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Old 1st July 2005, 06:56 AM   #1
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I have build a 1.8-32Vdc/ 3A power supply, but when i turn on the power, the 47uF(tantalum) capacitor BURN! So can anyone tell me what's wrong with my schematic diagram?????

I have attach a schematic diagram in JPG format.
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Old 1st July 2005, 07:57 AM   #2
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The voltage rating of the 47uf capacitor should be 50 volts.
Check that you didn't install it backwards.
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Old 1st July 2005, 08:22 AM   #3
Bakmeel is offline Bakmeel  Netherlands
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I recommend you do remove the 47uF tantalum. It is overshadowed by the 6800uF electrolytic, and does not really add to hi-freq noise cancellation. Replace it with one or two 100nF ceramics.

Some tantalum types (like solid tantalum) are not very good with high ripple currents. I have seen some self-healing tantalums explode violently in some (test) conditions. They seem to be limited in esr dissipation.

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Old 1st July 2005, 09:09 AM   #4
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- yes i use 50V 47uF tamtalum capacitor. At first, i have a 3A fuse attach in the circuit before the voltage pass through the 47uF capacitor, when i turn on the power, the fuse blow! And then i bypass the fuse, turn on the power again, and this time the 47uF capacitor blow!

- Is there anything to do with the diode(1N5402) and the 6800uF 50V capacitor?? Maybe i should change the diode bridge rectifier and change the capacitor to >20,000uF???

- See, i attach the schematic into multisim, and it seems like not really stabil when i view the osciloscope.

- Any other suggestion for the schematic???more reliable......??
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Old 1st July 2005, 10:20 AM   #5
Jennice is offline Jennice  Denmark
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What's your purpose with the inductor?

Jennice
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Old 1st July 2005, 11:03 AM   #6
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It oscillates -- this is a switching regulator design -- and you have to pay very careful attention to the current handling capabilities of the capacitors --
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Old 1st July 2005, 01:01 PM   #7
Eva is offline Eva  Spain
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Tantalum capacitors are polarized. Are you sure that you are not connecting them backwards? They usually have a small '+' sign printed near the positive leg.
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Old 1st July 2005, 02:13 PM   #8
Jennice is offline Jennice  Denmark
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Hmmm... a SMPS with a 317 !?

Maybe I really do need a quiet weekend...
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Old 1st July 2005, 02:39 PM   #9
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Quote:
Originally posted by Jennice
Hmmm... a SMPS with a 317 !?

Maybe I really do need a quiet weekend...
Yes, the schematic is identical to the one found on National Semiconductor's website --

Click the image to open in full size.
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Old 2nd July 2005, 03:40 PM   #10
Jennice is offline Jennice  Denmark
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Thanks,

I didn't know that one... but interesting indeed.

Jennice
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