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Old 1st July 2006, 04:42 PM   #1
RX5 is offline RX5  Philippines
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Talking my 1st ever D-amp, WORKING!!!

hello all,

Got my 1st D-amp... UcD way!!

mosfets used are only IRFZ44(hi) and IRFZ48(lo)... i know, but it works... the only mosfets I have in my junk... others were too low... in volts/amps.. others where logic level.... power supply used: +18/-18 @ 750mA.... i know its not much... but its for testing porpuses only... wish I had done these before i -KILLED- my 4 IRF540s... I used +30/-30 @ 8A..... man!! what a mosfet killer... there was obviously something wrong with the circuit.... thats why ive redone the PCB board using kartinos layout..... schematic is a mix of kartino and classd4sure.. added some parts in the board too(decoupling caps).... still need to make a bigger heatsink though.. BUT IT WORKS!!!

right now, im still waiting for the IRF540 to arrive, i have ordered locally.. they ran out of stock.... then will I connect the 8A supply..

got a few question though:

#1> is it normal for the Lo Side MOSFET to HEAT UP 1st???

#2> wont it do damage to speaker on power up/shut down ??

bellow is an image of my D-amp.... heatsink SMALL.. for testing porpuses only... i cant run it for more than a minute... MOSFETS get hot!!!

BUT... it does sound great... clear!!! no distortions... I think i had just the right resistor value for the daedtime.... Im guessing this amp is outputing 10Wrms?? i dunno....

anyway, im happy with the results.. i should be.. after killing original I.R. IRF540.....

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Old 1st July 2006, 05:04 PM   #2
RX5 is offline RX5  Philippines
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Default here it is

the picture.. sorry for the delay.. im only on a dial-up....

Click the image to open in full size.
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Old 1st July 2006, 09:10 PM   #3
rinox is offline rinox  Italy
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Please, attach a schematic if you want a suggestion.
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Old 2nd July 2006, 02:43 AM   #4
RX5 is offline RX5  Philippines
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Default schematic

Quote:
Originally posted by rinox
Please, attach a schematic if you want a suggestion.

http://i6.photobucket.com/albums/y20...inalfornow.png

http://i6.photobucket.com/albums/y20..._ucd_sch_2.png

those are my exact references....

modified/changed some parts.. on what was locally available here in our place...

still drawing the exact circuit i used....
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Old 2nd July 2006, 02:45 AM   #5
RX5 is offline RX5  Philippines
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Default info/slight prob

hello and good day,


oooppppsssss!!! i spoke too soon... I tested the amp at 11pm... so I

kept it at low volume.. now its 10am...i made a bigger heatsink for the

mosfets... now I am running it at 70% of its full power(still at +18/-18

@750mA) ... yup MOSFET gets hot... and the power supply too!! I use a small fan to keep it

cool.... tried playing it with some bass tracks .. THERE a hear a small

distortion... sounds like "kkkkrtttt" looks/feels like busted speaker..... I

think its in the 40Hz-60/Hz range.... higher frequency IS NO PROB....

To chris and kartino,

since you have explored much...

what could be the cause of this??? deadtime setting?? (still IRFZ44/48

as MOSFETS).....output filters??? btw, my power supply is 60Hz..

NOT 120Hz(fullwave).. its just halfwave... but filtercap is large....

6800uF + (1000uF+1000uF+180uF onboard)... certainly this could

NOT be the problem right???

help me out....

-raff
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Old 2nd July 2006, 06:51 AM   #6
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Hi,

I'd appreciate you linking to the thread which my schematic was posted to rather than uploading it from photobucket.

If you read the threads you got those from and I trust you have, you'll see part selection is very important in obtaining best performance, and I'd given a few good hints as to what matters where, so I hope you kept with that in your selection.

You lose me with your first post. "There was obviously some problem with the circuit, so I redid it with Kartino's layout".

