LYCOS RETRIEVER 
Capacitor: Voltages
built 660 days ago
It is important to understand that the lossy capacitor appears (electrically) as an infinite number of small capacitors, each with its own series resistance. This can be built using real capacitors, with a lumped parasitic capacitance of perhaps one tenth of the value of the actual capacitance. Use a 1 megohm resistor in series with the 'parasitic' cap, using the general scheme shown in Figures 2 and 5. The 'losses' in this capacitor are far greater than any metallised film cap, yet using it in a circuit will not degrade the performance one iota. Dielectric absorption simply does not affect the way a capacitor passes the signal. Dielectric loss becomes a problem when significant (high frequency signal) voltage appears across the capacitor, but is rarely even measurable as a loss at audio frequencies and at levels typical of audio systems.
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Note that you really need to pay attention to correctly hooking a polarized capacitor up (both with respect to polarity, as well as not pushing a capacitor past its rated voltage). If you "push" a polarized capacitor hard enough, it is possible to begin "electrolyzing" the moist electrolyte. Modern electrolytic capacitors usually have a pressure relief vent to prevent catastrophic failure of the aluminum can (but don't bet your eyesight on this).
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Power Source with Series Resistance: The following diagram shows how series resistance (not ESR) allows the capacitor to smooth the voltage even more. The series resistance will allow the cap to smooth the voltage but would cause a voltage drop if current is drawn from the capacitor. Some low current power supplies may be designed in this way to provide a very smooth output voltage. This will generally only work well if the current draw is constant and known when designing the power supply.
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[I]f replacing a 0.05 uF capacitor you can use a 0.047 uF; if replacing a 0.002 uF you can use 0.0022 uF. These replacements are virtually identical. If you are +/- 10% you be well within your radios factory specifications. (Just be sure your replacement capacitor has a working voltage is equal or greater than the original paper capacitor)
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Care must be taken to ensure that any large or high-voltage capacitor is properly discharged before servicing the containing equipment. For safety purposes, all large capacitors should be discharged before handling. For board-level capacitors, this is done by placing a bleeder resistor across the terminals, whose resistance is large enough that the leakage current will not affect the circuit, but small enough to discharge the capacitor shortly after power is removed. High voltage capacitors should be stored with the terminals shorted to dissipate any stored charge.
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This is the phenomenon where after a capacitor has been charged for some time, and then discharged, some stored charge will migrate out of the dielectric over time... changing the voltage value of the capacitor. This is extremely important in sample and hold circuit applications. The typical method of observing Dielectric Absorption is to charge up a cap to some known DC voltage for a given time, then discharge the capacitor through a 2 ohm resistor for one second, then watch the voltage on a high-input-impedance voltmeter. The ratio of recovered voltage (expressed in percent) is the usual term for Dielectric absorption.
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