# TRIAC ANALYSIS-Calculation of gate resistor

#### MrAl

Joined Jun 17, 2014
8,866
I'm building a dimmer + on off circuit using BT-136 and MOC-3021 optocoupler. I tried switch with only the BT-136 and a resistor b/w gate and M1 to see if it works. The resistor was a 10k 1/4 watt resistor and it fried up in seconds. So I thought I'll compute the power and realized that I would need 14k resistor of 3.3W to run this. I thought it was a lot, since the load was only a 5W led light. 3.3W was too much extra power.

After looking at this post, I realized if I want the triac to turn on earlier then the resistance should be lower. Say I want to switch on at 20V then, R = 20/0.015 = 1.3k. Max current = 240/1333 = 180mA. Power = 43W?

Is the equation really correct? (I guess I should use Vpeak instead of Vrms then its much higher). But 43W to just turn on a switch seems to be a lot. What am I missing here?
Hi,

You should probably start your own thread, and provide a schematic of what you have there.