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| university:labs:closed_loop_buck_adalm2000 [23 Mar 2020 19:35] – Add first power stage measurements Mark Thoren | university:labs:closed_loop_buck_adalm2000 [04 Nov 2021 16:44] (current) – [Activity 4: Current-mode loop optimization] add links to power labs, university home Mark Thoren |
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| Several analysis methods will be demonstrated using LTspice - AC simulation of continuous time circuits, extracting the frequency response of switching circuits using step and measure techniques in LTspice, Middlebrook's method for extracting open loop gain from a closed loop system. Where possible, these will be replicated on the ADALM-SR1 hardware. | Several analysis methods will be demonstrated using LTspice - AC simulation of continuous time circuits, extracting the frequency response of switching circuits using step and measure techniques in LTspice, Middlebrook's method for extracting open loop gain from a closed loop system. Where possible, these will be replicated on the ADALM-SR1 hardware. |
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| ==== Materials ==== | ===== Materials ===== |
| * ADALM2000 (M2K) Active Learning module OR: | * ADALM2000 (M2K) Active Learning module OR: |
| * Two-channel oscilloscope with external trigger input | * Two-channel oscilloscope with external trigger input |
| * ADALM-SR1 Switching Regulator Active Learning Module | * ADALM-SR1 Switching Regulator Active Learning Module |
| * User Guide: [[university:tools:lab_hw:adalm-sr1|ADALM-SR1 hardware]] | * User Guide: [[university:tools:lab_hw:adalm-sr1|ADALM-SR1 hardware]] |
| * CN0508-RPIZ power supply OR: | * [[resources:eval:user-guides:circuits-from-the-lab:cn0508|EVAL-CN0508-RPIZ]] power supply OR: |
| * 0-12V, 3A Adjustable benchtop power supply | * 0-12V, 3A Adjustable benchtop power supply |
| | * LTspice files for this exercise |
| | * [[downgit>education_tools/tree/sr1/m2k/ltspice/cl_buck|LTspice files for this exercise]] |
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| ===== Background ===== | ===== Background ===== |
| Applying traditional control theory to switching regulators presents some challenges. A continuous time system - even a "messy" one that may be nonlinear or time-variant - can often be approximated by a linear system by limiting the range of amplitudes and / or frequencies. There is no such good fortune with switching regulators - the power stage inherently involves a switching circuit that traverses several distinct states. One approach to this problem is to derive a continuous time model that approximates the behavior of the power stage at the timescales of interest. Once this model is derived, traditional methods can be used to design feedback compensators to meet the application requirements. [[https://www.analog.com/media/en/technical-documentation/application-notes/AN149fa.pdf|Application Note 149: Modeling and Loop Compensation Design of | Applying traditional control theory to switching regulators presents some challenges. A continuous time system - even a "messy" one that may be nonlinear or time-variant - can often be approximated by a linear system by limiting the range of amplitudes and / or frequencies. There is no such good fortune with switching regulators - the power stage inherently involves a switching circuit that traverses several distinct states. One approach to this problem is to derive a continuous time model that approximates the behavior of the power stage at the timescales of interest. Once this model is derived, traditional methods can be used to design feedback compensators to meet the application requirements. [[adi>media/en/technical-documentation/application-notes/AN149fa.pdf|Application Note 149: Modeling and Loop Compensation Design of |
| Switching Mode Power Supplies]] is an excellent resource for this general approach, while this lab exercise will focus on the specific case of the ADALM-SR1. Some additional resources on the subject are:\\ | Switching Mode Power Supplies]] is an excellent resource for this general approach, while this lab exercise will focus on the specific case of the ADALM-SR1. Some additional resources on the subject are:\\ |
| [[https://www.analog.com/en/technical-articles/loop-gain-and-its-effect-on-analog-control-systems.html|Loop Gain and its Effect on Analog Control Systems]]\\ | [[adi>en/technical-articles/loop-gain-and-its-effect-on-analog-control-systems.html|Loop Gain and its Effect on Analog Control Systems]]\\ |
| [[https://www.analog.com/media/en/technical-documentation/application-notes/an170f.pdf| Application Note 170: Honing the Adjustable Compensation Feature of Power System Management Controllers]]\\ | [[adi>media/en/technical-documentation/application-notes/an170f.pdf| Application Note 170: Honing the Adjustable Compensation Feature of Power System Management Controllers]]\\ |
| [[https://www.analog.com/media/en/technical-documentation/application-notes/AN140fb.pdf|Application Note 140 Basic Concepts of Linear Regulator and Switching Mode Power Supplies]]\\ | [[adi>media/en/technical-documentation/application-notes/AN140fb.pdf|Application Note 140 Basic Concepts of Linear Regulator and Switching Mode Power Supplies]]\\ |
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| ===== Activity 1: An Overcompensated Voltage-Mode Buck Converter ===== | ===== Activity 1: An Overcompensated Voltage-Mode Buck Converter ===== |
| At low frequencies, it is remarkably similar! Note the strange behavior around 10kHz - this is because the power stage is switching at 20kHz, so it only has 20,000 discrete "opportunities" to modify the output voltage per second, and thus can be looked at as a sampled system - and all sampled systems are subject to Nyquist criterion, and will alias if this is violated. (We can dig into that later...) | At low frequencies, it is remarkably similar! Note the strange behavior around 10kHz - this is because the power stage is switching at 20kHz, so it only has 20,000 discrete "opportunities" to modify the output voltage per second, and thus can be looked at as a sampled system - and all sampled systems are subject to Nyquist criterion, and will alias if this is violated. (We can dig into that later...) |
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| But we found the dominant pole of the power stage - about 362Hz for the linearized model, and about 103Hz for the switching model! | But we found the dominant pole of the power stage - about 362Hz for the linearized model, and about 232Hz for the switching model! |
| <WRAP todo> | <WRAP todo> |
| Dig into discrepency - are we discontinuous? | Dig into discrepency - are we discontinuous? |
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| </WRAP> | </WRAP> |
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| | **Return to [[university:labs:power|Power Based Lab Activity Material]]**\\ |
| | **Return to [[university:|Engineering University Program Home]]** |
