paralling four 6A4 Diodes in Bridge

[katiyar]

Can four 6A4 Diodes be placed in parallel in each arm in a bridge configuration to get 24 A supply circuit in place of a single bridge of 25 Amps.

[benb]

Yes and no. If you parallel diodes for more current than each diode's rating, you need a resistor in series with each diode to equalize the current. If you don't one will have a slightly lower voltage drop than another, and thus carry substantially more of the current, and then heat up more than the others, reducing its voltage drop and causing it to carry even more of the current, exceeding its rating.

I think the resistors should be scaled to drop a couple of tenths of volts (is that good, folks?) at full current to equalize the currents 0.2V / 6A = 0.033 ohms), and then of course the power rating for greater than the product of their voltage drop and 6 amperes. And then have all these 16 diodes and 16 resistors spaced out enough to insure adequate ventilation for cooling.

You can do it but when you look at all those parts, it's easier to get a single part of the full rating.

[katiyar]

Thanks for valuable reply. I did not thought of putting resistors in series to equalise current sharing.

[!]

benb is only partially correct. As current rises, the forward voltage of a silicon diode rises too. There is the drop from heating but it is only a few mV per degree, quite overshadowed by the tenths to hundreths of a volt Vf change as current rises.

Considering they are the same model of diode and probably even from the same batch(?), A resistor isn't really necessary, you just need to derate them a little.

Maybe consider them 4A instead of 6A for this purpose, but is the average forward current actually close to 24A? That seems fairly high and 6A4 are rated for 250A surges.