EE136 STABILITY AND CONTROL LOOP COMPENSATION IN SWITCH MODE POWER SUPPLY Present By Huyen Tran

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

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.

Methods of stabilizing the loop Type 1 Compensation + - OUT R1 C1 Vi VREF 0 Vo

Methods of stabilizing the loop Type 2 Compensation

Methods of stabilizing the loop Type 3 Compensation

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

Set up the transient load test

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.

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

A typical Bode plot

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

Design example calculate Lo and Co And the cutoff frequency of the output LC filter Is

Design example the frequency of the ESR zero is Then the modulator gain :

Design example Then the total open loop gain Gt = Glc + Gm +Gs is draw in fig.1

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.

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