I got the 100nF cap, and it's easy to change the 100uF to 10uF. Adding a fuse on the powercable is no big deal...

 

You misunderstood..I think.
the 100nf ones should be like touching the 7805...meaning they are the ones close to the Reg pins, then you can place the 10uf next to the 100nf
Place the 100uf close to the USB.

 

Oh... OK, I'll add them tomorrow.

 

If you went for a 6V battery and a low overhead regulator would you not have to dissipate less in the regulator?

 

You might want to protect your regulator by placing a diode from output to input, to avoid the event where the output cap is discharged thru the regulator (i.e. if battery power is removed). The regulator data sheets usually recommend this, though most folks seem to treat it as optional.

 

USB Power pin is Pin one.
U are on the right track Jens

 

If you went for a 6V battery and a low overhead regulator would you not have to dissipate less in the regulator?

Don't know. I have the before mentioned batteries.

You might want to protect your regulator by placing a diode from output to input, to avoid the event where the output cap is discharged thru the regulator (i.e. if battery power is removed). The regulator data sheets usually recommend this, though most folks seem to treat it as optional.

I haven't seen that in my datasheet. But it is a good idea, since the battery for sure will be removed.

USB Power pin is Pin one.
U are on the right track Jens

Thanks!

 

OK, I've done some editing.

Will this work better? I've got a fuse on the cable from the battery.

 

I would check the USB pinout a few more times. I'm not saying yo have it wrong, just that these things always make me nervous and it is so easy to mistake male for female, up for down, front from back and all that. Big penalty for making a simple mistake.

 

I know!

I've compared, googled, read, and checked again. They are a pain in the ...

 

You could make that PCB more compact.If you want the PCB file just ask.

Here is a try in 10-15min. It's around 3x2cm.

UPDATED!

 

ISB123, try rotating the caps, or actually rearrange the diodes as well. C3 and C1 have a very poor path to ground- narrow, spiraly and veeery long. I would rotate C1 and C2 180° and rotate C3 and C4 to match. C1 and C2 should be closer to U1 than C3 and C4 are.
Also C2 is not connected to the output at all.
Connection of the output ground to input ground and U1 reference point is poor as well.

 

Yeah I was thinking about that tiny ground connection going between two caps. Didn't really pay attention to distance between caps and regulator.I seen that there was no output connection but couldn't update the image because for some reason internet went off....
Just gonna update the old post with better one so I don't spam the topic.

 

Jens you forgot to add a 10uf at the output of the 7805.
The 100uf is actually optional one

The PCB can be smaller if you place the input diode vertically I think.

 

Yes, I know it can be smaller, but... I'm going to add a fuse, an indicator LED, and a sliding switch.

 

I think that you won't need a fuse at small currents like yours.
7805 has short circuit protection so you should be safe,you could use POLYFUSE if you want a small fuse.

 

I still don't see provision on the pcb for a heatsink. Perhaps put U1 at the edge of the board to allow attachment of off-board heatsink?

 

I still don't see provision on the pcb for a heatsink. Perhaps put U1 at the edge of the board to allow attachment of off-board heatsink?

I'm working on it. Bought some today, and I'm re-designing now.

 

Another revision...

I got the 1N4004 in SMD format, so I'll go for that. They will be working next to their limits. I've also added a 3-pole slide switch and a 440* Ohm resistor for the green LED. The 38.1mm measure is for the heatsink I bought earlier today.


I noticed right now that I can move the 100uF Capacitor closer to the USB connector.

* (12-3.2) / 0.02 = 440 Ohm

 

If you're planning on drawing 1A from the 5V supply then the regulator would have to dissipate 7W. It would need a LARGE heatsink. Your circuit board doesn't seem to make allowance for any heatsink. The 1N4004 will be running at its rated maximum; not good practice.

AFAICR; most of the 78xx type regulators are available in TO3 cans with ratings from 3 - 5A, the OP would still need to put it on a heatsink, but the regulator would be a lot less stressed.

Most of the big name suppliers publish appnotes - one shows the 78xx with an input current sensing resistor, the voltage developed across that resistor turns on an external pass transistor, probably still needs a heatsink though.

A better alternative is a cigar lighter socket USB charger - where I am, the £1 store sometimes has them, I've never paid more than £4.99p for one.