EE Pro for TI - 89, 92 Plus
Equations - OpAmp Circuits
73
26.6 Level Detector (Non-Inverting)
This section computes the value of the resistor RR1 attached to an OpAmp non-inverting input. The next equation
calculates the hysteresis (or memory)
∆
VH of the level detector circuit. The next two equations define the upper and
lower trip voltages VU and VL for an ideal inverting level detector, a reference voltage VR and breakdown voltages
Vz1 and Vz2, in terms of Rp and Rf.
RR
Rp Rf
Rp
Rf
1
=
⋅
+
Eq. 26.6.1
∆
VH
Vz
Vz
Rp
Rf
Rp
=
+
+
⋅
1
2
b
g
Eq. 26.6.2
VU
VR Rf
Rp
Rp Vz
Rf
=
⋅
+
+
⋅
b
g
2
Eq. 26.6.3
VL
VR Rp
Rf
Rp Vz
Rf
=
⋅
+
−
⋅
b
g
1
Eq. 26.6.4
Example 26.6 -
For a non-inverting level detector with the same specifications as the inverting level detector in
the previous example, compute the hysteresis, the upper and lower detection thresholds, and the input resistance.
Entered Values
Calculated Results
Solution -
Use the first three equations to compute the solution for this problem. Select these by highlighting each
equation and pressing the
¸
key. Press
„
to display the input screen, enter all the known variables and press
„
to solve the equation. The computed results are shown in the screen displays above.
-PQYP8CTKCDNGU4H
A/
Ω
4R
AM
Ω
84
A8
8\
A8
8\
A8
%QORWVGF4GUWNVU
∆
8*
A8
44
A
Ω
87
A8
26.7 Differentiator
These equations define all the components required for a differentiator. The first
equation defines the feedback resistor Rf in terms of the maximum output voltage
Vomax and current IIf. Typically, IIf is of the order of 0.1 - 0.5 mA. The
second equation computes the value for the resistor Rp used to cancel the effects
of OpAmp input bias current. CC1 is the input capacitor required for the
differentiator, and RR1 is the resistor utilized for stability. The characteristic
frequency of the differentiator fd is expressed by the fifth equation. The last two equations compute the bypass
capacitor Cp and the feedback capacitor Cf.