Effect Of Busted Diode Of A Diode Bridge Rectifier

Congratulations ! You now have a half wave rectifier !

Well that does depend on what "busted" means. The most common way a diode fails is by becoming effectively an open circuit. In this mode it will be a half wave rectifier. However, a diode can also fail by the reverse breakdown voltage now being insufficient. Thus an effective short circuit for half of the waveform will exist.

Haha, yes that's true. I guess I took "busted" literally, as in broken to bits.

My experience on this is that in most cases a rectifier diode originally fails as a short circuit, and if the power source current capability is more than a few dozen times the diode's capacity, AND fuse or other protection measure is slow enough, then "meltdown" to open circuit happens. S.M.

You will still get DC output but it will be pulsed.

How does it effect my load and circuit? Say I have a solenoid load.

Well since we still don't know if the failing diode is an open, short, if there's a fuse in the circuit of if there's any other components in this circuit at all besides a bad diode I cannot tell how it will affect a solenoid of unknown specification.

My nominal consultant fee is $10. I'll send you a bill.

Silicon rectifiers usually internally fuse into a short circuit when they fail. If one of the four diodes were to short out, half of the AC being supplied would be shorted.

Dear Friend

Every diode which you select has forward current If, forward voltage, reverse voltage, and IxIxt rating. When you select a bridge rectifier, all should have the same rating, voltage, current and I2t. and also you should provide a protection less than the I2t rating. If do not provide protections, the load will blow both the transformer and the circuit connected to it.

when the load is applied, the rectifier with take the load, when it switches off for any fraction of second, there will be reverse current flowing in the bridge rectifier.

To prevent this fluctuation, we use an inductor or a choke to give protection to the rectifier.

email back to <email removed> for any doubts.

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<busted> may be in two sense in Electronics. It is:

Short circuited or open cicuited>

Both have different effects:

Open circuited:

Short circuited

Now work yourself

It sounds like you guys are doing this guy's homework. I wonder if this is a multiple choice test, because it sounds like this guy missed a few days of class.

Seems like no one has really answered your question here - there are two ways a diode can 'break', and they will cause different effects. A physical break (open) will lower the output voltage going to the load. A solenoid may function normally under this condition providing there is adequate filtering at the bridge output to stabilize the voltage - depending on the specific function of the solenoid.

The second failure type is going to be a short - in a diode bridge this will result in severe voltage fluctuations that will likey cause a solenoid to chatter.

"...severe voltage fluctuations that will likey cause a solenoid to chatter."

...or make a buzzing sound.

Yep, you're absolutely correct. Nobody has answered the question because nobody can answer the question with the information given. We do not know if there is any filtering network other than the natural filtering that the inductance of a solenoid produces. Since it is a solenoid, we do know that the current will lag behind the voltage across the solenoid. How much behind the voltage, we haven't a clue. We also have no idea how long it takes for the presumed slug inside the solenoid to move. I could go on and on about this but since our AP1 cannot provide any more information I'll list all possibilities what can happen with one busted diode of a diode bridge driving a solenoid:

To the user the circuitry

1. appears to work just as before.
2. appears to work until the solenoid is turned OFF. Now the solenoid will not activate. Buzzing maybe heard in the solenoid.
3. fails to engage the solenoid as soon as the diode fails. Buzzing maybe heard in the solenoid.
4. appears to work just as before until other circuits attached to the bridge are additionally energized. Then either #2 or #3 will happen.
5. blows open the fuse installed in the supply. The solenoid fails to activate. Buzzing is impossible.
6. blows open the fuse not installed in the supply. (Remember every circuit has a fuse whether you designed one to be there or not.) If this fuse is the power distribution wiring then the insulation is likely to ignite and can possibly burn a wooden frame structure to the ground.

I'll consider this as included in my $10 fee.

Well, in an ideal scenario, the upstream circuit protective device(s) will operate, thereby disconnecting the load.

Another possibility is that something will heat up to the point where smoke comes out and it becomes an open circuit.

Another possibility is that something heats up to the point where a fire breaks out, with threat to life and limb.