[SOLVED] Identify this TRIAC circuit

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Jodh

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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
 

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.
 

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
 

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