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vb.net barcode reader source code Semiconductors and Diodes in Software
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+ V ~ ripple _ rZ RL rZ RL + RS
= 0016 V that is, 16 mV of ripple is present in the load voltage, or approximately onesixth the source ripple Comments: Note that the DC load voltage is affected by the unregulated source voltage; AC equivalent circuit
if the unregulated supply were to uctuate signi cantly, the regulated voltage would also change Thus, one of the effects of the Zener resistance is to cause imperfect regulation If the Zener resistance is signi cantly smaller than both RS and RL , its effects would not be as pronounced (see Check Your Understanding Exercise 810) Check Your Understanding
88 Show that the DC voltage output of the fullwave recti er of Figure 842 is 2N vS max / 89 Compute the peak voltage output of the bridge recti er of Figure 844, assuming diodes with 06V offset voltage and a 110V rms AC supply
810 Compute the actual DC load voltage and the percentage of the ripple reaching the load (relative to the initial 100mV ripple) for the circuit of Example 810 if rZ = 1 SignalProcessing Applications Among the numerous applications of diodes, there are a number of interesting signalconditioning or signalprocessing applications that are made possible by the nonlinear nature of the device We explore three such applications here: the diode limiter, or clipper; the diode clamp; and the peak detector Other applications are left for the homework problems Limiter circuit rS D1 + Vmax D2 RL Vmax + + vL
The Diode Clipper (Limiter) vS(t) + _ Figure 858 Twosided doide clipper
The diode clipper is a relatively simple diode circuit that is often employed to protect loads against excessive voltages The objective of the clipper circuit is to keep the load voltage within a range say, Vmax vL (t) Vmax so that the maximum allowable load voltage (or power) is never exceeded The circuit of Figure 858 accomplishes this goal The circuit of Figure 858 is most easily analyzed by rst considering just the branch containing D1 This corresponds to clipping only the positive peak Part II
Electronics
voltages; the analysis of the negative voltage limiter is left as a drill exercise The circuit containing the D1 branch is sketched in Figure 859; note that we have exchanged the location of the D1 branch and that of the load branch for convenience Further, the circuit is reduced to Th venin equivalent form Having e reduced the circuit to a simpler form, we can now analyze its operation for two distinct cases: the ideal diode and the piecewise linear diode 1 Ideal diode model For the ideal diode case, we see immediately that D1 conducts if RL vS (t) Vmax rS + R L (825) rS +
+ v (t) R L _ S
vL
D1 + Vmax
rS   RL RL v (t) + _ rS + RL S D1 + Vmax
and that if this condition occurs, then (D1 being a short circuit) the load voltage, vL , becomes equal to Vmax The equivalent circuit for the on condition is shown in Figure 860 Figure 859 Circuit model for the diode clipper
Limiter circuit for rS
RL v (t) Vmax rS + RL S
Limiter circuit for rS
RL v (t) < Vmax rS + RL S
+ vS(t) + _ + Vmax RL vL(t) vS(t) + _ + RL + RL vL(t) = r + R vS(t) S L Vmax
Figure 860 Equivalent circuit for the onesided limiter (diode on) Figure 861 Equivalent circuit for the onesided limiter (doide off) If, on the other hand, the source voltage is such that RL vS (t) < Vmax rS + R L then D1 is an open circuit and the load voltage is simply vL (t) = RL vS (t) rS + R L (827) (826) The equivalent circuit for this case is depicted in Figure 861 The analysis for the negative branch of the circuit of Figure 858 can be conducted by analogy with the preceding derivation, resulting in the waveform for the twosided clipper shown in Figure 862 Note how the load voltage is drastically clipped by the limiter in the waveform of Figure 862 In reality, such hard clipping does not occur, because the actual diode characteristic does not have the sharp onoff breakpoint the ideal diode model implies One can develop a reasonable representation of the operation of a physical diode limiter by using the piecewise linear model 2 Piecewise linear diode model To avoid unnecessary complexity in the analysis, assume that Vmax is much greater than the diode offset voltage, and therefore assume that V 0 We do, however, consider the nite diode resistance rD The circuit of Figure 859 still applies, and thus the determination of the diode

