Bridge rectifier

Thread Starter

mhtplsh

Joined Jul 29, 2007
27
In full wave rectifier 4 diodes r used. If i use in4001 x 4 , how much current i will get from this rectifier? 2A or 4 amp? The diode is rated 1A each. I understand that bridge will not used for full load in practice. This question is for academic interest.
 

beenthere

Joined Apr 20, 2004
15,819
You will get the 2 amps a bit longer than you will the 4, but the duration will be no more than a few seconds. Those diodes are rated for 1 amp, and so will fail when passing more than the rated current. Much better to choose a bridge rated for somewhat more than the load output.
 

beenthere

Joined Apr 20, 2004
15,819
Even the 1 amp is a bit of a stretch if the diodes are not able to dissipate the heat. Any component is going to be stressed and potentially fail when run right at its rated maximum.
 

Wendy

Joined Mar 24, 2008
23,415
You can buy bridge rectifiers as components. The come in many packages, some are designed to be easily heatsinked (metal case, with a hole in the middle). The come in many ratings, you can buy pretty much off the shelf what you want, anywhere.
 

SgtWookie

Joined Jul 17, 2007
22,230
Actually, the 1N400x series is rated for 1A average current. When used in a rectifier bridge, only 1/2 of the bridge (2 diodes) will be conducting at any given time.

However, when carrying a constant 1A, the Vf (forward voltage) of the diode is about 1.1v. This means power dissipation is 1.1 Watts. They're rated for 3W maximum. The higher the current flow through the diode, the higher the Vf becomes, until the diode is destroyed due to heat.
 

Thread Starter

mhtplsh

Joined Jul 29, 2007
27
Thanks SgtWookie,
U hv explained nicely.
When two diodes r used in bridge at a time, means 1A current will be shared by 2 diodes. Each will carry current of .5A. it is 50% of the current capacity of 1N400X. Is this ok, as i understand.
 

Audioguru

Joined Dec 20, 2007
11,248
The 1N400x has an absolute max average half-wave rectified current rating of 1A. The diodes on each side of the full-wave bridge are half-wave rectifiers. Two diodes are in series on each side and they can pass an average of 1A. So if the rectified and filtered DC current is 1A or more then the 1N400x diodes are overloaded and are in trouble.
 

SgtWookie

Joined Jul 17, 2007
22,230
The 1N400x has an absolute max average half-wave rectified current rating of 1A.
That is not correct.
It has an absolute maximum average rectified forward current of 1A, at 75°C with 0.375" lead length. "Half-wave" would indicate a 50% duty cycle.

It can also take a single 8.3mS half-sinewave current of 30A (non-repetitive)

The diodes on each side of the full-wave bridge are half-wave rectifiers. Two diodes are in series on each side and they can pass an average of 1A. So if the rectified and filtered DC current is 1A or more then the 1N400x diodes are overloaded and are in trouble.
Not correct. Since the rectifiers are running at a 50% duty cycle, they could actually pass 2A and be within the maximum ratings. However, I would not deliberately operate components at their absolute maximum specifications and expect them to last for any amount of time.
 

italo

Joined Nov 20, 2005
205
NO you will not get 2 amps if the diodes are rated for 1 amps the diodes conduct two at the time in series so if a manufacture say 1 amp only 1 amp can flow. This is basic guys
 

SgtWookie

Joined Jul 17, 2007
22,230
According to Fairchild (I didn't look at Chinese and Indian datasheets), the 1N400x diode has a max allowed average half-wave rectified current of 1A.
The temperature is 75 degrees C on the text but is any temperature up to 75 degrees C on the graph.
We were looking at the same datasheet from Fairchild. In your prior post, you said:
The 1N400x has an absolute max average half-wave rectified current rating of 1A.
I maintain that this is still an incorrect statement, as the evidence you posted is a combination of the "Absolute Maximum Ratings" (which is as I stated), and the graph is from the "Typical Characteristics" on Page 2 of the same datasheet; the latter of which is not an absolute maximum rating.

However, we ARE in complete agreement that it would be unwise to operate a 1N400x rectifier at or near it's maximum ratings, which I inferred in my reply.
 
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