the right diode bridge ampere

ballfire · Post by **ballfire** » 10 Oct 2019, 04:34

hello people of the planet freestompbox..

i have a question how many amperage of the diode bridge if i use a transformer 220volts on primary and 15-0-15v on secondary and its a 6 ampere transformer??

alexradium · Post by **alexradium** » 10 Oct 2019, 06:01

ballfire · Post by **ballfire** » 10 Oct 2019, 06:12

alexradium wrote:25A

25A??? i thought using 4 ampere diode bridge is okey???

why is it 25A??

any explanation..by the way its for my amp power supply..

plush · Post by **plush** » 10 Oct 2019, 08:17

ballfire wrote:hello people of the planet freestompbox..

i have a question how many amperage of the diode bridge if i use a transformer 220volts on primary and 15-0-15v on secondary and its a 6 ampere transformer??

Your diode bridge power rating is defined mostly by how much power (current) your circuit draws from the transformer in peak. Extra power rating is good, but not always.

Also there is no circuit protection implemented in your schematic. I suggest adding 2 fuses before your diode bridge (they will protect from both short circuit and diode rectifier failure). Fuses power rating must be defined according to your circuit power draw.

Also your schematic shows using zener diodes as power regulators. I myself'd replace them with linear voltage regulators with additional build'in protection.

Manfred · Post by **Manfred** » 10 Oct 2019, 20:21

Hi ballfire,
download the Duncan PSU-Designer with it you can find all voltages and currents by simulation.
http://www.duncanamps.com/psud2/index.html
BTW the load is missing in your circuit it is required for correct results.

george giblet · Post by **george giblet** » 11 Oct 2019, 01:19

Firstly, do you realize for a 6A transformer you can only pull about 3.2A *average*? However, for a power amp the current is drawn from one half of the +V/-V supply at a time. Also, the supply current waveform is half-sinusoidal.

Anyway, if you have a transformer capable of 6A AC and you connect it up to a rectifier and filter, then pull the full load DC of 3.2A average off the DC rail (in your case what would be across +V and -V) then the peak current in the rectifiers will be in the order of 14A or so a 25A rectifier is a safe choice.

For a continuous load, the bridge rectifier will dissipate about 9W of heat. Which is a lot, and the rectifier will need a heatsink or will need to be mounted on the metal enclosure.

Smaller rectifiers will have higher diode drops and will get a little bit hotter.

george giblet · Post by **george giblet** » 11 Oct 2019, 03:31

For a continuous load, the bridge rectifier will dissipate about 9W of heat.

IIRC that should be 6W (Maybe if 6 was 9 it would correct.)

ballfire · Post by **ballfire** » 11 Oct 2019, 06:10

george giblet wrote:
For a continuous load, the bridge rectifier will dissipate about 9W of heat.
IIRC that should be 6W (Maybe if 6 was 9 it would correct.)

the only available diode bridge here in our place is 25 ampere...so i can use this??

george giblet · Post by **george giblet** » 11 Oct 2019, 09:15

he only available diode bridge here in our place is 25 ampere...so i can use this??

No problem using that. That one is a fairly common part.

alexradium · Post by **alexradium** » 11 Oct 2019, 09:28

ballfire wrote:
george giblet wrote:
For a continuous load, the bridge rectifier will dissipate about 9W of heat.
IIRC that should be 6W (Maybe if 6 was 9 it would correct.)

the only available diode bridge here in our place is 25 ampere...so i can use this??

I was just referring to that bridge,it costs just a bit more than a plain 4A plastic case,you can bolt it to chassis for better heat dissipation, plus,if you need to feed filament heaters you are ok with the startup inrush current, which can be 2 or 3 times the nominal.

ballfire · Post by **ballfire** » 14 Oct 2019, 04:39

hello guys

this is now my final diagram using a 25ampere diode bridge ..actually i will put it to my marshall mg15cd power supply section because of no availability of 16-o-16 center tap power transformer im gonna use a 15-0-15 transformer 6 ampere with a 25ampere diode bridge suggested by the great people here..

please check my new diagram below if it will work on my mg15 marshall amplifier power section or if my amp will work normally or gonna blow up

..

george giblet · Post by **george giblet** » 14 Oct 2019, 06:36

please check my new diagram below if it will work on my mg15 marshall amplifier power section or if my amp will work normally or gonna blow up

Wired exactly like you have drawn it - it will blow up!

Notice there a "+" terminal. The terminal is pointing in a different direction to all the other terminals. The "+" terminal should connect to your +V DC rail

Diagonally opposite to the "+" terminal is the "-" terminal. That should connect to your -V DC rail.

The other two terminals are the AC terminals, which are diagonally usually marked "~". or "AC" those terminals connect to the transformer.

http://copyright.lenardaudio.com/laides ... supply.gif

ballfire · Post by **ballfire** » 14 Oct 2019, 07:42

george giblet wrote:
please check my new diagram below if it will work on my mg15 marshall amplifier power section or if my amp will work normally or gonna blow up
Wired exactly like you have drawn it - it will blow up!

Notice there a "+" terminal. The terminal is pointing in a different direction to all the other terminals. The "+" terminal should connect to your +V DC rail

Diagonally opposite to the "+" terminal is the "-" terminal. That should connect to your -V DC rail.

The other two terminals are the AC terminals, which are diagonally usually marked "~". or "AC" those terminals connect to the transformer.

http://copyright.lenardaudio.com/laides ... supply.gif

ok sir thanks for the advice about the orientation of the bridge diode.. actually i will figure it out what should be the positive and negative..

if i put it right it will work sir???the whole power supply?? i compute the voltage after the big capacitor is 21 volts going to the power amp am i right ??

george giblet · Post by **george giblet** » 14 Oct 2019, 22:24

if i put it right it will work sir???the whole power supply?? i compute the voltage after the big capacitor is 21 volts going to the power amp am i right ??

Yes it should work.

You might get a bit more voltage, say 22V at no load. At no load the transformer output will be a little higher than 15V rms due to regulation, say 7% higher, then you lose a bit of voltage through the rectifier.

ballfire · Post by **ballfire** » 15 Oct 2019, 04:26

george giblet wrote:
if i put it right it will work sir???the whole power supply?? i compute the voltage after the big capacitor is 21 volts going to the power amp am i right ??
Yes it should work.

You might get a bit more voltage, say 22V at no load. At no load the transformer output will be a little higher than 15V rms due to regulation, say 7% higher, then you lose a bit of voltage through the rectifier.

can i mount the body of the diode bridge to the chassis of the amp?? can i put a screw on the middle hole of it and mount it to the amplifier chassis??

george giblet · Post by **george giblet** » 15 Oct 2019, 07:18

can i mount the body of the diode bridge to the chassis of the amp?? can i put a screw on the middle hole of it and mount it to the amplifier chassis??

No problem, a lot of people do that.

ballfire · Post by **ballfire** » 16 Oct 2019, 00:56

george giblet wrote:
can i mount the body of the diode bridge to the chassis of the amp?? can i put a screw on the middle hole of it and mount it to the amplifier chassis??
No problem, a lot of people do that.

ok sir thanks..im gonna test this transformer and diode bridge..

thank you very much for the advice and opinions...