wes Posted October 26, 2005 Report Share Posted October 26, 2005 I need help. I have a machine that gives me a 24vdc timed output with very little current...enough to light up an LED.I need to switch this timed output to turn a 24vdc relay on and off at the same time that the timed output is turned on and off.I have a MOC3020 opto coupler triac driver which turns on and off but the output triac turns on and stays on.Can anyone help? Quote Link to comment Share on other sites More sharing options...
ante Posted October 26, 2005 Report Share Posted October 26, 2005 Hi wes,Welcome to our forum.Can you post the circuit so we can try to locate the problem? Quote Link to comment Share on other sites More sharing options...
Ldanielrosa Posted October 27, 2005 Report Share Posted October 27, 2005 I need to switch this timed output to turn a 24vdc relay on and off...By this do you mean that the relay you are controlling is running on DC? If so then that's likely your problem. Triacs (and SCRs too) are regenerative switches- when you turn them on they latch. To turn them off you need to interrupt the current. They are very useful for AC becauce for every voltage zero-crossing the current crosses zero as well and the thyristor turns off. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 27, 2005 Report Share Posted October 27, 2005 You should use an opto coupled transistor maybe driving another transistor for enough current to drive the DC relay. Don't forget about adding an anti-spike diode across the relay's coil. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 27, 2005 Report Share Posted October 27, 2005 I wonder if you used an optocoupler with a diode whether the voltage generated by the diode could be enough to turn on a low threashold voltage MOSFET. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 27, 2005 Report Share Posted October 27, 2005 I don't think a diode gives enough voltage as a photodetector to turn-on a Mosfet. IR make some opto-coupled Mosfets with some kind of photo-voltaic cell as the detector. The Mosfets are tiny and can't drive much current for an ordinary relay. Quote Link to comment Share on other sites More sharing options...
ante Posted October 27, 2005 Report Share Posted October 27, 2005 WES ! ;D Quote Link to comment Share on other sites More sharing options...
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