My internship started 2 weeks ago (at least the full time one). I got a nice place (PBF group, website under construction already for 2 years), nice salary, nice people (one of the boss is half indonesian, and the beautiful secretary is also half indonesian). And I got a position in Research and Design department. So they gave me my own desk with complete tools, a computer, and maybe they will give me a telephone. I worked with 3 seniors who design and test the power supply. I'm quite happy with my task, and I'm getting good at it. Yesterday I blew up 3 powersupply that I made for testing a new prototype, it was fun... hahaha. The powersupply has to deliver a minimum voltage of 42V with maximum load current of 12A at minimum input voltage of 90V AC. The prototype that I made deliver 40V DC, so I need 2 more Volts. We changed the value of a resistor from 47Kohm to 56Kohm to make the resonant frequency of the mosfet lower so it can produce more output voltage. It was ok at 6A, at 9A still ok, 10A start making sound.., 11A getting louder, 11,8A BOOM!!! I blew it up..." hmm thats not good", we said it almost in the same time. We thought it was out of regulation, so we put a diode accross the controler to bypass some current and to maintain the reference voltage at 2 volt, we thought everything will be ok because it will always be inside the regulation. Apparently what we thought was wrong, once again it blew up at 11,8A. Things was getting worst when I blew the 3rd powersupply at normal condition without modification, but still at 56K.
Today we made several change to it, Wouter (the boss) said it will be better if we decrease the resonant impedance by lowering the value of the Inductor, and change the resistor to its original value (47K) so we ask the production department to make a 25uH inductor instead of the 30uH that we used before. Then the test came... 10A still OK, 11A still OK, 11,9 A still OK... hmm this is good. 12,3A still OK.. huh?? This is bad, it should reach the current limit now.. 12,9A click the current limiter start to work, the powersupply died.. Thats a good sign..
So my task tomorrow, modified it and test the short circuit current (16A).. It will be fun.., playing with big Amps and large Voltages...
"1 apple a day, keep your doctor away. 3 powersupply per day, make your doctor awake"
