Help

The design begins with the choice of a converter circuit, entering of its parameters and initial calculation.
Then you need to adjust component values in accordance with simulation results.
The next step is the correction of the gain loop frequency response to prevent self-excitation.

Literature: Christophe Basso, "Switch-Mode Power Supplies, Spice Simulations and Practical Designs",
Christophe Basso, "Designing Control Loops for Linear and Switching Power Supplies",
Markus Zehendner, Matthias Ulmann, "Power Stage Topology Reference Guide",
TI, Power Stage Designer, User Guide,
TI, "Switch-mode power converter compensation made easy".
V. Vorpérian, "Simplified Analysis of PWM Converters using Model of PWM Switch, parts I and II"
IEEE Transactions on Aerospace and Electronic Systems, Vol. 26, NO. 3, 1990

The desing is made for ideal components with simplified models. Only active diode losses are taken into account.

Current version supports only Current Mode (CM) with Continuous Conduction Mode (CCM).

If you see a straight line at 0 dB after power stage design, then computation for that circuit or its mode is not supported.

Here you can see transfer functions.

The information below is:
Crossover Frequency - the frequency when the gain is 0 dB.
Phase Margin - the phase margin at the crossover frequency.
Min Phase Margin - the minimum phase margin in the region where the gain is more than 0 dB.
Gain Margin - the gain at the frequency where the phase margin is zero.
Undershoot Voltage - the voltage drop at step load from 0 to maximum output current. Magnitude of the output capacitor impedance at the crossover frequency is also shown.

The result of initial calculation is:

• The switch voltage, RMS and peak currents.
• The diode voltage, average and peak currents.
• The minimum Cin, Cout values and their voltage and current ripple rating.
  The Cout and Cin equations assume zero ESR, so increase the capacitance accordingly based on the combined ESR.
• The minimum inductor values.
• The maximum turn ratio from the primary to secondary winding for the specified maximum duty cycle.

Current forms in the switches, diodes and the inductor are shown.

Current version supports only Continuous Conduction Mode (CCM).

Current Mode (CM):
Rsense - the current sense resistor, mOhm.
Asense - the gain of the current sense resistor voltage amplifier, times. Usually 1.
Gmp - the transconductance of the current sense resistor voltage amplifier, mA/V.
Compensation - the slope compensation to avoid subharmonic oscillations when duty cycle is more than 50 %, from 50 % to 75 %.
Vslope - the slope compensation voltage, V.

A datasheet can have either Rsense and Asense, or Gmp, enter the value you have.
Compensation and Vslope are also linked, enter the value you have or use the default value.

Voltage Mode, (VM):
Vramp - the peak to peak voltage of the PWM generator, V.

If the power stage is changed, compensation circuit parameters refill automatically.

Vout - the output voltage to calculate the voltage divider network.
Vref - the reference voltage, should not be greater than the output voltage.
Boost Frequency - the frequency where a gain and phase boost are specified. Usually it is a crossover frequency of the total network.
Gain boost - the desired gain boost at the boost frequency, in dB and V/V.
Phase boost - the desired phase boost at the boost frequency, in degrees.
Zero 1, 2 Frequency - the zero frequencies, usually lower than Boost Frequency.
Pole 1, 2 Frequency - the pole frequencies, usually higher than Boost Frequency.
Transconductance - the transconductance of an amplifier, in uA/V.
Current Transfer Ratio - the current transfer ratio of an used optocoupler, in times.

You can enter either pole and zero frequencies or a desired phase boost. In the last case the pole and zero frequencies are located automatically.

The compensation circuits with an optocoupler with fast lane are limited in gain selection, because the pole 0 and zero 1 frequencies are linked, and the LED load resistor defines the gain.

For circuits with an optocoupler, initial calclulation is done with a default load resistor value and CTR. Enter their values after the initial calculation. Press the "Make Compensation" button again to make auto compensation with their new values.
You should subtract the parasitic capacitance of your optocoupler to get a final value of the Cp capacitor. To get the parasitic capacitance meausure the optocoupler bandwidth at used load resistor value and calculate it using the equation: C = 1/(2 π bandwidth R).

"Compensation, Type III, Transconductance Amplifier" has limitations and no solution is possible for selected control frequencies. In that case you should find the frequencies with a solution which can also require changes of the power stage parameters.
Usually the problem is a too big difference between fp1 and fz2, so you should either make fp1 lower, or make fz2 higher.

Switching-Mode Power Stage Designer v2.5
email: dmilvdv@gmail.com
© 2020 vdv