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Old 17th December 2002, 10:12 AM   #1
hacknet is offline hacknet  Singapore
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Question parelleling output devices

is it advisable to parellel o/p devices to increase power handling?

IE: i have 15 amps flowing through a mosfet... i need a mosfet rated abt 20 amps to handle the power

can i use 2*10 amp rated mosfets to do the job?
as lower rated devices are cheaper?

i dun mind the distortion as it wud be for a sub.
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Old 17th December 2002, 03:16 PM   #2
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Yes, you can parallel output devices. But depending on your application you may need to add source and gate resistors. Usually 100 to 1000 ohms in series with the gates, and .05 to .5 in series with the sources. (I usually use 330 gate, with .2 source resistance)

As for power dissipation, you need to look carefully at how much power you want to get rid of, the size of your heatsink, and thermal resistance of the device. Also, remember that the wattage of a device is usually specified with the case operating at 25 deg C. You will have to reduce the rating when the heatsink temp rises above the 25 degree point.

If you look around some of the MFR web sites, you can find info on how to size heatsinks. I'm sure there are also web sites on the net to show how to do that also...

-Dan
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Old 18th December 2002, 10:35 AM   #3
hacknet is offline hacknet  Singapore
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will more mosfets mean that i wud need smaller heat sinks? becuz they dissispate heat equally...
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Old 18th December 2002, 04:32 PM   #4
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Quote:
Originally posted by hacknet
will more mosfets mean that i wud need smaller heat sinks? becuz they dissispate heat equally...
Possibly, that depends on how much heat you need to get rid of, but you may be able to get away with a smaller heatsink, if several devices share the load.


-Dan
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Old 18th December 2002, 04:49 PM   #5
hacknet is offline hacknet  Singapore
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wud this be rite to sae if i can build a 100w amp with irf610s as o/p devices?
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Old 18th December 2002, 04:51 PM   #6
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You could, yes, with enough in parallel.

IRF620/630 are close to the same price and have larger die inside, which give you higher power dissipation and transconductance in the same package, though. If your driver stage can drive the extra input capacitance, you might want to go that route.
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Old 18th December 2002, 11:09 PM   #7
hacknet is offline hacknet  Singapore
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irf610 are a dollar each... irf350s are $12 each... i can afford to put 10 irf610 for the price of 1 irf350... it prob will handle more power
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Old 18th December 2002, 11:21 PM   #8
hacknet is offline hacknet  Singapore
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i checked...

irf350 has 2600pf input capz.
irf610 has 450pf

therefore.... i can put almost 6 devices for the same capacitace....

does any one know how cud i build a driver stage to power pavel marcura's 17w mosfet amp with even higher input capz.....

im running my music of the computer.... do i still need the drive stage?
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Old 18th December 2002, 11:22 PM   #9
hacknet is offline hacknet  Singapore
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here are the schematics
Attached Images
File Type: gif mosfet amp 1.gif (7.2 KB, 203 views)
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