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-   -   High-Voltage JFET (http://www.diyaudio.com/forums/solid-state/8866-high-voltage-jfet.html)

IIR 20th December 2002 06:53 PM

High-Voltage JFET
 
Does any one know of ANY JFET that is available for higher voltage applications (140v). Current is very small(less than 1mA).

What is the current state-of-the art?


Thanks!

jcarr 20th December 2002 07:13 PM

Depends on whether you really need a JFET or simply a normally-on device. If the latter, and if N channels will suffice, you could look at static-induction transistors or depletion-mode MOSFETs.

Or if you really need JFETs, don't mind a bit of extra complexity, or need both P's and N's, how about using JFETs and maintaining a constant, safe VDS across them by adding bootstrapped cascodes?

regards, jonathan carr

IIR 20th December 2002 07:28 PM

This is being used in an application where they will be used to switch a bi-directional AC signal on or off(max 140v @ 500uA). JFETs are nice for this purpose!

The application invloves a large array of piezo actuators that need to be indivually charged and discharged. We want to have one Driver and a row/column switch matrix to select the piezo actuator. Essentially what we have is a large matrix of capacitors. We cant use MOSFETs. The body diode in a MOS FET causes problems with isolation between elements. There is an array of 256 elements. the array has to be scanned at a 6hz rate (about 650uS per element). Switch has to be fast.

jcarr 20th December 2002 08:31 PM

Tokin's static-induction transistors may possibly do the job. AFAIR, these are all N-ch depletion mode (normally on) devices, so I hope that is OK with you.

http://tokin.intercraft.co.jp/pdf/sit000001.pdf

Warning. Text is in Japanese.

Incidentally, some of these devices would be interesting to use in an audio power amp, I reckon. For instance, the 2SK181 has a drain voltage of 800V, a max drain current of 20A, and a power dissipation of 300W. OTOH, Gm is 10S, and the Cis is 2500pF, so the driver and bias circuitry may require some thought...

hth, jonathan carr


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