N CHannel Depletion mode MOSFET

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ruffrecords

ruffrecords

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Joined
Nov 10, 2006
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Location
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I am toying with the idea of trying an SRPP topology using depletion mode MOSFETs because they are available with relatively high operating voltages and currents. What types would you recommend and where can I find spice models for them?

Cheers

Ian
 
I have no clue, but see a vital point missing:

> What types would you recommend

How long is a rope?

I need a jack. Well, for a kitchen cabinet? a lawn tractor? a sedan/saloon? a backhoe? a house? (I'm reading about building million-pound roofs on the ground and then jacking them up to put walls under; but this week I only have a house to lift.)

Or in your terms: a VF14 or 6550/KT88 or UV 862?

There may not be the selection in MOSFETs. Still a large-die 10A beast may not do well at 2mA.
 
Manley is advertising "Hi-current WFDRIVE Balanced Output Impedance: 50 Ohms"  on their new Force mic preamp (it also has a fully switching PSU for all voltages) . I understand this "WFDRIVE" is a MOSFET White follower, electronically balanced on output. I've built mic preamps with 6922 and 7308 used in a White follower for the current stage (not my design). Wondering how Manley is doing it....
 
To narrow things down a little I would be looking for types capable of operating to 60V and comfortably passing 10 or 20mA  quiescent and for which spice models are available.

Specifically it is for pro audio - it is not for  a kitchen cabinet, a lawn tractor, a sedan/saloon, a backhoe, or a house.

Cheers

Ian
 
AusTex64 said:
Manley is advertising "Hi-current WFDRIVE Balanced Output Impedance: 50 Ohms"  on their new Force mic preamp (it also has a fully switching PSU for all voltages) . I understand this "WFDRIVE" is a MOSFET White follower, electronically balanced on output. I've built mic preamps with 6922 and 7308 used in a White follower for the current stage (not my design). Wondering how Manley is doing it....
Click to expand...

Interesting. WFDRIVE seems pretty meaningless to Google. Probably some weird Manley acronym. Where did you get the info about it being a MOSFET White follower?

I know there is a jumper inside for changing the gain so users must be able to pop the lid. Anyone done this or got any pics of the inside?

Cheers

Ian

Edit: Just found the Manly manual with a nice drawing of the innards. Looks like two beefy transistors on heat sinks plus a smaller one making up the output stage.
 
I'm still googling what SRPP means,,,,    :-[

I messed around with some high voltage enhancement mode MOSFETs when I was designing a extremely high input impedance (>100M @ 500V) touch sensor and mosfets do that well enough.

Have fun.

JR
 
Maybe IRF820? Used these in HV power supplies.

http://uk.farnell.com/vishay/irf820pbf/mosfet-n-500v-2-5a-to-220/dp/8648514

Also have IRF830 and IRF840 with higher current handling.

 
JohnRoberts said:
yup that's what google says too.... sounded like some old tube  who-ha.

JR
Click to expand...

It is - originally invented I believe for high power transmitter use aeons ago but it can also be done with FETs.

Cheers

Ian
 
ruffrecords said:
Interesting. WFDRIVE seems pretty meaningless to Google. Probably some weird Manley acronym. Where did you get the info about it being a MOSFET White follower?

I know there is a jumper inside for changing the gain so users must be able to pop the lid. Anyone done this or got any pics of the inside?

Cheers

Ian

Edit: Just found the Manly manual with a nice drawing of the innards. Looks like two beefy transistors on heat sinks plus a smaller one making up the output stage.
Click to expand...

Almost everything Manley makes uses a conventional tube based White CF. Don't remember where I read they had moved to MOSFET based WCF output stages in their newer gear. I assume "WFDRIVE" stands for "White follower drive".
 
AusTex64 said:
Almost everything Manley makes uses a conventional tube based White CF. Don't remember where I read they had moved to MOSFET based WCF output stages in their newer gear. I assume "WFDRIVE" stands for "White follower drive".
Click to expand...

Makes sense to me.

Cheers

Ian
 
I've been looking into doing this for a while, and the gate capacitance presents the main problem in higher-voltage MOS'fets.

Any reason why Jfets can't be used? Like IFN6450 or such?

Jfets were widely used in the fetrons, solid-state tube replacements - http://hrsasa.asn.au/docs/Fetron.pdf - which sorta is like what we want? Yes, 12AX7 available: TS12AX7

1973 WE Patent for simulated pentode: https://www.google.com/patents/US3767946

Jakob E.
 
Depletion mode and enhancement mode MOSFETs aren't usually interchangeable. If low Ciss for an enhancement mode MOSFET is needed, I will propose Hitachi 2SK216/J79.
 
gyraf said:
I've been looking into doing this for a while, and the gate capacitance presents the main problem in higher-voltage MOS'fets.

Any reason why Jfets can't be used? Like IFN6450 or such?
Click to expand...

No reason at all. I began looking s  jFETs but could not find any rated above 40V Thanks for the link. Don't suppose you have a spice model for it?

Cheers

Ian
 
moamps said:
Depletion mode and enhancement mode MOSFETs aren't usually interchangeable. If low Ciss for an enhancement mode MOSFET is needed, I will propose Hitachi 2SK216/J79.
Click to expand...

I am looking at N channel depletion types simply because they bias much like a tube.

Cheers

Ian
 

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