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lab05_en:inverting_op-amp_photo_diode_as_current_source [2026/04/20 14:54] – mexleadminlab05_en:inverting_op-amp_photo_diode_as_current_source [2026/05/07 12:37] (current) – mexleadmin
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 === Photodiode 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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 <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.\\ +
-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.\\+
 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.\\ 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.\\
 We can now estimate the current we would expect from the photodiode at 300 lx:\\ We can now estimate the current we would expect from the photodiode at 300 lx:\\
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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.\\+**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 scematic of the circuit in <imgref Fig-100_inverting_op-amp_photo_diode>.\\ +Complete the arrows in the circuit diagram in <imgref Fig-100_inverting_op-amp_photo_diode>.\\ 
-Calculate ${\rm R_2}$ so that $U_{\rm OUT}$ = 5 V at 300 lx. +\\ 
 +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.\\ 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 $U_{\rm OUT}$.\\ Also enter the values for $I_{\rm 1}$, $I_{\rm 2}$, $U_{\rm 2}$ and $U_{\rm OUT}$.\\
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-What value would you expect for $U_{\rm D}$ and why?\\+What value would you expect for $U_{\rm D}$ in <imgref Fig-100_inverting_op-amp_photo_diode> and why?\\
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-What value would you expect for $U_{\rm D}$ at 300 lx when it is not connected to the Op-Amp or any other electronic component (open-circuit voltage) and why?\\+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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 ${\rm ................................................................................................}$\\ ${\rm ................................................................................................}$\\
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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}}\\ {{drawio>lab05:Table-1_inverting_op-amp_photo_diode.svg}}\\
-<tabcaption lab05:Table-1_inverting_op-amp_photo_diode | Photodiode measured values> </tabcaption> +<tabcaption lab05:Table-1_inverting_op-amp_photo_diode | Photodiode measured and calculated values> </tabcaption>\\ 
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