaer(a)localnet.com> schreef in bericht
news:T_ednUwB8uFWKr_WnZ2dnUVZ_hSdnZ2d(a)posted.localnet...
> 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.

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


From: Phil Allison on 11 Dec 2009 18:25

"Robert Baer"
> 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.


** 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


From: Paul Hovnanian P.E. on 12 Dec 2009 15:45
Robert Baer wrote:

> 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).

Maybe I was looking at the datasheets sideways, but it seems to me that the
IL420 is non-zero crossing as well.

> Perhaps the difference is microseconds or less.
> Which type should be used,and exactly why?

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.

> Thanks.

--
Paul Hovnanian paul(a)hovnanian.com
----------------------------------------------------------------------
Have gnu, will travel.
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