Application of Supercapacitor in Rectifier filter(III)

    By using two pin type 16V / 33000 μ F aluminum electrolytic capacitor shunt as filter capacitor rectifier filter circuit. When the average output voltage of rectifier is 9V and the output ripple voltage of load current 2.2A is as shown in Fig. 3, the oscilloscope used is F105B digital oscillograph. Select A channel / AC coupling, time base 5mS / div (5mSU / g), channel set 100mV divr / r (100mV / g / g). It can be seen from the diagram that the peak value of ripple voltage (Δ Y) is 412mV, and the time of charge and discharge (rise and fall of voltage waveform) is basically the same. Because of the leakage inductance of the power frequency transformer, the filter capacitor almost works in the state of charging or discharging, which is different from the state of direct rectifier.

The test results show that the peak value of the ripple voltage of the output voltage is about 510mV when the filter capacitor of 10000 μ F / A (10,000 micrometer per ampere output current) is selected, which is very close to the theoretical analysis result of 600mV / A. Therefore, for the low-voltage rectifier filter circuit, in order to obtain low ripple voltage, it will have to use a very large filter capacitor, not only large volume but also high price.

    Now we're using a 90mF / 12V bestcap from AVX. ®The supercapacitor acts as a rectifier filter capacitor, and under the same test conditions as in the example above, the peak ripple voltage peak of the output voltage is measured at 312mV, as shown in figure 4. From the peak of ripple voltage, we can see a 90mF / 12V bestcap. ®The peak value of ripple voltage peak of super capacitor as filter capacitor is 100 MV less than that of two aluminum electrolytic capacitors with 16V / 33000 μ F parallel as filter capacitor. A 90mF / 12V bestcap. ®The filtering effect of supercapacitor as filter capacitor is better than that of two aluminum electrolytic capacitors with 16V / 33000 μ F.

The effect of supercapacitor as rectifier filter is not like the ideal capacitor to make the output voltage close to a straight line, but there are some fluctuations, because supercapacitors have relatively large ESR capacitors. A 90mF / 12V bestcap. ®The ESR of supercapacitor is about 90m Ω, and the current difference between charge and discharge on filter capacitor is about 2 times of the average output current, so there is a voltage fluctuation of 310mV due to ESR at the output, even so. You can still get a very low ripple voltage.