B40C800 Bridge Rectifier question.

[Smithy]

Hi there, i need to know if the 0.8a Bridge Rectifier is rated upto 800mA, or if its output is 800mA?

I'll be using it in the Optimised 8xSid C64 PSU Circuit.

Could i use an alternative such as 1.2A “W04 400V" bridge rectifier which is used in Wilbas MB6582 instead?

I really need to know this, because i dont want to blow the thing up.

Would prefer to pick up an alternative one up locally instead of ordering one component online, minimum orders and all that.

0.8a diodes seem to be rarer than others.

[TheAncientOne]

The rating is a max - never use one anywhere near it's max rating. A bridge rectifier can be used at anything up to it max rating. For instance, in a volume compressor I'm building, a 1 amp rated bridge is used to rectify the incoming audio signa1 for control - and that isn't even 10 mA (10 thousands of an amp).

A bigger bridge won't hurt. There are lots of 2 amp ones that will do fine.

The voltage for a bridge is trickier. Use a wide margin: it you think about it, the maximum voltage on any one diode is the voltage stored on the reservoir capacitor at the other side plus the opposite peak AC voltage from the transformer. This is roughly twice the peak AC, so for a 12 volt transformer, the diode PIV will be around 34 volts. It makes sense to use a 100V rated rectifier, (they are quite common),  to give a reasonable safety margin. Indeed, if you check the B40C800 data sheet. it says max PIV 100V, recommended, 40V.

Hope this helps

[Smithy]

The rating is a max - never use one anywhere near it's max rating. A bridge rectifier can be used at anything up to it max rating. For instance, in a volume compressor I'm building, a 1 amp rated bridge is used to rectify the incoming audio signa1 for control - and that isn't even 10 mA (10 thousands of an amp).

A bigger bridge won't hurt. There are lots of 2 amp ones that will do fine.

The voltage for a bridge is trickier. Use a wide margin: it you think about it, the maximum voltage on any one diode is the voltage stored on the reservoir capacitor at the other side plus the opposite peak AC voltage from the transformer. This is roughly twice the peak AC, so for a 12 volt transformer, the diode PIV will be around 34 volts. It makes sense to use a 100V rated rectifier, (they are quite common),  to give a reasonable safety margin. Indeed, if you check the B40C800 data sheet. it says max PIV 100V, recommended, 40V.

Hope this helps

Prof that helps a lot alright!

Thanks a lot.

I was just worried that they output was the value they gave, and if i went 200mA higher id blow it up!

I can get 1.0a ones at my local store which is the next best thing.

Thanks a lot.  ;)

[Smithy]

Edit: the datasheet says Average rectified  Current Output = 0.8A

Surely if i bought 2A one as you say, it would be putting out too much current?

Its not the rating thats 0.8A i think, its actually the output it gives.  :-\

[DragonMaster]

Surely if i bought 2A one as you say, it would be putting out too much current?

Nope, it would just be able to output a maximum of 2 amps. The rectifier just converts AC to DC, nothing else. The circuit will use the current it needs, and the rectifier output voltage is 1.414 x input voltage.

Average rectified  Current Output @Ta = 50°C= 0.8A

The maximum output current at 50°C. Average is probably the average rating that tested units produced. (Those tests are done on multiple units, some can handle more current than others)

An higher voltage rating like in Wilba's circuit is much safer as the diode has much less chances to fail. (Because if it fails, it shorts, that means both AC lines will get connected together in the bridge and the DC outputs as well. Not only will it destroy the whole circuit, but also get the transformer outputs shorted, and if there are no fuses (Likely), the transformer will overheat and there are following consequences. A shorted transformer used for small projects like this one don't pull enough current to get the 15A breakers to shut off if they're shorted at their outputs, so fuses and >200V bridges are always recommended.

[TheAncientOne]

Current is like the water flowing in a pipe, the amount that flows depends on what the device connected draws. A 2 Amp bridge can SUPPLY current up to a maximum of 2 Amps. If your MIDIbox draws 300mA, then that's all that will flow through the circuit.

The situation you don't want is a rectifier rated at less that the required current; more current than it is rated for could overheat it and make it burn out, which may in turn damage other parts.

So: current required = 600mA, rectifier rated at 2 Amps = Good

Current required = 600mA, rectifier rated at 500mA = Bad.

Just don't go too big - they are expensive and take up too much space!.

On the same analogy of flowing current in a wire being like water in a pipe, the Voltage can be thought of as the pressure pushing it along. This is why it is very important to make sure your voltage regulators are working properly, if the voltage is too high, too much current will flow through your box, and the chips will overheat and burn out.

[Smithy]

Lads thank a lot for the in depth replies.  ;D

The terminology of the average current rating had me confused, and made me real paranoid!

I was wondering alright how the hell could  4 diodes increase current lol.

But just had to make sure!!!

Thanks again.

[DragonMaster]

I was wondering alright how the hell could  4 diodes increase current lol.

Unless this bridge has an hidden constant current source in it :D (Joking) With a constant current source, the voltage is adjusted by the circuit so that a constant current is output -> BAD for digital circuits.)