⚡ DC-DC Buck Converter Controller Design using Type 2 Compensator ☀️ Calculations & MATLAB & TINA-TI

[@esca1453]

Great!

[@CanBijles]

Thanks!

[@esmfamil3929]

Nice , thank you

[@CanBijles]

You are welcome!

[@fablearchitect7645]

The same method can be used with the other switched converters such as the boost and buck-boost but deriving the plant transfer function is more complicated and requires state space averaging. This involves deriving a state space for all the switching states and averaging them. DCM will have a different transfer function to CMM due to the additional zero current state.

[@CanBijles]

Thanks for your message. Indeed, this method can be also used for other converter types. Not only the derivation will be somewhat difficult, but also also different for the modulator transfer function depending on the operating mode. For continuous conduction mode, the transfer function is much easier than for the discontinuous conduction mode.

[@fablearchitect7645]

@@CanBijles yes one could dedicate an entire video to deriving the transfer function per converter and operating mode

[@CanBijles]

Indeed, it is all about time and how far we need to go in the derivations.

[@petrusbosman4264]

How do you get the given transfer function, if you compare to the videos from Prof Marcos Alonso, he designs by choosing the inductor and output capacitor first from other design criteria , and then the transfer function is established from that, followed by the actual component values, Thank you for great Videos, Greetings, Petrus Bosman.

[@CanBijles]

Hi Petrus, thanks for your mail. Great to know you liked the video! The transfer function F(s), which is taking into account the filter and load, is determined using the output voltage divided by the input voltage for F(s) circuit only. When you carry out the analysis, you will get the transfer function F(s). The calculations of the component values really depend on the design specifications and of course on the available components.

[@SMV1972]

Hello,Thank you for a useful and informative lesson. It's just not clear why the divider R1 R3 is at the input and not at the output of the converter? Where in this scheme is the feedback from the output of the system to its input?

[@CanBijles]

Thanks for your message. The error amplifier compares the reference voltage Vref with the part of the output voltage. This should be done at the input of the error amplifier The part of the output voltage is set equal to the Vref using the voltage division created by the resistors R1 and R3. This is also explained in the video. Comparison is made best at the input of the error amplifier, because the circuit can act faster to changes in the output voltage.

[@CanBijles]

In addition: the circuit in the TINA-TI Spice simulator is for AC analysis. Here, we look at the loop transfer function, so we apply a AC signal at the point (output node) where we also measure the output voltage, thus we make a complete loop. The Vg is also Vo for normal operation. This is just for AC analysis.

[@SMV1972]

@@CanBijles Yes, everything is clear now, thank you!

[@CanBijles]

Great to know👍

[@SMV1972]

@@CanBijles And also, could you tell me, the step response can somehow be seen according to the scheme from TINA TI

[@udohuhn-rohrbacher1406]

I've learned that Type 2 compensators are used for current mode control, and type 3 compensators are for voltage mode control. Can you make a comment to that issue and, if possible, to demonstrate an example for current mode controlled converters. Thank you very much!

[@CanBijles]

Type 2 or 3 or any other compensator can be used for current-mode and voltage-mode control. I have not seen a restriction for able to do both methods. Where did you read this?

[@udohuhn-rohrbacher1406]

@@CanBijles One can find the Type II/Type III compensator selections in practical designs and suggested in several books, such as in Basso's books and also in the TI-literature. Let me add one part of a TI Report SLVA662, listed as follows: "Demystifying Type II and Type III compensators". A Type II compensation amplifier adds an RC branch to flatten the gain, and improve the phase response in the mid-frequency range. The increased phase is achieved by increasing the separation of the pole and zero of the compensation. Note that this type of compensator always has a net negative phase, and it cannot be used to improve the phase of the power stage. For this reason, Type II compensators cannot be used for voltage-mode control in CCM where there is a large phase drop just after the resonant frequency. Type II compensators are usually reserved for current-mode control compensation, or for converters that always operate in the DCM region. The Type III amplifier is the one for the voltage-mode converters operating in CCM. ------- Regards Udo

[@CanBijles]

@@udohuhn-rohrbacher1406 I see that is written in this paper of TI www.ti.com/lit/an/slva662/slva662.pdf, but for example in this paper, it does use the Type 2 in voltage-mode control: www.infineon.com/dgdl/an-1162.pdf?fileId=5546d462533600a40153559a8e17111a I have to check those in more detail to understand why TI is mentioning this in his paper.

[@udohuhn-rohrbacher1406]

@@CanBijles Check this from Basso's book: Basso book Switche-Mode Power Supplies 3.5.9 pages 297/298 Selecting the Right Amplifier Type Type I As it does not offer any phase boost, type I can be used in converters where the power stage phase shift is small at the desired crossover frequency. Type II: Most widely used and works fine for power stages lagging down to 90° and where the boost brought by the output capacitor ESR must be cancelled (to reduce the gain in high frequency). This the case for current-mode CCM and voltage-mode (direct duty ratio control) converters operated in DCM. Type IIa: This application field looks the same as for type 2, but when the output capacitor ESR effect can be neglected, for example, the zero is relegated to high-frequency domain, then you can use a type 2a Type IIb: By adding the proportional term, it can help reduce the under-or overshoots in several design conditions. We have seen that it prevents the output impedance from being too inductive, therefore offering superior transient response. Nevertheless, you pay for it by a reduction in the dc gain, hence a larger static error. Type III: You use this configuration where the phase lag brought by the power stage can reach 180°. This is the case for CCM voltage-mode buck or boost-derived types of converters.

[@CanBijles]

@@udohuhn-rohrbacher1406 Thanks for the detailed feedback. I will check this also. Great to have this discussion.

[@patrickliew2756]

Hello Sir, based on 25:43 the phase boost of the designed compensator will be 68.5 degree?

[@CanBijles]

How did you get the 68.5 degrees of phase contribution for the compensator?

[@patrickliew2756]

@@CanBijles Is is by 90 - 21.5 = 68.5 phase boost since the compensator starts from -90 degree to -21.5 degree.

[@CanBijles]

​@@patrickliew2756 You can see in 25:25 in MATLAB that the phase contribution of the compensator is -21.5 degrees. This is not taking into account the 180 degrees phase shift due to inverting amplifier action of the error amplifier. At 28:05 you can see that the phase of the compensator is 157 degrees in TINA-TISPICE, which is close to 180 - 21.5 = 158.5 degrees. TINA-TI Spice and MATLAB calculation the phase of the compensator different, because MATLAB does not include the phase inversion due to inverting amplifier action of the error amplifier.

[@patrickliew2756]

Hello sir, I had emailed you some question regarding the design of type 2 compensator. Hope you can have a look when you are free. Thank you.

[@CanBijles]

Ok, I will get back to it as soon as possible. In the mean time, you can send the documents and files you have where necessary.