diode is overheating

[Travis Shaffer]

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.

 

[kam1787]

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?

 

[Travis Shaffer]

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.

 

[dick_freebird]

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.

 

[kam1787]

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?