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LED tube biasing, pros and cons
LED tube biasing, pros and cons
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Old 11th July 2018, 05:26 PM   #91
jackinnj is offline jackinnj  United States
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LED tube biasing, pros and cons
Just to throw some smoke into the discussion -- I used a current injector to look at the dynamic impedance of some older (pre-Avago) LED's and an Lite-ON Infra-Red device. First graph uses 1mA, the second 2.5mA:
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File Type: png LED_Impedance_2_5mA.png (57.5 KB, 105 views)

Last edited by jackinnj; 11th July 2018 at 05:33 PM.
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Old 11th July 2018, 06:20 PM   #92
DAK808 is offline DAK808  United States
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LED tube biasing, pros and cons
Pardon my ignorance but technically what is impedance magnitude. i have not seen that value on a graph before.
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Old 11th July 2018, 07:21 PM   #93
jackinnj is offline jackinnj  United States
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LED tube biasing, pros and cons
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Originally Posted by DAK808 View Post
Pardon my ignorance but technically what is impedance magnitude. i have not seen that value on a graph before.
Ohms
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Old 11th July 2018, 08:03 PM   #94
DAK808 is offline DAK808  United States
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LED tube biasing, pros and cons
Why is there a question mark in parantheses?
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Old 11th July 2018, 08:37 PM   #95
Merlinb is offline Merlinb  United Kingdom
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Originally Posted by 20to20 View Post
The voltage on the diode comes from the voltage through the tube.
The diode voltage is a function of the tube current. Voltage doesn't go 'through' anything. When the tube current gets very small, the diode voltage (i.e. bias) drops rapidly towards zero. But I don't understand what point you're making.
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Old 11th July 2018, 08:46 PM   #96
trobbins is offline trobbins  Australia
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jackinj, those are very interesting curves. Can you elaborate on what the test signal was, and the measurement circuit.
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Old 11th July 2018, 09:13 PM   #97
jackinnj is offline jackinnj  United States
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LED tube biasing, pros and cons
Quote:
Originally Posted by DAK808 View Post
Why is there a question mark in parantheses?
Artifact of converting image on the from the clipboard to MSPaint -- the "omega" doesn't make the transfer.
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Old 11th July 2018, 09:55 PM   #98
jackinnj is offline jackinnj  United States
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LED tube biasing, pros and cons
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Originally Posted by trobbins View Post
jackinj, those are very interesting curves. Can you elaborate on what the test signal was, and the measurement circuit.
Test signal was 0 dBm. When I run the test at -30 dBm the low frequency dip is much less pronounced.

Test setup is from Omicron-Labs measurement of DC-Biased impedance:

https://www.omicron-lab.com/fileadmi..._Caps_V2_0.pdf
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Old 11th July 2018, 10:20 PM   #99
trobbins is offline trobbins  Australia
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Thanks
For viewers without calculators, could provide those test signal levels in mA rms or pp?
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Old 12th July 2018, 12:03 AM   #100
20to20 is offline 20to20  United States
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Originally Posted by Merlinb View Post
The diode voltage is a function of the tube current. Voltage doesn't go 'through' anything.
The source of the voltage on the cathode is the voltage from the plate. Pull the cathode resistor and put your meter on the K pin. Wiz...
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