At present, there are more and more sophisticated instruments: such as electric bicycle chargers, high-end radios, laptops, walkmans and other electronic appliances. These electronic products require absolute polarity when the external power supply is required, otherwise the appliance will burn out when charging. The author uses four 1N4007 diodes to form a bridge rectifier circuit, which is used as a non-polar power input terminal. It can be solved by installing it on the input end of the electrical power supply. The schematic diagram is shown in the attached drawing.
When the input terminal 1 is the positive pole of the power supply and the second terminal is the negative pole, the diodes VD1 and 4 are turned on, thereby ensuring that the input terminal 3 of the meter is positive and the terminal 4 is negative; when input 1 is negative and 2 is positive, then VD2 and 3 are turned on, and VD1 and 4 are reversely loaded. Similarly, the three terminals are positive and the four terminals are negative. Therefore, regardless of the polarity of the input termination power supply, the input terminals "+" and "one" polarity of the meter are fixed, and the user does not have to consider the polarity of the external power supply used. Practical and interesting, if you are interested, you may wish to make it.
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