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Old 22nd May 2006, 10:07 PM   #1
mastero is offline mastero  India
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Default Need urgent help with SMPS SG3525 based

Hello all,

I have started building the valveaudio car power amp almost similar to the ESP P89 (JUST the power section)

I have completed the PSU section when i power it up .. nothing happens i get 5.5v on the PIN 13 and 15 the data sheet of 3525 says 8~35v. I connect the 12vdc directly to the pin 13 & 15 and the output volt jumps to +/- 29volt .

But within seconds the toroid secondary ground wires become red hot and they start glowing .. i mean glowing like a light bulb

Toriod details

Material = Ferrite core (Looks like a ring magnet)
OD = 46mm
ID = 44.2 mm
THK = 10 mm

Primary winding done first with 0.8mm wire

5 wire x 4 turns tap then 4 again

Secondary winding done with 0.8 mm wire

2 wire x 17 turns tap then 17 again

What should be the voltage on PIN 13 and 15 of 3525 ?

What am i doing wrong...?

BTW nothing blew and nothing got warm except the glow from the toroid wires.

MOSFET Z44n
Diode BYW29

Please help

Thanx
Mastero

PS: I have read almost every thing the search gave me with 3525
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Old 22nd May 2006, 10:53 PM   #2
mastero is offline mastero  India
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I have prepared a PCB layout of ESP P89 in Express PCB

Enjoy

Mastero
Attached Files
File Type: zip car amp.zip (25.6 KB, 266 views)
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Old 23rd May 2006, 09:58 AM   #3
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No output with Vcc = 5.5 V is not surprising since the 3525 has an undervoltage lock-out feature requiring Vcc > 8V.

Wrt. the glowing wires - did you check for inadvertent shorts, such as ground loops through meters, o'scopes etc.? Any shorts in the output windings themselves (wire-to-wire, bad insulation)?

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Old 23rd May 2006, 12:43 PM   #4
mastero is offline mastero  India
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yes there is a short in the secondary winding fixed it ...

Giving 12v to pin 13 &15 works to give me +/- 30vdc output.

Thankx ..

Any comment on the express pcb design ... ?

Does it need any changes ... BTW its a single side PCB design.

Mastero
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Old 23rd May 2006, 03:02 PM   #5
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Mastero,

Don't have the pcb viewer, can you convert it to a .jpg or .bmp or even better a .PDF? Good to hear you solved the other problems, as I would have been mystified about the +5.5V on pins 13 (Vc) and 15 (Vcc). Don't want to let the magic smoke out!

Regards,

Steve
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Old 23rd May 2006, 07:04 PM   #6
mastero is offline mastero  India
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N channel you can down load expresspcb for free from www.expresspcb.com

Good software easy to use..

It was a faulty transistor ... not give 12v to pin 13 and 15.. small things make big difference

15 downloads and no comments

Cheers
Mastero
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Old 23rd May 2006, 07:30 PM   #7
sss is offline sss  Israel
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please make a jpg image , not all of us using the same pcb software...
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Old 23rd May 2006, 10:39 PM   #8
PM650 is offline PM650  United States
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pic of board here.
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Old 24th May 2006, 02:25 AM   #9
bawang is offline bawang  Malaysia
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Mastero, it would be nice to have your schematic..... Is it fully functional now?
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Old 24th May 2006, 02:56 AM   #10
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Default Nice Board

Mastero,

Download was easy. Board looks good. Couple o' questions:

1) Why put the output inductors after the filter caps? Wouldn't it be better to put them before the caps, and perhaps couple them onto the same core? Just an idea I stole from looking inside every AT & ATX box I could get my hands on.

2) What is the pinout for the BYW29? Since I don't know, please forgive me if I'm talking out of school, but it looks like one leg of the secondaries is jumpered directly to the (+) output bus, and the (-) side of one of the BYW29s is tied to the other AC leg of the secondary. Since I do not have the datasheet for this diode, I could be wrong. Is this diode similar to the MUR1520 diode?

3) Have you considered using high-voltage Schottkys? I have used some MBR10100s (10A, 100PIV) with great success, and their forward voltage drop at full load is only 0.65 - 0.7V.

Please give us your thoughts. Thanks a bunch for giving me another project idea!

BTW, did you ever publish your DC-DC ATX schematic from the MP3car.com forum?

Steve
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