Dias nummer 1

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H-Bridge, Function and ConstructionApplications
Motor Controller
Power, 2008 By Bo Rohde Pedersen
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Today's Lecture

• FETs
• Strømvejs diagrammer
• H-bridge with terminologies
• Input for practical design of FET drive

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MOSFETmetal-oxide semiconductor field-effect
transistor
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Characteristics of MOSFET
iD g (uGS - UT), aktive område
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RDS,on dependence of temperature
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MOSFET more details
- Pasitic capacitors are often in datasheets
described as input, output and transfer
capacitance
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Turn-on of a MOSFET
Switching losses Lost energy for
switching (energy put in to the gate) Energy
lost in the switch doing switching
http//www.ipes.ethz.ch/ipes/switching/e_switchdet
ail.html
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Turn-off of a MOSFET
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H-bridge

• -Inductor
• Current flow

Remember
- Alternative using two FETs and two diodes -
Often controlled by a PWM signal
http//www.ipes.ethz.ch/ipes/Inverter/e_H_Bruecke.
html
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Control of H-bridge
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Dead time
Switching characteristics varies between
manufacture of FETs
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Gate Driver Transformer
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Boodstrap Gate Drive
- When choosing the bootstrap diode has the
minimum duty radio to be taken into acocund (or
called the modulation index). Usually is there
used a shottky-diode which is very fast.
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Bootstrap driver IC
The showed driver is the HIP2113 from
IRF. Alternative can a gate driver transformer be
used
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Protection

• Overhead
• Under-voltage of FET-driver
• Over current Ex Measure voltage over RDS,on .

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Diodes Dynamic Response
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Snubber
A step-down converter with stray inductance and a
snobber circuit for the free-wheeling diode.
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Design Around FET Drive

• Have a good ground-plan!
• Make the tracks as short as possible. du/dt and
  di/dt are very large
• This shall minimize voltage peaks (specks) doing
  switching by minimizing pasitic inductions and
  capacities.

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Working with high frequencies
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Designing Output Stage
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Exercise H-bridge

• A motor is driven by a H-bridge.
• H-bridge 12V, fs20kHz, d0.75
• Motor Le300µH, R2O the motor rotates with a
  constant speed.
• Draw the PSU capacator.
• (Hint stømvejsdiagrammer and find the constant
  voltage across the motors inductance)