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It’s now time to actually modify the notebook PSU. Your Password Forgot your password? Similar projects worth following. Hello, i have the same problem as users above: It was not that precise, but well, there it was. SMPS are much more complex, but this is enough to give a good understanding on the theory of operation. The oscillating start only with load. Almost every SMPS feedback circuit works by dividing the output voltage using a voltage dividerthen comparing the divided voltage with a reference voltage.
But when I connect even very small load, it shuts off. The original values were 15kOhms for R40 and 2. When you turn on the power supply, the switch is open and the capacitor is discharged, at 0V.
Let’s take a closer look: As the current flows into the capacitor, the output voltage starts to rise. For a step down power supply, that is, a power supply which outputs a lower voltage than you have on the input, you have a switch and a capacitor.
What we want datasheeet do is to change the voltage divider, changing the voltage at which the comparator tells the control circuit to charge the capacitor.
If R2 is 1kOhm, you have: Description This project was part of my Soldering Station project, but I’ve decided to make it a standalone project, as it’s a little more detailed than I intend to detail the rest of the Soldering Station project.
The comparator gets the value and compares it to the voltage reference. For the R42, I’ve put a single 10kOhms resistor.
S9012 . Datasheet. Equivalente. Reemplazo. Hoja de especificaciones. Principales características
This project was part of my Soldering Station project. The voltage divider I wanted was connected to pin 2 of the comparator IC.
Become a member to follow this project and never miss any updates. That helps a lot. Already have an account? Feedback circuit working like a charm.
Some undervoltage protection, or??? If we compare this voltage divider to the one at the previous post, R40 is R1 and R41 is R2. You now have a voltage divider which halves your voltage. There are two clear divisions on this circuit board, the rubber pads are even marking it, along with silkscreen and areas without components. The part closest to the AC power cord is the input high voltagethe middle part is the control circuit high voltage and the part closest to the DC output is the feedback circuit low voltage.
Now, with a basic understanding of how a SMPS works, there should be no problem modifying one to output our desired voltage. Just when it’s about to reach 18V 19V – 1Vthe voltage suddenly drops to 3V. This finishes the explanation of how a SMPS works.
Nice, but what is what on this power supply? Wait at least one minute after disconnecting it from mains before handling it again while open.
Modifying a notebook power supply |
Testing pin 3 I’ve read 2. Sign up Already a member? A better view of the optocoupler: Grabbed my multimeter and tested the output: I connect the variable power supply to the power supply I want to modify and measure the voltage at the optocoupler.
These steps keep repeating, maintaining the output voltage at the desired value. There’s no real secret to that. Uploaded everything to hackaday. Also, when I changed the voltage on the variable power supply, I could see the voltage on pin 2 changing according to it. Nice, but how do we identify the voltage divider? I have the same problem like David with modifying 20V Fujitsu Siemens laptop power brick.
This is the feedback circuit telling the control circuit to stop charging the output capacitor.
A simple variable power supply based on the LM The feedback circuit notices this and, when the voltage is below the threshold, it tells the control circuit so, which closes the switch again. Test the power supply with a variable voltage power supply.
It’s done, now your power supply outputs the desired voltage. The problem was somewhere else. I reconnected the variable power supply and changed the voltage while measuring the output at the optocoupler.