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Hi Ray,
I want to drive the OSPi Ver 1.3 triac from my own +5V Open Collector output (ULN2803). Is it safe to connect the gate directly to the OC output without the 220 ohm resistor (with a 500 ohm pullup to +5V)? See partial circuit attached.
I am concerned about whether the gate will handle a direct short to GND.
Please help ASAP. Thank you for your time.
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Is there any reason you want to use ULN2803 to drive the triac? The triac functions like a transistor (except it’s switching AC current instead of DC). It can be switched by logic level signals. If you want isolation you can use an opto-isolator, but I don’t know why you need ULN2803 (which is typically used to drive steppers and motors) to drive it.
I am using the ULN2803 (which has 8 Darlington pairs) for other functions (like driving relays) and since I had a spare Darlington left on it, I thought of using it to drive the triac.
I don’t care about isolation so this will work fine. Just need to know if the gate will sink high amounts of current into the OC output when it’s active (low) without a series resistor. If so, I will use the series resistor but that will add 220+500 ohms to +5V when the ULN2803 output is high — hopefully that won’t be insufficient current into the gate of the triac.
I am ready to cut traces and solder, so the above answer would greatly help me.
Thank you.
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