IS THERE WAY TO CHECK INFRA RED LED IN REMOTE TV IS GOOD OR

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Chris Smith
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Post by Chris Smith »

You got to keep those YOUNG minds on their toes, or else they start to tell you what can and cant be done,...much like any fool with out any experience.

Nothing new.
dyarker
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Post by dyarker »

Joseph,

Me, for one. And that is only true if there are no resistors biasing the base lead, just light.

If I remember right; someone else did, third someone disagreed, then I agreed with first and added a line or two of explanation.

Cheers,

(last sentence edited)
Dale Y
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Chris Smith
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Post by Chris Smith »

The base lead of any photon receiver is for increasing or decreasing the avalanche effect of all photo diodes. [Sensitivity]
rshayes
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Post by rshayes »

The basic sensitivity of a silicon photodiode is about .4 to .6 amp/watt in the region of peak sensitivity. If the radiation is not accurately focussed, the photocurrent will be proportional to the photodiode area. Only a small fraction of the emitted radiation will be intercepted by the photodiode. This depends on distance and geometry, and may be in the .1 to 1 percent range. The photocurrent for a 1 mW emitter could easily be in the 1 to 10 microamp ramge.

In a phototransistor, the collector-base junction is increased in size to increase the area available for collecting light. The emitter-base junction is usually located in one corner of the device and occupies a few percent of the total device area. The current gain of this transistor is not tightly controlled, and will vary with temperature and with the individual part. Current gains in the 20 to 40 range are probably reasonable. The collector current might be in the 20 to 400 microamp range.

With a good LED, a simple series connection of a phototransistor and an LED might be sensitive enough to give a usable indication. A photodarlington would be more sensitive.

The large junction area in a phototransistor has a high capacitance, which tends to limit the response time of the phototransistor to the tens of microseconds.

If the base lead is brought out on the phototransistor, it is possible to use feedback to speed up the response. By ignoring the emitter, it is possible to use the collector-base junction as a photodiode, which will give response times in the microsecond range. A steady current can also be removed at this point to avoid saturating the phototransistor with ambient light.
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Joseph
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Post by Joseph »

Dale, thanks for mentioning first that information.

Chris, I may have noticed some improvement of speed by connecting the collector to the base with a normally reverse biased Schottky diode. The term for that configuration is Baker clamp.

R, I am interested in checking out that photodiode idea on the LTspice simulator.
VIRAND
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Post by VIRAND »

Put a tiny solar cell or photodiode on a plastic VU meter with a needle
that you might have found in an old tape deck, receiver, or battery tester.
Then touch it to the remote and push buttons, looking for the needle to wiggle.
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Chris Smith
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Post by Chris Smith »

Joseph

Pre loading the base voltage/ current sets the diode into a avalanche mode.

Meaning that you set the diode right below the tripped level, then when a tiny amount of light strikes the diode, ..it sets off the trigger over the point which reads as a whole signal.

You increase the trip point of the diode with electricity instead of light.
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