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I have a rectifier bridge with 4x (GP)1N5062 diodes (body made of black plastic tube - like 1N4007). I have seen that they are getting hot, even if the current passing through the rectifier is 0.95 A.

I can only keep my finger on its terminal for 3-4 seconds, so let's say 45 Celsius.

Is this normal? I think, the diodes are rated for 2A, even though this forum says 1 A.

My digital multi-meter measures 23V DC voltage at the output of the bridge. However, if I switch to AC voltage it measures also about 2.1 VAC.

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  • \$\begingroup\$ Is it genuine part from reputable distributor? Or you bought it from ebay/aliexpress? \$\endgroup\$ – Chupacabras Jan 2 '18 at 21:57
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    \$\begingroup\$ Please don't add detail as comments on your own question, new visitors would have to piece it all together to help you. Can you edit your question, adding this information and as much other detail as you can. \$\endgroup\$ – TonyM Jan 2 '18 at 21:59
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    \$\begingroup\$ General rule of thumb.. If something is running at half it's rated value it will be at least half way to it's max temp. \$\endgroup\$ – Trevor_G Jan 2 '18 at 22:12
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    \$\begingroup\$ 3-4 seconds is more like 60 degrees C according to my calibrated finger. 45C is barely above body temperature (37C). P.S. do not use calibrated finger on energized high voltage parts. Don't ask. \$\endgroup\$ – Spehro Pefhany Jan 2 '18 at 22:14
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    \$\begingroup\$ diotec.com/tl_files/diotec/files/pdf/datasheets/1n5059 perhaps \$\endgroup\$ – Trevor_G Jan 2 '18 at 22:17
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You have 0.95A current, it makes 1V forward voltage according to proper datasheet of 1N5062GP. That is 0.95W dissipated.
Thermal resistance is RthJA=45K/W
So the temperature of that diode will be 43C+ambient temperature. So in room temperature 25C that diode will have 68C.

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  • \$\begingroup\$ PS: The body of my diodes is not made of glass. They are like 1N4007 (black plastic tube). \$\endgroup\$ – Ultralisk Jan 2 '18 at 22:14
  • \$\begingroup\$ Update: my diodes are getting ridiculous hot. Looks like they are only 1A. I will switch to a different rectifier that is clearly rated 2A. \$\endgroup\$ – Ultralisk Jan 2 '18 at 22:18
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    \$\begingroup\$ @ElectroMan OK, but different material will not change the amount of heat that has to be dissipated. Thermal resistance can be different but I do not expect a huge difference. It will be in ballpark that explains that the diode warms up. If you want less heat you can use schottky diodes. \$\endgroup\$ – Chupacabras Jan 2 '18 at 22:19
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    \$\begingroup\$ @ElectroMan Or you can go new-tech with MOSFETS and one of there puppies cds.linear.com/docs/en/datasheet/4320fb.pdf \$\endgroup\$ – Trevor_G Jan 2 '18 at 22:34
  • \$\begingroup\$ "The body of my diodes is not made of glass" - 1N5062GP \$\endgroup\$ – Bruce Abbott Jan 3 '18 at 6:00
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Check the data sheet for RthJA. It is specified at 100 degrees K per watt for a reasonable board mount. If you are running 1 amp, you will have 1/2 amp average through each diode. Since the voltage drop is 800 mv, your power is .8 volts x .5 amps or 0.4 watts. Your temperature rise is 100 degrees/watt x .4 watts or 40 degrees.

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  • \$\begingroup\$ To run cooler, solder the diode between wide long regions of copper foil; the default 1 ounce/foot^2 foil has 70 degree Cent per square (any size square) of foil, unless the heat can be dumped into underlying planes or cooled by airflow. \$\endgroup\$ – analogsystemsrf Jan 3 '18 at 2:04
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Your link provides a further link to yet another link to http://pdf.datasheetcatalog.com/datasheet2/4/09q49x6sjtg6gywhzelg3t31ug7y.pdf and this specifies a limit of 1 A. So where you're getting 2 A from is beyond me.

And the AC you're seeing is perfectly reasonable. A CD player will not have an enormous filter capacitor, and a certain amount of ripple is inevitable for any finite capacitance. Assuming your 2 VAC corresponds to about 3 V pk-pk, your minimum voltage will be on the order of 34.5 volts, and this ought to pose no problem.

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    \$\begingroup\$ Hi. The link I provided opens (in MY computer) the mXuxsuy.pdf which says "Nominal current: 2 A". The link you show takes me to a totally different document that is for a glass (round) diode. I have the plastic/tubular/black one. \$\endgroup\$ – Ultralisk Jan 2 '18 at 22:10

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