| Electronics > Projects, Designs, and Technical Stuff |
| USB charger circuit for car |
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| Charybdis:
Hi there, lurking through some technical datasheet of LM338 I've come with this scheme of a USB 1A charger to be installed in my glorious Fiat Panda ;) What do you think about it ? Any suggestion? I've replaced the 1N4xx diode with smth that can handle safely 1A, and this is what TME sells.. Thank you for your advice!! |
| madires:
At 1A that circuit would produce about 7-8W heat and it requires a matching heatsink. Is there any particular reason why you are going for a linear voltage regulator? In most cases a simple buck converter makes more sense. |
| Charybdis:
Basically because I'd like to learn something :D Thanks I didn't consider that at all ! Do you think this " FISCHER ELEKTRONIK FK 222 SA " 20K/W will do the job ? |
| madires:
Sorry, that heatsink is much too small. Another thing to consider is the ambient temperature in your car. During the summer time it could be about 50°C. So you would need a fairly large heatsink to cool the LM338. I'd suggest to use a buck converter for the car and the LM338 for a simple lab PSU. |
| ebastler:
--- Quote from: Charybdis on April 04, 2019, 06:11:47 pm ---Basically because I'd like to learn something :D Thanks I didn't consider that at all ! Do you think this " FISCHER ELEKTRONIK FK 222 SA " 20K/W will do the job ? --- End quote --- In the interest of „learning something“: The 20K/W spec means that each Watt of power which the heatsink has to dissipate, will cause its hot side (i. e. your voltage regulator) to get 20 degrees warmer than ambient temperature. Hence, at 7-8 W power dissipation and 50 C ambient temperature, your regulator would run at 200 C. Way too hot!! As stated earlier, you would need an unpractically large heat sink too cool the linear regulator properly. Hence the suggestion to use a buck converter, which has negligible power loss in comparison. |
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