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.