|"Hi-Fi svět" federmann.cz
|Používat nebo nepoužívat blokovací kondenzátory ve zdrojích
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|Autor:||vladzin [ sob 15. říj 2011 18:34:09 ]|
|Předmět příspěvku:||Používat nebo nepoužívat blokovací kondenzátory ve zdrojích|
Četl jsem dnes tento zajímavý článek a rád bych znal názor odborníků na danou problematiku.
celý článek je zde__http://users.ece.gatech.edu/~mleach/lowtim/pwrsply.html___
Power Supply Decoupling and Grounding
I have seen some circuits in which the values of the decoupling capacitors are far too small. When I first started designing the Low TIM amplifier, I used a single 0.1 uF capacitor to decouple each power supply rail at the points where they connect to the circuit boards, i.e. in place of C21 through C24. I used that value because I had seen it used in so many other circuits. In taking measurements on the amplifier, I found a very large AC signal would appear on the power supply rails when I tested the amplifier at high frequencies. At 1 MHz, the AC signal on the rails had the same amplitude as the amplifier output signal. When I removed the 0.1 uF decoupling capacitors, the AC signals on the rails would almost disappear. Replacing the 0.1 uF capacitors with 10 uF capacitors eliminated the problem. I settled on 100 uF capacitors to be on the safe side.
I was describing this experience to a former student who had worked as a repair technician for a company that did factory repair service for several audio equipment manufacturers. He told me that whenever they received a particular KLH receiver for repair, the first step was to remove the 0.1 uF power supply decoupling capacitors because they were causing the amplifier sections of the receivers to fail. What was happening was the inductance of the wires that ran from the circuit boards back to the power supplies and the 0.1 uF capacitors formed high-Q resonant circuits on the power supply rails. This was causing the amplifiers to oscillate and fail. Rather than removing the capacitors, a far better solution is to make them larger. With the 100 uF values that I used, I found no evidence of resonance effects on the rails.
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