Harmonic current suppression

The suppression of harmonic current is important for membrane switches. There are some ways. Let's talk about it.

1. Choke coil input

This is to add a choke coil, noise filter or reactor at the input end of the power supply. Currently, hybrid small chokes, small reactors and special harmonics are used to suppress both harmonic currents and electromagnetic interference. Small noise filters for current suppression are under development.

2. Single conversion

The circuit design is simple. There is no need to connect a reactor to the input end. The AC input can be directly connected to the load. The PWM converter does not need to be modified. As long as a few components are added, the functions of the double conversion can come true. There are stabe DC voltage, primary and secondary isolation, reduction of harmonic current, and improved power factor.

3. Double conversion

There are two converters to stabilize the DC output voltage and improve the power factor. Those converters have large degree of freedom in design. This is an ideal circuit method to reduce harmonic current and improve power factor.

4. Partial smoothing method

It uses a combination of passive components to expand the current conduction angle, and suppress harmonic currents.

Tester

Membrane switch tester is a machine to test the performance of membrane switches. So, how much do you know about it?

Membrane switch tester is a non-standard testing instrument. The functions and performance of each brand may be different, but they generally have the following functions.

a. Test various types of membrane switches;

b. Test the circuit (short circuit and open circuit) of the membrane switch;

c. Detect poor insulation;

d. Test the circuit resistance (whether the value exceeds the standard).

Nowadays, we have membrane switch testers with testing functions of semi-finished products and membrane switch testers with LED display. And the testing speed has been greatly improved. The size of tester has become smaller.

In the past, people need a dedicated room to carry a computer monitor, or a dedicated area for testing. Now, the tester has become an instrument that is only the size of a folder. It can be placed directly on the assembly line for testing. Some membrane switch testers also have the following functions.

a. Only test leakage;

b. Automatically count good and defective products;

c. Test LEDs on membrane switches (LEDs connected in series can also be tested);

d. Test semi-finished product (Membrane switch generally has upper and lower circuits. The tester can be used for these two separately. The two layers of testing are OK before assembly. In this way, the yield of the finished product will be greatly improved. The test time will be very short, usually within 1s.).