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Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
When I look at the datasheet for the UCC37321/2 chips, the enable pin (3) is pulled high internally by a 100k resistor. This turns the chip on by default, just as I am observing on my controller board. Is there a preferred way to keep the driver turned off off until the modulator is turned on and can control the output?
Just use a pull down resistor on pin 3 to ground. You'll have to play around with values to get it balanced right depending on your modulator's output voltage, but it shouldn't be too hard to find a good working range.
Note: most 555 modulators have the output grounded when sending a LOW or OFF, so this would keep the UCC chip off without the need for a pull down resistor.
Registered Member #6038
Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
Aaaahhhh that explains it. I only really noticed the voltage difference when I removed the 555 modulator to hook up a fiberoptic modulator. I new there was a simple explanation. A 1K resistor seems to be working just fine (.2v), but I could go a little lower.
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