About ceramic capacitors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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The article considers the problem of the dependence of the capacitance of ceramic capacitors on the applied voltage.
Once, while working on another electronic device, the author had to face the fact that the capacitance of some ceramic capacitors was significantly dependent on the applied voltage. In order to more accurately determine the nature of this dependence, a simple stand was assembled (Fig. 1), where the capacitance of two capacitors connected in series was measured: Cx - the one under study and Co - the auxiliary one.
Fig. 1
In this case, a voltage with a variable resistor R1 was applied to the capacitor under study, which could be changed from 0 to 50 V (the nominal operating voltage of the capacitor under study). Since the resulting capacitance of a series connection can be calculated using the formula
C \uXNUMXd Cx * Co / (Cx + Co),
with known Cism and Co, it is easy to find Cx:
Cx \uXNUMXd Co * Sism / (Co-Sism).
Capacitor capacitance Co is selected in the range of 0,1 ... 10 Cx, you can use, for example, capacitors of the K73-17 type. Resistors R1 and R2 - any type. Resistor R1 and a voltmeter can be completely abandoned if there is a power source at hand with regulation and control of the output voltage. In this case, the power supply can be connected to the tested capacitor through resistor R2.
Thus, several imported ceramic capacitors were tested - analogues of domestic K10-17 of various capacities with different TKE groups. The result was unexpected. The capacitance of some capacitors with increasing voltage from 0 to 50 V decreased by 10 ... 15 times! At a voltage of 10 V, their capacity was already only 35 ... 40% of the nominal value. This can only be explained by the very low quality of the applied dielectric. Of course, not all imported capacitors have such parameters, but the conducted experiment suggests that we need to be prepared for any surprises presented to us by foreign manufacturers.
Author: V.Tsibin, Berezovsky, Sverdlovsk region
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