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diode is overheating

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Travis Shaffer

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I made a solar powered usb charger, like the altoids tin ones, and one of the diodes keeps getting really hot. I am fairly new to DIY electrical projects, but I can't figure it out. What I have Is a 9v solar pannel on the positive lead I have a 12v diode on the negative side of the diode I have the positive lead to the battery and another positive lead. on this lead I have another 12v diode then that is conceded to a 5v regulator and that is conceded to the usb. It is the second diode that is getting really hot. Anything helps thanks.
 

can you make a diagram or schematic?

I don't know what a 12V diode is ...........can you give a part number?

is it like this

solar panel------------diode----------battery----------diode-----------5V regulator------------USB


it is giving 5V at the USB pin?
perhaps you are using the wrong type of diode
or have a short
or mis-wired it somewhere

- - - Updated - - -

is the 5V regulator an IC?
it could be it is unstable and oscillating, pulling too much current
what battery are you using?
 

Yes your layout is correct for the set up. And the diode is rated for up to 12v. It is reading 5v at the usb, and I forgot to say that I can turn the system on ( with out a device plugged in) and it does not heat up. Once I plug a device in and turn the system on it starts to heat up.
 

What heat sinking does your diode have? Assume you
gave some care to the regulator, but the diode sees
the same current (albeit lower voltage drop). Figure
a standard silicon diode at 500mA burns 350-400mW.
Take a normal thetaJA (and bearing in mind those are
always at some spec airflow, which is nil inside an
Altoids can) and do the warm-n-toasty math. Then
look into how you can mount the diode and any
other series-path lossy components to the can wall
for conduction cooling.
 

Do you have a part number for the diode? Or could you take a photo?
Is it something like a 1N4001 ?


Maybe you are not using a 'power' diode. Usually USB devices don't pull more than 500mA, which would give a power dissipation of 300mW - which should be ok if you are using a 'power' diode like the 1N4001. But if you are using something like a 1N914 it will get hot.

How much current is the load pulling?
 

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