As we all know a laptop runs using a DC potential from an in built Li-Ion battery just as our cell phones do.
Normally we utilize a AC DC adapter for charging a laptop battery in homes and offices, these adapters are actually SMPS power supplies rated with the required and matching specs of the laptop battery.
However the above power supply units work only with AC supplies, and in places where an AC outlet may be available. These units will not work in places where an AC source is not present such as in cars and other similar vehicles.
A novel little circuit presented here will allow a laptop battery to be charged even from a DC source such as a car or truck batteries (12V). It's a very simple, cheap, versatile and universal circuit which may be dimensioned for charging all types of laptops by adjusting the relevant components provided in the circuit. It's a simple plug and play charger circuit.
Normally most of the laptop adapters are rated at 19V/3.5Amps, however some may be rated at higher currents for facilitating fast charging.
PWM Charging Control
The discussed circuit has a voltage adjustment features (via PWM) which may be suitably adjusted as per the required specs.
The current may be suitably safeguarded by adding a 3 ohm 5 watt resistor at the output positive terminal.
As can be seen in the circuit diagram, the design is basically a powerful DC to DC voltage doubler circuit which utilizes a push pull mosfet stage for the required boosting of the voltage.
The circuit requires an oscillator stage for initiating the proposed operations which is configured around IC1a.
The components R11, R12, C5 along with the two diodes becomes a neat little PWM controller which sets the duty cycle of the entire circuit and can be used for adjusting the output voltage of the circuit.
Typically the circuit would generate around 22V from a 12V source, by adjusting R12 the output may be tailored to an exact 19V, which is the required laptop charging voltage.