I have a laptop which its battey is charged from a 5V charger.
I'm not sure though how much current it draws from the charger.
(I dont have the laptop here so i cant tell you its type and firm).
Could you tell me please if its possible to drive a laptop from the car's battery?
Meaning if the car's battery can supply the current that the laptop requires?
It is said in the datasheet, that for Vin = 6.5V to 12V and Iout = 0A to 0.8A, the output voltage is 4.9V to 5.1V.
Do you think it could do the job without getting too hot?
I want the car's battery to drive it for 2-3 hours.
I wanted to build such PSU by myself (and due to the other thread, its not becaues i wanna spare a few bucks, its a project i took on myself).
Is there anyway to use a few regulators or mosfets/transistors, maybe connecting them in parallel, in order for them to provide the laptop with the required current?
I wanted to build such PSU by myself (and due to the other thread, its not becaues i wanna spare a few bucks, its a project i took on myself).
Is there anyway to use a few regulators or mosfets/transistors, maybe connecting them in parallel, in order for them to provide the laptop with the required current?
You need a high-current switchmode regulator, EPE magazine did a design a year or two ago. To do it with linear regulators is going to be really HOT!!.
I though of a simple idea but i'm not sure if it would work.
Is it possible to connect a resistor in series with the car's battery, like a source impedance, and connect the laptop to the resistor?
This is how i calculated the resistor's value.
Assuming that my laptop draws 7A.
The resistor's voltage drop should be 7V (=12V - 5V).
Therefore, the resistor's value should be 7V / 7A = 1Ω.
And the resistor's power dissipation should be 49W.
(Of course that I can connect several larger resistors in parallel, so their equivalent resistance equals to 1Ω, and that way they will disipate less power and will get less hot).
I see thanks.
I guess I'll have to put some thought about it and read about high current switch mode regulator designs.
By the way, how is a laptop charger built?
I assume that it converts tha AC mains to a DC voltage using a transformer and half/full wave rectifiers + output capacitor,
but does it convert the AC mains voltage directly to 5VDC or does it convert it to some higher value and then uses a regulator in the midway?
It's more a power supply than a charger, very similar to any computers SMPS. Your laptop will have an internal charger that'll shutoff the supply voltage when the battery is full. https://en.wikipedia.org/wiki/Switched-mode_power_supply
I read a lot about SMPS.
I understand the structure of half/full wave rectifier with an output capacitor, and that afterwards there's usually a buck converter (discontinuous/continuous mode - depends on the required current).
My idea was that if this laptop charger uses a regulator/buck converter after the transfoermer & rectifiers, then I could disassemble the charger and drive the buck converter with the car's battery.
You think its possible to pull it off?
I read a lot about SMPS.
I understand the structure of half/full wave rectifier with an output capacitor, and that afterwards there's usually a buck converter (discontinuous/continuous mode - depends on the required current).
My idea was that if this laptop charger uses a regulator/buck converter after the transfoermer & rectifiers, then I could disassemble the charger and drive the buck converter with the car's battery.
You think its possible to pull it off?
They don't use a mains transformer - that wouldn't be a SMPSU.
They rectifiy the mains, to give 320V DC (on 240V mains), this is then chopped using a switching transistor and applied to a small high frequency transformer. The output of that is rectified and smoothed, and used to feed an error voltage back to the switching transistor, which alters it's mark/space ratio to correct the voltage error.
I was thinking of disassembling some charger that i could use its inside to convert the 12Vdc car's battery to 5VDC that the laptop requires.
You got any idea?