The choice of aluminum electrolytic capacitor capacitance

Aluminum electrolytic capacitor of capacitance can choose according to the general electronic circuit, in rectifying filter circuit, high ripple current, etc into consideration. 1. General electronic circuits for electronic circuit, average bypass and decoupling capacitors capacitance choice, should be when the job is the lowest frequency capacitive reactance of bypass capacitor should be far lower than with the parallel circuit impedance. 2. General rectifier filter circuit power frequency in general power frequency rectifier filter circuit, main consideration after the rectifier filter ripple voltage, generally require 1 v fengfeng ripple voltage value, can press each Ann [ Mr] Need 6000 & mu; F the electric capacity of choice, to this point in the 5 v output low voltage rectifier filter circuit is particularly important, not only can guarantee the quality of the output rectifier filter, more major is can reduce the input voltage rectifier, improve the efficiency of the whole power supply. For low voltage (average 12 ~ 25 v) Rectifier filter output, we suggest each Ann [ Mr] 3300 ~ 6800μ F。 So we can get 1 ~ 2 v fengfeng value of ripple voltage, the voltage regulator circuit only add 0. The additional voltage 5 ~ 1 v. The voltage of power supply according to the voltage regulator circuit for 60 db rejection ratio, will generate about 1 mv on the output side of ripple voltage. Aluminum electrolytic capacitor rated ripple current is definitely can meet the requirements; If per ampere & 470 ~ 1000 mu; F is chosen, will produce the ripple voltage of 3 ~ 7 v fengfeng, need add 1 in voltage regulation circuit. 5 to 3. The additional voltage of 75 v, it will produce more on the output side of 2 ~ 4 mv ripple voltage. Considering every output 1 a current rectifier circuit, filter capacitor will flow through 2 ~ 3 a ripple current, in this case of aluminum electrolytic capacitor rated ripple current may not be able to meet the requirements. For ac 220 v direct rectification, in accordance with the requirements of ripple voltage can choose 1 & mu; F/W, but in considering the filter capacitor on the premise of guarantee life whether can withstand such ripple current, you need to choose 3 & mu; F/W。 3. High ripple current and high ripple current application refers to the frequency converter rectifier filter, dc support, etc. In such applications, the ripple current is too large, has become the principal contradiction, aluminum electrolytic capacitor of capacitance selection is mainly according to the ripple current, which is no longer a ripple voltage. For example, three-phase 380 v input filter capacitor need to absorb the 3. 5 a/kW ripple current from the power frequency rectifier, at the same time, also absorbed from the inverter switch ripple current. The result is the ripple current to flow through the filter capacitor to 4 ~ 5 a/kW. This is only aluminum electrolytic capacitor can not afford, need more parallel solution only. Considering the size and cost of aluminum electrolytic capacitor, when choosing the capacitance of aluminum electrolytic capacitors, the ripple current can press at 25 ℃ and 40 ℃ ripple current 2 times the selected need how many aluminum electrolytic capacitor can be used. Is the press 2 ~ 2. 5 a/kW, this value to kW number multiplication is aluminum electrolytic capacitor ripple current, divided by single aluminum electrolytic capacitor ripple current value, is the number of aluminum electrolytic capacitors in parallel. For example, a 10 kw inverter, the three-phase 380 v power supply, & other; Filter capacitor & throughout; Requires 40 ~ 50 a ripple current, average 400 v or 450 v / 3300 & mu; F the ripple current of al electrolytic capacitor at room temperature is about 22 ~ 25 a, 2 times to 44 ~ 50 a, can use at this time only 400 v / 3300 & mu; F aluminum electrolytic capacitors in parallel. In order to reduce cost, also can use 400 v / 2200 & mu; F specifications of aluminum electrolytic capacitor, the rated ripple current at 20 a, if press 2. Five times the current ratio, also can meet the requirements. If the responsibilities of aluminum electrolytic capacitor ripple current too big, will be impossible for us to make the service life of aluminum electrolytic capacitor obviously shortened. If the working state of the inverter is not continuous work at full capacity, but in most cases in light load or no-load, is through the aluminum electrolytic capacitor & other The average & throughout; Ripple current will decrease greatly, aluminum electrolytic capacitor will have a longer life.
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