# Nominal current of diode bridge rectifier

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#### MikhailFrolov

##### Newbie level 3
Hi everyone!
I am choosing three-phase diode bridge rectifier now. I'm trying to understand what current is present in datasheet for such devices – the average current of a single diode or output bridge current. Can anyone help me with that?

#### KlausST

##### Super Moderator
Staff member
Hi,

I assume it is written in the datasheet.
Give us the link to your datasheet ... or the datasheet of any device you have in mind.

Klaus

#### BradtheRad

##### Super Moderator
Staff member
three-phase diode bridge rectifier

Waveforms through a diode are different, depending on whether your 3-phase is delta or star. It doesn't necessarily change average current, but it may make a difference in peak Amperes.

If you add a smoothing capacitor in the output stage, then it tends to draw brief bursts of current, rather than smooth flow.

#### KlausST

##### Super Moderator
Staff member
Hi,

Datasheet says:
* I_DAV --> current, diode, average
* bridge output current --> not input current
* rectangular --> not sine shaped
* d = 1/3 --> duty cycle = 33%

Now you need to know that if you want some output current, then always:
* two input phases out of three are involved
* two diodes out of six are involved

For the package power dissipation (that limits the average current) it makes no difference if always the same diodes are used or different diodes.

******

It even makes not much difference in power dissipation whether two diodes are involved or - the theoretical case - where three diodes are involved.

Klaus

#### wwfeldman

##### Advanced Member level 3
the data sheet says rectangular pulses, 1/3 of the time, as noted above, 90A output current

conduction by any one diode 1/3 of the time is the most one would expect from a 3 phase sine wave input

rectangular is worse than sinusoidal because the current is constant instead of increasing and decreasing
sinusoidally over the conduction time

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