Xiang Zhai is a blogger who keeps fiddling with various circuits and electronic tools. Adding to the list of these projects, he decided to work upon his car charger for a DIY task. In order to charge various devices while traveling, he had several adapters that could easily convert the 12V voltage of car’s socket into 5V voltage of USB standard. So he thought of converting the Vout of one of his 5V car chargers into a voltage output of 9V and it turned out that the task was quite easy.
In order to get the work done, Xiang thought of using LM7809 which is a 9V voltage regulator. Interestingly, it could generate a fixed output voltage for a preset magnitude that would remain constant irrespective of the change made to the input voltage. However, after opening his 5V charger, he realized that there was another way to do it which was much easier than installing a regulator.
For this, first he examined the internal structure and observed the configuration of all the parts. On the top, there was a 2A fuse that was connected to the anode of the car charger and two metal sheets that were connected to the ground. At the bottom, there was a circuit responsible for converting 12V voltage of the car socket into 5V of USB standard.
Apart from all these, he found the integrated circuit under the black wire that was the most crucial part of the whole setup. The part number was marked as MC34063A, a DC-DC voltage regulator. At this point, he was clear that making changes to the IC would certainly help him in getting the job done. In order to ensure that he had all the know-how about that IC, he gathered all the information on the internet relating to its specifications and features.
After this, he came to know that the regulator fitted inside could change the output voltage from 1.2V to 40V and could output up to 1.5A. He also went through the datasheet that mentioned a step-down circuit example. Later, he observed that the information matched exactly with the actual circuit fitted inside the car charger.
Using a multimeter he read the values of R1 and R2 which were 1K Ohm and 3K Ohm respectively and gave out an output voltage of 5V. So he just replaced the R2 with another resistor carrying 6.2K Ohm which in turn altered the overall output voltage to 9V. He went on to try the same thing on other car chargers and found that most of them had a similar identical chip. Apparently it was clear that this method would work for all other kinds of car chargers as well.
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