AS Electronics

AS Electronics

1. Equations

   • Resistance
     • V=IR
       • I=R/V
       • R=V/I
     • 1/R = 1/R1 + 1/R2
       • --OR--
         • R= (R1*R2)/(R1+R2)
       • --Parallel--
     • Vout = (Vin * R2) / (R1+R2) -- Voltage Formula across R2
   • Power
     • P=I^2R
     • P=R*I^2
   • Zenner
     • iz = pmax / Vz
       • iz = current zenner, vz = voltage zenner, pmax = zenner power rating

2. LED's

   • Choose R higher if possible to minimise current into the LED
   • You can connect them in series with one resistor, so they share the same current.

3. Effect of Load

   • When you add load across a circuit you add resistance in Parallel which reduces the overall voltage across that potential ladder.

4. Zenner Diodes

   • Zenner diodes are used in reverse bias and drop voltage to the specified voltage.
     • 5mA Turn on !
   • iz = Pmax / Vz
   • Protective resistor = imax + iz
   • PHIL
     • Power - High
     • Current - Low

5. Transistors

   • As a switch
     • With a transistor the voltage across R1 remains 0 until 0.5v then the voltage across goes up and Vs does down they meet at 0.7v, Vs stops and plautos at .2V

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