Electronic Power and Control Electronic Power and Control Semiconductors Semiconductors

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

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

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

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

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

.... and also during discharge. 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.

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

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

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

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

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

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

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

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

Three-Phase Waveforms 3-phase AC Features 2400 1200 Phase Voltages are 1200 out-of-phase

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

Three-Phase Half-Wave Rectifier (Animated)

Three-Phase Half-Wave Rectifier VRipple = VPeak – (VPeak x 0.5) = VPeak x 0.5 Maximum value = VPeak Minimum value = VPeakx0.5

Three-Phase Full-Wave Rectifier VRipple = VPeak – (VPeak x 0.866) = VPeak x 0.134 Maximum value = VPeak Minimum value = VPeakx0.866

The Zener Diode voltage appears across the load. 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 The Zener Diode voltage appears across the load. Excess voltage (12 – 8.2 = 3.8V) is dropped across the SERIES RESISTANCE (RS) 8.2V 3.8V 8.2V 1W 12VDC

Voltage Regulator ZENER SHUNT REGULATOR Assume the load has a resistance of 200 ohms Load current = 8.2 volts ÷ 200 ohms = 0.041 amps = 41mA Power rating of RS = 3.8 volts x 0.097 amps = 0.37 watts MINIMUM Zener Current = IRS – ILoad = 97mA – 41mA = 56mA 97mA 8.2V 3.8V 41mA 8.2V 1W 12VDC

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

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

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

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

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

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

Electronic Control Devices (Thyristors) Silicon Controlled Rectifier (SCR) Varying R1 varies the voltage available at the Gate at any instant. This varies the Trigger Point, controlling the average load current Trigger Point can be delayed ONLY to 900 Animated

Electronic Control Devices (Thyristors) Silicon Controlled Rectifier (SCR) Varying R1 varies charging rate of the Capacitor. This varies the Trigger Point, controlling the average load current Trigger Point can be delayed up to nearly 1800 Animated

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

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

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

Electronic Control Devices (Thyristors) TRIAC Waveform across Load Waveform across TRIAC