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Old 6th June 2006, 10:37 AM   #1
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Default Bridge With IRF 540 & IRF 9540

Hello Friends,

I want to know is IRF 540 & 9540 can handle in Bridge with +/- 50V supply.

Need to parallel them for full power output in that +/- voltage?
How many MAX Watt can get at 4 ohm & 8 ohm?
What AMP of fuse can use in +/- rail?

Pls, help me.
Thanks.
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Old 6th June 2006, 10:42 AM   #2
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A single pair will be just about OK with 8 ohm load on +/- 50V supply, 4 ohms will be dicing with fire. Basically you should expect no more than about 75 watts RMS from a single pair. You can then use this basis to determine voltage rails (and bridge specs) and fuse ratings for your chosen load impedance.
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Old 6th June 2006, 11:27 AM   #3
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hello friend,

U said one pair can handle only 75watts?
In Bridge we must use two pair.
Can that handle abt 150 Watts?


For Bridge with +/- 50V supply
My calculation is
Power max for 8 ohm ~ 253Watts.
Power max for 4 ohm ~ 507Watts.
Is that true?

For 8 ohm load in Bridge
Must use 2pair or 4 pair or 6 pair or .......?

Can u advise for me or give me calculation method ?
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Old 6th June 2006, 12:19 PM   #4
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One pair = 75W so however many pairs you use you multiply by that number.

Assuming 50V rails with 5V rail loss and 4 ohm load, a single-ended (un-bridged) amp would be:

Ppeak = (V * V) / R = (45 * 45) / 4 = 506 W

Prms = Ppeak / 2 = 506 / 2 = 253 W

253 / 75 = 3.37

Therefore to run this you would need 4 pairs of output devices.

If you were to build two of these single-ended amps you would have a 2x 253 W into 4 ohm amp and use a grand total of 8 pairs of output devices for the stereo pair. If you were to bridge them, you would be limited to no lower than 8 ohm load (as each amp sees half the load impedance) so you would have a 1x 506 W into 8 ohm amp.

Note also that you must use IRF540 and IRF9540 not the newer IRF540N and IRF9540N devices as these newer types will not cope well with linear amplifier application and may go up in smoke.
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Old 6th June 2006, 02:56 PM   #5
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With one pair of these devices you can get without problems 100 W into four Ohms...
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Old 6th June 2006, 10:15 PM   #6
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Hello friends

Some years ago i had build a power amp with this mosfets.
Bridge amp with +- 43 volts supply,2 pair of IRF540 and 2 pairs of 9540 each amp(total 8 mos x channel)with low amount of NFB.
Some difficulties were taken place.
At the first the dumping factor of 25 / 8 Ohms,for me too much low.
Another problem of this mosfets is the difference between us , like result in a great number of refuse:40 mosfets in order to use 8.Neglect this selection,the current would be different and distortion increase.
I advice against to construct an amp whit this topology,i think that a bipolar is much better for a bridge power amp.

It would appeal to me that someone can reply to this
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Old 7th June 2006, 10:18 AM   #7
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Yes there can be a problem with current sharing because HEXFETs are not as tightly matched, this can be made less of a problem by using 0.33 ohm source resistors.

Without seeing a schematic it's impossible for me to comment further.
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Old 7th June 2006, 03:12 PM   #8
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Here is my diagram
Attached Images
File Type: gif irf 540&9540.gif (6.0 KB, 1706 views)
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Old 7th June 2006, 03:20 PM   #9
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If I parallel with another pair,

where can I connect?

From emitter of transistor OR end of 100R



MOSFET is voltage follower in that diagram ?

OR

MOSFET is current control in that diagram ?

Can u explain me roughly about MOSFET ?

I know little about transistor .
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Old 7th June 2006, 03:31 PM   #10
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That amp will blow up after time because it has no thermal compensation.

Are you going to try and lay that board out yourself? Because it will be quite sensitive to board layout, a simpler design would be advised.

You would add additional parallel output devices by replicating the gate resistor (220R), MOSFET and source resistor (0R22).

I suggest you just build a proven design that is right for your needs and skill level, or you will simply waste time and parts and get frustrated.
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