Introduction to Boost Converters

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Introduction to Boost Converters

• Team 1 ECE 480
• Technical Lecture

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Boost Converter

• L1 Charges (SW1 closed)
• L1 Discharges into C1 and load (SW1 open)
• L1 Charges (SW1 closed)
• L1 Discharges into C1 and load (SW1 open)
• etc
• reaches steady state w/ small ripple

http//www.coilgun.eclipse.co.uk/images/prototypes
_pages_images/cs_p01A/boost_converter_simple_circu
it_1.gif
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Boost Converter
Inductor
Capacitor
http//www.powerdesigners.com/InfoWeb/design_cente
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http//power.ece.uiuc.edu/balog/images/Non-linear
20techniques20for20Future20Enegy20Challenge20
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Boost Converter
Calculate duty cycle

• Average voltage across L1 has to be 0

• Conservation of Energy

http//upload.wikimedia.org/wikipedia/commons/thum
b/3/34/Dutycycle.png/350px-Dutycycle.png
http//www.alltek.com/images/app/6power_012.gif
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555 Timer

• First Timer IC
• External Resister and Capacitor
• TRxC
• Still in current use.

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555 Timer

• 555 Timer Package

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Transistor

• Used since 50s
• Small controls large
• Analog switch
• Digital storage

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Transistor

• Replace Vacuum Tubes
• Smaller
• IGBT for over 1Kv
• Bipolar junction
• Field-effect transistor

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Boost Converter Output Filter

• Filters made of inductor and capacitor
  combinations are often added to a converters
  output to improve performance.

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Output Filter

• Main reason
• Compensating Ripple
• Reducing Noise due to the switch

http//www.ericsson.com/campaign/powermodules/arch
ive/picov/28701-EN_LZT14606_EN_A_PDFV1R2.pdf
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Basic LC Filter
C1 reduces the ripple to a relatively low level.
L1 has a high value of inductance which offers a
high reactance to the ripple frequency. At the
same time, C2 offers a very low reactance to ac
ripple. L1 and C2 form a LC filter.
http//www.tpub.com/content/neets/14179/css/14179_
204.htm
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Transfer Function of the LC filter
http//focus.ti.com/lit/an/sloa119/sloa119.pdf
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Low Pass Filter using Op Amp

• 1/R1Ccut off frequency
• -R1/R2 Gain
• Problems
• Output is limited
• Extra power needed
• Expensive

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Output Filter
http//www.ericsson.com/campaign/powermodules/arch
ive/picov/28701-EN_LZT14606_EN_A_PDFV1R2.pdf
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APPLICATIONS OF BOOST COVERTER

• Hybrid Electric Vehicles (HEV)
• Battery Powered Application of Chip
• - THE ML4851 - Low Current, Low Voltage Boost
  Converter
• Applications in Small Devices

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Hybrid Electric Vehicles (HEV)

• A hybrid electric vehicle (HEV) is a vehicle
  which combines a conventional propulsion system
  with an on-board rechargeable energy storage
  system (RESS) to achieve better fuel economy.
• HEVs became widely available to the public in the
  1990s with the introduction of the Honda Insight
  and Toyota Prius.
• The Toyota Prius HEV contains a motor which
  utilizes voltages of 500 V. Without a boost
  converter, the Prius needs almost 417 batteries
  to power the motor. However, a real Prius only
  uses 168 batteries and boosts the voltage from
  202 V to 500 V.

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Battery Powered Application of Chip

• THE ML4851 Low Current, Low Voltage Boost
  Converter
• The ML4851 is intended for single cell
  applications requiring less than 25mA of load
  current, high efficiency, and a minimum number of
  external components. The ML4851 includes a low
  battery detect comparator and is available in two
  different output versions a 3.3V output
  (ML4851-3), and a 5V output (ML4851-5).

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Typical Application Circuit Schematic for a ML4851
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• Find boost converters in
• Cell Phones
• Laptops
• MP3 Players
• Car Navigation Systems
• Digital Camera

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Buck vs. Boost Converters

• A step down DC DC converter
• Duty cycle dependence
• Up to 95 efficiency when used in integrated
  circuits
• On State Storing Power in the inductor
• Off State Discharging power from the inductor
  into the load

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Differences

• Boost
• - DC-DC voltage step up

• Buck
• - DC-DC voltage step down

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Similarities

• Very similar devices
• Usage of transistors
• Charging/Discharging of inductors
• Energy accumulation into a capacitor
• Dependence on a switch
• - Duty cycle of switch
• Voltage conversion (main purpose of both
  devices)

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• Questions?