PSU and TRIAC control

[DPJ]

Dear All,
I need a power supply circuit run from 24V AC using a common ground for TRIAC firing. Unfortunately, with the one I have at present, when I turn the TRIACs on and bring on mains voltage contactors, I get HORRIBLE spikes in my 5V supply to my micro. I cannot use contact suppressors as other people supply the contactors already installed.
Any help would be much appreciated!
David

 

[jbartos]

Suggestion: Notice that there are various principles the power supplies are based on. Also, there may be need for filtering in the TRIAC circuit. Please, could you provide more information, e.g. power supply nameplate data/technical data, and TRIAC data. Also, could you describe the circuit in more detail. Normally, transient voltage suppressors are used and must be added if spikes occur or else things get more involved and expensive.

 

[DPJ]

Many thanks for replying.
The power supply has a 24v Ac Transformer 0 rail is grounded
24v rail comes through a 33 Ohm res then through a diode
(Half Wave Rec) smoothed by a 220uF cap then to a 12V Reg
Then a 22uF cap + 100nF followed by a 5v Reg at this point there is a 10uF cap.
The problem is, even when I switch the 240v contactor on and off with no connection to my board I get terrible spikes on my 5v Dc Supply
many thanks in anticipation.

 

[don01]

DPJ,
Your problem centres around the coils of the contactors spiking the 240v cct. This will be reflected thru the 24v secondary then punch through the regulators. I imagine the regulators are something like 78XX or lm338 3 terminal jobs. I would guess the 78xx are more likely since this reads like a "very cost effective" psu. You could try getting hold of a commercial contactor coil suppressor and put on the 240 supply to the psu (or the control cct to the contactor (the best spot is on the coil terminations). The contactor manufacturer will sell you one.
I suggest you have a look at the power supply unit again, A switch mode will give you more effective isolation from the 240 ac but I doubt that it will knock down a spike of that order.
Another source of info would be the national semiconductors linear devices book. It will detail the regulator and they have typical ccts with some indication of how to limit interferance -typically .01uf poly caps on the output leg to ground or vcc leg to ground.
The easiest way I can think of would be the commercial suppressor.

Let us know how it goes
Don