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--- lab_electrical_engineering:6_opamps_2 [2026/06/17 11:01] – mexleadmin
+++ lab_electrical_engineering:6_opamps_2 [2026/06/17 13:08] (current) – mexleadmin
@@ Line 1: / Line 1: @@
-=====Duty Cycle Adjustment=====
+<wrap onlyprint>{{drawio>lab_electrical_engineering:namingtitle.svg}}</wrap>
+\\
+====== Experiment 6: Operational Amplifier II - Pulse Width Modulation ======
+  * Circuits on the breadboard
+  * Integrator
+  * Non-inverting Schmitt trigger
+  * Triangle–square-wave generator
+  * Pulse-width modulation and control of a DC motor
-====Background Information====
+<wrap #challenge-description>
+{{page>.:6_opamps_2:Challenge_description&nofooter}}
+</wrap>
-After combining the Schmitt trigger and the integrator, the circuit generates a periodic signal with a fixed duty cycle. For many PWM applications, however, it is necessary to adjust the duty cycle in order to control the average power delivered to the load. In the case of an LED, changing the duty cycle directly affects the perceived brightness. Therefore, the oscillator circuit is modified so that the duty cycle can be varied to control the brightness of the LED.
+<wrap #nuggets>
+  {{page>Rectangular-to-Triangle_Signal_Conversion_(Integrator)&nofooter}}
-====Experimental Tasks====
+  {{page>Triangle-to-Rectangular_Conversion_(Schmitt_Trigger)&nofooter}}
+  {{page>Combination_of_Integrator_and_Schmitt_Trigger_(Oscillator)&nofooter}}
-To analyze how to adjust the duty cycle of the PWM-signal, the following circuit is used:\\
+  {{page>Duty_Cycle_Adjustment&nofooter}}
-\\
+  {{page>LED_Brightness_Control_using_PWM&nofooter}}
-\\
-<wrap left>
-{{drawio>mexlefirst_intern:duty_cycle_experiment.svg}}
 </wrap>
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-  - Build the circuit on the MEXLE-board. Connect channel 1 of the oscilloscope to TR and channel 2 to SQ. The duty cycle can be adjusted using R1. Perform the measurements for the minimum, maximum, and midpoint duty-cycle settings with the capacitances **C1 = 10nF** and **C1 = 1nF**. Sketch the oscilloscope screen for each case. \\ \\ \\ **C1 = 10 nF, minimum duty cycle**\\ \\ <wrap left>{{drawio>mexlefirst_intern:oscilloscope_screen.svg}}</wrap>\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\    \\ \\ \\ **C1 = 10 nF, maximum duty cycle**\\ \\ <wrap left>{{drawio>mexlefirst_intern:oscilloscope_screen.svg}}</wrap>\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\   \\ \\ \\ **C1 = 10 nF, middle position**\\ \\ <wrap left>{{drawio>mexlefirst_intern:oscilloscope_screen.svg}}</wrap>\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\    \\ \\ \\ **C1 = 1 nF, minimum duty cycle**\\ \\ <wrap left>{{drawio>mexlefirst_intern:oscilloscope_screen.svg}}</wrap>\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\    \\ \\ \\ **C1 = 1 nF, maximum duty cycle**\\ \\ <wrap left>{{drawio>mexlefirst_intern:oscilloscope_screen.svg}}</wrap>\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\    \\ \\ \\ **C1 = 1 nF, middle position**\\ \\ <wrap left>{{drawio>mexlefirst_intern:oscilloscope_screen.svg}}</wrap>\\ \\ \\ Channel 1: $\frac {Volt}{Div}=$\\ \\ Channel 2: $\frac {Volt}{Div}=$\\ \\ \\ Time basis: $\frac {T}{Div}=$\\ \\ \\ \\ \\ \\ \\ \\
-  - Explain how this circuit works in a few sentences.
+===== Preparation =====
-====Test Questions - Integrator====
+For this experiment, you should be able to apply and explain the following concepts:
+  - "golden rules" for the negatively feedback, idealized operational amplifier
+  - deviating properties of the real operational amplifier (e.g., output swing range, slew rate)
+  - output-voltage waveform $U_A$ of the inverting integrator (inverting integrator) for different input voltages $U_E$, e.g.
+    - DC voltage
+    - square-wave voltage
+    - arbitrary voltage waveform
+  - integration time constant of the inverting integrator
+  - Schmitt trigger
+    - difference in feedback compared to the inverting integrator
+    - idealized relationship between $U_E$ and $U_A$
+    - idealized line diagram: $U_E$ and $U_A$ as a function of time
+    - switching thresholds
+    - threshold voltage
+    - hysteresis
+    - real behavior: output "in saturation"
+  - structure of the triangle–square-wave generator