Ch9 Intro to Power Supplies

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```					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

Power  Voltage  Current              Example :
P  VI                                Given Voltage and Current
V  10 V
 Energy(J)   Charge(C)                                 Units :

 Charge(C)    Time(s) 
P                                 I 1A                 C  Coloumbs

                                 Calc ulate Pow er :
J  Joules
s  Seconds

 Energy(J)                         P  10V  1A          Watts 
J

 Time(s) 
P          
s

                                   P  10 W J/s        1 electron  - 1.6x10-19 C

Electrical power (P) is equal to the product of electrical
current (I) and a voltage (V).
What is a Power Supply?
Source             Input     Power Supply                    Output   Load
1) Battery (DC)                                                        1) LED
2) Wall Outlet (AC)                                                      2) Micro
12 V                                      5V
1A                                       1A

•   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                                   Power supplies are not
η  OUT        42%
P     12 W                                     100% efficient.
IN
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
Vout =
AC-to-DC        12Vdc
t    Converter                t

DC to DC
V                                   V
Vin =
12Vdc
DC-to-DC Vout = 5Vdc
Converter
t                              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                                    V
DC-to-DC
Vin = 5V           Converter         VOUT = 12V
“Boost”

t
Vin < Vout                   t

Buck - Step Down (Linear or Switching Regulators)
V Vin = 12V                           V
DC-to-DC         VOUT = 5V
Converter
“Buck”
VIN > VOUT
t                                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                                   VOUT
Buck -
15V
10V                  Step Down
Converter 10V
5V                   VIN > VOUT 5V
0V                               0V
t                                 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                                 Saturation            Linear

Collector Current
VIN                Pass Transistor      VOUT                                          IB = 300 uA

(IC)
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

Linear Power Supply

Input         Pass Transistor
Output
2.   “PNP” or Low Drop Out (LDO)

Control

3.   MOS Low Quiescent Current

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

VBE ~ 0.7V
VCE ~ 0.5V

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
VIN                     ~ 1.2V                  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
VIN                                         VOUT

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

Charge
CONTROL                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         Low Drop Linear             Low Quiescent
Regulator               Regulator                   MOS Linear
Regulator
VIN               VOUT VIN             VOUT   VIN                      VOUT

CONTROL

Charge
CONTROL   Pump

CONTROL

Drop Out Voltage 3                          1 (Tie)                     1 (Tie)

Quiescent           3                       2                           1
Current
Features            3                       2                           1
Cost                1                       2                           3
Total               10                      7                           6
(Lower is better)
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
Bandgap                                            Voltage
Reference                                           Divider

VREF
VINT
Control
Block
VREF
OVERTEMP

1) Op Amp
2) Protection
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      R7
R6 + 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
VOUT
+
VEB
-   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)
lo 4.9 hi 5.1
VREF = VBE+2(R2/R1)VTln10                V5,13
REF
1
+ 2%   5,10                                                      2
3
4
5,07                                                      5
6
+ 1% 5,04                                                         7
8
9
10
11
VREF               5,01
TARGET                                      12
VREF, nom                                                          13
14
4,98                                                      15
16
17
- 1%   4,95                                                      18
19
20
4,92                                                      21
22
- 2%   4,89
23
24
-50   -25   0   25          50   75   100    125   25

TEMP
Temp
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

Control               VINT
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
Control          VINT
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
Characteristic Symbol   Min    Typ    Max    Unit   Condition

1   Output Voltage VOUT     4.90   5.00   5.10    V     IOUT = 1mA
VIN = 14V

Output Voltage VOUT     4.80   5.00   5.20    V     1mA < IOUT < 50mA
2                                                       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     ISC     200   ---   ---   mA     -40C < TJUNCTION < 125C
Current

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          IQ     ---   100   200   A     IOUT < 1mA
Current                                            VIN = 14V

Quiescent          IQ     ---    4     8    mA     IOUT = 50mA
Current                                            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          ---    ---   120    C/W      Package mounted on
Resistance                                                 FR4 PCB
Junction-Ambient                                           80x80x1.5mm3

Thermal       Rthjc           ---    ---   35     C/W      To lead frame
Resistance
Junction-Case

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

TJUNCTION  TAMBIENT  PD   R thj a 
Characteristics of Linear Voltage Regulators
Thermal Resistance Calculation Example
1      GIVEN:                                    VIN
1) VIN = 14 V
Voltage Regulator      VOUT
2) VOUT = 5 V
3) IOUT = 30 mA                             IIN                                  IOUT
4) Iq = 0.5 mA
5) TAMBIENT = 85° C                                              Iq
6) TJUNCTION = 150° C

2                                                      3
Thermal ResistanceCalculatio n :
Power Calculatio n
PD  (VIN - VOUT )  I OUT   VIN  I q 
T
R thj a  JUNCTION
 - TAMBIENT 
PD
PD  (14 V - 5 V)  (30 mA)  (14 V)  (0.5 mA)
PD  0.277 W                                                           150 C  85 C
R thj a                    286 C/W
0.227 W
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          IQ     ---   100   200   A     IOUT < 1mA
Current                                            VIN = 14V

Quiescent          IQ     ---    4     8    mA     IOUT = 50mA
Current                                            TJUNCTION = 85C

Quiescent          IQ     ---    1     2    A     INHIBIT = TRUE
Current

• 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
VOUT
Voltage Regulator                 Microcontroller
RESET

Watchdog      STROBE

RESET
Voltage

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
VOUT
Voltage Regulator                 Microcontroller
RESET

Watchdog     STROBE

RESET             Missing STROBE
Voltage

time
Auxillary Functions of Voltage Regulators
Early Warning Function
•   Senses an analog input and then a transmits a digital signal to a
triggered.
•   Commonly used to provide an “Early Warning” to the
microcontroller that the battery voltage has dropped and reset
may occur.
VBA                              VOUT
Microcontroller
VIN
T
Voltage
Regulator      WARN_OUT
RSI1
WARN_IN

RESET
RSI2

VIN         RESET
Voltage

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
Capacitive
Inductive                 Switching Regulators
Switching Regulators        • Uses external capacitor(s)
•   Uses inductor or transformer      for passive charge control
for passive charge control      • Relatively low output
•   Output current may range from     current for the price
1mA to many Amps
•   PCB design is moderately
complex                         • PCB design is relatively
automotive applications         • Not traditionally used in
automotive applications
Types of Switching Voltage Regulators
Inductive Buck Regulator (VOUT < VIN)

VFEEDBACK
VIN               VSWITCH
VOUT

Buck
Regulator
Types of Switching Voltage Regulators
Inductive Boost Regulator (VOUT > VIN)

VSWITCH
VIN
VOUT
VFEEDBACK
Boost
Regulator
Types of Switching Voltage 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          Switching
1. Output Voltage
Accuracy             +   1. Switching
Frequency
2. Output Current           2. External
3. Dropout Voltage             Components Size
4. Quiescent Current           and Cost
5. Thermal Resistance       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
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         Efficiency vs. Input Voltage
95%                                 95%
VIN = 24V
VIN = 12V
75%
75%

0A     0.5A    1.0A           65%
10        20      30
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 Calculatio n :

PD 
TJUNCTION  - TAMBIENT 
R thj a

I OUT 
TJUNCTION  - TAMBIENT 
Vin - Vout   R thj a 
I OUT 
150 - 85  152 mA
16 - 5  39

3. The efficiency of a linear regulator cannot maintain the junction
temperature below the specified maximum (150 C)
Thank You!
www.btipnow.com

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