Need a fast MOSFET badly!! Please help!
Guyz! Finally the project is moving, I have been building a power supply to drive an electrostatic transducer and then connect the whole thing to my SigmaDSP for processing etc. Everything is ready, the soft is written, input is completely ready also, but now it turned out to be a big problem to find a really fast MOSFET which has really short on-off times, can sustain 50v and has continuous current rating about 2 or 3a. Please help!
Hi Skfir,
To find a fast MOSFET, look for one rated for low gate charge (Qg). This measures how much charge the FET needs to switch. The FET's switching action depends upon your gate drive circuit supplying this charge, so the less the FET needs, the faster it can switch. The switching time is approximately:
Tsw = Qg / Ig
where Qg is the rated gate charge, and Ig is the peak current your gate drive circuit can do. For example, the IRFIZ14 has a gate charge of about 11nC. If your gate drive circuit can supply 10mA during the switching interval, then its switching time is approx. Tsw = 11 x 10^(-9) AS / 0.01 A = 1.1 microsecond. Actual time may be somewhat longer.
This also means that increasing the drive current to any FET (by adding a high current buffer, for example) can improve switching times more effectively than just choosing a fast FET. ICs specially designed to drive MOSFETs at top speed are available from International Rectifier, Texas Instruments, and others.
In any event, understanding MOSFET operating principles will help you achieve a fast switching result. For more info see application notes from device manufacturers, like this one
http://www.irf.com/technical-info/appnotes/an-1084.pdf
Bob
Thank you Bob, again. You helped me so much already, I do not even know what would I do without your help. Thanks again.
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