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Old 28th July 2004, 08:51 AM   #1
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Default copper area size

Hi,

How do you calculate the required copper area to be used as a heatsink for components e.g. rectifier diodes ? (I think this area is called Thermal Territory)

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MB
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Old 28th July 2004, 09:14 AM   #2
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3 things. Tube diodes (except possible high power specialty types) do not use, nor need heatsinks; SS diodes (except zeners) do not dissipate enough power to bother; and heatsinks are rarely copper.

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Old 28th July 2004, 11:17 AM   #3
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OK. First of all, I am talking about SS diodes. For example, SB560 (package: DO-201AD) has theta-ja 25C/W. Assuming 3W dissipation (it is rated at 5W), its temperature rises to ambient + 75C. That seems too much and must be taken into consideration. Only thing can be done is to mount diode in vertical direction and leave a copper area. This is mentioned in ON Semiconductors - Rectifier Applications Handbook - Chapter 2.
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Old 28th July 2004, 12:31 PM   #4
SY is offline SY  United States
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metebalci, to eliminate confusion (and maybe help you get an answer more quickly), I've moved this over to Solid State.
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Old 28th July 2004, 12:37 PM   #5
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The SB560 has a voltage drop of 0.67V so if you have 3W dissipation you have a current of ~4.5A which is very close to max rating.

I would never use a diode in this package for 3W dissipation, If I needed 4.5A I would select a TO 220 package and screw it to the chassis, it is very bad engineering practice to be so close to device limit as you indicate in this case. I would never exceed more than half the max rating for a rectifier diode, it is easy to find diodes for higher ratings so there is no need to be so close.

Regards Hans
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Old 28th July 2004, 05:18 PM   #6
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SY, Thanks...

tubetvr, OK. I got it...
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Old 28th July 2004, 07:26 PM   #7
cpemma is offline cpemma  United Kingdom
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Quote:
Originally posted by metebalci
...Only thing can be done is to mount diode in vertical direction and leave a copper area. This is mentioned in ON Semiconductors - Rectifier Applications Handbook - Chapter 2.
A few specs will quote thermal resistance mounted on a pcb, example is Zowie spec for DB102 1A bridge. Junction-to-ambient 40C/W, falls to 15C/W mounted on 0.5" square copper pads, quite significant.

ON's AN1040/D (Mounting Considerations For Power Semiconductors) pdf has a graph showing heat-sink rating against pad area for one pcb example.

More useful files at http://www.onsemi.com/site/support/l...otes_0,00.html
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Old 28th July 2004, 10:10 PM   #8
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True that copper is more dense and a better conductor than aluminum, electricity and heat. But copper has one major drawback, it corrodes. Unless you plate the copper with something to stop this.
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