Help with Triac Controller

Discussion in 'The Projects Forum' started by prb22786, Sep 19, 2010.

  1. prb22786

    Thread Starter Member

    Sep 19, 2010
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    Here's what I thought was a pretty simple project. Up-counter fires off a series of opto-triacs sequentially which in turn fire power triacs for the AC load. Its use is for theatrical lighting. My power triacs are BTA20-700BW, and the 8 triac resistors (R4-R11) are 5.1k 2W. I'm thinking that these values might be off, I wasn't at all sure how to calculate them. I'm very new to using triacs.

    The problem I'm having is that all 4 AC load lines are always ON. Can anyone see why this might be? I'm wondering if I need higher values for the gate resistors? Also, which the power triac gate connected as it currently is, I'm thinking the floating voltage is turning the triac on even when the opto-triacs aren't conducting. If I move the gate connection to the other pin of the opto-triacs, will that solve my problem?

    Any suggestions/criticism are definitely appreciated.

    View attachment ControlBox.bmp

    View attachment ControlBox.sch
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    When in doubt double check the datasheet of the optoisolator, I've found them to be confusing at times and sometimes drawn incorrectly for the two devices to "sync" together.
     
  3. prb22786

    Thread Starter Member

    Sep 19, 2010
    15
    0
    Do you mean as far as MT1 and MT2 of the TLP3064 syncing with the BTA20-700? If that was reversed, wouldn't it cause them to not turn on, rather than always be on?

    Now that I've kind of stepped back, I think the problem is when the opto's aren't conducting, the gate of the power triac is connected to a voltage on the HOT wire. I think moving the gate connections to the other lead pin of the TLP3064 opto-triac will solve my problem. Unfortunately, I made boards so I'll have to cut leads and run jumpers.

    I'll probably get to work tomorrow, if anyone can confirm/deny I'm on the right track I'd be grateful.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,788
    945
    Try it with the trigger connected to R4 vs. R5. and see what difference that makes. I think the trigger maybe should be connected to your non conduction side of the hot line, instead of the incoming side.

    Not that it should really matter since you get a zero crossing point on either side, but the few circuits I've seen using these devices were connected that way. Worth a try since its a simple change.
     
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    I've run into the very same thing despite the spec sheet's application example showing it as opposite.
     
  6. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    If the LM555C is running fast, at several hundred hertz or above, then all four loads will appeared to be constantly ON.

    We don't know as OP does not show values of the component used in the schematic.

    Perhaps he can check this out by removing either the 555 or 4017 from circuit if they are in a socket. Failing that, disconnect the Reset pin of 4017 from Q4 and connect to V+ to stop the 4017.
     
  7. prb22786

    Thread Starter Member

    Sep 19, 2010
    15
    0
    Thats what the problem was. Silly design mistake. As Kermit was saying when the opto-triacs aren't conducting, there's still a voltage present on that node, which is where I originally had my power triac gate connected. So every cycle there would be voltage present to gate on the triac. Once I switched it to the other pin of the opto-triac it works perfectly as intended.

    New schematic and image uploaded if anyone wants to use it.
     
  8. prb22786

    Thread Starter Member

    Sep 19, 2010
    15
    0
    Could use some advice here, as I'm still pretty green. I tried adding a couple of options to the design, and had some interesting consequences. I'd like to have two SPDT switches for turning off lines 3 & 4 should the user not need them. I've wired them into the counter RESET but they don't work. When line 3 is off the counter will go to 4 THEN reset. When line 4 is off the counter will count all the way to 10 THEN reset. I must've wired something wrong because in principle, this should work right?

    I also want to add the option to switch it from AUTO mode to MANUAL mode, where a pushbutton switch will manually clock the counter. Seems easy enough with a pull-up voltage divider, but there were some crazy transients present on pin 14, sine waves with noise spikes. The effect is that all 4 opto-triacs are switching rapidly. I added a simple low-pass filter, I may need to tweak the values but the transients on pin 14 are all but gone, just a slight DC ripple. Still not operating correctly though. When the pushbutton switch is closed, it will freeze the counter until the switch is open again. The effect I'm going for here is to have it always frozen, and advance when the button is pushed. Am I missing something simple here?

    Bit more information: I'm using CMOS devices with a 12v supply. The supply is taken off Line 1 AC through a 10:1 transformer, bridge rectified, filtered, LM7812 voltage reg. Very smooth output, slight ripple because I have a 12v cooling fan taken off the supply. Turning the fan on and off does seem to have an effect on the erratic AC switching I'm noticing, so I'm guessing I have noise problems in the circuit. Again, the circuit works beautifully when ran directly off the counter, I just can't manually clock the circuit.

    Edit: d'oh, forgot to add new schematic.
     
  9. campeck

    Active Member

    Sep 5, 2009
    194
    3
    Why are you using a voltage divider on the manual clk switch? being CMOS it should just except the +12v right?
     
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