HDS Freq/Duty Cycle

JJohn

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I wonder what the phosphor decay time is. I'll bet some of the slope on the falling edge is due to this factor.

JJohn
 

riffraff

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JJohn said:
I wonder what the phosphor decay time is. I'll bet some of the slope on the falling edge is due to this factor.

JJohn
You realize that the Tektronix TDS 3054B is a digital 'scope, right? Its display is an LCD (i.e., no phosphors).
 

JJohn

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cmaylodm said:
I think he means the LED phosphors, thats what I assumed JJohn was talking about at first.

The LED is what I wondering about. If I am not mistaken blue light is used to drive the phosphor within the LED package to generate that nice white light output that we desire in our lights.

The sharper edge of the rise time shown on the scope trace is a good indication that your phototransister setup has a time constants short enough to give you the information you want. The slower falling edge time is probably a combination of capacitance and the decay time of the LED phosphors. I was hoping someone more knowledgeable than I would chime in as to what order of magnitude that decay time was. I don't know if it is microseconds or 10's of microseconds. If it is really short than HDS probably added some C to their drive circuit.
 

kromeke

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Funny you should mention that riffraff. That scope is digital, but it does simulate a phosphor screen. It is a DPO (Digital Phosphor Oscilloscope). I have access to one like it at work.
 
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