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What can you say about this?

What can you say about this?. Kirchoff’s Law. PN-Junction. Depletion Layer. +. +. -. -. -. -. +. +. -. -. +. +. -. +. +. -. -. +. -. -. +. -. +. +. -. -. +. +. +. -. +. -. -. +. -. -. -. +. +. +. -. -. +. +. +. +. -. -. -. +. -. -. -. +. +.

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What can you say about this?

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  1. What can you say about this?

  2. Kirchoff’s Law

  3. PN-Junction Depletion Layer + + - - - - + + - - + + - + + - - + - - + - + + - - + + + - + - - + - - - + + + - - + + + + - - - + - - - + + + - + - + + + - - - - - + - + + + - + + - + + - - - - + - - + + + - + + - + + - - N-region P-region

  4. PN-Junction Depletion Layer A K Cathode Anode Diode Symbol

  5. Biasing the Diode - Forward K A + + + - + - - - - - + + + + - - - - + - - + + + + + + + - - - - - - + - - + + + - - - + + + + - N-type P-type R V

  6. Biasing the Diode - Forward P-region N-region P-region N-region

  7. Characteristics

  8. Diodes Will this work? Almost shorting the supply High current in the loop.

  9. Diodes Will this work? Approach Assume diode drop to be ≈ 0.7V. Rest of the voltage should be across resistor. R limits the current Choose R value such that diodes current is within its ratings. Wait there is more!

  10. Diodes Caveat The resistor power rating should also be considered. Power rating of resistor should be at least max. drop (Vr) time max current (I).

  11. LEDs How to drive an LED? Always remember LED drop is ≈ 2V LED current can be from 10mA to 20mA. Adjust resistor value based on intensity required.

  12. Interfacing LED with µC Quiz What is the value of VCC? ≈3V What is the voltage at PA.1? ≈3V Will the circuit work? Yes

  13. Alternative Arrangement Sourcing Sinking

  14. Now are we there? I know there are 52 IO on µC. I’m going to connect 52 LEDs to the µC

  15. But!!

  16. Why didn’t that work? What more do we need to know? Well! Lets Look at the Data sheet

  17. µC Datasheet 2mA, 4mA and 8mA pad drive for digital communication, up to four pads can be configured With an 18-mA pad drive for high-current applications.

  18. What should we do? Boost the current • from the µC. Use a…

  19. Transistor collector n p p n base n p emitter

  20. Diffusion in Transistor collector + + + + + - - - - - + + + + + - - - - - + + + + + - - - - - N + + + + + - - - - - + + + + + - - - - - + + + + + - - - - - P + + + + + + base - - - - - - + + + + + - - - - - - - - - - + + + + + - - - - - N + + + + + - - - - - + + + + + - - - - - + + + + + - - - - - + + + + + emitter

  21. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Transistor Operation C N B P - - - - - N - - - - - - - E

  22. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Transistor Operation … C IC N B P IB - - - - - N IE - - - - - - - E

  23. Quiz • What type of device is a transistor? • Active • Current operated • What do you mean by current operated? • It is changes in input current that produces changes in output current.

  24. Transistor Characteristics saturation Cutoff

  25. Transistor (BC108) Data sheet

  26. Interfacing LED with µC revisited…

  27. Interfacing LED with µC revisited…

  28. Interfacing LED with µC revisited…

  29. Interfacing LED with µC revisited…

  30. Interfacing LED with µC revisited…

  31. But, How can we design this? • WKT, transistor has to operate in saturation and cut-off regions. • In saturation, VCE ≈ 0.2-0.4V and LED drop of 2V. • Calculate value of RC for Ic ≈ 15mA to 20mA. • Calculate IB with β=100. • Calculate Rb = (Vcc-VBE) / IB

  32. Finally !

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