Power supply/ diode question

[Ptownkid]

How does one figure out how much current a psu design can handle. I've seen 4 diodes used many times in designs instead of a bridge rectifier, but I'm at a loss as to how max current is deciphered.

Is it just the max forward current rating of the diodes used...so let's say 1n4007 has a 1 amp rating, does that mean that the psu has a 1 amp rating?

This is probably a really dumb question...

 

[Svart]

it's actually not a dumb question. First we need to figure out if you are going to be building the PSU for something or just building it for general usage.

If you are building it for something then we figure out the needed current and work backwards into the supply design. This way you design as much as you need and can choose parts that would be "enough" but not too much(read: cost more than needed..).

If you are going the general usage route, then start with your transformer. How much current does it say it can supply? that will be your maximum current supplied no matter what. Usually tranny designers are conservative in their specifications so we will use that to our advantange here. Now that you know the max your tranny can supply you can choose your diodes accordingly but remember that you are looking to be able to handle the maximum current draw. You'll also adjust your fuse rating to be lower than the max primary current draw so that you'll never even reach the secondary Imax.


but to answer this question directly:

Is it just the max forward current rating of the diodes used...so let's say 1n4007 has a 1 amp rating, does that mean that the psu has a 1 amp rating?

Yes, it would only be a 1 amp powersupply since it *could* be the weak link in the circuit if your tranny has a higher rating. In other words your diodes would burn before your tranny did...

either way, diodes are cheap for the most part, you can overspec them and forget them. I'm currently(no pun intended) using MUR860 diodes for most everything. way overkill but very quiet and efficient.

 

[Ptownkid]

Thanks man, i figured that I had it right. I'm designing it as an all-round psu for many projects, so I'm going to overspec the diodes to get about 2A.

Any suggestions on common and readily available diodes?

However, i may just go back to a bridge rectifier. The reason I wanted to use diodes was because i figured that we all have some 1n400X's kicking around, so in a pinch we could swap em easy in the event of a failure.

 

[Greg]

I also prefer to go with individual diodes to make my bridge rectifier rather than a package bridge rectifier. This is merely personal preference.

 

[Svart]

It's usually hard to find any quiet diode in a full bridge package that's why I do discrete when I can!