42/14V-Automotive Converter

1
D.D.S.
Designing Dependable Solutions

• 42/14V-Automotive Converter

2
The Team
David Huckaby
Desmond Ladner
Shane Cravens
Dr. Mike Mazzola, P.E.
Advisor
3
Abstract

• Since future vehicles will have a 42 volt
  electrical system.
• Our group is designing a Black Box that will
  convert 42 volts to a regulated output voltage of
  14 volts.
• We will design build a scaled 150W model and
  design a full scale 1kW model.

Converter
42V
14V
4
System
-The 150W prototype and the 1kW model can be
broken down into three parts.
DC-AC Inverter Stage
Resonant Stage
AC-DC Rect./Filter Stage
DC-AC Inverter Stage
42V
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DC-AC Inverter Stage

• Solution a single point ground allows for the
  integration between the two circuits.

• Problem we attempted to supply power to the gate
  driver using 42V. However, the problem with this
  setup is that the source return is also attached
  to the ground, which causes a short.

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DC-AC Simulated Pulse

• This gate source pulse turns the FET on/off.
• The current flowing through the FET takes on the
  switching frequency.

7
System
DC-AC Inverter Stage
Resonant Stage
AC-DC Rect./Filter Stage
42V
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Resonant Stage

• The resonant stage is made up of a parallel
  loaded resonant tank.
• The tank shapes the current through the FET so
  that it will switch at zero current.

9
Resonant Stage Simulation
-At full load, any reverse current through the
body diode amounts to excess VA resulting in some
power loss.

• By increasing the characteristic impedance of the
  resonant tank, the reverse current was lowered
  along with peak currents.

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System
DC-AC Inverter Stage
Resonant Stage
AC-DC Rect./Filter Stage
42V
11
AC-DC Rect./Filter Stage

• The inductor acts like a current source
• The capacitor filters out the ripple voltage

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AC-DC Rect./Filter Simulations

• Design Constraint- 3 ripple
• Simulation- 3 ripple

• Prototype- 10 ripple

• PCB- 5.5 ripple

13
150W Thermal Analysis

• Specified Operating Temperature -25ºC to 85 ºC
• The switch used in the converter has a maximum
  junction temperature of 175 ºC.
• Calculations revealed one IRFP2907 with a heat
  sink having a thermal resistance of 2.2 ºC/W is
  capable of continuous operation in the specified
  temperature range.

14
150W PCB

• The 150W converter had a peak current of 30A, a ½
  oz. PCB could be used to reach our package goals.

• Package Constraint 6 x 6 x 6

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Check List
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150W Manufactured Cost
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Scalability 1 kW Model

• Determined Maximum Peak Current
• Thermal Analysis
• Simulated Design
• PCB Design

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1kW Thermal Analysis

• Maximum peak current 150A
• Temperature ranges -25ºC to 85 ºC
• Heat sink thermal resistance 1 ºC/W with forced
  convection cooling
• Using the IRFP2907
• Due to package limitation max current 90A
• So we would need 4
• Using the FB180SA10
• FB180SA10 has no package limitation we can use
  the device rating max current 180A
• So we would only need 2
• It is physically possible to get the converter
  down to one switch. However, the tradeoff is in
  a cost savings.

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1kW Schematic
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1kW Simulation Results
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1kW PCB Design

• There are three design options for a full scale
  1kW PCB.
• Increase the thickness of the PCB
• Increase the trace width of the PCB
• Use laminated buses (multi-layered boards)
• The thickness of the PCB cannot be increased due
  to skin depth.
• Increasing the trace width of a PCB with currents
  of 150A would give us an unrealistic board size
  of 180 x 120.
• Therefore the only option would be a
  multi-layered PCB.
• This would allow us to design a PCB similar to
  the size of our 150W model.

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Current / Future Work

• 4th Revision of gate driver
• Improve the regulation.
• Finish designing the enclosure.
• Packaging
• Decrease the size of the gate driver PCB and the
  power conversion PCB.
• Finish 1kW PCB (multi-layer) design

23
Acknowledgements

• We would like to thank the following people for
  their support.
• Dr. Michael Mazzola
• Mr. Jim Gafford

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ANY QUESTIONS???