Voltage Regulators

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Voltage Regulators
CHAPTER 1

• 1.1 Voltage regulation
• 1.2 Basic series regulators
• 1.3 Basic shunt regulators
• 1.4 Basic switching regulators
• 1.5 Integrated voltage regulators

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1.1 Voltage Regulation

• Two basic categories of voltage regulation
• Line regulation maintains constant output
  voltage when input voltage varies
• Load regulation maintains nearly constant
  output voltage when load varies

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1.1 Voltage Regulation
Line Regulation

• Line regulation
• When DC input (line) voltage, Vin changes,
  voltage regulator must maintain constant output
  voltage, Vout (static)
• Line regulation percentage change in the output
  voltage for a given change in the input (line)
  voltage

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1.1 Voltage Regulation
Load Regulation

• Load regulation
• When the amount of current through a load changes
  due to a varying load resistance, the voltage
  regulator must maintain a nearly constant output
  voltage across the load
• Load regulation percentage change in the output
  voltage for a given change in load current

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1.1 Voltage Regulation
Example
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1.2 Basic Series Regulation
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1.2 Basic Series Regulation
Block diagram of series regulators
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1.2 Basic Series Regulation

• Regulating Action
• If the output voltage tries to increase or
  decrease, the sample circuit will detect the
  change.
• The error detector will compare the sample
  voltage with the reference voltage.
• And drive the control element producing a stable
  output voltage.

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1.2 Basic Series Regulation
Basic Op-amp series regulator
The regulated output voltage
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1.2 Basic Series Regulation

• Short-Circuit or Overload Protection
• Excessive amount of current can damage or
  destroy the series-pass transistor.
• Use constant-current limiting or Fold-Back
• Current Limiting to prevent this from
  happening.
• Current is restricted to a maximum constant
• value

Constant-current limiting implementation
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1.2 Basic Series Regulation
Circuit operation

• The load current will flow through resistor R4
  
• produces a voltage between the base and the
  emitter.
• When the load current exceed a predefined load
  
• current, the voltage across R4 will
  activate Q2.
• Q2 will direct the current from the base of Q1
  so that
• load current is limited.
• The current is restricted to a maximum
  constant
• value

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1.2 Basic Series Regulation
Fold-back current limiting
A method used particularly in high-current
regulator whereby the output current under
overload conditions drops to a value well below
the peak load current capability to prevent
excessive power dissipation
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1.2 Basic Series Regulation
Operation
In an overload or short circuit condition, load
current increases to a value, IL(max) causing Q2
to conduct. Due to the overload or short circuit
condition, the output voltage decreases results
in the decrease in the voltage across R5. Thus
less current through R4 is required to maintain
Q1. Vout decrease, IL decrease.
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1.2 Basic Series Regulation
Operation

• Use for high-current regulators
• Cons The regulator is allowed to operate
• with peak current load up to IL(max).

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1.3 Basic Shunt Regulators
The control element (transistor) is in parallel
(shunt) with the load
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1.3 Basic Shunt Regulators
Basic op-amp shunt regulator with load resistor
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1.3 Basic Shunt Regulators
Regulating Action

• If the output voltage tries to decrease, the
  sample
• circuit will detect the change.
• The error detector will compare the sample
  voltage
• with the reference voltage.
• The difference in voltage will reduce the
  op-amp
• output, thus driving Q1 less.
• Thus reduce the collector current and
  increasing
• the effective collector-to-emitter
  resistance, rCE.
• Since rCE acts as a voltage divider with R1,
  this
• action offsets the attempted decrease in
  VOUT
• and maintain the VOUT.

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1.3 Basic Shunt Regulators
The shunt regulator is less efficient than the
series type but offers inherent short-circuit
protection If the output is shorted (VOUT0), the
load current is limited by the series resistor R1
to a maximum value (IS0)
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1.3 Basic Shunt Regulators
Example
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1.4 Basic Switching Regulators

• 3 basic configurations of switching regulators
• - Step-Down Configuration
• - Step-Up Configuration
• - Voltage-Inverter Configuration

• Greater efficiency than linear regulators.
• Greater load current at low voltage.
• High efficiency.
• For high power application.

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1.4 Basic Switching Regulators
Step-Down Configuration
Typical Circuit
Step down - The VOUT always less
than VIN
Equivalent circuit
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1.4 Basic Switching Regulators
Step-Down Configuration
Circuit Operation

• Q1 is use to switch the input voltage at a duty
  cycle based on the load requirement.
• LC filter is then used to average the switched
  voltage.
• During Q1 on (ton), the capacitor is charged at
  an interval time of ton.
• During Q1 off (toff), the capacitor is discharged
  at an interval time of toff.
• When ton is larger than toff, the capacitor
  charge more.
• The output voltage increase.
• When toff is larger than ton, the capacitor
  discharge more.

