paralel MOS-FET´s HELP

[viki]

Hello, i built an amplifier using mos fet IRF 540 and 9540, can I paralel two IRF 540 and the two 9540 so that can dissipate more power and to use lower impedances speakers

Or paraleling MOS-FET´s will affect the circuit and sound quality?

Tanks

[richie00boy]

It depends on the design of the amp. The voltage amplifier stage (VAS) must be able to supply enough current to drive the additional MOSFETs. 10mA should be OK as a bare minimum.

Each MOSFET must have a low value (0.22-0.47 ohm) resistor in the source. It is also recommended that the MOSFETs are matched as the Vgs can vary quite a bit.

Do a search for parallel MOSFET and MOSFET matching for more info.

[Konrad]

A while ago i bought a tube of 100, the spread in Vgs on is significant!
Dependent of konfiguration you may need to adjust some compensation network.
like simple cfp and doubling the mosfets driven by a transistor the BC cap ( slow down ) may nead some adj.

[jackinnj]

Originally posted by Konrad
A while ago i bought a tube of 100, the spread in Vgs on is significant!
Dependent of konfiguration you may need to adjust some compensation network.
like simple cfp and doubling the mosfets driven by a transistor the BC cap ( slow down ) may nead some adj.

I usually find that International Rectifier TO-247 devices come in a tube of 25. The only thing I know which comes in a tube of 100 are SO-8 opamps. The Hitachi (now Renesas) Lateral MOSFETs come in tubes of 30.

When I do matching -- I find that the distribution of devices along Vgs with Id of 1.000 amp is normal or at worst bimodal. Of course this means that you have devices on the tails of the curve. If you are finding a wide distribution of Vgs you may want to make sure that the time for each test remains constant and that the ambient temperature is the same --

[Konrad]

Well i didnt do any statistic calculations.
for clarity : i bougt 100 irf640, 100 irf9640 , in to220, total of "4 tubes".