What is the reason for the heating of the power amplifier power filter electrolytic capacitor when it is powered on
The first type is that the electrolytic capacitor itself has leakage, resulting in dielectric loss and causing temperature rise.
The second type is insufficient voltage resistance, which causes dielectric loss and heating due to the critical breakdown state of the electrolytic capacitor.
The third type is relatively rare, where the positive and negative electrodes of the electrolytic capacitor are welded in reverse, causing a sharp increase in temperature due to a sharp increase in leakage current when powered on, until the slurry bursts. This phenomenon is usually prone to occur in carelessness or beginners during circuit manufacturing.
There is another situation that needs to be explained, which is the dielectric loss caused by a large amount of high-frequency ripple in the power filter circuit to the electrolytic capacitor.
Due to the fact that the positive and negative electrodes of an electrolytic capacitor are made up of double layered metal oxide thin films that are insulated from each other, and the electrolyte is filled between the positive and negative electrodes as the working medium, the process properties determine how much inductance loss the electrolytic capacitor will have. High harmonic rich power circuits, such as the DC output circuit of a switching power supply, the power supply circuit of a computer motherboard CPU, etc., make it very easy for electrolytic capacitors that perform filtering tasks in these areas to heat up and swell due to medium degradation caused by high-order harmonics.
In the past, the power supply filter capacitors of older generation computer motherboards and CPUs often experienced swelling due to this reason. Nowadays, they are mostly solid-state capacitors, and swelling is rarely seen.
It should refer to the filtering capacitor of the power amplifier. It heats up when powered on and can clearly understand the internal situation of the power amplifier. It is estimated that you made your own power amplifier test machine when powered on. It is impossible for you to know which component heats up in the finished machine. Personally, I think there are three situations,
1: If the polarity of the filtering electrolytic capacitor is reversed, there will be a large leakage current when powered on, resulting in a power consumption of several tens of watts, and the capacitor will inevitably quickly heat up
2: It is common in the market that the purchased electrolytic capacitors have a false standard capacitance and withstand voltage. In the past, false standards were often purchased by mail order. Some capacitors were fitted with a high standard plastic sleeve on top of a low standard capacitor, and the outer layer was torn open to see the original label, such as 16v2200uf and 50v4700uf. They obtained sales at a low price or sought profits by raising the price. Good Fruit used such capacitors on a power supply with a voltage of more than 20 volts, causing excessive withstand voltage and exponential increase in leakage current, resulting in capacitor heating
3: The selected capacitor specification is incorrect. For example, in a power amplifier power supply with an AC output of 20 volts from a power transformer, the selected capacitor has a withstand voltage of only 25 volts. On the surface, it seems that the withstand voltage of 25 volts is greater than the power supply voltage of 20 volts. However, the filtered DC voltage is close to the peak value of 28 volts. When the grid load is light, the grid voltage reaches 250 volts, and the output can reach more than 32 volts, causing significant leakage and heating of the capacitor, (The nominal withstand voltage of a capacitor is generally the lowest withstand voltage of all products, and most actual withstand voltages are higher than the nominal withstand voltage, such as the nominal value of 25V. The actual withstand voltage may reach twenty-eight, nine, or even thirty volts. However, for safety reasons, it cannot be used on top of the grid, and a 20% margin should be left because the internal heating will increase the leakage of the electrolytic capacitor, resulting in a decrease in withstand voltage. If possible, it is best to test the actual withstand voltage of the electrolytic capacitor yourself, that is, the leakage current is limited to within 0.5mA of the withstand voltage.)
