punkieys17
- Feb 7, 2016
- 45
- Joined
- Feb 7, 2016
- Messages
- 45
So I have a 230v a.c. supply switched pump that uses the exact circuit below. After a major failure the resistor was fried. I am puzzled by my calculations as the resistor in the circuit was no where near the wattage. I take the 230v a.c. and tb at gives me a peak of say 330v. The gate current is shown as between 5 and 50ma. Taking 30ma as the target this gives me 330v / .03=11,000 ohms. However the wattage using v2/r gives 330×330/11000=9.9W. The resistor was more like a quarter watt in size. What am I missing please and how is it calculated