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lab05_en:inverting_op-amp_photo_diode_as_current_source [2026/04/17 15:02] – mexleadminlab05_en:inverting_op-amp_photo_diode_as_current_source [2026/05/07 12:37] (current) – mexleadmin
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-=== Photo Diode as current source ===+=== Photodiode as current source === 
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 +A photodiode is a special type of diode which, **in the absence of light**, exhibits a **current-voltage relationship** very similar to that of a standard diode (see the **dark current** characteristic in the **\(I-V\) diagram**).\\  
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 +**When illuminated**, it generates additional electron-hole pairs within the crystal.\\ 
 +{{drawio>lab05:Fig-150_inverting_op-amp_photo_diode_function_principle.svg}} 
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 +Photodiodes are often operated **in reverse bias**, **where** the charge carriers (electrons and holes) generated by the incident light cause an increased **reverse** current flow (**third quadrant** of the I-V diagram). The higher the light intensity, the greater the reverse current. **Forward bias operation** is also possible, where the photodiode behaves like a solar cell (**first quadrant** of the I-V diagram). 
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 +**Applications include** remote controls (IR range), galvanic isolation (optocouplers), light measurement, positioning, and light barriers.\\ 
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 +{{drawio>lab05:Fig-160_inverting_op-amp_photo_diode_i_v_diagramm.svg}}\\ 
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 +<imgcaption Fig-160_inverting_op-amp_photo_diode_i_v_diagramm | Inverting Op-Amp: Operating principle of a photodiode> </imgcaption>\\ 
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 {{drawio>lab05:Fig-120_inverting_op-amp_photo_diode_housing.svg}}\\ {{drawio>lab05:Fig-120_inverting_op-amp_photo_diode_housing.svg}}\\
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-<imgcaption Fig-120_inverting_op-amp_photo_diode_housing | Inverting Op-Amp: Photo Diode BPW 34 S> </imgcaption>\\+<imgcaption Fig-120_inverting_op-amp_photo_diode_housing | Inverting Op-Amp: Photodiode BPW 34 S> </imgcaption>\\
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 <imgcaption Fig-110_inverting_op-amp_photo_diode_diagramms | Inverting Op-Amp: Diagramms of BPW 34 S> </imgcaption>\\ <imgcaption Fig-110_inverting_op-amp_photo_diode_diagramms | Inverting Op-Amp: Diagramms of BPW 34 S> </imgcaption>\\
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-We assume a good illuminated room of 300 lx, illuminated by a white LED. White light is a mixture of many wavelengths across the visible spectrum, roughly 380 to 780 nm.\\ +We are assuming a well-lit room with an illuminance of 300 lx, lit by a white LED. White light is a mixture of many wavelengths across the visible spectrum, roughly 380 to 780 nm. For a typical white LED, the spectrum usually comes from a blue LED chip with a peak around 450 nm, plus a broader phosphor emission that spreads across green, yellow, and red wavelengths. For an easier calculation, we take a mean value of 500 nm which is close to the peak value of the blue LED and 300 lx for the illumination. (500 nm is in reality a greenish light and not blue)\\ 
-For a typical white LED, the spectrum usually comes from a blue LED chip with a peak around 450 nm, plus a broader phosphor emission that spreads across green, yellow, and red wavelengths.\\ +The graph in <imgref Fig-110_inverting_op-amp_photo_diode_diagramms> shows that the photodiode sensitivity at 500 nm is only 30%. The maximim current (100%) at 300 lx is 30 ${\rm\mu}$A.\\ 
-For an easier calculation, we take a mean value of 500 nm which is close to the peak value of the blue LED (in reality a greenish light) and 300 lx for the illumination.\\ +We can now estimate the current we would expect from the photodiode at 300 lx:\\
-In <imgref Fig-110_inverting_op-amp_photo_diode_diagramms> we can see that the sensitivity of the photo diode at 500 nm ist only 30%. The maximim current (100%) at 300 lx is 30 ${\rm\mu}$A.\\ +
-Now we can calculate the current we expect from the diode at 300 lx:\\+
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-$I_{\rm 1} = 30 {\rm~\mu A} * 0.3$\\+$I_{\rm 1} = 30 {\rm~\mu A} * 0.3 = 9 {\rm~\mu A}$\\
 $I_{\rm 1} \approx 10 {\rm~\mu A}$\\ $I_{\rm 1} \approx 10 {\rm~\mu A}$\\
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 30% of 30 ${\rm\mu A}$ is roughly 10 ${\rm\mu A}$.\\ 30% of 30 ${\rm\mu A}$ is roughly 10 ${\rm\mu A}$.\\
 +**We will assume a current of 10 ${\rm\mu A}$ at 300 lx for our calculations.**\\
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 +Complete the arrows in the circuit diagram in <imgref Fig-100_inverting_op-amp_photo_diode>.\\
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-TODO +Calculate $R_{\rm 2}$ so that $U_{\rm OUT}$ = 5 V at 300 lx.  
 +Take a resistor from the E6 series that is as close as possible to the calculated value.\\ 
 +Also enter the values for $I_{\rm 1}$, $I_{\rm 2}$, $U_{\rm 2}$ and $U_{\rm OUT}$.\\
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-Complete the arrows in the scematic of the circuit.\\ 
-Take the values for $U_{\rm 1},~U_{\rm 2},~U_{\rm OUT}$ from .\\ 
-Use these values to calculate the sum of the voltages at node ${\rm N_{12}}$.\\ 
-Compare your result by measuerement.\\ 
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-$U_{\rm 1}{\rm~=}$\\+\\ 
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 +$I_{\rm 1}{\rm~=}$\\ 
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 +$I_{\rm 2}{\rm~=}$\\
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-Calculated $U_{\rm 12}{\rm~=}$\\ 
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-Measured $U_{\rm 12}{\rm~=}$\\ 
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-What are your results?\\ 
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-${\rm ................................................................................................}$\\ 
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-${\rm ................................................................................................}$\\ 
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-${\rm ................................................................................................}$\\ 
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-What will happen if you short-circuit $R_{\rm 2}$?\\ +\\ 
-Try it and explain your results.\\+\\ 
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 +$R_{\rm 2}{\rm~=}$\\ 
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 +What value would you expect for $U_{\rm D}$ in <imgref Fig-100_inverting_op-amp_photo_diode> and why?\\ 
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 +$U_{\rm D}{\rm~=}$\\
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 ${\rm ................................................................................................}$\\ ${\rm ................................................................................................}$\\
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 +What value would you expect for $U_{\rm D}$ at 300 lx when the photodiode is not connected to the Op-Amp or any other electronic component (open-circuit voltage) and why?\\
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 +$U_{\rm D}{\rm~=}$\\
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 ${\rm ................................................................................................}$\\ ${\rm ................................................................................................}$\\
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 ${\rm ................................................................................................}$\\ ${\rm ................................................................................................}$\\
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-${\rm ................................................................................................}$+${\rm ................................................................................................}$\\ 
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 +${\rm ................................................................................................}$\\ 
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 +Measure or calculate the values given in the table below. 
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 +{{drawio>lab05:Table-1_inverting_op-amp_photo_diode.svg}}\\ 
 +<tabcaption lab05:Table-1_inverting_op-amp_photo_diode | Photodiode measured and calculated values> </tabcaption>\\ 
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