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1.4 Basic Switching Regulators
Step-Down Configuration
Circuit Operation (cont..)
8. The output voltage is decrease 9. Changing
the duty cycle will vary the output voltage. 10.
Vout-
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1.4 Basic Switching Regulators
Step-Down Configuration
Waveform
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1.4 Basic Switching Regulators
Step-Up Configuration
Step-Up- The VOUT gt VIN
Typical Circuit
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1.4 Basic Switching Regulators
Step-Up Configuration
Circuit Operation

• Q1 operate as a switch to ground.
• On-Time of Q1 (ton)
• VIN is induce the inductor (L) and increase the
  inductor voltage, VL instantaneously
• Inductor voltage, VL decreases from its initial
  maximum and diode, D1 is reverse-biased
• The longer the ton, the smaller the inductor
  voltage, VL

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1.4 Basic Switching Regulators
Step-Up Configuration

• Off-Time of Q1 (toff)
• Inductor magnetic field is collapse
• Polarity of VL is reverse, so its voltage adds to
  VIN , diode D1 is forward-bias and allowing the
  capacitor to charge.

• Regulating Action
• When VOUT tries to decrease (because of
  increasing load or VIN decrease)
• ton decreases
• greater the VL
• thus greater the output voltage (greater the
  VL adds to VIN)

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1.4 Basic Switching Regulators
Step-Up Configuration
Regulating Action (cont..)

• When Vout tries to increase
• ton increase
• smaller the VL
• thus smaller the output voltage (smaller the VL
  adds to VIN)

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1.4 Basic Switching Regulators
Voltage-Inverter Configuration
Voltage-Inverter Configuration
Typical Circuit

• Produce VOUT with opposite polarity to VIN
• Switching regulator efficiency greater than 90

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1.4 Basic Switching Regulators
Voltage-Inverter Configuration
Voltage-Inverter Configuration

• Q1 on
• VL jump to VIN VCE(SAT) magnetic field
  rapidly expand
• Diode D1 is reverse-biased
• VL decrease for its initial maximum

• Q1 off
• Magnetic field collapses
• VL polarity reverse
• Diode D1 forward-biased, charges the capacitor
  produce negative VOUT

The repetitive on-off produce smooth voltage
level by LC filter
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1.4 Basic Switching Regulators
Voltage-Inverter Configuration
Regulating Action

• When VOUT tries to decrease
• ton decrease causing VL to increase
• This compensate for the attempted decrease in
  VOUT
• When VOUT tries to increase
• ton increase causing VL to decrease
• This compensate for the attempted increase in
  VOUT

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1.5 Integrated Circuit Voltage Regulators
Several types of both linear switching
regulators Are available in integrated circuit
(IC) form
4 types of integrated linear voltage regulators

• Fixed positive linear voltage regulators
• Fixed negative linear voltage regulators
• Adjustable positive linear voltage regulators
• Adjustable negative linear voltage regulators

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1.5 Integrated Circuit Voltage Regulators
Fixed Positive Linear Voltage Regulators

• Provide fixed positive voltage
• 7800 series 3 terminals (Input, Ground,
  Output)
• Last 2 digits represent the output voltage
• Input voltage at least 2V
• Have internal thermal overload protection
  short circuit
• current limiting features

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1.5 Integrated Circuit Voltage Regulators
Fixed Positive Linear Voltage Regulators
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1.5 Integrated Circuit Voltage Regulators
Fixed Positive Linear Voltage Regulators
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1.5 Integrated Circuit Voltage Regulators
Fixed Negative Linear Voltage Regulators

• Provide fixed negative voltage
• 7900 series 3 terminals (Input, Ground,
  Output)
• Last 2 digits represent the output voltage
• Almost same features characteristic with 7800
  series

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1.5 Integrated Circuit Voltage Regulators
Adjustable Positive Linear Voltage Regulators

• Example LM317
• Operated as floating regulator because the
  adjustment terminal is
  not connected to ground but float to whatever
  voltage is across R2
• VOUT can be varied from 1.2V to 37V depending on
  the resistor value
• LM317 can provide over 1.5A output current to
  load

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1.5 Integrated Circuit Voltage Regulators
Adjustable Negative Linear Voltage Regulators

• Example LM337 Negative output
• Requires two external resistors for voltage
  output adjustment
• VOUT can be adjust from -1.2V to -37V depending
  on the external resistor value
• LM317 can provide over 1.5A output current to
  load

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Complete Chapter 1
QUESTION ???