power supply

[jamesbooi]

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.

 

[Frank Berry]

The voltage rating of the 47uf capacitor should be 50 volts.
Check that you didn't install it backwards.

 

[Bakmeel]

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.

Bouke

 

[jamesbooi]

- 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......??

 

[Jennice]

What's your purpose with the inductor?

Jennice

 

[jackinnj]

It oscillates -- this is a switching regulator design -- and you have to pay very careful attention to the current handling capabilities of the capacitors --

 

[Eva]

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.

 

[Jennice]

Hmmm... a SMPS with a 317 !?

Maybe I really do need a quiet weekend...

 

[jackinnj]

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 --

An externally hosted image should be here but it was not working when we last tested it.

 

[Jennice]

Thanks,

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

Jennice

 

[mzzj]

- 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!

Tantal caps have bad habit to go dead-short and if availlable current is big enough they explode. They dont like heat, overvoltage(spikes?!) and especially not reverse-polarity. Ripple-current handling capacity varies wildly depending on manufacturer and series. Try something like 470uF 50v al-electrolytic + 100nF ceramics.

 

[Kenshin]

Some SMD tantalums have a line near the + terminal.
Different from SMD diods, which the line always appear near the -
terminal.

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.