How to choose the capacity of aluminum electrolytic capacitors?
Article Source：QUNIO ELECTRONICS
time visited：
issuing time：2019-04-09
The capacity of aluminum electrolytic capacitors can be based on general electronic circuits, high ripple current, and general rectification and filtering circuits.
1、General electronic circuit
For general electronic circuits, the capacitance of the bypass and decoupling capacitors should be chosen such that the capacitive reactance of the bypass capacitor should be much lower than the impedance of the parallel circuit at the lowest frequency of operation.
2、High ripple current
The application of high ripple current mainly refers to the rectification and filtering and DC support of the inverter. In this type of application, since the ripple current is too large, it has become a major contradiction. The choice of the capacitance of the aluminum electrolytic capacitor is mainly based on the ripple current, and is no longer the ripple voltage.
3、General power frequency rectification and filtering circuit
In the general power frequency rectification and filtering circuit, the ripple voltage after rectification and filtering is mainly considered, and it is generally required to obtain a peak-to-peak ripple voltage of 1V, which can be selected according to the capacity of 6000 μF per ampere, which is output at 5V. The low-voltage rectification and filtering circuit is especially important, which not only ensures the quality of the rectified and filtered output, but also reduces the rectified input voltage and improves the efficiency of the entire power supply.
For general low voltage (12~25V) rectified and filtered output, it is recommended to select 3300~6800μF per ampere. In this way, the ripple voltage of 1~2V peak-to-peak can be obtained, and only an additional voltage of 0.5~1V is added to the voltage stabilizing circuit. According to the voltage regulation ratio of the voltage regulator circuit of 60dB, a ripple voltage of about 1mV will be generated at the output. The rated ripple current of aluminum electrolytic capacitors can certainly meet the requirements; if it is selected according to 470~1000μF per amp, it will generate ripple voltage of 3~7V peak and peak, and need to increase the additional voltage of 1.5~3.75V on the voltage regulator circuit. A ripple voltage of 2 to 4 mV will be generated at the output. Considering that the rectifier circuit outputs 1A current per current, the filter capacitor will flow through the ripple current of 2~3A. In this case, the rated ripple current of the aluminum electrolytic capacitor may not meet the requirements.
For AC 220V direct rectification, 1μF/W can be selected according to the ripple voltage requirement, but 3μF/W is required when considering whether the filter capacitor can withstand such ripple current under the premise of guaranteed lifetime.
