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Best way of controlling Triac for my soldering station

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Full Member level 5
Sep 25, 2010
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Conventional method to control triac is to fire it at a desired angle i.e if i am controlling my 60W soldering iron at half the power and temperature then i m firing my triac at 90 degrees. but this design will not work if i am working with a UPS ( square wave ) system in case of power failure, so any ideas for what if i feed pwm to the opto coupler and controll the triac?? i think it should run fine :-D

Heater control is generally using full wave switching instead of phase angle control. According to power quality regulations, phase angle control is only permitted for lighting applications.

Full wave switching won't have problems with square wave input. By the way, I don't see why phase angle shouldn't work with UPS as well.

With a square wave UPS, there is not the nice gradual
sine slope for a differentiator-based peak detector to
work from; this is the scheme I recall using for SCR
motor drives, some decades back, anyway. The time
base probably needs some thinking if it's supposed to
be direct-mains.

Me, I think I'd rectify and filter (forgetting power
factor for a non-commercial article) and do a DC-DC
control. Much more forgiving of line power details,
but needing a pretty fat filter bank.

Zero crossing optocoupler MOC3041 is suitable in this application.

Input is not phase angle control but on/off with 3-5 degree hysteresis.

Not sure why you need a peak detector for phase control, why not use zero crossing? Sine and modifed sine both have zero crossing so a phase angle trigger will still work. As FvM pointed out, it isn't normal or even legal to use that kind of control on some loads. A better solution would be to use or drop full cycles, for example use one in ten for 10% power, five in ten for 50% or all of them for full power.


Triac phase angle control circuits will not work properly in Square wave supply unless it is specificaly designed for it

In a modified sine inverter there will be a longer zero voltage time than in a sine converter but other than that a phase angle controller should still work. The principle of delaying the turn-on point still applies and as in a sine system, it's primarily the mark/space ratio of the power transfer that decides how much reaches the load. The control may not be as 'linear' as it would with a sine wave but it should still work. Remember that in a heating aplication to objective isn't to control the voltage so there is no point in only using the falling part of the sine cycle. Switching for complete cycles is still the better way to do it though.


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