EE136

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EE136

• STABILITY AND CONTROL LOOP COMPENSATION IN
  SWITCH MODE POWER SUPPLY
• Present By Huyen Tran

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STABILITY AND CONTROL LOOP COMPENSATION IN
SWITCH MODE POWER SUPPLY

• potential risk for oscillation in a closed loop
  control system
• methods of stabilizing the loop

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Methods of stabilizing the loop

• By Circuit and Mathematical Analysis
• -Required fine tuning
• Interrogative Methods of Loop Stabilization
• -A difference techniques can be used to
  establish the required characteristics of the
  compensated control amplifier.

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Methods of stabilizing the loop

• Type 1 Compensation

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Methods of stabilizing the loop

• Type 2 Compensation

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Methods of stabilizing the loop

• Type 3 Compensation

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Stability testing methods

• One of these method is transient load testing
• -the transfer function changes under different
  loading conditions.

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Set up the transient load test
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Analysis for transient test
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Analysis for transient test

• For an under damped response, it will have a poor
  gain and phase margins and maybe only conditional
  stable. With this performance, the oscillation
  may occur.
• For an over damped response, it is very stable,
  but does not give the best transient recovery
  performance.
• For waveform c, it is stable transient response,
  and it will provide enough gain and phase margin
  for most application.

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Measurement procedure for the closed- loop power
supply systems
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Measurement procedure for the closed- loop power
supply systems

• voltmeter V1 is used to measure the ac input of
  control amplifier
• voltmeter V2 is used to measure the ac output
  voltage of power supply for each time changing
  the frequency

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A typical Bode plot
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Design example

• Stabilizing a Forward Converter Feedback Loop
  with a Type 2 Error Amplifier
• V0 5V
• I0(nom) 10A
• Minimum I0 1A
• Switching frequency 100 kHz
• Minimum out put ripple 50mV

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Design example

• calculate Lo and Co

And the cutoff frequency of the output LC filter
Is
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Design example

• the frequency of the ESR zero is

Then the modulator gain
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Design example

• Then the total open loop gain Gt Glc Gm Gs
  is draw in fig.1

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Design example

• At very low frequency, it is a straight line with
  -1.5dB and then it hit 2 poles at the frequency
  which is 806 Hz and start rolling down with slope
  of -40dB/dec until it hit a zero at 2500 Hz, and
  the line still rolling down but the slope only
  -20dB/dec.

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Design example
fz 5kHz, fp 80 kHz, gain 40