Bridging Theory in Practice
Transferring Technical Knowledge
to Practical Applications
Introduction to Power Supplies
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
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxiliary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage Regulators
8) Choosing Between Linear and Switching Voltage
Regulators
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
P ower  Voltage Current
P  VI
 Energy(J)  Charge(C) 
  

P  
 Charge(C)  T ime(s) 
 Energy(J)

P  
 T ime(s) 
Exam ple:
Given Volt age and Current
V  10 V
I 1A
Units:
C  Coloumbs
J  Joules
Calculat eP ower :s  Seconds
J
Watts
P  10V 1A
s
1 electron - 1.6x10
P  10 W J/s 
Electrical power (P) is equal to the product of electrical
current (I) and a voltage (V).
-19
C
What is a Power Supply?
Source
1) Battery (DC)
2) Wall Outlet (AC)
•
Input
Power Supply
12 V
1A
Output
5V
1A
Load
1) LED
2) Micro
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 η is:
P
5W
η  OUT 
 42%
P
12 W
IN
Power supplies are not
100% efficient.
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxiliary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage Regulators
8) Choosing Between Linear and Switching Voltage
Regulators
Types of Power Supplies AC-DC and
DC-DC Converters
AC to DC
V
V
Vin = 110Vac
t
Vout =
12Vdc
AC-to-DC
Converter
t
DC to DC
V
V
Vin =
12Vdc
t
DC-to-DC Vout = 5Vdc
Converter
t
Power supplies can be categorized into AC-DC and DC-DC.
Types of Power Supplies DC-to-DC
Converters Types
Boost - Step Up (Switching Regulator)
V
Vin = 5V
t
DC-to-DC
Converter
“Boost”
Vin < Vout
V
VOUT = 12V
t
Buck - Step Down (Linear or Switching Regulators)
V Vin = 12V
t
DC-to-DC
Converter
“Buck”
VIN > VOUT
V
VOUT = 5V
t
DC-DC Converters can be categorized as Boost or Buck.
Buck can be Linear or Switching regulator.
Types of Power Supplies Input Voltage of
Step Down Converter
VIN
15V
10V
5V
0V
t
Buck 15V
Step Down
Converter 10V
VIN > VOUT 5V
0V
VOUT
t
The actual input voltage does not need to be a true DC value.
However VIN > VOUT for step down converter.
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
Types of Power Supplies
What is a “Linear” Power Supply?
Linear Power Supply
Pass Transistor
VOUT
Collector Current
(IC)
VIN
Saturation
Linear
IB = 300 uA
IB = 200 uA
Cutoff
IB = 100 uA
Control
Collector to Emitter Voltage
(VCE)
A “linear” power supply regulates the output by operating
the pass transistor in the “linear/active” region.
IC  β  IB
Types of Power Supplies
Types of Linear Power Supplies
1.
“NPN” or Standard
2.
“PNP” or Low Drop Out (LDO)
3.
MOS Low Quiescent Current
Linear Power Supply
Input
Pass Transistor
Output
Control
Linear power supply can be broadly labeled:
1. Standard
2. Low Drop Out
3. Low Quiescent
Types of Power Supplies
“NPN” or Standard Linear Regulators
~ 2.0V
VIN
VOUT
VBE ~ 0.7V
VCE ~ 0.5V
VBE ~ 0.7V
CONTROL
NPN or “Standard” linear regulators use a NPN
Darlington pass transistor and ~ 2.0 V drop out
Types of Power Supplies
“Quasi” Low Drop Out Linear Regulator
~ 1.2V
VIN
VOUT
VBE ~ 0.7V
VCE ~ 0.5V
CONTROL
“Quasi” linear regulators use a single NPN pass
transistor ~ 1.2 V drop out
Types of Power Supplies
“PNP” or Low Drop Out (LDO) Regulator
VEC < 0.5V
VOUT
VIN
CONTROL
IQUIESCENT
PNP or “Low Drop Out” (LDO) linear regulators use a
single PNP pass transistor and < 0.5 V drop out
Types of Power Supplies
MOS LDO Low Quiescent Current Regulator
VDS < 0.5V
VIN
VOUT
IQUIESCENT  0
CONTROL
Charge
Pump
MOS linear regulators use a MOSFET as the pass transistor
offering low quiescent current and low drop out < 0.5 V.
