Highest power dissipation JFET?

[Petter]

I am looking for high power dissipation JFET either p or n channel in place of 2SK170.

Which linear devices can sustain the highest device power dissipation?

Any news of the SiC JFET's that Infineon are cooking up?

Petter

 

[mirlo]

Do you need a JFET or do you just want a depletion mode device?

Supertex makes power NMOS depletion mode devices.

 

[peranders]

Petter, you could also you a cascode to achieve a high power JFET.

 

[Sch3mat1c]

Uhm.. paralleled?

Wouldn't cascoded be used more for voltage handling?

Tim

 

[stadams]

Parallel.

I would say paralleled. And in this configuration it has the unique effect of reducing noise also. An example would be the Pearl Phono at Pass Labs. Make sure to use tightly matched JFET's or even use the 2sk389 dual monolithic JFET which is very close in specifications to the 2sk170.

Later,

 

[peranders]

Petter, what are you going to to with this JFET? You could connect a bunch of JFET's (maybe with small source resistors) in parallel and then connect a power BJT as a cascode.

 

[Petter]

Thanks!

Thanks to all for great answers.

I will check out depletion mode FET's. Great suggestion!

What I am using this for is output stage of pre-amp and input stage of power amp. I have already made a Pearl with 8 parallel 2SK170 for input stage, and another power project with parallel 2SK170 (just about to get tested) with small individual source resistors (as suggested here by Peranders) and a MOSFET cascode at 10V. I do feel, however that it would be more practical not to have to match up a load of JFET's every time I wanted to build something

The main reason for wanting higher output power is that I want to have the output impedance of the JFET output stage of the pre-amp as low as possible. I am using other tricks to help here also, but with my current topology I would be best served without high input capacitance resulting from parallel operation.

Thanks again

Petter

 

[jcarr]

Pettr: I have some experience with the Siliconix depletion MOSFETs. They are suitable for cascoding (when you would prefer not to have a separate bias circuit), but if your thought is to use these as output devices, in my opinion, JFETs sound considerably better.

Here are two high-current idss JFETs that I can recommend for follower duties:

N-ch: 2N4856. Minimum idss, 50mA. Maximum idss, 175mA.

P-ch: 2N5114. Minimum idss, 30mA. Maximum idss, 90mA.

The breakdown voltages are not very high, so I recommend that you keep the voltages constant with a bootstrapped cascode. Used as preamp output devices, in practice they can work quite well, are not too fragile (only if you bootstrap cascode them effectively), and can sound very good.

hth, jonathan carr