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| Visible Light Oscilloscope Probe |
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| not1xor1:
--- Quote from: graybeard on December 05, 2019, 06:02:35 pm --- --- Quote from: not1xor1 on December 04, 2019, 06:02:21 am ---In single supply circuits I'm used to put a switch on the positive rail and capacitors between the virtual ground and the negative and between the positive and the negative of the battery rails (close to the supply terminal of the opamps). I realize your circuit replicates the usual schematic of real ground circuits. So I wonder if I'm wrong or if that makes any difference. :-// --- End quote --- The battery and the switch are in series, the order of components in a series circuit does not matter, only the orientation (of some components) needs to be maintained. Thus it makes no difference where the switch is, if you like it better on the positive battery terminal you can put it there and it will function the same. --- End quote --- I meant that I thought the contact resistance of a real switch on the negative rail might increase the noise at the terminals of the TL431 while if it were on the positive rail that would just be in series to the resistance. But I guess I'm just paranoid ... :) |
| tggzzz:
--- Quote from: graybeard on December 05, 2019, 06:02:35 pm ---The battery and the switch are in series, the order of components in a series circuit does not matter, only the orientation (of some components) needs to be maintained. Thus it makes no difference where the switch is, if you like it better on the positive battery terminal you can put it there and it will function the same. --- End quote --- You have to include all the components for that statement to be valid. In some circuits the stray capacitance is critical, and in others a wire's inductance is important (rule of thumb for wires is 1nH/mm). Higher voltages and/or higher currents make those points more important. Whether that is relevant to this circuit is left as an exercise for the student :) |
| Yansi:
What is the bandwidth of such probe? Guessing not much... I'd use a PIN photodiode in photovoltaic mode (shorted, zero volts across it) with a transconductance amp instead of this. |
| graybeard:
--- Quote from: Yansi on December 06, 2019, 09:09:53 am ---What is the bandwidth of such probe? --- End quote --- The bandwidth is ~500KHz (700ns rise time) which is fast enough for the target application. |
| Yansi:
That seems quite good. Have expected about 100k. |
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