CURRENT ISSUE
Contests
Test your eq
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Issue #216 July 2008
A recently-failed compact fluorescent lamp (CFL) offers a great opportunity to exercise one’s reverse-engineering skills. A trace of the single-sided PCB found inside reveals the following circuit. Unfortunately, R3 and R4 were burned beyond recognition, which presumably had something to do with why the lamp failed. L1 is a small “drum” style inductor, while L2 is a larger unit that looks something like a small audio coupling transformer, except that it has a ferrite core rather than laminated iron. “B” is a small toroidal transformer with three windings, phased as shown. V6 is a small blue unit with an STMicroelectronics logo and the markings “DB3.”
Problem 1—What is the purpose of C1 and L1?
Answer
Problem 2—What is the purpose of the component marked “PTC”?
Answer
Problem 3—How does the oscillator circuit work in the steady state?
Answer
Problem 4—How does the oscillator circuit get started in the first place?
Answer
Problem 5—Why did R3 and R4 burn up?
Answer
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