1N Package Type: DO, PD: mW, VZ: V Features. VZ Typical Capacitance (pf) versus Zener voltage (VZ) Figure 2 – Derating Curve Figure 2 – Derating Curve. Power Dissipation (mW) 1N ± 1N ± 1N ± 1N 17 a sharp knee on the breakdown curve and to eliminate unstable units.
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Science Physics Electronics It was noted earlier that the reverse-bias saturation current of ZENER DIODE Introduction to Zener Diodes It was noted earlier that the reverse-bias saturation current of a general-purpose junction diode is so small that it ordinarily is masked by currents associated with high-resistance conducting paths across the junction.
But currents associated with other phenomena occurring in what is a very curvs physical junction environment also can mask the leakage current. If the reverse-bias voltage magnitude is increased above a threshold the specific value depends on the junction geometry and material parameters one or the other possibly even both concurrently of two new phenomena occur. Cufve the breakdown region of ucrve large current changes occur with very small changes in reverse-bias voltage, similar to forward-bias operation but for quite different reasons.
These phenomena occur in all semiconductor junction diodes. However the reverse-bias breakdown voltage characteristic can be reproduced with considerable precision by controlling doping and other manufacturing process parameters.
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For ordinary use diode breakdown is characterized simply by specification of a minimum reverse-bias breakdown voltage and current; the magnitude of the breakdown voltage is guaranteed to be no less and the current for a specified lower voltage no more crve specified values. Such diodes are not intended specifically for operation in reverse breakdown, and are expected to maintain a low-conduction state when operated in reverse-bias within the specified breakdown voltage limit. Diodes whose reverse-breakdown characteristics are controlled precisely during manufacture commonly are called Zener diodes.
Zener diodes command a premium because of the special production controls and selection, and are intended specifically for operation in the reverse-breakdown mode primarily as inexpensive voltage references. Zener Diode Breakdown Characteristics Ordinarily the reverse-bias blocking action of a PN junction allows only a small ‘leakage’ current to flow.
However if a sufficiently large reverse-bias is applied other junction phenomena develop which dominate the leakage current, allowing in effect much larger reverse-bias currents.
This is the ‘breakdown’ part of the diode characteristic; ‘breakdown’ here refers to the overshadowing of the semiconductor junction behavior by other phenomena rather than to a destructive effect. While all diodes display this reverse-bias breakdown phenomenon Zener diodes are manufactured specifically for operation in the breakdown condition with guaranteed specifications. The breakdown parameters of these Zener or voltage reference diodes receive special processing attention during their manufacture.
Two distinct phenomena, acting individually or concurrently depending on diode details, are involved in the breakdown phenomena. One mechanism is associated with the acceleration of carriers across the very strong junction electric field. Kinetic energy gained by an accelerated carrier, if sufficiently great, can cause additional impurity atom ionization during a collision with the atom.
Each additional carrier is then also accelerated and may cause additional cuurve the ionization grows exponentially. Circuits Zener Diode 1 M H Miller The second mechanism is a quantum mechanical effect more difficult to describe by a familiar analogy.
Quantum mechanics predicts the possibility of a spontaneous crossing of a semiconductor junction by carriers subject to 1n5320 strong electric field. While the breakdown characteristics for the two phenomena are not exactly the same they are close enough so that the distinction largely may be ignored in general for purposes of circuit design. Thus although the Zener effect originally referred to the quantum mechanical phenomena the label Zener diode is applied almost cirve whatever the details of the breakdown mechanism.
An illustrative breakdown characteristic is drawn to the left; the scale is exaggerated for clarity. The nominal Zener reference voltage of the diode is the reverse-bias voltage at which a manufacturerspecified ‘test’ current IZT flows, and typically represents a rated maximum diode current. In general the Zener voltage is a modest function of temperature; a representative temperature specification is 0.
The coefficient is negative for a diode with a reference voltage below about 5 volts, otherwise it is positive. This is related to the dominance of one or the other of the two phenomena producing ckrve terminal breakdown characteristics.
The inverse of the slope of the diode characteristic typically at the test point is xurve the ‘dynamic resistance’ of the diode, and is a parameter noted in the manufacturers’ specifications. The slope of the cueve does not vary greatly for currents in the curev roughly between 0. Note again that the scale in the figure is distorted curge illustrative purposes.
The minimum usable current is conditioned by the necessity of operation above the knee, i. The 1n530 characteristics are plotted for a broad temperature range. Note the small breakdown voltage sensitivity to temperature changes for a given diode current. Note also the narrow range of diode voltages at a given temperature corresponding to large diode current changes above the ‘knee’ of the characteristic. Since a forward-biased diode already provides large current changes for small changes in bias voltage why a special interest in breakdown operation?
The simple answer is that the breakdown voltage can be manufactured to precise specifications over a very large range of 1n523. For example, in a nominal 5 volt range the specified breakdown voltages for several diodes are: Diode-Zener Comparison An idealized-diode equivalent circuit for a Zener diode, allowing both for forward- and reverse-bias, is drawn to the right.
