RE: [TCML] Ac transistor (AC scr = triac )

[William Noble <william_b_noble@xxxxxxx>]

Triacs are inherently low frequency devices due to the gate capacitance and their structure.  They cannot be turned off once turned on without an eleaborate circuit - the simple traic motor speed control depends on the reversal of the AC waveform.  GTOs are used in some circumstances but again, these are as I recall 4 or 5 layer devices with a limited upper frequency.  A true AC device with a good upper frequency limit would be an exciting thing to play with - though whether it could be called a transistor is an interesting question - for example, in a typical transisotr, the ratio of base to collector current is called Beta and it's a positive number - in an AC device, a positive beta would imply an AC base drive as well - 
 
As far as I know, devices operating into the few hundred Mhz range all use classic 3 element transistors, though at the higher frequencies toploogy is adjusted very carefullyi, and SoS or SoD (e.g. sapphire or diamond substrates) as well as exotic doping is used to eliminate stray capacitance and enhance electron mobility.
 
If you are inventing cool devices, a 100 Mhz light modulated switch would be much more valuable for TC applications because it would allow you to isolate the drive system from the power and noise of the TC.> Date: Tue, 24 Jun 2008 03:33:35 -0700> From: a_pettit_jr@xxxxxxxxx> Subject: Re: [TCML] Ac transistor (AC scr = triac )> To: tesla@xxxxxxxxxx> CC: > > Is this what you are looking for ?> > TRIAC > > The TRIAC is a three-terminal device similar in construction and operation to the SCR. The TRIAC controls and conducts current flow during both alternations of an ac cycle, instead of only one. > > The triac is used in an ac environment, so it will always turn off when the applied voltage reaches zero at the end of the current half-cycle. If we apply a turn-on pulse at some controllable point after the start of each half cycle, we can directly control what percentage of that half-cycle gets applied to the load, which is typically connected in series with MT2. This makes the triac an ideal candidate for light dimmer controls and motor speed controls. This is a common application for triacs.> > _______________________________________________> Tesla mailing list> Tesla@xxxxxxxxxxxxxx> http://www.pupman.com/mailman/listinfo/tesla_______________________________________________
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