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Electronic Power and Control Semiconductors Electronic Power and Control Semiconductors.

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Presentation on theme: "Electronic Power and Control Semiconductors Electronic Power and Control Semiconductors."— Presentation transcript:

1 Electronic Power and Control Semiconductors Electronic Power and Control Semiconductors

2 The Elements Simpler Table of Elements Good Conductors Poor Conductors Inert Gases Semiconductors Silicon Germanium

3 Semiconductors A SEMICONDUCTOR has FOUR electrons in its outermost shell or orbit. Outermost Electrons form PAIR BONDS Adjacent atoms SHARE Electron Pair Bonds; the crystal structure behaves like an INSULATOR

4 If the semiconductor has a few per million atoms with THREE outermost (valence) electrons THREE valence atoms leave a HOLE in the crystal structure. The Hole is an absence of an electron, and is thus POSITIVELY charged. Semiconductors This is Called P-TYPE

5 If the semiconductor has a few per million atoms with FIVE outermost (valence) electrons FIVE valence atoms have an extra electron in the crystal structure. The extra electron is NEGATIVELY charged. Semiconductors This is Called N-TYPE

6 If external voltage is applied: Junction Diode NEGATIVE to ANODE; POSITIVE to Cathode The Depletion (Barrier) Zone is increased, BLOCKING CONDUCTION

7 Rectifier Filters The parallel load also draws current from supply during the charging period and also during discharge..... the resulting Ripple depends on the load resistance AND capacitor size.

8 Rectifier Filters No Load (load open circuit).... Capacitor charges and holds peak value.

9 Rectifier Filters Moderate Load.... Capacitor charges to Peak value as voltage rises, but discharges when voltage drops away.

10 Rectifier Filters Heavy Load.... Capacitor charges to Peak value as voltage rises, but discharges greatly when voltage drops away.

11 Rectifier Filters Series Choke Filter A SERIES INDUCTIVE CHOKE opposes change in CURRENT A PARALLEL CAPACITOR opposes change in VOLTAGE However, being SERIES, there will be some voltage drop across the resistance of the choke

12 Rectifier Filters Choke Input L/C Filter A Capacitor and Choke are often used together.The Choke filters changes of current; the Capacitor gives higher load voltage

13 Single-Phase Full-Wave Bridge Rectifier AC Supply - often from a transformer (example: 12V 50Hz) Diode – voltage, current and PIV ratings to suit application DC Load to be supplied by Rectifier

14 Single-Phase Full-Wave Bridge Rectifier Conduction During Positive ½ Cycle

15 Single-Phase Full-Wave Bridge Rectifier Back Conduction During Negative ½ Cycle

16 Three-Phase Waveforms 3-phase AC Features Phase Voltages are out-of-phase

17 Three-Phase Half-Wave Rectifier 3-phase STAR connected transformer secondary Diode in each Active Return to transformer Star Point (Neutral) AC Voltage is PHASE Voltage (Active-Neutral) V AC (RMS)

18 Three-Phase Half-Wave Rectifier (Animated)

19 Three-Phase Half-Wave Rectifier Maximum value = V Peak Minimum value = V Peak x0.5 V Ripple = V Peak – (V Peak x 0.5) = V Peak x 0.5

20 Three-Phase Full-Wave Rectifier Maximum value = V Peak Minimum value = V Peak x0.866 V Ripple = V Peak – (V Peak x 0.866) = V Peak x 0.134

21 Voltage Regulator ZENER SHUNT REGULATOR Assume the filtered rectifier output is 12 volts DC and the Zener Diode is rated at 8.2 volts, 1 watt Excess voltage (12 – 8.2 = 3.8V) is dropped across the SERIES RESISTANCE (R S ) The Zener Diode voltage appears across the load. 8.2V 3.8V 12VDC 8.2V 1W

22 Voltage Regulator ZENER SHUNT REGULATOR Assume the load has a resistance of 200 ohms Power rating of R S = 3.8 volts x amps = 0.37 watts MINIMUM Load current = 8.2 volts ÷ 200 ohms = amps = 41mA 8.2V 3.8V 12VDC 8.2V 1W 97mA 41mA Zener Current = I RS – I Load = 97mA – 41mA = 56mA

23 Voltage Regulator THREE-TERMINAL REGULATOR (7xxx Series) The 3-Terminal Regular is an integrated circuit chip with INPUT, OUTPUT and GROUND or COMMON terminals Input Output Ground

24 Voltage Regulator THREE-TERMINAL REGULATOR (7xxx Series) 7812 Input Output Ground Positive Output 7812 Regulated Voltage (12V)

25 Voltage Regulator THREE-TERMINAL REGULATOR (7xxx Series) 7912 Input Output Ground 7912 Regulated Voltage (12V) Negative Output

26 Voltage Regulator THREE-TERMINAL REGULATOR (Typical Connections) In operation, a small QUIESCENT CURRENT (I Q ) flows between INPUT and GROUND I Q = 2mA to 5mA

27 Electronic Control Devices (Thyristors) Thyristors are solid-state devices used to control power to a load Silicon Controlled Rectifier (SCR) The DIODE conducts when the Anode is POSITIVE relative to the Cathode. The SCR conducts when the Anode is POSITIVE relative to the Cathode, PLUS the GATE must be POSITIVE relative to the Cathode

28 Electronic Control Devices (Thyristors) Silicon Controlled Rectifier (SCR) Once the SCR is conducting, the GATE loses ALL CONTROL The SCR can only be turned OFF by removing the Anode-Cathode voltage

29 Electronic Control Devices (Thyristors) Silicon Controlled Rectifier (SCR) Varying R1 varies the voltage available at the Gate at any instant. Animated This varies the Trigger Point, controlling the average load current Trigger Point can be delayed ONLY to 90 0

30 Electronic Control Devices (Thyristors) Silicon Controlled Rectifier (SCR) Varying R1 varies charging rate of the Capacitor. Animated This varies the Trigger Point, controlling the average load current Trigger Point can be delayed up to nearly 180 0

31 Electronic Control Devices (Thyristors) Silicon Controlled Rectifier (SCR) Waveform across LoadWaveform across SCR

32 Electronic Control Devices (Thyristors) TRIAC To provide a short trigger pulse, a DIAC is often used with an R/C network Like the SCR, The TRIAC is used to control loads, but with current in EITHER direction MT2 MT1 Gate A DIAC is like a TRIAC without a Gate. It conducts in EITHER direction when a voltage across it reaches a required threshold value DIAC

33 Electronic Control Devices (Thyristors) TRIAC Varying R1 varies charging rate of the Capacitor. Animated This varies the Trigger Point, controlling the average load current

34 Electronic Control Devices (Thyristors) TRIAC Waveform across LoadWaveform across TRIAC


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