Transcript Electronic Power & Control NUE064

Electronic Power and Control
Semiconductors
The Elements
Simpler Table of Elements
Good
Conductors
Poor
Conductors
Inert Gases
Germanium
Semiconductors
Silicon
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
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
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
A SERIES INDUCTIVE
CHOKE opposes
change in CURRENT
across the resistance
of the choke
Rectifier Filters
Choke Input L/C Filter
A Capacitor
The Choke
and
filters
Choke
changes
are often
of current;
used together.
the Capacitor gives higher load voltage
Single-Phase Full-Wave
Bridge Rectifier
AC Supply - often
from a transformer
(example: 12V 50Hz)
DC Load to be
supplied by Rectifier
Diode – voltage, current and PIV
ratings to suit application
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
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)
12VDC
3.8V
8.2V
1W
8.2V
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
12VDC
3.8V
8.2V
1W
41mA 8.2V
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
Voltage Regulator
THREE-TERMINAL REGULATOR
(7xxx Series)
Positive Output
7812
Regulated Voltage (12V)
Voltage Regulator
THREE-TERMINAL REGULATOR
(7xxx Series)
Negative Output
7912
Regulated Voltage (12V)
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 DIODE
conducts
when
Anode
SCR conducts
when
thethe
Anode
is is
POSITIVE
relative
the Cathode.
POSITIVE
relative
to the to
Cathode,
PLUS ....
..... 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
Gate
MT1
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