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Comparator's Math

The document discusses two examples involving op-amp circuits, specifically focusing on determining threshold voltages and output waveforms. In Example 8-1, the output waveform is analyzed with a 741 op-amp and hysteresis voltage calculated at 50 mV. Example 8-2 examines a circuit with a zener diode, detailing the output voltage swing as limited to +5.1 V and -0.7 V.

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13 views5 pages

Comparator's Math

The document discusses two examples involving op-amp circuits, specifically focusing on determining threshold voltages and output waveforms. In Example 8-1, the output waveform is analyzed with a 741 op-amp and hysteresis voltage calculated at 50 mV. Example 8-2 examines a circuit with a zener diode, detailing the output voltage swing as limited to +5.1 V and -0.7 V.

Uploaded by

kingmahim725
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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EXAMPLE8-1

In the circuit of Figure 8-4(a), R =


100 , R S6 kil, va1VPP sine
wave, andthe op-amp is type 741 withsupply voltages 15 V.Detemne
the threshold votages Va and V, and draw the outputwaveform,
+Voc
+15 V
RoMR,R

741/351

-15 V
10 k
-VgE
Ra
ww
V

V 0.5V
VoT25 mV
0V
V-25mv
05 v +V

Hysteresis
voltege
+V+14V (o-V
OV

-V-14V
(c
SOLUTION
For 741 the maximum output voltage is + 14 V, that
swing is, + =
14 V and
V 14 V. From Equations (8-1a) and 8-1b).
100
(14) 25 mV
56,100
100
(-14) = -25 mV
56,100

The output , waveform is shown in Figure 8-4(b). From Equation (8-2), the
hysyeresis voltage V»y 50 mV.
=
EXAMPLE 8-2

In the circuit of Figure 8-7(a), =


500 mV peak 60-Hz sine wave, R
100 , IN3826 zener with Vz * 5.1 V,and tihe supply voltages +15 V.
tiie
=
D
tenmine output voltage swing. Assume that the voltage drop across the for-
ward-biased zener = 0.7 V.

SOLUTION

During the positive half-cycle of the input waveform, the output voltage would
beat-Vp =-0.7 V because the zener will be forward biased. However, dur-
ing the negative half-cycle of vin U, would be at +Vz = +5.1 V since the zener
will be reverse biased into zener breakdown. Thus, the use of a zener diode in
the feedback path limits v, to +5.1 V and -0.7 V. This
output voltage swing
will, therefore, make the op-amp comparator of Figure 8-7(a)
with TTL. compatible
in

R D

OV

-V J
741/351 -oV%

RL
S10 kN
ROM-R

(al -Vo

(b)

FIGURE 8-7 (a) Basic op-amp comparator with positive and negative output vologe
limiting. (b lis input and output waveforms.

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