Using this instruction, you can change the output voltage of almost any switching power supply, not just the one from a laptop. They all almost work on the same principle and the scheme is not very different.
For example, if you still have an unnecessary 19 V power supply, then you can easily convert it to 12 V, and, say, power an LED strip from it.
Changing the power supply voltage
Now let's take a closer look. The entire pulse source board can be divided into two sections. The center is the high-frequency transformer, this is the most massive part on the board. On the left is the low-voltage part, and on the right is the high-voltage part.
The high-voltage part has feedback from the low-voltage part via an optocoupler, which is controlled by a “TTL431” stabilizer chip or similar.
That is, when the output voltage reaches the required value, the stabilizer monitors this and transmits the signal through an optocoupler to the controller in the high-voltage part. This is how the power supply stabilizes the current and voltage.
The TTL431 stabilizer has adjustable parameters that are set by a bias chain, which consists of two resistors.
One resistor always goes to positive, the other to negative. To change the output voltage, you need to change the ratio of these resistors. The rule applies here: if the voltage at the input of the stabilizer increases, then the output voltage will decrease and vice versa.
- - Solder the resistor on top.
- - Remove both resistors and solder a potentiometer instead.
In this example we take the second path. Solder both resistors.
Solder in the potentiometer.
Switching on and testing
Before turning on, be sure to set the potentiometer to the middle position. Second: if you decide to increase the output voltage, then you must check the rating of the output capacitors so that they are designed for the new voltage.
We make adjustments.
Result
As for the computer power supply specifically, with an initial voltage of 19 V, it can easily be reconfigured to any voltage in the range of 9-22 V.
Now those who have laptop power supplies lying around unattended at home can remake them and use them according to their needs for new purposes.
