Diode Selection Guidelines in Circuit Design

Diodes, also known as crystal diodes, are referred to as diodes. In addition, there are early vacuum electronic diodes; they are electronic devices with unidirectional conduction currents. Inside the semiconductor diode there is a PN junction with two lead terminals. This kind of electronic device has a unidirectional current transducing property according to the direction of the applied voltage. In general, a crystal diode is a pn junction interface formed by sintering a p-type semiconductor and an n-type semiconductor. A space charge layer is formed on both sides of the interface to constitute a self-built electric field. When the applied voltage is equal to zero, the diffusion current and the drift current caused by the self-constructed electric field are equal to each other due to the concentration difference of the carriers on both sides of the pn junction, which is in the state of electric equilibrium. This is also the diode characteristic in the normal state.

1. According to the choice of circuit function, high-frequency detection circuit should use helium detector diode, which is characterized by high workpiece frequency, low forward voltage drop and small junction capacitance. 2AP11～17 is used for 40M or less, 2AP9～10 is used for 100M or less, 2AP1 ~8 for 150M and 2AP30 for 400M or less.

2. According to the overall size of the entire machine to the direction of miniaturization, thinness and lighter, the supporting diodes are required to be miniaturized and chipped. The length of the glass bulb of the DO-35 type switching diode and the frequency band switching diode is 3.8 mm, the length of the glass bulb of the DO-34 frequency switching diode is 2.2 mm, and the length of the SOD-23 type plastic variable capacitance diode is 4 mm.

3. According to the overall cost-effective choice of diodes reasonable selection based on the overall cost-effective and supporting diodes in the role of the whole machine, a reasonable choice, the circuit installation diode guidelines:

1. Use 2 below the maximum rating. Derate use.

3. Use well below the maximum junction temperature.

4. Cut, shape and install diode 5 correctly. Cautions for use Since the diode is micro-sized. The development of ultra-miniature and chip-shaped, in the use of special attention should be paid to the following:

1. For point-junction and glass-shell diodes, prevent them from falling onto hard ground.

2. For bulb diodes, prevent the soldering iron from directly contacting the glass bulb during soldering.

3. No forward voltage can be applied to zener diodes.

4. Schottky diodes are susceptible to electrostatic damage, and people and equipment should be grounded.

5. For a chip diode, pay attention to the coefficient of expansion of the diode itself and the printed board.

6. For diodes with pairing requirements, the use of mixed diodes should be avoided to avoid affecting the debugging.