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Car usb charger protection circuit.

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Faddei

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Hi all,

I want to build a car usb charger using the 12v of the cigarette lighter. I already found a regulator for the job but how do i protect my circuit? I have heard that the 12v of the car varies a lot. Is a high power zener enough? Should i use a crowbar circuit? Maybe a low pass filter?

Thank you in advance.
 

I took apart a USB car charger a while back (it was a reputable one, some brand name, I can't remember which mnfr) to see what was inside.
Here are some pics.
car_charger1.jpg
car_charger2.jpg
From the fused input, it had a small (maybe 220nF) SMD ceramic cap to ground. Then, the supply went to a 0.5mH inductor, the output of which went to the switching regulator ic power supply, and also to a varistor connected to ground. Varistor value was 22V, it was part number **broken link removed**, 7mm dia.
On a board I created (mine was not a USB charger, it was a different purpose, but it was for a car supply), this was the input circuit.
pwr_input.jpg
I used an 18V varistor (Littelfuse V18MLA1210H) and a 30V TVS (ST Micro SM15T30CA).
 
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    Faddei

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Faddei said:
Hi all,

I want to build a car usb charger using the 12v of the cigarette lighter. I already found a regulator for the job but how do i protect my circuit? I have heard that the 12v of the car varies a lot. Is a high power zener enough? Should i use a crowbar circuit? Maybe a low pass filter?

Thank you in advance.
Click to expand...

You dont have that problem with voltage, because USB working on 5V, in car you have 12V and up. You just need to have stable and good circuit nothing else. Ordinary 7805 78S05 78T05 can do the job. Car voltage will be always higher then 8V, which asures regulated 5V.

You mention usb charger, but you didnt say charger for what ? Li-Ion, NiMh, ...


Look this example with MC34063 :

iPOD - MP3 Player Charger
https://electronics-diy.com/electronic_schematic.php?id=139

105841_6mg.jpg
 
Last edited:

tpetar said:
You dont have that problem with voltage, because USB working on 5V, in car you have 12V and up. You just need to have stable and good circuit nothing else. Ordinary 7805 78S05 78T05 can do the job. Car voltage will be always higher then 8V, which asures regulated 5V.

You mention usb charger, but you didnt say charger for what ? Li-Ion, NiMh, ...


Look this example with MC34063 :

iPOD - MP3 Player Charger
https://electronics-diy.com/electronic_schematic.php?id=139

105841_6mg.jpg
Click to expand...

I am going to use it with my mobile. It has a 1500 mAH Li-ion battery. I think i only have to supply the 5V the mobile will regulate the charging.
 

I am going to use it with my mobile. It has a 1500 mAH Li-ion battery. I think i only have to supply the 5V the mobile will regulate the charging.
Click to expand...

Ok, then. Word "Charger" can be lots of designs. Your last post give new photons on case. You can use 78S05 (up to 2A) or MC34063 circuit. 78S05 is simpler to make. For thise purpose I suggest to avoid simple usage of zener diode. :wink:
 

tpetar said:
You dont have that problem with voltage, because USB working on 5V, in car you have 12V and up. You just need to have stable and good circuit nothing else. Ordinary 7805 78S05 78T05 can do the job. Car voltage will be always higher then 8V, which asures regulated 5V.

You mention usb charger, but you didnt say charger for what ? Li-Ion, NiMh, ...


Look this example with MC34063 :

iPOD - MP3 Player Charger
https://electronics-diy.com/electronic_schematic.php?id=139

105841_6mg.jpg
Click to expand...

Hi, i have a similar project on charging rechargeable li ion battery packs for smartphone use. Can an LM7805 IC get the job done and what about the protection circuit to implement?

Thanks.

- - - Updated - - -

For your information, the input voltage is 12Vdc and to step down to 5vdc for charging battery packs. The IC to use is just LM7805 but with proper protection circuits to protect load.

Thanks.
 

The circuits in this thread are not for the purpose of charging Li-Ion batteries directly. The circuits in this thread rely on the
mobile device' in-built charging circuitry. For direct charging of batteries, these circuits could be dangerous or damage your battery,
because 5V is not used for these batteries. They require some special considerations, including very accurate charge termination.
A 7805+"proper protection circuits" won't cut it.
For information on what is required to charge them, see a Li-Ion charger IC datasheet, e.g. this one.
Personally I would use a dedicated charger IC for the specific battery chemistry, unless you are really sure you knew what you are
doing. And even if you knew what you were doing, I would think twice. I've seen what happens when things go wrong with charging
(not specifically with Li-Ion chemistry, but I'm not curious in that respect).
 

sky_123 said:
The circuits in this thread are not for the purpose of charging Li-Ion batteries directly. The circuits in this thread rely on the
mobile device' in-built charging circuitry. For direct charging of batteries, these circuits could be dangerous or damage your battery,
because 5V is not used for these batteries. They require some special considerations, including very accurate charge termination.
A 7805+"proper protection circuits" won't cut it.
For information on what is required to charge them, see a Li-Ion charger IC datasheet, e.g. this one.
Personally I would use a dedicated charger IC for the specific battery chemistry, unless you are really sure you knew what you are
doing. And even if you knew what you were doing, I would think twice. I've seen what happens when things go wrong with charging
(not specifically with Li-Ion chemistry, but I'm not curious in that respect).
Click to expand...

Hi, thanks for the information provided. I have another question to ask, can a li ion battery charger be used to charge a li ion powered smartphone too? Also how do i find out how many cells the rechargeable battery packs have? I only know its mAh, input voltage and current as well as output voltage and current. Please help.

Thanks.
Sunny55.
 

A 'charging circuit' is used to charge cells and battery packs. The charging circuit has functionality to prevent the cell/battery from overcharging.
A power supply is used to power smartphones and to charge their internal batteries, because the smartphone has a built-in 'charging circuit'.
This thread was about power supplies suitable for smartphones/ipods, not about 'charging circuits'.
That should answer your question about what can be used to charge what.
Regarding number of cells, you can tell that from the voltage. The cell voltage is at the wikipedia page for Li-Ion.
 

sky_123 said:
A 'charging circuit' is used to charge cells and battery packs. The charging circuit has functionality to prevent the cell/battery from overcharging.
A power supply is used to power smartphones and to charge their internal batteries, because the smartphone has a built-in 'charging circuit'.
This thread was about power supplies suitable for smartphones/ipods, not about 'charging circuits'.
That should answer your question about what can be used to charge what.
Regarding number of cells, you can tell that from the voltage. The cell voltage is at the wikipedia page for Li-Ion.
Click to expand...

I understand. But how the USB ports on desktops and laptops can be easily used to charge any product like smartphones and battery packs? I wish to make something like that so i can charge any products ranging from smartphones, mp3 players to battery packs. Could you guide me on how to achieve that?

Thanks.
Sunny55.
 

Sunny55 said:
I understand. But how the USB ports on desktops and laptops can be easily used to charge any product like smartphones and battery packs? I wish to make something like that so i can charge any products ranging from smartphones, mp3 players to battery packs. Could you guide me on how to achieve that?

Thanks.
Sunny55.
Click to expand...


We must distinguish charger from psu. thise two things are different. People often call small phone adapter as charger.

For most cases you just need to provide enough current at stable 5V for most devices which uses USB port and nothing more. Small charging IC is inside device, and you cant affect on charging process directly.

But if you whant to charge Li-Po/Ion battery alone without device then you need charging circuit with adequate design for that type of battery which controls temp, voltage and current.
 

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