25-08-2017, 09:32 PM
Type 1, 2 and 3 Control Schemes
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Type 1, 2 and 3 control schemes are characterised by having 1, 2 and 3 poles respectively in the
compensation response. This document gives the mathematical formulae, resulting bode plots and real
world implementation for these control schemes using standard voltage feedback op-amps. Most
modern PWM IC’s have the error amplifier built in but, for clarity, the error amplifier is shown in this
document as a stand-alone component. The op-amp is assumed to be ideal.
All of the mathematical expressions here include a minus sign at the start which relates to the
‘subtraction’ part of the feedback loop when the output voltage is compared to the reference. The
actual compensation bode plots ignore this minus sign to give the conventional transfer function
responses.
Type 1 Control
Type 1 control places a pole at DC to give pure integral control action. Figure 1 shows the typical op-
amp arrangement and resulting transfer function for this type of control.