What parameters of diode are easily overlooked?

What parameters of diodes are easily overlooked?

One of the basic components in a diode electronic circuit. As one of the common components, the basic performance parameters of diodes are familiar to us, but there are also some very important parameters that are easy for us to ignore, what are their parameters?

1. The diode conduction voltage diode characteristics are unidirectional and therefore widely used in rectifier circuits, switching circuits, protection circuits and other occasions. The so-called unidirectional conductivity means that when the reverse voltage is connected across the diode PN junction, the diode is cut-off; The diode can only turn on when a certain value of forward voltage is connected across the PN junction. This certain forward voltage is the forward voltage drop of the diode. University studies often identify the diode on-voltage drop as 0.7V, but in fact, the diode's forward voltage drop is not fixed, but related to the diode current and ambient temperature, and their relationship is as follows: i=IS(equ/kt-1) where IS is the diode's reverse saturation current, q is the electronic charge, k is the Boltzmann constant, and T is the thermodynamic temperature. A graph of the forward voltage can also be seen in the diode's datasheet

When the temperature is constant, the greater the current flowing through the diode, the greater the on-voltage. Connect 1N4148 to the power supply output for anti-reverse connection, when the current flows through 0~100mA, the voltage ripple of the 1N4148 output terminal reaches 600mV, resulting in the system working normally. Since the on-voltage drop of the diode is proportional to the current flowing, reducing the runout range of the current can reduce the amplitude of the on-voltage drop. A constant load of 10mA is added to the diode output, and the output voltage ripple drops to 260mV as the current flowing through the 1N4148 ranges from 10mA to 100mA.

2. diodejunction capacitancediode junction capacitance is also an important parameter that is easy to be overlooked. In low-frequency circuits, the effect of junction capacitance is negligible. However, in high-frequency circuits, excessive junction capacitance can even cause the circuit to work incorrectly. Take ESD protection diodes as an example. In order to prevent external static electricity from damaging the internal circuitry, ESD protection devices are usually added to the high-speed communication interface. ESD itself has tens of picofard junction capacitance, due to the limited high-speed signal driving capacity, the larger the junction capacitance, the higher the bus frequency, the greater the signal rise time, and eventually may cause bus communication failure. Therefore, when applying diodes to high-speed signals, try to choose a model with a small junction capacitance. What if the diode model is determined to be impossible to modify and the junction capacitance is reduced? As can be seen from the table below, the diode junction capacitance is inversely proportional to the reverse voltage it is subjected to, and the larger the reverse voltage, the smaller the junction capacitance. Therefore, the junction capacitance of the diode can be reduced by increasing the reverse voltage to which the diode is subjected.