A fixed capacitance is a capacitor with a fixed capacitance. The deviation of the actual capacitance of the capacitor from the nominal capacitance is called the error, and the tolerance is called the accuracy.Selection method of fixed capacitor:
(1) Choose the model reasonably according to the requirements of the circuit
Generally used in low frequency coupling and bypass applications, paper capacitors should be used; in high frequency circuits and high voltage circuits, mica capacitors and ceramic capacitors should be used; electrolytic capacitors should be used in power filter or decoupling circuits.
(2) Reasonably determine the accuracy of the capacitor
In most cases, the capacity requirements of the capacitor are not strict. But in the oscillation, delay circuit and tone control circuit, the capacity of the capacitor should meet the calculation requirements as much as possible. In some filter circuits and some highly demanding resonant circuits, the capacitance value of the capacitor is required to be very accurate, and its error value should be less than ±0.5% or even lower.
(3) Determination of capacitor rated working voltage
The working voltage of the capacitor should be 10% to 20% lower than the rated voltage. Note that the AC voltage and current passing through the capacitor should not exceed the given rating.
(4) Pay attention to the temperature stability and loss of the capacitor
The capacitor used in the resonant circuit must be selected with a small error capacitor, and its temperature coefficient should also be selected to avoid affecting the resonance characteristics.
Selection method of fixed capacitor mainly for the above 4 elements。