What was wrong with the circuit is that you first used 30V 8amps as your first test without optimising the values for your given components. Changing the layout alone will do nothing for this, although a decent layout is obviously equally important, and I'm not sure this is it. The values you see on my circuit were what worked best with simulation, and not intended to be "real world" values, so they'd require changing in some places, I think I mentioned all this in my original thread though.

Now you're using lower voltage and have apparently limited the current to less than an amp (how you did this we don't know).. I'd say it is the lower voltage that's saving you though, given your selection of caps high currents will still flow through the outputs if you raise the voltage level.

At this voltage level you should be able to obtain mosfets that run perfectly cool and without the use of a fan. This of course has to do with component selection, and not just the mosfets, but the entire circuit really.

There are certain things in Kartino's circuit I can't vouch for, which could be causing your problems, as well as the layout of the PCB.

Without seeing your exact circuit with component selection it would be pointless to comment further on where your slight distortion is comming from, could be anything, I'd start with a half decent supply though, half wave?? noooo.


At least measure your DC offset, and start adopting some troubleshooting procedure that will allow you to make sense of things as opposed to changing your layout immediatly after the first problem.

If you want to perfect this at those voltage levels, you're simply going to have to become familiar with optimizing it based on the components you chose, and that also includes the possibility of re-evaluating your choice of components. It is more important to use components that are right for the job over what is more easily available.

That's really all I can help you with, it took me nearly two years to get as far as you've come with it in less than a month, but being given that doesn't really allow you to just build it and go, you'll have to become familiar with it enough to be able to tweak and optimize it based on your design choices.

. So you're in for a bit of work and learning yet, and I know it's worth it, you probably have found this out yourself already, despite the zzzzrrrtttt sound, I bet it is uniquely pleasing in a kind of high end way?
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Old 2nd July 2006, 07:05 AM   #7
Baldin is offline Baldin  Denmark
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The IRFZ48 you are using for lower side is almost 5 time slower than the IRFZ44 you are using for the high side. It will therefore see a higher loss than the high side.

What switching freq are you running at?

If the MOSFETs are heating up without load, I'm not so sure you got the timing spot on. (If your PSU heats up, I think you have some shoot throught)

You should use the same mos for upper and lower, as a start. Then adjust the deadtime (better starting with too much delay as a start until everything else works).

Check all waveforms on a scope.

Have you checked that you don't have any DC on the output?

Does the filter heat up as well?
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Old 2nd July 2006, 09:16 AM   #8
RX5 is offline RX5  Philippines
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hello and thanks for the replies

Im here.. still optimizing values....

post back later on....
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Old 3rd July 2006, 05:09 AM   #9
RX5 is offline RX5  Philippines
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hello again,

I changed almost all passive parts...... as per chris' schematic....

some active parts too.... some parts not available in our area... ( pls

see attached scheme)
http://i6.photobucket.com/albums/y20...l8st_cheme.gif


>> MOSFET, HOT!!
>> power suppy, HOT too!! +18V/-18V @750mA
>> filter coil: barely warm
>> TIP31C : warm (no heatsink)

IS this why its STILL hot because I have still not changed the

MOSFET? im currently playing with IRFZ44(hi) IRFZ46(Lo).... IRF540

still coming... soon...maybe this wednesday parts will arrive...

HOW do I prevent shoot through? (heating of power supply)

HOW to prevent heating?? re change value of 250ohms? 470ohms?? is this because of deadtime?

Is the input section...ok to use?( i removed the OP amp)

how do I increase amp gain?? changing the feedback resistor, right??

(7.2K).. kartino tippd me on this... too much gain results in (sort of) flat

top/bottom signal output... <clipped output signal>... i simulated it too

help! i dont want it to heat up!!
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Old 3rd July 2006, 05:16 AM   #10
RX5 is offline RX5  Philippines
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Default now the amp

the power supply.... +18V/-18V @ 750mA

Click the image to open in full size.

the amp....
operating WITH a FAN.... it heats UP!

Click the image to open in full size.

whew

-raff
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