Selasa, 08 November 2011

voltage regulator diode

Zener diode is applied in the reverse breakdown of the surface contact area of the special type of silicon diode. Zener diode volt-ampere characteristic curve and silicon diode volt-ampere characteristic curves exactly the same. Zener diode characteristic curve similar to ordinary, but the reverse diode voltage curve relatively steep. Normal operating range of the diode voltage, current characteristic in the reverse current on the sudden rise in the beginning part. This section of the current, commonly used for the regulator in terms of low power, typically a few milliamperes to tens of milliamps.
The main parameters of the diode voltage regulator
(1) stable voltage Vz: stable voltage regulator diode is in normal operation, the voltage across the tube. This value with the operating current and temperature changes slightly different, both the same type of Zener diode, voltage stability has some dispersion, for example, the stability of 2CW14 silicon diode voltage regulator 6 ~ 7.5V.
(2) dissipation PM: reverse current through the PN junction diode regulator, we should have some power loss, PN junction's temperature will rise. PN junction under the permissible operating temperature determine the power dissipated in the tube. Low power tube is usually about a few hundred milliwatts to several watts.
Maximum power dissipation PZM: a regulator of the maximum power dissipation depends on the PN junction area and cooling conditions. Reverse work, PN junction power loss: PZ = VZ * IZ, and VZ by the PZM can decide IZmax.
(3) Stable current IZ, the minimum stable current IZmin, large and stable current IZmax steady current: working voltage equal to the voltage stability of the reverse current; minimum stable current: voltage regulator diode in the steady reverse current minimum required; maximum stable current: Zener diode allows the maximum reverse current.
(4) dynamic resistance rZ: the concept and the same general dynamic resistance of the diode, but the dynamic resistance of diode voltage regulator is to strike it on the reverse characteristics of the. rZ smaller, reflecting the breakdown characteristics of the regulator more steep.
rz = â–³ VZ / â–³ IZ
(5) stable voltage temperature coefficient: VZ temperature change will change in the regulator, when | VZ |> 7 V when, VZ has a positive temperature coefficient, the reverse breakdown is the avalanche breakdown.
When | VZ | <4V time, VZ has a negative temperature coefficient, the reverse is the zener breakdown.
When 4V <| VZ | <7V time, the regulator can get close to the zero temperature coefficient. This regulator diode can be used as a standard regulator.
Zener diode test
(1) positive and negative electrodes of the judge from the appearance point of view, the metal package Zener diode cathode tube-shaped end of the plane, the negative side for the semi-circular surface shape. Plastic tube regulator diode color markers printed on one end of the anode and the other end is positive. Zener diode is not clear on the signs, you can also judge the polarity with a multimeter, measure the same way with ordinary diodes, that is, R × 1k file with a multimeter, then the two table T are the two electrode voltage regulator diode, a measured results, and then swap the two table T were measured. In the two measurements, the resistance that a small, black pen then the table is the positive regulator diode, the red pen then a negative regulator diode.
If the measured voltage regulator diode, the reverse resistance are very small or are infinite, then the breakdown of the diode is open or damaged.
(2) the value of the measurement of voltage 0 ~ 30V continuously adjustable DC power supply for the 13V zener diodes below, can be transferred to the output voltage of power supply 15V, the positive power series with a 1.5kΩ current limiting resistor measured after the negative regulator diode connected to the power negative and positive phase voltage regulator diode, then both ends of the multimeter to measure voltage regulator diode, the measured reading is the voltage regulator diode value. If the regulator regulator diode is higher than 15V, the power supply should be adjusted to 20V or more.
Also be lower than the Megohmmeter 1000V diodes for testing power for the regulator. The methods were: the positive terminal of the megger negative phase with the voltage regulator diode, the negative terminal megger the positive phase with the voltage regulator diode, the required uniform shaking megger handle, while monitoring the voltage with a multimeter voltage across the diode (multimeter, as the stability of the voltage profile should be the size of the voltage) until the meter indicates the voltage stability of the instructions, this voltage is stable voltage regulator diode.
If the measurement of the stability of the diode voltage regulator fluctuated, then the instability of the diode.
Application of voltage regulator diode
Regulator used in the rectifier filter circuit, the DC output voltage to stabilize the small power supply devices.
Selection of regulator diode
Zener diode is generally used in power supply as a reference or used in over-voltage protection circuit for protection diodes.
Zener diode selected should meet the application requirements of the main parameters of the circuit. The stability of the voltage regulator diode and application should be the same value as the reference voltage circuit, the maximum stable current regulator diode application circuit should be higher than the maximum load current 50%.
Substitution regulator diode
Zener diode is damaged, should be regulated the same model the same electrical parameters of diodes or Zener diodes to be replaced.
Stability can be used with the same high-voltage power dissipation zener diodes to substitution of low power dissipation zener diodes, but not with lower power dissipation zener diodes to substitution of high power dissipation zener diodes. For example, 0.5W, 6.2V zener diodes can be 1W, 6.2V voltage regulator diode replacement.

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