[SOLVED] Identify this TRIAC circuit

[Jodh]

I came acros this circuit, but I am unable to identify its use. It was sent to me by a client for designing its layout, now they want me to electrically test it. But I was not provided any detail as to what it does, please help.

• It is has 3 pins with a heat sink attached.
• It looks like a lamp dimmer circuit, but is missing a pot and has an extra resistor connected to the Gate of TRIAC.
• All resistors are 1/4 Watt rated.

View attachment unkown_circuit_triac.bmp

 

[esp1]

hi,
Its a simple Diac circuit for triggering the Triac.

https://www.google.co.uk/search?q=d...&oe=utf-8&gws_rd=cr&ei=qVEVVevFD4PU7AaO94HIAg

 

[Jodh]

EDIT: I would like to add some more information.

• The TRIAC appears to be BT 139-500. This is a high voltage, high power triac. I do not know the reason for using such a big component with 1/4 W chip resistors.

Secondly, two questions still remain

• How do I go about testing this circuit? Simulation and otherwise.
• Why is the extra resistor connected between Gate of TRIAC and pin 3?

Thank you for answering.

 

[esp1]

hi,
This is a LTSpice simulation of your circuit, its a simple zero crossing detector switch.
The 0.25W resistors are not passing high currents so their wattage rating can be low.

For the sim I have assumed a 230Vac RMS 50Hz supply.
E