Bridging Theory in Practice

1
Bridging Theory in Practice

• Transferring Technical Knowledge
• to Practical Applications

2
Introduction to Power Supplies
3
Introduction to Power Supplies

• Intended Audience
• Electrical engineers with little or no power
  supply background
• An understanding of electricity (voltage and
  current) is assumed
• A simple and functional understanding of
  transistors is assumed
• Expected Time
• Approximately 60 minutes

4
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxiliary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

5
What is Electrical Power?

• Power has not changed since collegiate physics P
  V I
• Output power is the product of the output current
  and the output voltage
• Input power is the product of the input current
  and the input voltage
• Input power must always be greater than output
  power

Electrical power (P) is equal to the product of
electrical current (I) and a voltage (V).
6
What is a Power Supply?
12 V 1 A
5 V 1 A

• Electrical Definition of Power Supply
• Conversion of a voltage into an desired voltage
• Example Car Battery (12 V) ? Microprocessor (5
  V)
• Efficiency Example
• PIN (12 V) x (1 A) 12 W
• POUT (5 V) x (1 A) 5 W
• The remaining 7W (12 W 5 W) of power is lost as
  heat
• The efficiency ? is

Power supplies are not 100 efficient.
7
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxiliary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

8
Types of Power Supplies AC-DC and DC-DC
Converters
AC to DC
DC to DC
Power supplies can be categorized into AC-DC and
DC-DC.
9
Types of Power Supplies DC-to-DC Converters Types
Boost - Step Up (Switching Regulator)
V
V
DC-to-DC Converter Boost Vin lt Vout
Vin 5V
VOUT 12V
t
t
Buck - Step Down (Linear or Switching Regulators)
V
V
Vin 12V
DC-to-DC Converter Buck VIN gt VOUT
VOUT 5V
t
t
DC-DC Converters can be categorized as Boost or
Buck. Buck can be Linear or Switching regulator.
10
Types of Power Supplies Input Voltage of Step
Down Converter
VIN
VOUT
15V
15V
10V
10V
5V
5V
0V
0V
t
t
The actual input voltage does not need to be a
true DC value. However VIN gt VOUT for step down
converter.
11
Types of Power Supplies What is a Switching
and Linear Power Supply?

• Switching Power Supply
• The pass transistor operates in a digital
  fashion.
• When in regulation, the pass transistor (power
  transistor between the input and output) is
  either completely on or completely off.
• An external passive component is used in the
  architecture for energy storage and transfer

• Linear Power Supply
• The pass transistor operates in an analog
  fashion.
• When in regulation, the pass transistor (power
  transistor between the input and output) is
  always on.
• No additional passive component is needed to
  create the desired output voltage

12
Types of Power Supplies What is a Linear Power
Supply?
A linear power supply regulates the output by
operating the pass transistor in the
linear/active region.
13
Types of Power Supplies Types of Linear Power
Supplies

• NPN or Standard
• PNP or Low Drop Out (LDO)
• MOS Low Quiescent Current

• Linear power supply can be broadly labeled
• Standard
• Low Drop Out
• Low Quiescent

14
Types of Power SuppliesNPN or Standard Linear
Regulators
NPN or Standard linear regulators use a NPN
Darlington pass transistor and 2.0 V drop out
15
Types of Power SuppliesQuasi Low Drop Out
Linear Regulator
Quasi linear regulators use a single NPN pass
transistor 1.2 V drop out
16
Types of Power SuppliesPNP or Low Drop Out
(LDO) Regulator
PNP or Low Drop Out (LDO) linear regulators use
a single PNP pass transistor and lt 0.5 V drop out
17
Types of Power Supplies MOS LDO Low Quiescent
Current Regulator
VDS lt 0.5V
IQUIESCENT ? 0
MOS linear regulators use a MOSFET as the pass
transistor offering low quiescent current and low
drop out lt 0.5 V.
18
Types of Power Supplies Summary of Linear
Voltage Regulators
19
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxiliary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

20
Linear Voltage RegulatorFunctional Diagram
VIN
Pass Transistor
VOUT
Voltage Divider
Bandgap Reference
VREF
1) Op Amp 2) Protection
VINT
Control Block
VREF
OVERTEMP
21
Linear Voltage RegulatorPass (Output) Transistor

• Below, the output transistor is PNP bipolar
  junction transistor
• The emitter-base voltage of the transistor will
  be adjusted in an analog fashion to maintain the
  proper output voltage

22
Linear Voltage RegulatorResistor Divider

• The resistor divider is from the output to ground
• Resistors are sized such that the intermediate
  node is equal to the bandgap reference voltage
  under typical conditions

Voltage Regulator
VOUT
R6
VINT
R7
VINT (VOUT)(R7) VREF
R6 R7
23
Linear Voltage RegulatorOperational Amplifier

• If VINT is higher (lower) than VREF, the
  operational amplifiers output voltage increases
  (decreases). This decreases (increases) the VEB
  voltage, and VOUT will decrease (increase).

