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Ch9 Intro to Power Supplies

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Ch9 Intro to Power Supplies Powered By Docstoc
					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
      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                              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
   •   Traditionally used in             simple
       automotive applications         • Not traditionally used in
                                         automotive applications
   •   Automotive grade parts          • Few automotive grade parts
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
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          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
                                    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         Efficiency vs. Input Voltage
 95%                                 95%
       VIN = 24V
 85%                                 85%         ILOAD = 100mA
                VIN = 12V
 75%
                                     75%

 65%                                                 ILOAD = 1A
       0A     0.5A    1.0A           65%
                                        10        20      30
            Load Current                     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 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!
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