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Bridge diode thermal problem

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Md Mubdiul Hasan:
Hi there!

Hope this post find you well.
Like my other post, you might think its silly! :-//

I am talking about a basic  bridge recrifier made of https://www.mouser.com/datasheet/2/345/rs601m-rs607m-5532.pdf
Take a look on my circuit that is been used for 20V/5A AC application, problem is diode and caps temparature is raising upto 52 and 45 degree respectively.. |O

My senior said " add more 2 similar capacitor to reduce ripple" then "heating can be minimized" :palm:

Dont you think its a wrong idea!
See the attched file.

mikerj:

--- Quote from: Md Mubdiul Hasan on October 07, 2019, 07:47:55 am ---Take a look on my circuit that is been used for 20V/5A AC application, problem is diode and caps temparature is raising upto 52 and 45 degree respectively.. |O

--- End quote ---

Why is this a problem?  The temperature of both the bridge rectifier and the capacitors will naturally rise as both component dissipate power and 52/45 Celsius are well within the operating range of these components.


--- Quote from: Md Mubdiul Hasan on October 07, 2019, 07:47:55 am ---My senior said " add more 2 similar capacitor to reduce ripple" then "heating can be minimized" :palm:

Dont you think its a wrong idea!
See the attched file. (Attachment Link)

--- End quote ---

Making the capacitors larger reduces the conduction angle of the rectifier, i.e. the peak to mean current ratio increases for both the rectifier and the capacitor and the power dissipation increases for a given DC current.  If your ripple voltage is acceptable with your current design then do not add more capacitance.

Md Mubdiul Hasan:

--- Quote ---Making the capacitors larger reduces the conduction angle of the rectifier, i.e. the peak to mean current ratio increases for both the rectifier and the capacitor and the power dissipation increases for a given DC current.  If your ripple voltage is acceptable with your current design then do not add more capacitance
--- End quote ---

Well said.

--- Quote ---Shouldn't the conduction angle for a full wave rectifier with filter capacitor be twice that of a half wave rectifier with filter capacitor?
Since the frequency of the output wave in case of a full wave rectifier is twice as that of a half wave one the conduction angle should be twice as well, but we've already taken the above into account while calculating the  Vr, so should we take it into account again?
--- End quote ---

Zero999:

--- Quote from: Md Mubdiul Hasan on October 07, 2019, 08:49:37 am ---
--- Quote ---Making the capacitors larger reduces the conduction angle of the rectifier, i.e. the peak to mean current ratio increases for both the rectifier and the capacitor and the power dissipation increases for a given DC current.  If your ripple voltage is acceptable with your current design then do not add more capacitance
--- End quote ---

Well said.

--- Quote ---Shouldn't the conduction angle for a full wave rectifier with filter capacitor be twice that of a half wave rectifier with filter capacitor?
Since the frequency of the output wave in case of a full wave rectifier is twice as that of a half wave one the conduction angle should be twice as well, but we've already taken the above into account while calculating the  Vr, so should we take it into account again?
--- End quote ---

--- End quote ---
I'm not sure what you're saying.

As mentioned above, the temperature is within the rating of the components, so isn't a problem.

A half wave rectifier only conducts on positive or negative cycles. A full wave rectifier conducts on both. The smoothing capacitor will discharge more, between the diode conducting, on half wave, than on a full wave rectifier, so the conduction angle will increase, but I don't think it's as simple as double. It depends on the load. A linear regulator or audio amplifier will draw roughly the same current, irrespective of the capacitor voltage, whilst a resistive load, such as an incandescent lamp won't. A constant current load will discharge the capacitor more, than a resistive load, so will increase the conduction angle.

Md Mubdiul Hasan:

--- Quote ---I'm not sure what you're saying
--- End quote ---
Talking about a reliable system where heating and ripple current is a issue >:D


--- Quote ---As mentioned above, the temperature is within the rating of the components, so isn't a problem.
--- End quote ---
To be aware with it, dont you suggest me to use Low ESR type caps!

 
--- Quote ---A constant current load will discharge the capacitor more, than a resistive load, so will increase the conduction angle.
--- End quote ---
Yeap sure! Then what would be the stress on caps! For this conduction angle dont you talking about, https://electronics.stackexchange.com/questions/257293/how-to-calculate-the-conduction-angle-of-a-cvd-diode

Talk more about RC time constant and dissipative power/loss.

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