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  1. jimthompson

    Optically isolated light dimmer

    Several years ago I designed an optically isolated triac circuit to be used in conjunction with a low voltage control for resturant applications. The product is still being manufactured and sells for several thousand dollars.
  2. jimthompson

    Fuse keeps tripping.

    I assume that the LED's in question are Red. Typical Red LED's have a two volt drop at 20 ma so 6 of them would have a drop of 12 volts and would not work with 9 volts. Since the actual voltage drop is a function of temperature a resistor in series with three LED's will give the best LED life...
  3. jimthompson

    SCR GEQ CR81 ?

    It is very common for SCR's to be screened for specific electrical parameters and those parts assigned a special customer specific part numbers. You might search for "GE SCR" and see if you can find a data sheet for parts with similar packaging and appropriate voltage and current spec's.
  4. jimthompson

    Photodiode and Op amp Question?

    Silicon Photodiodes respond to photons of light from the Blue region (450 nm) to infrared (around 1000 nm max). Each photon stricking the active area results in a very small current. Many photons result in a current that is easier to measure. Most applications use a low noise transimpedance...
  5. jimthompson

    Hot solder dip vs Tin-lead plate finish on Microcircuit

    Lead-Tin Plating and Solder Dip are basically the same coating. Dipping will result in a thicker coating because of the surface tension. The melting temperature is determined by the ratio of lead to tin.
  6. jimthompson

    Testing an SCR

    I worked in SCR and Triac applications for several years and the biggest problem I encountered was insufficient gate drive which would result in a partial turn on of the junction. All of the current would crowd into only part of the junction resulting in serious heating and junction failure. I...
  7. jimthompson

    Resistor size for LED?

    The Voltage drop for Red and Amber LEDs is approximately 2 volts, Green and Blue LED's have approximately 3.5 volt drops. Unfortunately the reverse voltage is usually rated at only 5 to 10 volts. Most of the 3 mm and 5 mm LED's can handle 20 ma continuous current. Since you are using the...

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