Interesting- SiC JFETs as next gen switching devices

Thread Starter

schmitt trigger

Joined Jul 12, 2010
872
Looking for something unrelated, I stumbled into this white paper, which I believe will be of great interest to people interested in Power Electronics.
The WP’s name is a little misleading, as the real breakthrough IMHO, is the use of JFETs as switching devices. JFET devices are normally ON, so how do you use them for switching? With a cascode configuration, that is how.

Please read and comment. As I mentioned earlier, if these devices really deliver the performance gains and don’t have some weird failure mechanisms, they have the power (pun intended) to revolutionize the SMPS industry.
What do you think?
 

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Papabravo

Joined Feb 24, 2006
21,159
Looking for something unrelated, I stumbled into this white paper, which I believe will be of great interest to people interested in Power Electronics.
The WP’s name is a little misleading, as the real breakthrough IMHO, is the use of JFETs as switching devices. JFET devices are normally ON, so how do you use them for switching? With a cascode configuration, that is how.

Please read and comment. As I mentioned earlier, if these devices really deliver the performance gains and don’t have some weird failure mechanisms, they have the power (pun intended) to revolutionize the SMPS industry.
What do you think?
The usual way to use a JFET as a switch is to take the gate negative with respect to the source. A cascode requires multiple devices IIRC.
 

crutschow

Joined Mar 14, 2008
34,285
I think biasing them, if they require a negative voltage to turn off, is a big negative (pun intended) to use them as switches.
 

Thread Starter

schmitt trigger

Joined Jul 12, 2010
872
Like all, or most, JFET circuits, biasing is accomplished via self-biasing, which is exactly what the cascode connection does.

The additional components of a cascode are a gate resistor and the low-voltage bottom stage Mosfet.

The greatest improvement, IMHO, is that the cascoding vanishes the Miller capacitance, which make high voltage Mosfets or IGBTs so notoriously difficult to drive efficiently.
Again, the white paper lists a number of advantages.
 

ronsimpson

Joined Oct 7, 2019
2,989
I am using some cascode parts. Both transistors are in one package. The high voltage part is on top and can be of several different types. The bottom part carries the same current but is a very low voltage part. There are several types of HV transistors that are hard to deal with. By placing a simple LV MOSFET on the bottom end, you have a HV transistor that is driven (Gate) just like and simple low voltage MOSFET.
1684293536594.png
 

Ian0

Joined Aug 7, 2020
9,671
That is an interesting thought!
I've already seen (but can't remember where) some flyback controller ICs done that way to work with a high-voltage silicon enhancement MOSFET. The 12V switching MOSFET is (apparently) easier to implement than the push-pull MOSFET gate driver.
 
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