IC

VEB
-
IB
24
Linear Voltage RegulatorBandgap Voltage Reference

• Internally generated with tight tolerance,
  traditionally 1.2V
• VOUT will be built from reference voltage (VREF)

VREF
2
1
TARGET
VREF, nom
- 1
- 2
Temp
25
Linear Voltage RegulatorCurrent Limit and Short
Circuit Detection

• The current through an alternate collector tap is
  measured. If it is too high, the regulator can
  limit the current from increasing further
  (current limit) or turn itself off (short circuit
  detect)

26
Linear Voltage RegulatorOver Temperature Detect

• At temperature increases, the VBE necessary to
  turn on a NPN decreases, so above 150C, the
  transistor turns on and OVERTEMP goes LO

VIN
VOUT
VREF
VINT
Control Block
VREF
OVERTEMP

VBE
-
27
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxiliary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

28
Characteristics of Linear Voltage Regulators

• Output Voltage Accuracy
• Output Current
• Dropout Voltage
• Quiescent Current
• Thermal Resistance

29
Characteristics of Linear Voltage Regulators
Output Voltage Accuracy
1
2

• Output Voltage Accuracy characterizes how
  reliable the output voltage will be under various
  operating conditions.
• Consider the entire operating condition when
  viewing the accuracy.

30
Characteristics of Linear Voltage Regulators
Output Current
Output Current Limit is the maximum amount of
current that can be sourced by the regulator.
31
Characteristics of Linear Voltage Regulators
Drop Out Voltage
Example Given VDROP 0.3 V VOUTPUT 5.0
V Calculate Minimum Input Voltage (VINPUT
VOUTPUT VDROP) VINPUT 5.0 V 0.3 V 5.3
V VINPUT 5.3 V MIN
Drop Out Voltage is the minimum voltage
differential between the linear regulators input
and output that is required for voltage
regulation.
32
Characteristics of Linear Voltage Regulators
Quiescent (Ground) Current
Quiescent Current is the current consumed by the
voltage regulator.
33
Characteristics of Linear Voltage Regulators
Thermal Resistance

• Thermal resistance indicates how much heat can be
  conducted by the regulator.
• Lower thermal resistance ? better thermal
  performance

34
Characteristics of Linear Voltage Regulators
Thermal Resistance Calculation Example
1

• GIVEN
• VIN 14 V
• VOUT 5 V
• IOUT 30 mA
• Iq 0.5 mA
• TAMBIENT 85 C
• TJUNCTION 150 C

3
2
35
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxillary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

36
Auxillary Functions of Voltage RegulatorsInhibit
Function

• Some voltage regulator outputs that can be
  enabled or disabled with an INHIBIT input
• When a voltage regulator is turned off, the
  quiescent current drops dramatically

37
Auxillary Functions of Voltage Regulators Reset
Function

• Most automotive modules are controlled by a
  microcontroller with a crystal oscillator
  stabilization time of 1 10 ms.
• Only when a stable clock signal is available, can
  a microcontroller be correctly initialized
• A Reset signal is sent from the linear voltage
  regulator to the microcontroller to indicate an
  established and valid operating voltage.
• A small (100nF) external capacitor controls the
  reset delay timing

38
Auxillary Functions of Voltage Regulators
Watchdog Function

• A microcontroller can be monitored through a
  watchdog circuit
• Periodically, a microcontroller is expected to
  strobe (pet) the watchdog to let the watchdog
  know it is still functioning

VOUT
Voltage Regulator
Microcontroller
RESET
Watchdog
STROBE
Voltage
STROBE
time
39
Auxillary Functions of Voltage Regulators
Watchdog Function

• However, if the microcontroller forgets to pet
  the watchdog, a software problem may have
  occurred
• Therefore, the voltage regulator resets the
  microcontroller to bring it to a known state

VOUT
Voltage Regulator
Microcontroller
RESET
Watchdog
STROBE
Missing STROBE
Voltage
time
40
Auxillary Functions of Voltage Regulators Early
Warning Function

• Senses an analog input and then a transmits a
  digital signal to a microcontroller once the
  analog input threshold has been triggered.
• Commonly used to provide an Early Warning to
  the microcontroller that the battery voltage has
  dropped and reset may occur.

