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| lab05_en:inverting_op-amp_photo_diode_as_current_source [2026/04/17 09:51] – [Photo Diode as current source] mexleadmin | lab05_en:inverting_op-amp_photo_diode_as_current_source [2026/04/28 16:13] (current) – mexleadmin | ||
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| - | === Photo Diode as current source === | + | === Photodiode |
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| - | === Photo Diode as current source === | + | \\ |
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| + | 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, | ||
| + | The graph in <imgref Fig-110_inverting_op-amp_photo_diode_diagramms> | ||
| + | We can now estimate the current we would expect from the photodiode at 300 lx:\\ | ||
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| + | $I_{\rm 1} = 30 {\rm~\mu A} * 0.3 = 9 {\rm~\mu A}$\\ | ||
| + | $I_{\rm 1} \approx 10 {\rm~\mu A}$\\ | ||
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| - | Complete the arrows in the scematic | + | 30% of 30 ${\rm\mu A}$ is roughly 10 ${\rm\mu A}$.\\ |
| - | Take the values for $U_{\rm 1},~U_{\rm 2},~U_{\rm OUT}$ from <imgref Fig-30_inverting_op-amp_inv_input> | + | **We will assume a current |
| - | Use these values to calculate the sum of the voltages at node ${\rm N_{12}}$.\\ | + | |
| - | Compare your result by measuerement.\\ | + | |
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| + | Complete the arrows in the circuit diagram in <imgref Fig-100_inverting_op-amp_photo_diode> | ||
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| - | $U_{\rm 1}{\rm~=}$\\ | + | 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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| + | $I_{\rm 1}{\rm~=}$\\ | ||
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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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| - | What will happen if you short-circuit | + | \\ |
| - | 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> | ||
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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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| + | Measure or calculate the values given in the table below. | ||
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| + | {{drawio> | ||
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