Bridge diode thermal problem  - Page 1
Forum section: electronics / projects

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: October 07, 2019, 07:47:55 am
content: 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 ofhttps://www.mouser.com/datasheet/2/345/rs601m-rs607m-5532.pdfTake 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..My senior said " add more 2 similar capacitor to reduce ripple" then "heating can be minimized"Dont you think its a wrong idea!See the attched file.

author: mikerj
author_rank: Super Contributor
timestamp: October 07, 2019, 08:12:20 am
content: Quote from: Md Mubdiul Hasan on October 07, 2019, 07:47:55 amWhy 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 amMaking 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.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: October 07, 2019, 08:49:37 am
content: QuoteWell said.Quote

author: Zero999
author_rank: Super Contributor
timestamp: October 07, 2019, 10:38:44 am
content: Quote from: Md Mubdiul Hasan on October 07, 2019, 08:49:37 amI'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.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: October 07, 2019, 11:33:46 pm
content: QuoteTalking about a reliable system where heating and ripple current is a issueQuoteTo be aware with it, dont you suggest me to use Low ESR type caps!QuoteYeap 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-diodeTalk more about RC time constant and dissipative power/loss.

author: Zero999
author_rank: Super Contributor
timestamp: October 08, 2019, 01:56:24 pm
content: 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.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 08, 2019, 07:27:41 pm
content: 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.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: October 08, 2019, 10:55:00 pm
content: QuoteYes. I did see in Saudi or middle east area, all componets were varified for higher temparature rate!QuoteAny mathematical equation exists relating those factor?

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: October 08, 2019, 11:02:07 pm
content: QuoteFor the high ripple current, adding more caps are not wise decision right?

author: RES
author_rank: Regular Contributor
timestamp: October 09, 2019, 09:10:39 am
content: 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

author: Zero999
author_rank: Super Contributor
timestamp: October 09, 2019, 12:39:56 pm
content: Quote from: Md Mubdiul Hasan on October 08, 2019, 10:55:00 pmYes, 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.

author: Md Mubdiul Hasan
author_rank: Regular Contributor
timestamp: October 10, 2019, 11:18:57 pm
content: Quote from: RES on October 09, 2019, 09:10:39 amExcellent !Could you compare part list between yours with mine!Does not it little bit expensive?Reliable for sure.