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LED Workshop October 19,2011

LED Workshop October 19,2011. Agenda. Basic LED structure & circuits Strip LED structure Calculating dropping Resistor Dual Supply connections Soldering Tips – discrete diodes Soldering Tips – strip diodes “Club” model voltages Proposed Club standard Demonstration. LED Basics.

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LED Workshop October 19,2011

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  1. LED WorkshopOctober 19,2011

  2. Agenda • Basic LED structure & circuits • Strip LED structure • Calculating dropping Resistor • Dual Supply connections • Soldering Tips – discrete diodes • Soldering Tips – strip diodes • “Club” model voltages • Proposed Club standard • Demonstration C. Bartel

  3. LED Basics • An LED is a diode with light emitting capability when powered with a dc voltage. • Semiconductor chip is very small compared to the size of the package. C. Bartel

  4. Options in LED Packages • Lens – point or diffused • Color (of interest for rr models) – red, yellow, green, white • Two color – polarity reversal changes color – red/green • Three color – polarity reversal or ac provides three different colors – red/green/yellow • LEDs with integrated IC – blinking (aircraft warning lights?) C. Bartel

  5. Voltage Drops • Standard diode  0.8 volts • Red LED  1.63 < V < 2.03 • Yellow LED  2.03 < V < 2.10 • Green LED 1.9 < V < 4.0 C. Bartel

  6. Critical Factors • Determine Delta Voltage drop from spec sheet • Use mid range value color • Determine Current Range • Use less than spec current for protection • Excessive current creates heat, heat kills die • Subtract Delta drop from power supply • Divide this voltage by the current • Provides resistor value to achieve spec current C. Bartel

  7. Standard Resistor Values • 100 220 470 • 120 270 560 • 150 330 680 • 180 390 820 • 100 to 820 ohms • Multiple by 10 to get 1,000 to 8,200 • Multiple by 100 to get 10,000 (10k) to 82 ,000 (82 k) • Multiple by 1000 to get 100K through 820K • 10% values – available from Radio Shack C. Bartel

  8. Non Standard Values • Parallel resisters • RT = R1*R2/(R1+R2) • Series resisters • RT = R1+R2 C. Bartel

  9. Current Calculation • Resistors rated in watts • Multiple current X voltage across resistor • ¼ watt, ½ watt, 1 watt & higher • 1/8 watt too small- do not use • Higher wattage (5, 10, 25) are sealed and screwed to a heat sink • Select smallest wattage possible (packaging) C. Bartel

  10. Circuits using discrete LEDs • LED in parallel have limitations • Better in series C. Bartel

  11. Calculations • Parallel • Use diodes with same drop • Add currents for each diode • Calculate dropping resister • Series • Use lowest value of peak current of the leds • Add up total delta voltages, subtract from supply • Divide voltage drop by selected current, select resistor C. Bartel

  12. LED assemblies • LED Strips rated for specific operating voltage • Optimizes output light versus life • Has an operation range • For club strips, 12 v rated, operate to about 7 volts • Components are surface mounted • Includes dropping resistor to limit current C. Bartel

  13. Dual Supplies • Based on LED strips • Rated for 12 vdc, highest lumens output • Visible in building light (Fair display, Gardens) • If used on home layout without power distribution • Use 9 vdc transistor battery • Each 3 LEDs draw about 17 ma • Duracell 9 volt batter rated 800 ma hours • Estimated hours of operation: 40 hours C. Bartel

  14. Battery Performance C. Bartel

  15. Dual Supplies • If setting up model for dual operation • Install batter holder (Radio Shack heavy duty 9 volt snap connector – in stock) • Connect to terminal strip C. Bartel

  16. Using LED lights to Set Time • Split model into zones • Day zones • Business, public places • Dusk zones • Houses, apartments above stores • Night zones • Bedroom areas, 24 hr factories, public areas (train stations, eating facilities, gas stations) C. Bartel

  17. Using LED lights to Set Time • Terminal strip • Common ground • Hot terminal for zone 1 • Hot terminal for zone 2 • Hot terminal for zone 3 • Hot terminal for “24’ Hour lights C. Bartel

  18. Soldering Tips • Individual diodes • Use heat sink to protect die (alligator clip works) • Use low wattage iron if available • Use electronic solder • Tin supply wire • Clean resistor and led lead wires if discolored • Mechanical joint first, than solder C. Bartel

  19. Soldering Tips • LED strips • Strips are “flexible” Printed Wiring Board (PWB) • Strips have adhesive on back • Recommend not adhering to metal plate • PWB is double sided, plated through holes • PWB has solder mask for production soldering, do not remove • Do not open holes for wire, use # 20 or smaller to terminal strips (opening holes cuts the plating) C. Bartel

  20. “Club” voltages • Donated power supply for model lighting & sound systems • Voltages available: + 12 Vdc 20 amps + 5.0 Vdc 30 amps + 3.3 Vdc 5 amps • 5.0 Vdc • 12 Vdc C. Bartel

  21. Proposed Club Standard • All lighting be rated at 12 Vdc or 5 Vdc • All ground wires be brown • + 12 Vdc be gray wire • + 5 Vdc be violet wire • + 3.3 Vdc be blue wire • Model terminal strip be marked Grd (-), Zone 1 through Zone 3 and/or 24 hr C. Bartel

  22. Demonstration • 12 vdc versus 9 volt battery • Zone 1 and 2 example • Single point source LED • Blinking led C. Bartel

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