usb charger with lm7805

[hannobisschoff@gmail.com]

I built a super simple circuit to take any voltage down to 5v from any Vin, but now 'n hooked it to a USB port, pluged my ipod in. no magic smoke, since I checked it with my multimeter, but the ipod is also not showing a charging symbol like it would if I charged it with a computer. Is this bad?
Theoretically any USB gives out 5V, so I figured it will work.

 

[birdman0_o]

The USB gives 5V, the lm7805 has a dropout of about .7V. This means you need to put in above 5.7V or it will not work.

 

[HommerSimpson]

Just adding something I have seen pop up in walgreens just the past few months.. Tiny USB chargers for cig lighter or 110 outlet... 9.99 and they are tiny

 

[hannobisschoff@gmail.com]

Thanks for the reply. The dropout voltage is really not a problem, all I want to know is if the device will work if I power only the 5V rail of the female usb port, and do nothing to the data rails.
Please see the link for a better understanding of what I'm trying to say
Thanks

LINK:https://pinouts.ru/Slots/USB_pinout.shtml

 

[birdman0_o]

I'll let somebody else answer this hazardous question

 

[House0Fwax]

now 'n hooked it to a USB port

That gives the impression that you are connecting it to a computer.

I suspect that you are trying to charge your iPod with it, from some other power supply.
Could you clarify?

 

[hannobisschoff@gmail.com]

OH, sorry about that poor choice of words. Yes, I want to use another input (higher than the dropout voltage) to charge my iPod.
Would it damage the device?

 

[cr0sh]

The USB gives 5V, the lm7805 has a dropout of about .7V. This means you need to put in above 5.7V or it will not work.

I thought an LM7805 needed at least 7 volts to operate? But hey, if you know of a version that only needs .7 volts above Vin, and comes in a TO-220 case - I'd love to hear about it...

 

[Reloadron]

As drawn the original drawing should work fine.

USB pin assignment as follows :

Pin 1 -- VCC (5 VDC)
Pin 2 -- D- (Data -) typical cable color is White
Pin 3 -- D+ (Data +) typical cable color is Green
Pin 4 -- GND (Ground)

Just make sure you get the pinout correct. The data lines are ignored. This is true for charging most USB devices with the exception of a few.

As to dropout voltage on a side note. Any standard LM78XX device (regulator) I am familiar with has a 2 volt dropout voltage. Therefore in the case of a LM7805 the input voltage must be a minimum of 7 or more volts.

As to low dropout versions there are chips like the LM3940 low dropout regulator in a TO 220 case and good for about an amp and the LP2954/LP2954A low dropout regulators good for only about 250 mA but in a TO-220 case.

That's My Take
Ron

 

[audioguru]

You need some load on the data pins for an ipod to charge. Look in Google for the circuit.

EDIT: One link says this: "The Data+ and Data- lines need to be held at a certain voltage for the phone to recognize that it should charge. The Data+ pin needs to be held at 2.8 volts, the Data- pin needs to be held at 2.0 volts."