Hi everyone!

In my zero crossing circuit i have connected two 30k resistors each rated 2W . They are producing more than 60 degree centigrade heat .. I experimented with 1/2 watt and 1watt also same heat i'm observing.. How can i reduce the heat ?.

 

Use a small transformer.
Max.

 

A 4N25 is a very bad choice for this application. It's current transfer ratio is low and it is characterized at 10 mA IRED current. The thing really should have disappeared from the market 20 years ago.

Double or triple the pullup resistor on the output of the coupler and get a better coupler. Even a 4N35 is a big improvement and still very inexpensive. There are couplers that are well-specified with sub-milliampere drive for the IRED, though some are a bit more expensive.

 

1/2 watt resistors is not high enough, see Fairchild AN-3006.
Max.

 

Use a small transformer.
Max.

Thanks for reply
Here I'm not using any transformer.. I'm directly connected two power resistors each of 33k rating 2W to phase and neutral lines before bridge diode. .. These two resistors are dissipating more than 60 degree centigrade of heat .... Do we have any solution so that we can reduce heat?

 

A 4N25 is a very bad choice for this application. It's current transfer ratio is low and it is characterized at 10 mA IRED current. The thing really should have disappeared from the market 20 years ago.

Double or triple the pullup resistor on the output of the coupler and get a better coupler. Even a 4N35 is a big improvement and still very inexpensive. There are couplers that are well-specified with sub-milliampere drive for the IRED, though some are a bit more expensive.

Thanks for your reply
I'm facing problem in resistor side they are dissipating too much heat.....I'm directly connected two power resistors each of 33k rating 2W to phase and neutral lines before bridge diode. .. These two resistors are dissipating more than 60 degree centigrade of heat .... Do we have any solution so that we can reduce heat?