AC working , RC surge absorption circuit design & component selection Share

 AC voltage operation: Under AC or DC voltage, or in combination of DC, you can use all HVC membrane capacitors. The principle of successful application is: 1) Do not exceed the voltage capacity of the dielectric; 2) Keep capacitor cooling; 3) Do not carry corona operation. As a practical application, here is how you use these three rules.

The limiting voltage peak is a rated DC voltage. Limit the product of the current peak in the rating of the amount of capacity and the DV / DT rated value. For high frequency operations to limit power dissipation, so that the temperature rise of the outer casing does not exceed 15 ° C, and at the same time the outer casing temperature is not higher than the maximum operating temperature.

For rule 3, limit the external voltage to each type of maximum AC rating to avoid corona.
Corona is an insulating system in the insulating system to cause dielectric partial breakdown by air pores. Its occurrence is accompanying the application AC voltage because the effective capacitance of the pore is lower than the surrounding dielectric material. As a low-value capacitor is connected in series, the pore is broken by a higher voltage gradient. Corn Dizzy is to be avoided because sparks cause the dielectric carbonization to convert it into a conductor material, and the final carbon travo is short-circuited.


RC absorption/snubber circuit design

Surge absorption is a variety of simple energy absorption circuits to eliminate voltage spikes caused by loop inductance ----- When mechanical or semiconductor switches are turned on. The purpose of surge absorption is to remove transient voltages and oscillations that occur when the switch is turned on.
It happens to provide an optional circuit when the current flows in an inherent leakage inductor when the switch is turned on. Sub-absorption in the switch mode power supply provides one or more of the following three important functions:
1) Change the carrier line of a bipolar conversion transistor to keep it in a safe operating area;
2) Remove energy from the steering transistor, consume energy in the resistor to reduce the joint temperature;
3) Reduce oscillation on the switching transistor or rectifier diode to limit the peak voltage, reduce EMI by reducing emission and reducing its frequency


The most commonly used soot absorption circuit is a capacitor and a series resistor through a switch connection. Here is how to design a usual RC damper:
Component Selection: Select a non-inductor resistor. A good choice is a carbonaceous resistor. Carbon film resistance is a good choice unless it is subtracted to reduce its resistance in a spiral friction. Avoid winding because it has an inductance. Selecting the resistance from the data sheet to withstand the high-profile current of the same temperature in the damper. For the above 0.01 μF capacitance, the mica capacitor of the immersion epoxy resin is first considered. For higher capacitance values, vertical lead polypropylene, foil film capacitors are considered. In addition to the inherent high inductance of the axial device, the WPP type of the axial lead is also as good. The maximum rated voltage is 630 volts DC, the highest is 1000 volts DC. For higher voltage and capacitance, a polypropylene foil film capacitor is selected, including floating, metallization film as a general foil film to achieve a small size. The use of the metallization film reduces the peak current capacity to form 1/3 to 1/5 of other high pressure selection.
The selection process in the datasheet is simple--peak current and RMS current capacity is provided with rated power capacity. The peak capacitance is the product of DV / DT capacity and nominal capacitance. The RMS current capacity is a smaller value in which the capacitor is 10 ° C or the current of the capacitor to reach its alternating current voltage.

Our DV / DT capacity table can be used to compare CDE surge absorption capacitors and other brands. For all surgeon absorption, the DV / DT value can withstand the DV / DT value, and the HPP type can withstand more than 2000 V / μs. For high pressure surge absorbers, HPFF and HPPS types can process more than 3,000 V / μs; HPMF and HPPM types, withdrawing more than 1000 V / μs. To see the data table according to the length of the housing.


Other capacitors: Here is the last sentence of capacitor selection, to help you enter the uniced capacitance field, which is not specified in the use of the surge absorber, nor is it in this part.

It is to be aware of the type and high K ceramic types that have limited peak current and transient carrying capacity, and the order is 50 to 200 V / μs. The polyester has 15 times the polypropylene loss, and the polyester is only suitable for low RMS current or liability cycle cycle. At the same time, make sure the voltage and temperature coefficients are considered. Although mica or DPP type capacitance is almost independent of voltage and temperature, the high-k ceramic dielectric (like Y5V) can lose 1/4 of its capacity from room temperature to 50 ° C (122 ° F), from 0 to 50%. Another 1/4 capacity can be lost during the rated voltage.

Fast Board Absorber Design: When power consumption is not a critical, there is a quick way to design a surge absorber. Plan with a 2 watts of carbonaceous resistance. Select the resistance value so that the same current can continue to flow without voltage overload, and the current is turned to the surge absorber after the switch is turned on. The time current flow through the switch before the measurement or calculation of the switch is turned on, and the time current flowing before the switch is turned on.