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lab_electrical_engineering:2_capacitors:diodes [2026/03/21 23:13] – mexleadminlab_electrical_engineering:2_capacitors:diodes [2026/03/21 23:35] (current) – mexleadmin
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 === General information on diodes === === General information on diodes ===
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 The diode (also called rectifier diode) is a semiconductor device with two terminals that has a nonlinear current-voltage-characteristic. It can be regarded as a voltage‑dependent switch. The function of a rectifier diode in normal operation can most easily be imagined as a check valve, s. <imgref Fig-14_V2-Comparison-valve-pics>. If pressure (voltage) is applied to this valve (diode) in the blocking direction, the current flow is blocked. In the opposite direction the pressure must become large enough to overcome the spring pressure of the valve (blocking voltage). Then the valve opens and current can flow. The voltage needed in this mechanical model to overcome the spring pressure corresponds to the so‑called forward voltage. A certain forward‑direction voltage must first be present for the diode to go into the conducting state. For ordinary silicon diodes this necessary forward voltage is approx. 0.7 V for currents in the mA range. The diode (also called rectifier diode) is a semiconductor device with two terminals that has a nonlinear current-voltage-characteristic. It can be regarded as a voltage‑dependent switch. The function of a rectifier diode in normal operation can most easily be imagined as a check valve, s. <imgref Fig-14_V2-Comparison-valve-pics>. If pressure (voltage) is applied to this valve (diode) in the blocking direction, the current flow is blocked. In the opposite direction the pressure must become large enough to overcome the spring pressure of the valve (blocking voltage). Then the valve opens and current can flow. The voltage needed in this mechanical model to overcome the spring pressure corresponds to the so‑called forward voltage. A certain forward‑direction voltage must first be present for the diode to go into the conducting state. For ordinary silicon diodes this necessary forward voltage is approx. 0.7 V for currents in the mA range.
  
 {{drawio>lab_electrical_engineering:2_capacitors:Fig-14_V2-Comparison-valve-pics.svg}} {{drawio>lab_electrical_engineering:2_capacitors:Fig-14_V2-Comparison-valve-pics.svg}}
 <imgcaption Fig-14_V2-Comparison-valve-pics | Valve characterization> </imgcaption> <imgcaption Fig-14_V2-Comparison-valve-pics | Valve characterization> </imgcaption>
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 == Z‑diode == == Z‑diode ==
  
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 {{drawio>lab_electrical_engineering:2_capacitors:Fig-15_V2-Zener-diode-symbol.svg}} {{drawio>lab_electrical_engineering:2_capacitors:Fig-15_V2-Zener-diode-symbol.svg}}
 <imgcaption Fig-15_V2-Zener-diode-symbol | Circuit symbol for a Z-diode> </imgcaption> <imgcaption Fig-15_V2-Zener-diode-symbol | Circuit symbol for a Z-diode> </imgcaption>
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 **Inform yourself about Z‑diodes and their circuit.**  **Inform yourself about Z‑diodes and their circuit.** 
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 The function generator is to feed a rippled voltage into a circuit consisting of a Z‑diode and series resistor. The generator voltage and the voltage at the Z‑diode are to be measured with the oscilloscope. Draw the circuit with generator, Z‑diode and series resistor as well as oscilloscope with the given values: \\ The function generator is to feed a rippled voltage into a circuit consisting of a Z‑diode and series resistor. The generator voltage and the voltage at the Z‑diode are to be measured with the oscilloscope. Draw the circuit with generator, Z‑diode and series resistor as well as oscilloscope with the given values: \\
   * Zener diode: Z 2.4 V / 0.01 W   * Zener diode: Z 2.4 V / 0.01 W
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   * DC offset: +5 V   * DC offset: +5 V
   * Frequency: 50 Hz.    * Frequency: 50 Hz. 
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 Determine the required resistor for current limiting of the Zener diode under the above condition (document your calculation below!).  Determine the required resistor for current limiting of the Zener diode under the above condition (document your calculation below!). 
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 Which resistors from the E‑series can be used? \\ Which resistors from the E‑series can be used? \\
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 Is it better to choose a higher or lower resistor? Why?  Is it better to choose a higher or lower resistor? Why? 
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 Build the circuit and set the generator voltage accordingly. Now measure with the oscilloscope the voltage after the generator with Channel 1 and after the Zener diode with Channel 2. Enter the oscilloscope traces in the <imgref Fig-13_V2-Zener-Screen-diagram> shown below. Label the traces of the corresponding voltages.  Build the circuit and set the generator voltage accordingly. Now measure with the oscilloscope the voltage after the generator with Channel 1 and after the Zener diode with Channel 2. Enter the oscilloscope traces in the <imgref Fig-13_V2-Zener-Screen-diagram> shown below. Label the traces of the corresponding voltages. 
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 == Recording a diode characteristic curve with the oscilloscope in X–Y mode == == Recording a diode characteristic curve with the oscilloscope in X–Y mode ==
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 The representation of a diode characteristic on the oscilloscope is done using the circuit in <imgref Fig-11_V2-Diode-Osci>. As an AC source for recording the characteristic, the function generator is used, which feeds a sine signal with a frequency of 20 Hz into the circuit. This sine signal must not contain any DC component (no offset), otherwise the characteristic cannot be displayed correctly on the oscilloscope. The diode voltage $u_{\rm D}$ must be applied to Channel 1. The voltage drop across the resistor $u_{\rm R}$ is proportional to the current through the diode and is applied to Channel 2. The necessary ground connection for the oscilloscope lies between the resistor and the diode. For this reason, Channel 1 must also be inverted for the measurement. The representation of a diode characteristic on the oscilloscope is done using the circuit in <imgref Fig-11_V2-Diode-Osci>. As an AC source for recording the characteristic, the function generator is used, which feeds a sine signal with a frequency of 20 Hz into the circuit. This sine signal must not contain any DC component (no offset), otherwise the characteristic cannot be displayed correctly on the oscilloscope. The diode voltage $u_{\rm D}$ must be applied to Channel 1. The voltage drop across the resistor $u_{\rm R}$ is proportional to the current through the diode and is applied to Channel 2. The necessary ground connection for the oscilloscope lies between the resistor and the diode. For this reason, Channel 1 must also be inverted for the measurement.
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 {{drawio>lab_electrical_engineering:2_capacitors:Fig-11_V2-Diode-Osci.svg}} {{drawio>lab_electrical_engineering:2_capacitors:Fig-11_V2-Diode-Osci.svg}}
 <imgcaption Fig-11_V2-Diode-Osci | Diode characteristic with oscilloscope> </imgcaption> <imgcaption Fig-11_V2-Diode-Osci | Diode characteristic with oscilloscope> </imgcaption>
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 Record the screen image of the diode characteristic in <imgref Fig-12_V2-Diode-charc> and determine the forward voltage of the diode by placing a straight line in the screen diagram.  Record the screen image of the diode characteristic in <imgref Fig-12_V2-Diode-charc> and determine the forward voltage of the diode by placing a straight line in the screen diagram. 
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 Give the determined forward voltage of the diode 1N4005P: Give the determined forward voltage of the diode 1N4005P:
  
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