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本帖最后由 大尾鱼 于 2013-8-21 13:31 编辑
kensony3000 发表于 2013-8-21 11:04 
大尾鱼兄：
“理论上讲，VC流经二极管 就不是"波"的DC，故而理解为"拒＂VC于外。”
K兄你好！
再回顾下本人上述有关整流桥"拒杂波"的解释是太过牵强了，现本人决定把这个说法收回。抱歉了。
还是回到7Mu兄在第17楼的注解，很合适。
现也找到原图作者相关的注解，出处：http://sound.westhost.com/earthing.htm。逐步来理解消化吧。
注：文中的loop breaker就是指小电阻和电容的组合体。本人把它试译为：地回环破解器。文中又特别注明，必须按照标记正确接上整流桥，否则有危险。
The loop breaker works by adding a resistance in the earth return circuit. This reduces circulating loop currents to a very small value, and thus breaks the loop. The capacitor in parallel ensures that the electronics are connected to the chassis for radio frequency signals, and helps to prevent radio frequency interference. Finally, the diode bridge provides the path for fault currents. The use of a large chassis mounting (35A) type is suggested, since this will be able to handle the possibly very high fault currents that may occur without becoming open circuit. Note the way the bridge is wired, with the two AC terminals shorted, and the two DC terminals shorted. Other connection possibilities are dangerous, and must be avoided.
In the event of a major fault, one (or more) of the diodes in the bridge will possibly fail. Semiconductors (nearly) always fail as short circuit, and only become open circuited if the fault current continues and 'blows' the interconnecting wires. High current bridge rectifiers have very solid conductors throughout, and open circuit diodes are very rare (I have never seen a high power bridge go open circuit - so far at least). Use of the bridge means that there are two diodes in parallel for fault current of either polarity, so the likelihood of failure (to protect) is very small indeed.
When a loop breaker is used, it is vitally important that all input and output connectors are insulated from the case. If not, they will instantly defeat the loop breaker by providing a direct connection from the zero Volt point to chassis, and no benefit is obtained. (Electricity has an annoying - but perfectly logical - tendency to travel along the path of least resistance, and a direct short circuit will always have less resistance than the loop breaker.)
It is not uncommon to have a voltage of 1V RMS between the earth connections of power outlets that are wired separately back to the switchboard. This small voltage, with a total resistance of perhaps 0.2-0.5 Ohm, will cause a loop current of 2 to 5 Amps, all of which flows in the shield of the interconnect. This is sufficient to cause a voltage difference across the interconnect, which the amplifier cannot differentiate from the wanted signal. By breaking the loop with the 10 Ohm resistor, the current is now less than 200mA, and the voltage across the interconnect will be very much smaller, reducing the hum to the point where it should no longer be audible.
Never route an earth wire to the main (star) earthing point on a chassis in such a way that it forms a partial (or full) turn around a transformer. It is better to relocate either the star earth point or the transformer to ensure that no earth conductor can create a partial turn. There may often be conflicting requirements, but there is usually no reason that proper earthing for minimum hum and maximum safety should be mutually exclusive. Both are important, and both must be accommodated in the final design. |
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发表于 2013-8-21 10:12
