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university:courses:electronics:electronics-lab-32 [24 Jul 2017 16:11]
Antoniu Miclaus change amplitude value to peak-peak
university:courses:electronics:electronics-lab-32 [25 Jun 2020 22:07] (current)
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 =====Hardware Setup:===== =====Hardware Setup:=====
  
-AWG1 is connected as V<​sub>​IN</​sub>​ and should be configured as a sine wave with an amplitude greater than 6 volts, zero offset and a frequency of 100 Hz. The scope inputs are used to monitor various points around the circuit such as V<​sub>​IN</​sub>,​ V<​sub>​OUT</​sub>,​ the voltage across R<​sub>​S</​sub>​ and thus the current through R<​sub>​S</​sub>,​ and the gate of M<​sub>​1</​sub>​.+AWG1 is connected as V<​sub>​IN</​sub>​ and should be configured as a sine wave with an amplitude greater than 6 volts peak-to-peak, zero offset and a frequency of 100 Hz. The scope inputs are used to monitor various points around the circuit such as V<​sub>​IN</​sub>,​ V<​sub>​OUT</​sub>,​ the voltage across R<​sub>​S</​sub>​ and thus the current through R<​sub>​S</​sub>,​ and the gate of M<​sub>​1</​sub>​. 
 + 
 +{{ :​university:​courses:​electronics:​active_rectifiers_hardware_setup.png |}} 
 + 
 +<WRAP centeralign>​ Figure 2 Active half wave rectifier with self-powered op amp Bread Board Circuit </​WRAP>​
  
 =====Procedure:​===== =====Procedure:​=====
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 Start by using the large value 220 uF capacitor for C<​sub>​1</​sub>​. The 220 uF and 4.7 uF capacitors are polarized so be sure to connect the positive and negative terminals to your circuit correctly. Start by using the large value 220 uF capacitor for C<​sub>​1</​sub>​. The 220 uF and 4.7 uF capacitors are polarized so be sure to connect the positive and negative terminals to your circuit correctly.
  
-Use the two scope inputs to monitor the input AC waveform at V<​sub>​IN</​sub>​ and the DC output wave form at V<​sub>​OUT</​sub>​. VOUT should be very close to the peak value of V<​sub>​IN</​sub>​. Now replace the large 220 uF capacitor with the much smaller 4.7 uF capacitor. Observe the change in the waveform seen at V<​sub>​OUT</​sub>​. When is V<​sub>​OUT</​sub>​ closest in value to V<​sub>​IN</​sub>​ and compare that interval of the AC input cycle with the voltage at the gate of transistor M<​sub>​1</​sub>​.+Use the two scope inputs to monitor the input AC waveform at V<​sub>​IN</​sub>​ and the DC output wave form at V<​sub>​OUT</​sub>​. VOUT should be very close to the peak value of V<​sub>​IN</​sub>​. Now replace the large 220 uF capacitor with the much smaller 4.7 uF capacitor. Observe the change in the waveform seen at V<​sub>​OUT</​sub>​. When is V<​sub>​OUT</​sub>​ closest in value to V<​sub>​IN</​sub>​ and compare that interval of the AC input cycle with the voltage at the gate of transistor M<​sub>​1</​sub>​. ​\\ 
 + 
 +{{ :​university:​courses:​electronics:​active_rectifiers_scopeshot_220uf.png |}} 
 +<WRAP centeralign>​ Figure 3 Vout and Vin at 220uF capacitor </​WRAP>​ 
 +{{ :​university:​courses:​electronics:​active_rectifiers_scopeshot_4.7uf.png |}} 
 +<WRAP centeralign>​ Figure 3 Vout and Vin at 4.7uF capacitor </​WRAP>​
  
 With scope channel 2 connected across shunt the 10Ω resistor R<​sub>​S</​sub>,​ use the Measure feature to obtain the peak and average value of the current. Compare the average value with the DC current in the 2.2 KΩ load resistor R<​sub>​L</​sub>​ you calculate based on the voltage you measure at V<​sub>​OUT</​sub>​. Repeat this measurement for both the 220 uF and 4.7 uF capacitor values. How do the peak and average values compare between these two capacitor values? ​ With scope channel 2 connected across shunt the 10Ω resistor R<​sub>​S</​sub>,​ use the Measure feature to obtain the peak and average value of the current. Compare the average value with the DC current in the 2.2 KΩ load resistor R<​sub>​L</​sub>​ you calculate based on the voltage you measure at V<​sub>​OUT</​sub>​. Repeat this measurement for both the 220 uF and 4.7 uF capacitor values. How do the peak and average values compare between these two capacitor values? ​
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 =====Questions:​===== =====Questions:​=====
  
-Change the peak amplitude of the AC input waveform. What is the minimum peak value of the AC input where the PMOS transistor is still actively rectifying the input, i.e. the V<​sub>​GS</​sub>​ is greater than the threshold voltage and the device is turned on? What determines this minimum voltage?+Change the peak-to-peak amplitude of the AC input waveform. What is the minimum peak value of the AC input where the PMOS transistor is still actively rectifying the input, i.e. the V<​sub>​GS</​sub>​ is greater than the threshold voltage and the device is turned on? What determines this minimum voltage?
  
 Try different frequencies for the AC input. How does the frequency effect the peak value and the width  of the current pulse in R<​sub>​S</​sub>?​ Try different frequencies for the AC input. How does the frequency effect the peak value and the width  of the current pulse in R<​sub>​S</​sub>?​
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 There are other potential uses for a circuit that essentially allows current flow in only one direction with very low voltage drop across the switch. In battery chargers, where the input power source might be intermittent such as a solar panel or wind turbine generator, it is necessary to prevent the battery from discharging when the input power source is not generating a high enough voltage to charge the battery. Generally a simple Schottky diode is used for this purpose but as was pointed out in the background section this can lead to losses in efficiency. If an op amp with sufficiently low operating supply current is employed this can often be lower than the reverse leakage current in a large Schottky diode. There are other potential uses for a circuit that essentially allows current flow in only one direction with very low voltage drop across the switch. In battery chargers, where the input power source might be intermittent such as a solar panel or wind turbine generator, it is necessary to prevent the battery from discharging when the input power source is not generating a high enough voltage to charge the battery. Generally a simple Schottky diode is used for this purpose but as was pointed out in the background section this can lead to losses in efficiency. If an op amp with sufficiently low operating supply current is employed this can often be lower than the reverse leakage current in a large Schottky diode.
 +
 +<WRAP round download>​
 +**Resources:​**
 +  * Fritzing files: [[downgit>​education_tools/​tree/​master/​m2k/​fritzing/​active_rectifier_bb | active_rectifier_bb]]
 +  * LTspice files: [[downgit>​education_tools/​tree/​master/​m2k/​ltspice/​active_rectifier_ltspice | active_rectifier_ltspice ]]
 +</​WRAP>​
  
 **For Further Reading:** **For Further Reading:**
university/courses/electronics/electronics-lab-32.1500905474.txt.gz · Last modified: 24 Jul 2017 16:11 by Antoniu Miclaus