41
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxillary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

42
Types of Switching Voltage RegulatorsInductive
and Capacitive

• Capacitive
• Switching Regulators
• Uses external capacitor(s) for passive charge
  control
• Relatively low output current for the price
• PCB design is relatively simple
• Not traditionally used in automotive applications
• Few automotive grade parts

• Inductive
• Switching Regulators
• Uses inductor or transformer for passive charge
  control
• Output current may range from 1mA to many Amps
• PCB design is moderately complex
• Traditionally used in automotive applications
• Automotive grade parts

43
Types of Switching Voltage Regulators Inductive
Buck Regulator (VOUT lt VIN)
44
Types of Switching Voltage Regulators Inductive
Boost Regulator (VOUT gt VIN)
45
Types of Switching Voltage Regulators Additional
Inductive Switching Regulators

• Inverting Regulators
• VOUT - VIN
• Buck-Boost Regulators
• VIN,MIN lt VOUT lt VIN,MAX
• Multiple Output Regulators
• VOUT1 2VIN, VOUT2 -VIN
• VIN 16V, VOUT1 3.3V, VOUT2 5V, VOUT3
  12V

46
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxillary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

47
Characteristics of Switching Voltage Regulators

• Linear Switching
• Output Voltage Accuracy
• Output Current
• Dropout Voltage
• Quiescent Current
• Thermal Resistance

• Switching
• Switching Frequency
• External Components Size and Cost
• Ripple Voltage
• Efficiency

48
Characteristics of Switching Regulators
Switching Frequency

• Frequency is probably the most often cited
  characteristic of a switching regulator
• Usually (but not always!), high frequency
  translates into
• Higher efficiency
• Smaller external components
• Higher price
• High frequency can also mean additional design
  problems

49
Characteristics of Switching Regulators External
Components, Size and Cost

• The design of a power supply is a true
  engineering challenge in the optimization of
  performance, price, and space
• Larger valued, higher quality, higher price
  external components usually translate into higher
  performance
• An optimal power supply design, however, will
  meet the required performance requirements while
  using acceptable external components (smaller
  values of inductance and capacitance, higher
  values of parasitic resistance)
• Possible value ranges may approach two orders of
  magnitude

50
Characteristics of Switching Regulators Ripple
Voltage

• Because the switching power supply is constantly
  being switched on and off, the output voltage
  will oscillate around a typical value

Load Discharging COUT
VMAX
VTYP
VMIN
Power Supply Charging COUT
51
Characteristics of Switching Voltage Regulators
Efficiency

• The most important characteristic of a switching
  regulator is efficiency because this is the
  primary reason for their use.
• Efficiency will also vary with output current
  load, input voltage, and temperature

Efficiency vs. Input Voltage
95
ILOAD 100mA
85
75
ILOAD 1A
65
20
10
30
Input Voltage (V)
52
Outline

• What is a Power Supply?
• Types of Power Supplies
• Linear Voltage Regulator
• Characteristics of Linear Voltage Regulators
• Auxillary Functions of Voltage Regulators
• Types of Switching Voltage Regulators
• Characteristics of Switching Voltage Regulators
• Choosing Between Linear and Switching Voltage
  Regulators

53
Choosing Between Linear and Switching Regulators

• When possible, most designers would prefer to use
  a linear voltage regulator rather than a
  switching voltage regulator
• Why Linear?
• Linear regulators are usually lower in price
• Linear regulators are usually simpler to
  implement
• Linear regulators do not have associated
  noise/ripple problems apparent in switching
  regulators

54
Choosing Between Linear and Switching Regulators

• When to use a switching regulator
• When the minimum input voltage is at or below the
  desired output voltage because linear regulators
  cannot provide an output voltage greater than the
  input voltage
• The heat sinking of a linear regulator is
  prohibitive in price or space
• The efficiency of a linear regulator cannot
  maintain the junction temperature below the
  specified maximum (150 C)

55
Thank You!

• www.btipnow.com