I'm not certain about the the others, but SCRs and Triacs both fall under the Thyristor category. The SCR (Silicon-Controlled Rectifier) is a 3-terminal device that is effectivly a diode that won't conduct a forward current until a current enters the gate terminal. After that, the SCR continues to conduct even after the gate current has been removed. It's not to be confused with a transistor because it only operates on an on/off basis. This is to say it can't truely amplify.
A triac is essentially two SCRs paralleled with on another, except they're back-to-back so that it can conduct current in either direction once the gate current arrives.
Looking at The First Google Result for "Thyristor" that came up, I found a more detailed description of them. If anyone can describe them in a little more detail, I'm interested because SCRs and Triacs aren't really discussed a lot in the EE courses.
A trigger is a signal (imagine it as a binary gate, either open or off), when given turns on the device,and the device will not turn off until some other condition(depends on the device) occurs.Once triggered . the subsequent trigger has no control over the current . read the working of the device for more details
A gate on the otherhand can control the current flow thru the device.
Are u shure it is the "reverse" voltage reqd to breakdown,if yes what is the difference b/w diac and zener ?.Does a diac has forward breakdown voltage?
Why does a diac have no trigger to conduct ?