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Key parameters and precautions for Zener diodes!
1) Stabilized Voltage Uz
Stabilized voltage is the operating voltage of a Zener diode in the reverse breakdown region, which is the voltage across the diode. This value changes slightly with the working current and temperature. Even for the same type of Zener diode, the stabilized voltage value has a certain degree of dispersion. For example, the stabilized voltage of a 2CW14 silicon Zener diode is 6～7.5V.
2) Temperature Coefficient
Changes in temperature will cause VZ to change. In Zener diodes, when |VZ|>7V, Vz has a positive temperature coefficient, and the reverse breakdown is avalanche breakdown. When |Vz|<4V, VZ has a negative temperature coefficient, and the reverse breakdown is Zener breakdown. When 4V<|Vz|<7V, the Zener diode can obtain a temperature coefficient close to zero. Such Zener diodes can be used as standard Zener diodes.
3) Stabilized Current Iz
Minimum stabilized current Izmin, maximum stabilized current Izmax. Stabilized current: reverse current when the operating voltage is equal to the stabilized voltage; Minimum stabilized current: the minimum reverse current required when the Zener diode operates at the stabilized voltage; Maximum stabilized current: the maximum reverse current allowed to pass through the Zener diode.
Dynamic resistance rz. Its concept is the same as the dynamic resistance of a general diode, except that the dynamic resistance of a Zener diode is obtained from its reverse characteristics. The smaller the rz, the steeper the breakdown characteristics of the Zener diode. rz=△Vz/△Iz4)
Power Dissipation Pz
When the reverse current passes through the PN junction of the Zener diode, a certain amount of power loss will be generated, and the temperature of the PN junction will also increase. The power dissipation of the diode is determined by the allowable PN junction operating temperature. Typically, low-power diodes are a few hundred milliwatts to a few watts. Maximum power dissipation Pzm: the maximum power loss of the Zener diode depends on the area of the PN junction and heat dissipation conditions. During reverse operation, the power loss of the PN junction is: Pz=Vz*Iz, and Izmax can be determined by Pzm and Vz.
Zener diodes are widely used and extremely common. While their application seems simple, they are easily damaged if not handled carefully. Here are some precautions when selecting them:
1. Multiple Zener diodes can be used in series, but due to the large dispersion of diode parameters, they must not be used in parallel.
2. The Zener diode leads must be soldered at a distance of more than 5mm from the casing. It is best to use a soldering iron with a power of less than 30W. If a 40～75W soldering iron is used, the soldering time should not exceed 8～10s. Try to use solder-cored solder wire for soldering, and do not use the method of adding rosin to large pieces of solder.
3. In order to compensate for the voltage temperature coefficient of the Zener diode, the Zener diode can be used in series with a silicon diode (including a silicon Zener diode). The number of forward-biased diodes in series should not exceed three. It can also be used in series with a special temperature compensation diode.
4. Temperature has a significant impact on the characteristics of semiconductor devices. When the ambient temperature exceeds 50℃, the maximum power dissipation should be reduced by 1% for every 1℃ increase in temperature.
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2021-07-19
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