LM7805 + Resistor Voltage Divider

lm7805 example

Hi All,
I want to supply my USB MP3 Player from my 12 Volt car battery. Normaly my USB MP3 Player supplies with an AAA battery with 1.5 volt, and I want to replace the AAA battery using some stepdown and voltage divider. I look LM7805 can stepdown voltage from 12v to 5v, but I don't know to step down again to get 1.5 volt output for my MP3 player.
Could any body give suggestions, help or schematic to realize this ?

TIA

lm7805 adjust voltage

Hi,

I think you should also regulate the current from your car battery, or it might burn your mp3 player right away(a sad situation). Anyway, can you specify the output current from your car?

(I'll try to help you, dude)

lm7805 with resistor regulator

My car battery is 12volt with capacity 50Ah and my MP3 need 1.5volt and 100 ~ 300 mA.

lm7805 adj vs lm317

You can do the direct conversion, using a switching DC-DC converter IC like cheapest NCP3063 from ONsemi... (it's only an example... if you do a websearch you'll find many options)

h**p://www.onsemi.com/pub/Collateral/NCP3063%20DATA%20SHEET.PDF

anyway as an advice: If you are beginner in electronics dont use a switching IC variable or above 150KHz, because you will have problems with the PCB...

hope this helps,
//a

lm7805 car usb

Hi Cyberbrite,

Use this, bolt the LM317 to a heatsink and solder the capacitors and
the resistors to the LM317.

on1aag.

lm7805 resistors

You must use an Lm 317 regulator that with the referencee at 0V gives 1.25V
If you regulate the reference you can pull 1.5V easy by an diode or using resistors.

The resistor of 1k at the output must be there always becouse if no courrent circulates the potencial goes to 12V, that appen with you disconect the Mp3 for example
With the resistor We grant thet the regulator is always working
Second picture the is no cherge connected like the Mp3.
In the 3rd picture you can se an charge connected of 3.3 that gives an courrent of 0.5A aprox
You must use an 1A lm 317 regulator if you want to deal with more than 100mA if not use an lm371 L
You can use the 1rd circuit and the output tension is given by V0 = (1+ Rv1/R4)*1.25V
An example is given with Rv1 at 0 and at the maximum.

In this example you can remove the 1k resistor becouse r4 with rv1 makes the charge offset.


C1 estabilizas the tension of refence.

you can put an output capacitor

Regards

lm7805 circuit car diode

Thank Guys,
I will try, and first time I choose to try schematic in picture SNAG-0267.jpg.

TIA

lm7805 diode reference

Use the circuit suggested by on1aag.
The LM317 works best with 220~240 ohms between the ADJ and output.
You may need to adjust the 47 ohm resistor, to make sure you get exactly 1.5V. Other than that, it will work just fine, provided the heatsink is adequate.

lm7805

VVV said:

Use the circuit suggested by on1aag.
The LM317 works best with 220~240 ohms between the ADJ and output.
You may need to adjust the 47 ohm resistor, to make sure you get exactly 1.5V. Other than that, it will work just fine, provided the heatsink is adequate.

Click to expand...

You are correct

And high resistor can make the lm not regulate Just need to insure that 100uA for the adjust Pin.
He can pull up a litlle bit the resistences to decrese the stanby courrent to the minimal possible.


Regards