BT139-600G Triac Equivalent
allisonportable at gmail.com
Sun Dec 17 08:23:27 CST 2017
On 12/17/2017 08:24 AM, Peter Coghlan via cctalk wrote:
>> I have a suspicion that this component may be faulty on the input side of my
>> H7826 PSU. A little tester I have does not recognise it, it is possible that
>> the currents it uses are too low for this particular triac, but I am not
> What is the function of this triac in your power supply?
> I have come across a triac which is used to switch between 115V and 230V input
> in the PSU of a DEC 3000/300. My triac went short circuit which caused some
> release of magic smoke when the PSU was used on 230V. I also had difficulty
> finding a replacement for it so I ended up leaving it out. The PSU worked
> fine on 230V only without it once I replaced the other damaged components.
> If your triac has a different function, ignore the above.
> Peter Coghlan.
The common use is to create a hard short circuit across the output if
the output voltage
exceeds a safe limit. The logic is that a power supply is cheap
compared to the rest
of the computer. The typical output where this is done is the 5V rail.
The tester likely cannot test a triac its not a simple transistor or
diode. They are easy to test
a light bulb (12V) and a DC source.
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