BUZ 901x4s 500w Mosfet - Has anyone ever used these - I am about to! - diyAudio
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Old 6th June 2010, 11:14 PM   #1
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Default BUZ 901x4s 500w Mosfet - Has anyone ever used these - I am about to!

Just putting some feelers out there to see if anyone has used these before. I am planning a very simple amp, with minimal board components, and only 2 output devices. These are rated at 500W each, so using one per rail should leave me with a board that will deliver 450W from 70-0-70dc. Any thoughts?
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Old 6th June 2010, 11:33 PM   #2
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I have used the BUZ901 before in a power amp and got good results.

Be careful how you work out power dissipation.
40% of power is lost in the heatsink in class AB.
However, each MOSFET is only on for half the time.
You lose a bit of dissipation due to cross conduction to eliminate crossover distortion.
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Last edited by nigelwright7557; 6th June 2010 at 11:59 PM.
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Old 7th June 2010, 02:38 AM   #3
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Hey Nigel

Yes I am aware of that. I usually allow for 50%, thus having plenty room for SOA. These mosfets however are rate at 500W per device. Its package looks like bridge rectifier, and it has 4 tabs. This is why having one P and one N device, I reckon should be safe for 500W RMS Total....?

Also check out BUZ905x4s. Similar setup. If you google it, it should bring up the PDF.

The board, excluding output devices, measures 20mm x 50mm - with no drilled holes! Perfect for DIY!


Should have some pics up later on today...
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Old 7th June 2010, 03:08 PM   #4
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Exellent transistors but way too expensive. Well, no pain no gain!
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Old 7th June 2010, 03:33 PM   #5
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i would like to see the circuit also ...and will be happy with a link to an AN also ...since was not possible to find
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Old 7th June 2010, 09:55 PM   #6
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I will post the circuit and board asap. Just finishing off some details.


The link to the Mosfets is :

BUZ905X4S pdf, BUZ905X4S description, BUZ905X4S datasheets, BUZ905X4S view ::: ALLDATASHEET :::

I thought that thay were expensive, but if you work it all out, at the end of the day, I think they are worth it. I can get then for AU$28 each. If you take into account that the 125W version is around AU$6, multiply that by 4, and remember all of the gate and drain resistors you don't need anymore, as well as all of the soldering and drilling and board size!

I think we may be onto something, but I am looking for feedback about them - so far, it sounds really good!
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Old 8th June 2010, 08:57 AM   #7
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I think it could work very well, I would drive them with EF though, capacitances are likely to be quite high with these.
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Old 8th June 2010, 10:50 AM   #8
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Those are based on Hitachi die. The Rds on over temperature is about 1R7 per die (1R0 at room temp), or 0R425 for four. 450W/4R requires 15A peak, or a 6.375V loss. The gate drive is about 1V per amp, so add another 3.75V, or ±64V gate drive (over temperature) for 450W/4R.

I hope your ±70V DC is regulated.

Ever wonder why a Hafler DH500 used an unregulated ±93V supply?
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Old 8th June 2010, 01:13 PM   #9
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Quote:
Originally Posted by Coastben View Post
I will post the circuit and board asap. Just finishing off some details.


The link to the Mosfets is :

BUZ905X4S pdf, BUZ905X4S description, BUZ905X4S datasheets, BUZ905X4S view ::: ALLDATASHEET :::

I thought that thay were expensive, but if you work it all out, at the end of the day, I think they are worth it. I can get then for AU$28 each. If you take into account that the 125W version is around AU$6, multiply that by 4, and remember all of the gate and drain resistors you don't need anymore, as well as all of the soldering and drilling and board size!

I think we may be onto something, but I am looking for feedback about them - so far, it sounds really good!
Not to be too much of a buzz kill (sorry...) but take a close look at the thermals. The die to case thermal resistance on the data sheet is almost 50% higher than that of four typical TO-3P devices (where thermal resistances act like resistors in parallel), so you'll run a bit hotter. Success depends on how hard you are pushing it.

The higher the bias the more I'd tend towards separate parts. Just guessing, but on a heat sink with a nice thick base to spread the heat from a concentrated source the BUZ905X4S should do well in moderately biased AB operation.

BTW, where can you buy them?
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Old 8th June 2010, 02:39 PM   #10
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You make a good point about needing a nice thick base plate to spread the heat
on the heatsink. But the thermal resistance junction to case is .3 C/W where
the junction to case of the 901 is 1 C/W so 4 of them would be .25 C/W.
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