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So, I just started getting into electronics, and I have built a bridge rectifier using the 1N4007 diodes.

So far I have been using this rectifier with a 24 volts step down transformer, but now I need a higher voltage for other purposes. The AC current in my country comes at 220 Volts, 50 Hertz, so my question is: Can this bridge rectifier be directly connected to the AC mains, or do I have to get a transformer?

If you have links to other sources, please post them.

If you don't but you have experience, please answer anyway.

Thanks!!

Dakshin
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    As the answers say, you *can* use diodes that are rated high enough to directly modify AC mains voltage. It's a little concerning that they haven't spoken to the safety issue in going through this route. The transformer gives isolation of one circuit from the mains voltage. If you remove a transformer, and your diodes fail, you'll end up with a completely fried circuit and a very dangerous piece of equipment if anyone were to be touching a wire on it and be grounded somehow. If you go this route, be very careful. http://en.wikipedia.org/wiki/Galvanic_isolation – horta Jul 14 '14 at 14:21

2 Answers2

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The first criteria is how much voltage the diodes need to block. Above a certain voltage (the breakdown voltage) the diode will conduct large current in the reverse direction (destroying itself and probably another diode that is conducting in the forward direction (by overcurrent since the two will be in series across the mains).

Since the peak voltage on a 220V RMS mains is \$220\sqrt 2\$ = 311V and the 1N4007 is rated at 1kV PIV (Peak inverse voltage) that would seem to be plenty of margin.

You should also consider transients from other things that may be connected to the mains- for example if you had a motor and opened the connection to the motor and bridge, the inductive energy in the motor would cause a voltage spike that could exceed 1kV. In such cases a varistor across the input of the bridge can absorb moderate occasional spikes. The MOV (rated for 230V RMS) might conduct 25A or 50A at 600V, so provided that kills the spike even a 1N4006 would be okay.

In fact, a 1N4007 will probably be okay without the MOV in many cases. You should have a series fuse before the bridge (and before the MOV if you use one). They both tend to fail short.

schematic

simulate this circuit – Schematic created using CircuitLab

Spehro Pefhany
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The parameter that determines whether a diode can be used at a certain voltage is the blocking voltage. This table from the 1N400* datasheet shows the 'RMS reverse voltage'.

enter image description here

As you can see, the 1N4004 and 'higher' can work at 230V AC.

Wouter van Ooijen
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