dnmun said:
so you are saying that a triac is a DC device with a gate?
there is a 'steering' voltage that steers it? does it make it go negative or positive?
how does a thyrister convert DC to AC?
as for the thyristor, pardon me, I meant to say AC to DC, and even that is incorrect,
Blame my years of not touching the stuff in the drawers for that!
I'm not really too well versed in electronics,we only had 1 or 2 hours a week back in my school days.
Triac:
Depending on the composition PNP or NPN,there's a positive,or negative voltage to be applied to the gate.
A triac has 3 'legs'.
On the first leg you connect a positive terminal. On the last leg you connect the other terminal of your machine, just like what you do with a diode.
First and last leg are used as power circuit.
On the gate you put a separate steering voltage, that is usually much lower than the powered line you connected to the other legs (eg: powered voltage is 220V, gate voltage is 9V). It's good for steering electric equipment without being exposed to high voltage lines.
basically a triac is a diode that's always open (meaning no current flows through), until you apply a voltage on the gate! Then, depending on the voltage you put on the gate, the other two will close (meaning there will be a current flow, in direct correlation to the input voltage on the gate); eg: you put 3V on the gate, there will still be no flow; 6V and from say the 100V you put over the outter legs, there's a voltage drop of a few volts, acts like a resistor, 9V, and the triac nearly acts like a copper wire.
A thyristor is basically the same as a triac. Together with a graetz bridge (diode bridge) it can be used as an AC to DC convertor.
From what I just read, is that a thyristor is more used like a switch. Once voltage is applied to the gate, the device remains closed (meaning a current will continue to flow) even if you turn off the gate.
In other words,you won't need to constantly be supplying it with a steering voltage.
It's used in TV's. as soon as you turn on your tv, you don't need to keep your finger on the power button, as soon as you release it, the tv will continue to be in the 'on' state, until you break the electrical connection. That's the work of a thyristor. (you break the connection by unplugging and replugging the tv, it should be in an 'off' state; or another electronic chip will break the electronic circuit to the thyristor long enough for the thyristor to shut down.
It is also used when voltage on it's legs reaches a maximum, it will turn on.
Say an AC socket lightning protection. When the voltage is within specs, nothing unusual happens. When the voltage suddenly increases (eg: with a lightning strike), a thyristor will short circuit the socket, so your electronic device will be spared from overvoltage and damage (or likewise, when lightning strikes your household appliance,a thyristor will short circuit, to protect the net from a voltage spike. A fuse works much slower than a thyristor, and with a fuse it's possible to create a voltage spike over the net and damage other electronic equipment plugged in.
Wikipedia will tell you more.