Verification of the characteristic shown is left as an exercise. For curvee voltages less than the Zener voltage the diode behaves roughly as a voltage 1n5320 in series with a small resistor; for larger voltages it behaves roughly as an idealized diode. A test circuit as shown to the left is analyzed numerically using the PSpice computer analysis program.
A detailed idealized-diode analysis is left as an exercise. However it should be clear that for the positive half-cycle of the sinusoidal input voltage the diode is reverse-biased and Vo will ‘stick’ at the breakdown voltage. For the negative halfcycle the diode is forward-biased and Vo will be small. The plot shows the output voltage ‘clipped’ by the forward-bias characteristic of the diode. Note that Vo is slightly negative diode threshold for forward-bias operation. VS and RS represent the Thevenin equivalent circuit as seen looking back into the terminals of a power supply, and RB and the Zener diode serve as a control devices to regulate the voltage across the load RL.
Note the standard icon used to represent the Zener 1n55230. This variability of the power supply terminal voltage is described 1n530 the ‘regulation’ of the power supply, defined formally as the change in terminal voltage between ‘no load’ and ‘full load’ conditions, divided by the ‘no load’ voltage.
It is essentially a measure of the effect of the internal resistance of the supply on the terminal voltage, as the load current changes from one to the other extreme of its specified operating range. To obtain an improved regulation the power supply will be made to provide a essentially constant current, large enough to provide at least the maximum load current needed. When a smaller current is to be provided to the load the excess part of the constant power supply current will be diverted through the Zener diode.
Both these actions are obtained by adding the Zener diode and ballast resistor RB to modify the load as seen by the supply. Because the Zener resistance rZ is not exactly zero the Zener voltage increases slightly as the diode current increases and 1n2530 causes the supply cjrve to decrease slightly.
The essential idea, as noted before, is to shunt ‘excess’ current through the Zener diode when RL is a maximum, and then decrease the amount of this shunted current as load current demand increases. Since the power supply itself tends to ‘see’ a fixed current, its terminal voltage changes little.
The Zener diode provides an approximation to a constant voltage source over a large current range, and RB provides a corrective voltage drop between the supply voltage generally larger than the Zener voltage and the Zener regulated load voltage. Because the diode is a nonlinear circuit element an analytical examination would be an ccurve one.
Hence, as a simplifying measure more than adequate to provide an appreciation of the regulating action and a good estimate of performance, the Zener breakdown characteristics curbe approximated as shown to the right of the circuit diagram above.
The piecewise linear representation of the Zener characteristic, which is applicable over the range of normal operation of the Zener diode i. Do not confuse the idealized diode used in the model with the Zener diode whose characteristic is being modeled; the Zener diode characteristic is being approximated over a limited range of operation by a combination cuve idealized circuit element models.
Verify the model does have the indicated characteristic. The regulating action is observable in the curves obtained by an analysis of the circuit using the piecewise-linear Zener diode approximation; these are n15230 below. Circuits Zener Diode 4 M H Miller The unity slope reference dashed line is the voltage transfer characteristic of the power supply alone, i. This provides a reference against which to display the effect of regulation.
The other solid line curve describes the circuit with the regulating elements inserted. RB and RL form a resistive voltage divider, making VL somewhat smaller than VS, and so the regulation curve is a line segment of slope somewhat less than 1.
As VS is increased the breakdown voltage VZ of idealized diode model is reached; because of the voltage-divider action VS will be somewhat larger than VZ when this occurs see figure. An important implicit requirement not always recognized explicitly is that the regulating action depends on the assumed operation of the Zener diode in its breakdown region.
This is not something that happens automatically; it must be designed to be so by proper choice of element values. It means, for example, enough current must be drawn by the Zener diode to maintain proper operation even in the ‘worst case’ situation when the maximum load current has been siphoned off from the supply current, i. Hence at full-load current one should design the circuit to provide at least a minimum Zener ‘keep-alive’ current of roughly 0.
On the other hand when the load draws the minimum current the increased current through the Zener the source current will not change much should not exceed the rated IZT.
Between these operating requirements, and of course knowing the nominal Zener diode voltage, an appropriate value of RB can be determined. This calculation is particularly noteworthy here because it is rather different from the more familiar case of solving for specific element values common in introductory courses.
Two extreme ‘worst-case’ conditions are involved in the form of inequalities, not equalities. The result of the calculation is not the ccurve of the n15230 to use but rather inequalities that specify a range of acceptable resistances, greater than some value but less than another value. The details of the circuit behavior will depend to some extent on the choice made.
A computed set of regulation characteristics using a nonlinear diode mode is shown below for comparison to the calculated regulation 1n2530. Regulation computations are shown for several Circuits Zener Diode 5 M H Miller choices of load resistance and so load current.
1N datasheet & applicatoin notes – Datasheet Archive
Detailed comparison between the computed and analytical curves is left as an exercise, e. The regulated regulation curve also was computed, and is drawn below. The data are shown using two scales, one to provide detail on the computed load voltage values and the other to provide some perspective on the overall effect of the regulation. Write Up Assignment 1. Cuurve Diode – Iona Physics.
A Quantum Optical Diod.