Production of Car Laptop Power Supply and Analysis of Typical Circuits

I recently helped a friend make some DC~DC non-isolated conversion power supply circuits. They were originally used to power car GPS. I feel that the circuit structure is relatively simple and suitable for electronic enthusiasts to make by themselves. With a little modification, it can be used for notebook power supply, car equipment, etc., so I share it with you here. Two batches of this power supply were made, with different input voltages of 12V and 24V, and the output voltage is 19V.

1. 12V to 19V circuit

The circuit is shown in Figure 1. This circuit is a boost type voltage regulator circuit. It uses UC3843 as the control IC. It can convert 10.5-15V DC input voltage into 19V DC. The maximum output current is about 3A, and the efficiency is about 82%~87%. The principle of the circuit is very simple. It controls the on and off of the switch tube Q03 through the pulse output of the IC, and superimposes the back electromotive force generated by the inductor L02 on the input voltage, so that the output voltage increases. Then, by adjusting the IC duty cycle, the required stable 19V output voltage is obtained. The operating frequency of UC3843 is determined by the value of the RC connected to its 4th pin. This circuit is about 170kHz. The value of the output voltage is determined by the resistance of the voltage divider resistor connected to its 2nd pin. By changing the size ratio of the resistor, the required voltage can be obtained within a certain range. Figure 2 is the corresponding PCB diagram, Figure 3 does not install the switch tube and rectifier diode, and Figure 4 is the appearance after installation.

Figure 2

2. 24V to 19V circuit

The circuit is shown in Figure 5. The circuit here is a step-down regulator. In order to obtain higher conversion efficiency, Linear's surface mount product LTCl624CS8 is used here. This is a circuit with a fixed frequency of 200kHz.

The output voltage is determined by the resistance of the voltage divider resistor connected to pin 3. Figure 6 is a real shot of the bottom layer of the circuit board, and Figure 7 is a real shot of the component mounting surface of the circuit board.

Figure 6: Real shot of the bottom layer of the circuit board

Figure 7: Actual shot of the circuit board component mounting surface

3. Production Instructions

When making the circuit, please carefully check the component marking values ​​in the circuit schematic diagram and strictly select high-quality components. For resistors, it is recommended to use five-color rings, and for small-capacity capacitors, it is recommended to use solid tantalum capacitors. The inductors in the two circuits are the same, except for the main inductor L02. L01 uses 0.8mm wire to double-wind 4T on a 13×7×5mm magnetic core. L02 uses 0.8mm wire to wind on an 18×8×7mm magnetic core, with a boost circuit of 30T and a buck circuit of 15T. L03 uses 0.6mm wire to wind 8T on an 8X4X2.5 magnetic core. As shown in Figure 8, the main switch tube and the fast recovery diode are installed together on an aluminum heat sink with a bent corner treatment, with a size of 55X55mm and a thickness of 1.8mm, and an insulating heat conductive sheet and an insulating buckle must be installed on the metal-encapsulated main switch MOS tube. Of course, applying an appropriate amount of thermal conductive silicone grease is also essential.

Figure 8

Finally, we would like to remind everyone to take good anti-static measures during the production process, especially during the soldering process, to prevent damage to MOS, IC and other devices!