Author Topic: Bridge diode thermal problem  (Read 2229 times)

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Offline Md Mubdiul HasanTopic starter

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Bridge diode thermal problem
« on: October 07, 2019, 07:47:55 am »
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.
« Last Edit: October 07, 2019, 07:54:26 am by Md Mubdiul Hasan »
Hasan
 

Offline mikerj

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Re: Bridge diode thermal problem
« Reply #1 on: October 07, 2019, 08:12:20 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

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.

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)

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.
 

Offline Md Mubdiul HasanTopic starter

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Re: Bridge diode thermal problem
« Reply #2 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

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?
Hasan
 

Online Zero999

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Re: Bridge diode thermal problem
« Reply #3 on: October 07, 2019, 10:38:44 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

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?
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.
 

Offline Md Mubdiul HasanTopic starter

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Re: Bridge diode thermal problem
« Reply #4 on: October 07, 2019, 11:33:46 pm »
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I'm not sure what you're saying
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.
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.
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.
Hasan
 

Online Zero999

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Re: Bridge diode thermal problem
« Reply #5 on: October 08, 2019, 01:56:24 pm »
Obviously use low ESR capacitors.

The bridge rectifier you're using is rated to 150oC, so 53oC is no problem.

What is the temperature rating of the capacitors? I've not seen any rated to any less than 85oC, so 45oC is no problem.

The components are clearly working at well below their maximum temperature ratings, with plenty of headroom to spare. You should only be worried if you plan to use the device in an environment 35oC hotter, than where you tested it and measured these temperatures. If so, use higher temperature rating capacitors: 105oC is pretty common nowadays. The bridge rectifier can stand much higher temperatures before being damaged and the forward voltage has a negative temperature coefficient, so power dissipation, thus heating will decrease, with increasing temperature.
 

Offline SiliconWizard

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Re: Bridge diode thermal problem
« Reply #6 on: October 08, 2019, 07:27:41 pm »
Apart from using lower ESR capacitors, obviously to minimize losses you can select diodes that have a lower Vfd. Here it's an integrated bridge with a typical Vfd of 1.1V for the diodes. @5A, that's 5.5W of power dissipation for each. Enough to get them hot.

You could always try and find better. Problem is, most high-current rectifying diodes will have a Vfd in this range (~1V) at this current, and rarely lower.

Alternately, you could replace the bridge with an active synchronous rectifier. That'll be a bit more complicated and costly.
 

Offline Md Mubdiul HasanTopic starter

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Re: Bridge diode thermal problem
« Reply #7 on: October 08, 2019, 10:55:00 pm »
Quote
You should only be worried if you plan to use the device in an environment 35oC hotter, than where you tested it and measured these temperatures.

Yes. I did see in Saudi or middle east area, all componets were varified  for higher temparature rate!

Quote
The bridge rectifier can stand much higher temperatures before being damaged and the forward voltage has a negative temperature coefficient, so power dissipation, thus heating will decrease, with increasing temperature.

Any mathematical equation exists relating those factor?

Hasan
 

Offline Md Mubdiul HasanTopic starter

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Re: Bridge diode thermal problem
« Reply #8 on: October 08, 2019, 11:02:07 pm »
Quote
You could always try and find better. Problem is, most high-current rectifying diodes will have a Vfd in this range (~1V) at this current, and rarely lower.
For the high ripple current, adding more caps are not wise decision right?
« Last Edit: October 09, 2019, 03:35:34 am by Md Mubdiul Hasan »
Hasan
 

Offline RES

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Re: Bridge diode thermal problem
« Reply #9 on: October 09, 2019, 09:10:39 am »
You can use an ideal diode bridge controller LT4320, or create a MOSFET bridge yourself (see diagram below) Instead of diodes MOSFETs are used.

https://www.analog.com/en/products/lt4320.html
« Last Edit: October 09, 2019, 09:14:14 am by RES »
 
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Online Zero999

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Re: Bridge diode thermal problem
« Reply #10 on: October 09, 2019, 12:39:56 pm »
Quote
You should only be worried if you plan to use the device in an environment 35oC hotter, than where you tested it and measured these temperatures.

Yes. I did see in Saudi or middle east area, all componets were varified  for higher temparature rate!

Quote
The bridge rectifier can stand much higher temperatures before being damaged and the forward voltage has a negative temperature coefficient, so power dissipation, thus heating will decrease, with increasing temperature.

Any mathematical equation exists relating those factor?
Yes, the temperate coefficient of an ordinary silicon diode is −2 mV/˚C. A very high currents though, it's not quite so clear cut, as there is a parasitic resistance, but it's normally negligible within the ratings.

Another way to reduce the power dissipation is to use Schottky diodes for the bridge, which typically drop half the voltage.
 

Offline Md Mubdiul HasanTopic starter

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Re: Bridge diode thermal problem
« Reply #11 on: October 10, 2019, 11:18:57 pm »
You can use an ideal diode bridge controller LT4320, or create a MOSFET bridge yourself (see diagram below) Instead of diodes MOSFETs are used.

https://www.analog.com/en/products/lt4320.html

Excellent !
Could you compare part list between yours with mine!
Does not it little bit expensive?
Reliable for sure.
Hasan
 


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