Author Topic: Bridge rectifier current  (Read 822 times)

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Offline JwillisTopic starter

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Bridge rectifier current
« on: November 29, 2019, 04:59:37 am »
How do I determine the current rating of a full bridge rectifier. I'm thinking it  to be the same as the current rating of any one of the diodes used. But them I'm thinking that any one diode will only pass current every half cycle. So I could use lower rated diodes than the current i want to pass. Or am I  second guessing and the first idea is correct?
 

Offline floobydust

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Re: Bridge rectifier current
« Reply #1 on: November 29, 2019, 06:54:47 am »
The current rating is for any one diode, as far as the junction's capability.
But in a bridge rectifier, the diodes are on in alternating pairs, so heat is generated from two diodes. The package might not actually be able to dissipate the heat even though the diodes have the current rating. Both parameters have to be considered.

Careful if you have a capacitive load, the current waveform is not sinusoidal at all. But the rectifier's datasheet usually assumes 50/60Hz sine loads for the ratings.
On power up there is a surge for many cycles until a filter capacitor charges up.
 
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Offline gbaddeley

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Re: Bridge rectifier current
« Reply #2 on: November 29, 2019, 09:50:02 am »
Lower rated diodes than what is needed is generally a bad idea. It leaves no margin for overload or thermal demands and will probably fail in the long run. As an estimate, I suggest a rating at least 2 - 4 times the average current.
Glenn
 
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Offline JwillisTopic starter

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Re: Bridge rectifier current
« Reply #3 on: November 30, 2019, 08:53:24 am »
Thanks for the help.I was trying figure out why I was getting such screwy wave forms on the scope so I thought the rectifier was hosed. Since I didn't have one rated for what I needed I could throw something together to get me going again . But after some contemplation I realized that in order for the rectifier to work properly it needs a load on it . :palm: . Slapped 100k resister across the positive and negative now it works as expected.
 


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