Types of Power Supplies
Summary of Linear Voltage Regulators
Standard Linear
Regulator
VIN
Low Drop Linear
Regulator
VOUT VIN
VOUT
Low Quiescent
MOS Linear
Regulator
VIN
VOUT
CONTROL
CONTROL
CONTROL
Drop Out Voltage 3
1 (Tie)
1 (Tie)
Quiescent
Current
3
2
1
Features
3
2
1
Cost
1
2
3
Total
10
7
6
(Lower is better)
Charge
Pump
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxiliary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage Regulators
8) Choosing Between Linear and Switching Voltage
Regulators
Linear Voltage Regulator
Functional Diagram
VIN
Pass
Transistor
VOUT
Voltage
Divider
Bandgap
Reference
VREF
Control
Block
OVERTEMP
1) Op Amp
2) Protection
VINT
VREF
Linear Voltage Regulator
Pass (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
VIN
VOUT
VINT
VREF
Linear Voltage Regulator
Resistor 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
VINT = (VOUT)(R7) = VREF
R6 + R7
R7
Linear Voltage Regulator
Operational Amplifier
• If VINT is higher (lower) than VREF, the operational
amplifier’s output voltage increases (decreases).
This decreases (increases) the VEB voltage, and VOUT
will decrease (increase).
VIN
IC
+
VEB
VOUT
-
IB
VINT
VREF
Linear Voltage Regulator
Bandgap Voltage Reference
• Internally generated with tight tolerance, traditionally ~
1.2V
PACT s0784-b-1 ch. sta (29v*287c) 28-Dec-1 page 1
• VOUT will be “built” from reference voltage (VREF)
VREF = VBE+2(R2/R1)VTln10
lo 4.9 hi 5.1
V5,13
REF
+ 2%
5,10
5,07
+ 1% 5,04
VREF
TARGET
5,01
VREF, nom
4,98
- 1%
4,95
4,92
- 2%
4,89
-50
-25
0
25
50
TEMP
75
100
125
Temp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Linear Voltage Regulator
Current 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)
VIN
VOUT
VINT
Control
Block
VREF
Linear Voltage Regulator
Over 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
-
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxiliary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage Regulators
8) Choosing Between Linear and Switching Voltage
Regulators
Characteristics of Linear Voltage
Regulators
1.Output Voltage Accuracy
2.Output Current
3.Dropout Voltage
4.Quiescent Current
5.Thermal Resistance
Characteristics of Linear Voltage Regulators
Output Voltage Accuracy
Condition
Characteristic Symbol
Min
Typ
Max
Unit
1
Output Voltage VOUT
4.90
5.00
5.10
V
IOUT = 1mA
VIN = 14V
2
Output Voltage VOUT
4.80
5.00
5.20
V
1mA < IOUT < 50mA
6V < VIN < 30V
• Output Voltage Accuracy characterizes how reliable the output voltage
will be under various operating conditions.
• Consider the entire operating condition when viewing the accuracy.
Characteristics of Linear Voltage Regulators
Output Current
Characteristic
Symbol
Min
Typ
Max
Unit
Condition
Current Limit
ILIM
100
200
---
mA
VOUT = VOUT,TYP-100mV
TJUNCTION = 25C
Current Limit
ILIM
150
300
400
mA
VOUT = VOUT,TYP-100mV
-40C < TJUNCTION < 125C
Short Circuit
Current
ISC
200
---
---
mA
-40C < TJUNCTION < 125C
Output Current Limit is the maximum amount of
current that can be sourced by the regulator.
Characteristics of Linear Voltage Regulators
Drop Out Voltage
Characteristic
Symbol
Min
Typ
Max
Unit
Condition
Dropout Voltage VDROP
---
0.20
0.30
V
IOUT = 1mA
VOUT = VOUT,TYP – 100mV
Dropout Voltage VDROP
---
0.40
0.60
V
IOUT = 100mA
VOUT = VOUT,TYP – 100mV
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 regulator’s input and output
that is required for voltage regulation.
Characteristics of Linear Voltage Regulators
Quiescent (Ground) Current
Characteristic
Symbol
Min
Typ
Max
Unit
Condition
Quiescent
Current
IQ
---
100
200
A
IOUT < 1mA
VIN = 14V
Quiescent
Current
IQ
---
4
8
mA
IOUT = 50mA
TJUNCTION = 85C
Quiescent Current is the current
consumed by the voltage regulator.
Characteristics of Linear Voltage Regulators
Thermal Resistance
Characteristic Symbol
•
•
Min Typ Max
Unit
Condition
Thermal
Rthja
Resistance
Junction-Ambient
---
---
120
C/W
Package mounted on
FR4 PCB
80x80x1.5mm3
Thermal
Rthjc
Resistance
Junction-Case
---
---
35
C/W
To lead frame
Thermal resistance indicates how much heat can be conducted by the regulator.
