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university:courses:electronics:electronics-lab-22 [05 Mar 2019 12:33] – [Questions:] Antoniu Miclausuniversity:courses:electronics:electronics-lab-22 [23 Aug 2019 14:00] – Antoniu Miclaus
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-====== Activity 22. Optocouplers. ======+====== Activity: Optocouplers. ======
  
 ===== Objective: ===== ===== Objective: =====
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 In this activity you will construct an optocoupler from an infra-red LED and an NPN photo transistor. You will investigate the operation of an optocoupler based analog isolation amplifier and floating current source using integrated optocouplers. In this activity you will construct an optocoupler from an infra-red LED and an NPN photo transistor. You will investigate the operation of an optocoupler based analog isolation amplifier and floating current source using integrated optocouplers.
  
-===== 22.1 The NPN transistor Optocoupler =====+===== The NPN transistor Optocoupler =====
  
 ==== Background: ==== ==== Background: ====
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 ==== Hardware Setup: ==== ==== Hardware Setup: ====
  
-Configure the waveform generator for a 100 Hz triangle wave with 3V amplitude and 2.5V offset. Both scope channels should be set to 1V/Div.+Configure the waveform generator for a 100 Hz triangle wave with 3V amplitude peak-to-peak and 2.5V offset. Both scope channels should be set to 1V/Div.
  
 {{ :university:courses:electronics:a22_oc_bb.JPG? |}} {{ :university:courses:electronics:a22_oc_bb.JPG? |}}
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 ==== Hardware Setup: ==== ==== Hardware Setup: ====
  
-Configure the waveform generator for a 5 KHz square wave with 5V amplitude and 2.5V offset. Both scope channels should be set to 1V/Div.+Configure the waveform generator for a 5 KHz square wave with 5V amplitude peak-to-peak and 2.5V offset. Both scope channels should be set to 1V/Div.
  
 ==== Procedure: ==== ==== Procedure: ====
  
-Scope channel 1 now measures the input signal and scope channel 2 measures the output signal. The speed of the optocoupler can be characterized by the delay between the input and output waveforms. Another measure of the device speed is the rise and fall times of the output waveform. Another method of testing the frequency response of the optocoupler is to use the Network Analyzer instrument in the Scopy software. Set the frequency sweep from 10 Hz to 100 KHz. Set the AWG amplitude to 2V and the AWG offset  to 3V or whatever DC offset centers the output signal for your coupler circuit.+Scope channel 1 now measures the input signal and scope channel 2 measures the output signal. The speed of the optocoupler can be characterized by the delay between the input and output waveforms. Another measure of the device speed is the rise and fall times of the output waveform. Another method of testing the frequency response of the optocoupler is to use the Network Analyzer instrument in the Scopy software. Set the frequency sweep from 10 Hz to 100 KHz. Set the AWG amplitude to 2V peak-to-peak and the AWG offset  to 3V or whatever DC offset centers the output signal for your coupler circuit.
  
 ==== Questions: ==== ==== Questions: ====
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 ==== Hardware setup: ====  ==== Hardware setup: ==== 
  
-Now configure the waveform generator for a 1 KHz sine wave with 1.2V amplitude and 2.2V offset. Both scope channels should be set to 1V/Div. The offset might need to be adjusted slightly to make sure the output signal is relatively centered within the 0 to 5V range of the output. You want to make sure that the peaks of the sine wave are not too close to either 0V or 5V.+Now configure the waveform generator for a 1 KHz sine wave with 1.2V amplitude peak-to-peak and 2.2V offset. Both scope channels should be set to 1V/Div. The offset might need to be adjusted slightly to make sure the output signal is relatively centered within the 0 to 5V range of the output. You want to make sure that the peaks of the sine wave are not too close to either 0V or 5V.
  
 ==== Procedure: ==== ==== Procedure: ====
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 Open the frequency display within the scope window. Adjust the time base such that the fundamental and the first 5 or 6 harmonics are displayed. Write down and save the magnitudes of the fundamental and up to at least the 4<sup>th</sup> harmonic for future reference. Open the frequency display within the scope window. Adjust the time base such that the fundamental and the first 5 or 6 harmonics are displayed. Write down and save the magnitudes of the fundamental and up to at least the 4<sup>th</sup> harmonic for future reference.
  
-===== 22.2 Driving the LED with a voltage to current converter =====+===== Driving the LED with a voltage to current converter =====
  
 By putting the LED in the feedback loop of an op amp configured as a voltage to current converter we can greatly reduce the effect of the nonlinearity of the LED. By putting the LED in the feedback loop of an op amp configured as a voltage to current converter we can greatly reduce the effect of the nonlinearity of the LED.
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 ==== Hardware Setup: ==== ==== Hardware Setup: ====
  
-Configure the waveform generator for a 100 Hz triangle wave with 3V amplitude and 2.5V offset. Both scope channels should be set to 1V/Div.+Configure the waveform generator for a 100 Hz triangle wave with 3V amplitude peak-to-peak and 2.5V offset. Both scope channels should be set to 1V/Div.
 {{ :university:courses:electronics:a22_drv_bb.JPG? |}} {{ :university:courses:electronics:a22_drv_bb.JPG? |}}
  
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 Compare your distortion measurements for this circuit to what you measured for the previous circuit. How much have the harmonics improved? Compare your distortion measurements for this circuit to what you measured for the previous circuit. How much have the harmonics improved?
  
-===== 22.3 Analog Isolation amplifier. =====+=====  Analog Isolation amplifier. =====
  
 To make a more linear amplifier two matching optocouplers can be used. It is best to use integrated versions for this circuit. To make a more linear amplifier two matching optocouplers can be used. It is best to use integrated versions for this circuit.
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 ==== Hardware Setup: ==== ==== Hardware Setup: ====
  
-Start with the waveform generator set for a 100 Hz triangle wave with 4.8V amplitude and 2.5V offset as you have done for the previous two configurations. Both scope channels should be set to 1V/Div.+Start with the waveform generator set for a 100 Hz triangle wave with 4.8V amplitude peak-to-peak and 2.5V offset as you have done for the previous two configurations. Both scope channels should be set to 1V/Div.
  
 ==== Procedure: ==== ==== Procedure: ====
university/courses/electronics/electronics-lab-22.txt · Last modified: 04 Nov 2022 19:26 by Doug Mercer

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