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-   -   how much base current for Mosfet for an amp with 2.6 Bias (http://www.diyaudio.com/forums/pass-labs/226398-how-much-base-current-mosfet-amp-2-6-bias.html)

rhythmsandy 25th December 2012 03:56 PM

how much base current for Mosfet for an amp with 2.6 Bias
 
Im thinking to bias an amp at 2.6Amps so just wanted to know how much base current to be given for each output pair considering toshiba 2sj201 1530 pair? Lets consider I have 5 pairs of output Mosfets? which driver to be used for such configuration?

DUG 25th December 2012 04:29 PM

2 Attachment(s)
MOSFETs are driven with voltage, not current for DC biasing.

The jpg's show approximately how much voltage should be applied vs drain current.

The one on the right shows typical Vgs for variations in die temperature.

Gotta love data sheets.

:)

Mooly 25th December 2012 05:28 PM

As Dug says, FET's are voltage rather than current driven. At DC they draw no steady state gate current. You could feed them via 10 or 100Meg, but that would be no good for audio...

At AC you have to supply (or have available) enough current to charge and discharge the gate capacitance. Not enough and the output stage will suffer slew rate limiting and restricted HF response.

Zen Mod 25th December 2012 05:35 PM

5 parallel gates (or twice that , considering pairs) ...........

say 30mA , minimum , in driver stage , just by my taste , nothing more serious

rhythmsandy 25th December 2012 06:06 PM

Quote:

Originally Posted by Zen Mod (Post 3298756)
5 parallel gates (or twice that , considering pairs) ...........

say 30mA , minimum , in driver stage , just by my taste , nothing more serious

for a supply of +/-30V at the output how much will be the drain current from each output mosfet? since the bias is 2.6 amps so do we need to divide it by 5? so 2.6/5 = 500ma? for one mosfet?

so can I use 2sc5171 as driver for the 5 pairs at the output stage ?

AndrewT 27th December 2012 12:05 PM

Read what they told you.
The FETs do not draw gate current.
FETs do not draw base current, they don't have bases !!!!!


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