MOSFET bias current

[pengpeng]

Just ask in normaly for power mosfet, how many mA of bias to set? I have adjusted at 150mA, but it seem too hot.

Can anybody help me, thank in advance.

 

[h_a]

Mosfets? Bias them as high as you can afford.

These parts do not have a current at which crossover distortion is minimized (as it is the case for BJTs).

Have fun, Hannes

 

[lineup]

150mA - 200mA is quite normal for standard power amp output.

If 'only' 150mA makes too hot,
then you have either some other problem (like instability/oscillation)
or your heatsink is way too small.

 

[myhrrhleine]

150mA - 200mA is quite normal for standard power amp output.

If 'only' 150mA makes too hot,
then you have either some other problem (like instability/oscillation)
or your heatsink is way too small.

ditto

 

[AndrewT]

Borbely recommends a minimum 150mA through each Output FET and a minimum of a total 500mA through all the parallel output FETs.

He only designs and builds FET amplifiers and ancilliary gear.
Some good design papers on his website.

 

[pengpeng]

Thank above, I will check and try.

 

[mtlin12]

Just ask in normaly for power mosfet, how many mA of bias to set? I have adjusted at 150mA, but it seem too hot.

Can anybody help me, thank in advance.

I had same problem once, at +/-60V 150mA*4 (2 pairs power MOS)

the temperature of a normal 140mm width heat sink will probably up to 130~140¡¦F

and it is too hot.

So I ...

 

[mtlin12]

Use two heat sinks for 2 pairs power mosfet, and hope can get >250mA

bias current for each at normal temperature.

(+/-32.5V 500mA is just for testing, other 70mA is for the Relays.)

 

[darian]

It doesn't make sense : if you use a heatsink the size of the one in the picture, at idling the temperature should be max 100°F with 250mA.

What does your dissipation calculation says? If it's way too hot, there must be some HF ringing or so. It's just calculations, they don't lie.

Regards