Full Wave Bridge Rectifier

If there is no load and a smoothing capacitor downstream, absolutely nothing.

sir, there is a smoothing capacitor downstream. the case is that, the output voltage went off its rated output voltage. instead of having a 125 volt dc output, it became 200 volts dc. i have tested the diodes and found out that one is defective being open circuited. is this possible?

Yes. Because it happened.

So, why the question?

its just a guess sir. but i still consider the step down transformer to be the cause. but i wasnt able to test its turns ratio yet.

So, put a pair of zener rectifiers opposite-biased in series across the secondary AC downstream of a fuse, so that if the voltage goes too high, the diodes conduct and take out the fuse, thereby protecting the rest of the circuit.

Bridge rectifier failure should not occur unless you are operating it outside its ratings or operating it too hot.

I have seen bridge rectifier failures (both open circuit and short circuit) due to excessive heating caused by high current pulsed loads fed from a transformer (the current being actually less than the maximum ratings of the bridge rectifier).

Are What is the voltage and current rating of the bridge rectifier and the current and duty cycle of your load?

would it cause the diode to be open circuited when the there is a transformer failure? it is operated at 125 volts on its normal operation.

If by transformer failure you mean overload or short circuit downstream (after) the bridge rectifier resulting in the internal transformer thermal fuse operating, then yes.

It is also possible for an overheated or overloaded bridge rectifier to fail and damage the transformer. Don't assume the transformer failed all by itself, because they don't - something external to the transformer (component, voltage spike event, etc) has to cause the transformer to fail.

Wild guess; it becomes a half-wave diode bridge circuit. (But maybe not a 3/4 wave circuit.) [??]

At no load, who cares?

It acts like a 1/2 wave rectifier.

/J

I've seen this happen when one side of the full wave rectifier output was tied to chassis ground. If the transformer is not fully isolated then one diode is blown because you have now created an autotransformer clusterf**k.

If you must tie your DC bus to the same ground as your AC system, you have to pick a stepdown transformer that is fully (magnetically) isolated. You will see this if you re-draw your circuit with a ground connection to one side of your secondary. Dead short - no question!

what will then happen to the output voltage?

To answer your question properly, one has to know what else is attached and whether you are using a grounded secondary or an autotransformer that uses only one coil with various taps. The response will be different.

For a magnetically separate secondary coil, the voltage will drop some percentage due to the loading.

For an autotransformer, the voltage might increase under certain conditions. We could beat all around the bush with possibilities but it really depends on what you have. Below is the circuit I was talking about.

thanks for this sir. my rectifier is only compose of three diodes..

Now I'm really confused. I've never heard of a full wave bridge with three diodes. I could imagine a half wave bridge on a three phase circuit that uses three diodes but any full wave bridge circuit has to have an even number of diodes.

Perhaps you have a center tapped secondary with two regular diodes and some other type of diode such as a zenier.

Could you draw up the circuit and attach it? I still use MSPaint for simple drawings.

this is it sir.. i am not really familiar with the rectifier circuits. but i have checked the circuitry. this is what it looks like. im sorry i made this fast. peace out. please do understand.

thanks sir..

I think you should try rewiring your centre tapped transformer circuit correctly (you have the centre tap wired in parallel with one of the outer taps which is incorrect, and the open circuit diode is unnecessary).

This will help.

Link

thanks sir. il be reviewing it. i just made a glimpse of it when i opened the circuitry. ill try to make an accurate diagram from it.