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Fundamental Electronics

Fundamental Electronics. Electrical Charge. Electrical Charge is when atoms have TOO MANY electrons (a negative charge) or TOO FEW electrons ( positive charge). Potential, Potential Difference and VOLTAGE.

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Fundamental Electronics

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  1. Fundamental Electronics

  2. Electrical Charge • Electrical Charge is • when atoms have TOO MANY electrons (a negative charge) or • TOO FEW electrons (positive charge).

  3. Potential, Potential Difference and VOLTAGE • There is a force of attraction between atoms when they are positively or negatively charged. • The pressure on the atoms to EQUALIZE their charge is called Potential or Potential Difference or more commonly referred to as VOLTAGE. • Voltage is the PRESSURE upon the electrons to flow through a conductor. The unit that we use to specify how much pressure is the Volt.

  4. Potential, Potential Difference and VOLTAGE • A practical example of potential difference is the difference in pressure in a water tank that is suspended up in the air. • There is a pressure (caused by gravity) on the water to equalize, and if there is a hole in the bottom of the tank, the water will run out. • Depending upon the size of the hole (resistance to flow) a different amount of water flow (current) will be achieved.

  5. Resistance • Resistance is the restriction of the flow caused by the imperfect conductor. The unit that we use to specify how MUCH resistance is the Ohm. • Good conductors have a LOW resistance to current flow (1 Meter of copper wire has a resistance of < 1 Ohm, thickness?). • Poor conductors (insulators) have a HIGH resistance to current flow (1 Meter of rubber has a resistance more than 1 trillion Ohms).

  6. Current • The amount of current flow achieved (in the order of a billion electrons per second) is referred to as Current and the units that we use for current are Amps. • if 6.25x1018 electrons per second flow through a wire from left to right, we can call that 1A current flowing right to left.

  7. Closed pressure cooker pot on a stove • Consider an example of a closed pressure cooker pot on a stove half full of water with a small hole in the side near the bottom. Will water flow out of the pot? - YES! In this example, what corresponds to: • Voltage? -> the pressure inside the cooker • Resistance? -> the size of the hole (smaller hole = MORE resistance) • Current? -> the rate at which the water flows out (the Flow) • What 2 things could be modified to cause more water (Current) to FLOW and for each, should it be increased or decreased?: • The _____________ could be (increased , decreased) • The _____________ could be (increased , decreased)

  8. Ohms law • Ohms law provides the mathematical relationship between voltage, resistance and current. I = V / R Where: I is the current in Amps V is the voltage in Volts R is the resistance in Ohms • If Voltage is doubled then current will double. If resistance is doubled then current will be reduced by half. • When given 2 of the above 3 quantities, the 3rd can be calculated by using Ohms Law.

  9. the 3rd can be calculated When given 2 of the above 3 quantities, the 3rd can be calculated by using Ohms Law. • For a given Voltage and Resistance, the amount of current flow can be calculated: I = V / R • For a given V and I, R can be calculated: R = V / I • For a given R and I, V can be calculated: V = I X R

  10. Fundamental electrical symbols

  11. The Resistor • A resistor is an electrical componentdesigned to have a certain amount of resistance (Ohms). • Its primary purpose in a circuit is to limit the amount of current flow by providing some resistance in the circuit. • Without resistance, the current in a circuit would be too high. There must always be some resistance in a circuit.

  12. Resistor Colour Code • Usually resistors use a 4 band colour coding scheme to indicate the resistance value and the tolerance (% error). The first band indicates the first digit, the second band indicates the second digit and the third band is the multiplier (it indicates the number of zeros). A resistor coloured Red Black Orange Silver 20000 Ohms +/- 10% Because of the tolerance, the actual resistance could be anywhere between: 18000 to 22000 Ohms

  13. Resistor Colour Code

  14. Kirchoff's Voltage Law The algebraic sum of all voltages around a closed path is zero. • In an electric circuit, the voltages across the resistors (called voltage drops) always have polarities opposite to the source voltage polarity. • To state this another way, if all the voltage drops around a closed loop are added and then this total is subtracted from the source voltage, the result is zero. • This result is because the sum of the voltage drops across the components in a series circuit equals the source voltage.

  15. Kirchoff's Voltage Law

  16. Combination of Resistors • The simplest resistor combination is two identical resistors in series,as shown in Figure B–8(a). The current is the same in the two resistors • In general, the resistance of any number of resistors in series is the sum of the individual resistances: Rseries = R1 + R2 + × × + Rn

  17. voltage divider

  18. Parallel Resistors

  19. Thevenin Equivalent Vout = Voc - Iout × Rout

  20. Thevenin equivalent circuit

  21. Thevenin equivalent circuit

  22. Power When current passes through a resistor, energy is produced in the form of heat. When current passes through a light bulb filament, energy is produced in the form of light and heat. Power is a measure of how fast energy is being used.

  23. Power The common unit of power is the Watt. The Watt is also used in specifying the capacity of a computer’s power supply. The power capacity of a power supply is a combination of the voltages and currents that it can produce. Power can be calculated in one of 3 ways: P = V * I P = V2 / R P = I2 * R

  24. Power A resistor has a power rating expressed in Watts (1/4 Watt, 1/2 Watt, 1 Watt). This means that a resistor is capable of dissipating the specified amount of watts. If more power is applied then the resistor will get too hot and likely burn out. The Power rating for a resistor is normally determined by its physical size - larger resistors generally have a higher power rating.

  25. The Light Emitting Diode (LED) • The light emitting diode is one that produces light when it is forward biased and conducting current. • The amount of light produced is typically proportional to the amount of current flowing through it. • The voltage drop across a forward biased conducting LED is typically 1.6 Volts. • Many diode checking meters are not equipped to test LEDs since they don't produce enough voltage to turn the diode on.

  26. The Diode • The most common and the simplest type of semiconductor device is the diode. The diode will only allow current to flow in one direction. The two pins of a diode are called the Anode and the Cathode. • Electrons can ONLY flow from the cathode to the anode. In the 1st diagram of the next slide the diode is said to be "forward biased". When the reverse polarity is applied, the diode is said to be "reverse biased".

  27. Diode

  28. Driving an LED with an open-drain output

  29. Proper value of pull-up resistor, R VOL + VLED + (ILED × R) = VCC R = (VCC - VOL - VLED ) / ILED = (5.0 - 0.37 -1.6)v / 10 mA = 303 

  30. Light Emitting Diode using ordinary CMOS

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