Lower thermal resistance  better thermal performance
TJUNCTION  TAMBIENT  PD  R thja 
Characteristics of Linear Voltage Regulators
Thermal Resistance Calculation Example
1
GIVEN:
1) VIN = 14 V
2) VOUT = 5 V
3) IOUT = 30 mA
4) Iq = 0.5 mA
5) TAMBIENT = 85° C
6) TJUNCTION = 150° C
VIN
Voltage Regulator
IIN
2
P ower Calculat ion
PD  (VIN - VOUT )  I OUT   VIN  I q 
IOUT
Iq
3
T hermalResist anceCalculation :
R thja 
PD  (14 V - 5 V)  (30 mA)  (14 V)  (0.5mA)
PD  0.277W
VOUT
R thja 
TJUNCTION  - TAMBIENT 
PD
150 C  85 C
 286 C/W
0.227W
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxillary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage
Regulators
8) Choosing Between Linear and Switching
Voltage Regulators
Auxillary Functions of Voltage Regulators
Inhibit Function
Characteristic
Symbol
Min
Typ
Max
Unit
Condition
Quiescent
Current
IQ
---
100
200
A
IOUT < 1mA
VIN = 14V
Quiescent
Current
IQ
---
4
8
mA
IOUT = 50mA
TJUNCTION = 85C
Quiescent
Current
IQ
---
1
2
A
INHIBIT = TRUE
• 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
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
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
Voltage Regulator
VOUT
Microcontroller
RESET
Watchdog
STROBE
Voltage
RESET
STROBE
time
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
Voltage Regulator
VOUT
Microcontroller
RESET
Watchdog
Missing STROBE
Voltage
RESET
STROBE
time
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.
VBA
T
RSI1
VOUT
VIN
Voltage
Regulator
Microcontroller
WARN_OUT
WARN_IN
RESET
RSI2
Voltage
•
VIN
RESET
VOUT
WARN_OUT
time
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxillary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage
Regulators
8) Choosing Between Linear and Switching
Voltage Regulators
Types of Switching Voltage Regulators
Inductive and Capacitive
•
•
•
•
•
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
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
Types of Switching Voltage Regulators
Inductive Buck Regulator (VOUT < VIN)
VFEEDBACK
VIN
VSWITCH
Buck
Regulator
VOUT
Types of Switching Voltage Regulators
Inductive Boost Regulator (VOUT > VIN)
VSWITCH
VIN
VOUT
VFEEDBACK
Boost
Regulator
Types of Switching Voltage Regulators
Additional Inductive Switching Regulators
• Inverting Regulators
VOUT = - VIN
• Buck-Boost Regulators
VIN,MIN < VOUT < VIN,MAX
• Multiple Output Regulators
VOUT1 = 2VIN, VOUT2 = -VIN
VIN = 16V, VOUT1 = 3.3V, VOUT2 = 5V, VOUT3 = 12V
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxillary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage
Regulators
8) Choosing Between Linear and Switching
Voltage Regulators
Characteristics of Switching
Voltage Regulators
Linear & Switching
1. Output Voltage
Accuracy
2. Output Current
3. Dropout Voltage
4. Quiescent Current
5. Thermal Resistance
+
Switching
1. Switching
Frequency
2. External
Components Size
and Cost
3. Ripple Voltage
4. Efficiency
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
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
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
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. Load Current
95%
VIN = 24V
95%
85%
85%
VIN = 12V
75%
Efficiency vs. Input Voltage
ILOAD = 100mA
75%
65%
0A
0.5A
1.0A
Load Current
65%
10
ILOAD = 1A
20
30
Input Voltage (V)
Outline
1) What is a Power Supply?
2) Types of Power Supplies
3) Linear Voltage Regulator
4) Characteristics of Linear Voltage Regulators
5) Auxillary Functions of Voltage Regulators
6) Types of Switching Voltage Regulators
7) Characteristics of Switching Voltage
Regulators
8) Choosing Between Linear and Switching
Voltage Regulators
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?
1. Linear regulators are usually lower in price
2. Linear regulators are usually simpler to
implement
3. Linear regulators do not have associated
noise/ripple problems apparent in switching
regulators
Choosing Between Linear and
Switching Regulators
When to use a switching regulator:
1. 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
2. The heat sinking of a linear regulator is prohibitive in price or space
Output Current Calculation :
PD 
TJUNCTION  - TAMBIENT 
R thja
TJUNCTION  - TAMBIENT 
Vin - Vout   R thja 
150 - 85  152 mA

16 - 5  39
I OUT 
I OUT
3. The efficiency of a linear regulator cannot maintain the junction
temperature below the specified maximum (150 C)
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