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Thread: 70VAC drop across V02223 chip

  1. #1
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    Default 70VAC drop across V02223 chip

    Is it normal to have a 70VAC drop across the V02223 chip when 120VAC is being fed through it? I have wired up a duplicate of a DirkCheapSSR (except I have in-line LEDs on each trigger line) and across pins 6 & 8 of the V02223 chip, the AC voltage is showing a 70VAC potential when the trigger is active. If I check at pin 8 and the neutral side of the pigtail socket, it is showing 120V like expected, but if I check pin8 to the hot side, 40V. Would the additional LED with the 680Ohm resistor be causing this kind of voltage drop across the load pins? I am using an Arduino Mega with a Zero Cross module that is verified working, and zparticle's code. I have also gone with just turning on the ports with a simple sketch to see if anything changes and no dice. Basically a string of LED lights light up very dimly, but definitely on. A string of incans do not light up at all.

    Any ideas?

  2. #2
    Join Date
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    Default Re: 70VAC drop across V02223 chip

    It's a pretty simple circuit that is known to work well. Have you tested it without the LEDs in the circuit on the trigger side. You will probably have to adjust the value of the 680 ohm resistor. As designed by Dirk the current flow on the input side of the VO2223A chip is around 7ma. If you have 5 volt trigger lines coming from your controller with LEDs that drop 2-3 volts combined with a 680 ohm resistor there is not enough current left to properly trigger the input side of the chip. You probably need to change the resistor value but you will need to calculate the correct value based on the forward voltage of the LEDs you are using.

    I built a couple of SSRs with LED channel indicators and I used 360 ohm resistors. But make sure you calculate the correct value based on the LEDs you are using.

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  4. #3
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    Default Re: 70VAC drop across V02223 chip

    Quote Originally Posted by dvc2013 View Post
    It's a pretty simple circuit that is known to work well. Have you tested it without the LEDs in the circuit on the trigger side. You will probably have to adjust the value of the 680 ohm resistor. As designed by Dirk the current flow on the input side of the VO2223A chip is around 7ma. If you have 5 volt trigger lines coming from your controller with LEDs that drop 2-3 volts combined with a 680 ohm resistor there is not enough current left to properly trigger the input side of the chip. You probably need to change the resistor value but you will need to calculate the correct value based on the forward voltage of the LEDs you are using.

    I built a couple of SSRs with LED channel indicators and I used 360 ohm resistors. But make sure you calculate the correct value based on the LEDs you are using.
    This pretty much turned out to be one of those, "Until you post it to the world and make an idiot of yourself, you won't figure it out," type of thing. Not long after I posted and just before I was going to give up for the night to get some sleep, I decided to just test 4.5V manually across the trigger line (I made an LED tester out of one of those cheap finger LED flashlights a few weeks ago to troubleshoot something else) and the lights came on full. It is exactly as you described in that with the LED in place, the resistor I have in there is just way too high. I suspect that if I was to hook up a scope, I would see that trigger circuit is fluttering on/off as fast as it can due to the voltage dropping enough when firing both LEDs (mine + triac) through the resistor.

    Thanks for looking!

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  6. #4
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    Default Re: 70VAC drop across V02223 chip

    The Vf of the V02223 is about 1.2V, the Vf or a typical Red Led is about 2.0V and the V02223 needs about 6ma to make sure it fires. To calculate the resistor needed you follow ohms law Vdrop = 5.0 - 1.2 - 2.0 = 1.8V Then Ohm's law says R=V/I = 1.8/0.006 = 300 ohms, if you use a Blue, Green or White LED, then the Vf is closer to 3.0V for them, and you would need 0.8/0.006 = 133 ohms. Use the next largest standard resistor and it should work.

    With a 680ohm resistor you were not really turning on the V02223 all the way.

    See the wiki for more info http://www.doityourselfchristmas.com...sistor_Example
    http://www.christmasinwarren.com

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