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TRIAC question

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batman

New Member
how low of a gate voltage can i give a triac to switch it on?
i have the 6 amp 400 PIV radio shack model.

basically i want to be able to dump 300 volts for an instant into a transformer at the control of a 555 timer. how can i use the low current and voltage of the IC to turn on the TRIAC?
thanks
 

Sebi

Active Member
Use an optotriac for isolation and proper driving.
 

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Russlk

New Member
The Radio Shack specs for the 276-1000 are: Igt--50mA max, Vgt--2.5 volts max. The 555 can easily supply that. A series resistor to limit gate current is a good idea, and remember that if you drive it directly, the circuit is at 115 VAC.
 

batman

New Member
thanks everyone

how do i calculate the value of the resistor i need for the drop down at the gate?

how come if i drive it directly the output can only be 115VAC? i was hoping to switch around 350 volts :(
 

Russlk

New Member
If you are trying to switch 350 VDC, the triac is the wrong device because it will not turn off once turned on. A MOSFET is the proper device and you need a diode across the transformer primary to catch the back swing or else the MOSFET will get zapped.
 

batman

New Member
do you think you could show me a schematic of the MOSFET setup? and do i need to drive the mosfet with a transistor, or is it direct from the timer?
 

Russlk

New Member
The timer can dirve it direct. The 100 ohm resistor acts with the Cgs of the MOSFET to slow down the turn-on time. Too fast turn on can cause excessive current in the internal capacitance. Once you start current flowing in an inductor, it continues to flow even when the MOSFET is off. The diode provides a path for the "flyback" current.
 

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