How to see the PCB anode and cathode

1. Large-area copper foil line is ground wire. The ground copper foil is usually thicker than the normal wire, and is connected everywhere on the circuit board.

2. The metal shell of components is ground wire. Some components have metal enclosures, such as switchgear, that enclose grounding wires in the circuit.

3, shielding wire metal mesh is the ground wire. If the circuit board has metal shielding wire, the metal wire is the ground wire in the circuit board.

4. Negative plate grounding wire of the electrolytic capacitor with the largest volume. Another: according to the color of your line judgment is generally red to the positive pole, yellow to the negative pole. You can compare by yourself should understand.

How to add schottky diode to circuit board to prevent negative and positive electrode from being reversed

Schottky diode has a small forward voltage drop (generally 0.2 ~ 0.3v) and good high-frequency performance, which is suitable for use on circuit boards to prevent the power connection from damaging the components, and the cost is also very low. Two specific application circuits are described below.

1, a schottky diode composed of the protection circuit.

Capacitor C is the power filter capacitor on the circuit board. Some electronic beginners in electronic production or maintenance, sometimes due to the wrong polarity of the power supply and damage to the circuit board components. This can be avoided by attaching a schottky diode to the positive power input of the circuit board. In the figure above, if the polarity of the power supply is not wrong, VD will conduct, just like a closed switch (the positive voltage drop of about 0.2v is ignored here), and the circuit board will work electrically. If the polarity of the power supply is inversely connected, VD is inversely biased and cut off. At this time, VD ACTS as a disconnected switch, thus protecting the components on the circuit board from damage.

In the circuit above, when selecting schottky diode, it is required that its rectifying current should be greater than the working current of the circuit, the voltage withstand value should be greater than the power supply voltage, and a certain margin should be left. When the working current of the general circuit is below hundreds of mA and the power supply voltage is no higher than 30V, 1N5819 schottky diode can be selected, whose rectified current is 1A and the voltage withstand value is 40V. If the working current of the circuit is 1 ~ 2A, 3A schottky diodes such as 1N5822 and SR360 can be used.

2. Non-polar input circuit composed of 4 schottky diodes.

For some battery charging circuit board or low-voltage dc LED circuit board, if add a low-voltage drop rectifier bridge composed of four schottky diodes at its power input end, it will be more convenient to use. This connection with the dc power supply does not need to consider the polarity of the power supply, casually connected to the power supply, the circuit can work normally.

The specific circuit is shown in the figure above. No matter how the input power is connected, the dc voltage obtained on the circuit board is always “up plus down minus”. In this circuit, no matter how the polarity of the input voltage is connected to the circuit, only two schottky diodes are conducted. At this time, the loss voltage of the rectifier bridge circuit is only about 0.4v (the loss voltage of a diode like 1N4007 can be at least 1.4v).