Buck Converter

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瀧澤登
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瀧澤登

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This design demonstrates the use of the TDFS (Time Domain Frequency Sweep) simulation method, to measure the open-loop frequency response of an operating closed-loop system containing switching elements.The stability of the "Buck DC to DC Converter - Switching" design is assessed. This is a switching circuit, it does not use a state-average model for the modulator, so the standard AC Analysis method cannot be used. Rather, the frequency response is generated from time-domain simulation results. The TDFS approach can also be used for systems that contain sampling or digital control aspects.This particular example is directly comparable to the design titled "TDFS Loop Stability for Buck DC to DC Converter - State Average". In that design, both the TDFS and AC Analysis methods are used to measure the open loop transfer function of an equivalent non-switching circuit.Note that the approach used to characterize the loop stability, by injecting a small sinusoidal stimulus signal in series with the loop and then measuring the complex ratio of the ground referenced return signal to the injected signal, is described in:D. Venable, “Testing Power Sources for Stability”, Venable technical paper #1, Venable Industries

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PWM Modulator - VCVS - corrected

Norm
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PWM Modulator - VCVS-------------------------------------------------------------------------------------This is a structural representation of the language-based behavioral model found in SMSSA_modulator_v6p4. It is constructed from delay lines, summing and subtraction points, spectral quantity generatots (i.e. AS signal sources, passive R-C elements and Voltage-controlled voltage sources acting as high gain amplifiers and an integrator. It implements the same modulation expressions as v6p4 . All components are available from LTspice or any other Spice derivative.All formulas have been developed rigorously except for the final dependence of the switch drive output on the control voltage. The assumptions of a periodic Vctl and the scaling applied to that voltage. These factors have been adjusted t o match results below 1/2 Fsw as simulated with the TDFS mechanism developed at Mentor by Mike Donnely.Voltage-Controlled Voltage Sources act as ideal hi-gain opamps with infinite bandwidth, infinite Rin and zero Rout. Fixed AC sources account for the nonlinear behavior of the modulator. They are phase-shifted to 180 degrees to produce an in-phase result after three stages of summing points.

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Nonlinear SMPS AC Analysis - Buck Converter - V5p2.2

Norm
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Norm

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V5px is the culmination of my goal to construct a nonlinear SMPS that can be analyzed in the frequency domain without averaging out the switching cycle variations. The circuit modeling follows Vorperian's concept [1] of introducing equivalent circuits for the PWM modulator and the switch leaving the remainder of the converter as is. The PWM modulator and switch model nonlinearities by sourcing voltages at frequencies outside the external stimulae. With the restriction of averaging lifted the model becomes applicable at arbitrary frequencies across the spectrum up to and beyond the UHF band where EMI is studied, At frequencies below Fsw the model should produce the same results as the averaged switch.

This initial version of the modulator and switch is limited to voltage mode control and continuous conduction. It retains the assumption of small disturbances compared to steady state operation but the derivations make limited use of that assumption.

The test bench is the same buck converter Mike Donnelly used to demonstrate TDFS Loop Stability Analysis. I have replaced the switch assembly with an equivalent circuit derived by the methodology Vatche Vorperian documented in his May 1990 paper [1]. I drive the switch with a PWM modulator that sources the Fourier transform of the pulse sequence..

The key to coding the models is the use of VHDL-AMS spectral source quantities to formulate Fourier transforms involving products and ratios of waveforms. By this mechanism the models present all the characteristics of the non-linear components in the DC-DC converter.

swdrive continues to be derived as a closed form expression of the modulator output but now includes the combined steady state and transient drive signals. The switch model outputs a theoretically correct formulation of the switch outputs, the voltage at the common terminal and the current sourced out of the active terminal.

Potential applications:

1) Response at high frequencies to arbitrary disturbances including finite pulses, white noise, AM radio, X-Ray radiation...

2) Analyze susceptibility to electromagnetic interference (requires modeling of that interference).

3) Rad-Hard testing (requires modeling of that interference),

4) Generation of RF interference (e.g., by modeling the choke magnetics).

This version is under test to determine its accuracy and faithfulness to the actual switching characteristics.

[1] See Vorperian's "Simplified Analysis of PWM Converters Using Model of PWM Switch Part 1" in the May 1990 issue (Vol. 26, No. 3) of the IEEE Transactions on Aerospace and Electronic Systems.

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AhmedNahi
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Buck Converter

nahiahmed
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NCV881930 Virtual Eval Board_test

RobertDavis
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TDFS Loop Stability for Buck DC to DC Converter - Switching

Norm
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Norm

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Description

This design demonstrates the use of the TDFS (Time Domain Frequency Sweep) simulation method, to measure the open-loop frequency response of an operating closed-loop system containing switching elements.The stability of the "Buck DC to DC Converter - Switching" design is assessed. This is a switching circuit, it does not use a state-average model for the modulator, so the standard AC Analysis method cannot be used. Rather, the frequency response is generated from time-domain simulation results. The TDFS approach can also be used for systems that contain sampling or digital control aspects.This particular example is directly comparable to the design titled "TDFS Loop Stability for Buck DC to DC Converter - State Average". In that design, both the TDFS and AC Analysis methods are used to measure the open loop transfer function of an equivalent non-switching circuit.Note that the approach used to characterize the loop stability, by injecting a small sinusoidal stimulus signal in series with the loop and then measuring the complex ratio of the ground referenced return signal to the injected signal, is described in:D. Venable, “Testing Power Sources for Stability”, Venable technical paper #1, Venable Industries

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Buck Converter with Vorperian Switch v2.1

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ncv881930 load step

Pawel_1
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This version of the NCV891930MW01 "Virtual Evaluation Board" represents most of the features of the 3.65 V/4.0V output part. By changing various input stimulus and loading conditions, you can test these capabilities in the context of their intended usage.For the nominal configuration, the input voltage is set to 12V, the synci source is delayed for 10 msec (well beyond the simulation end-time), and the load resistance is fixed at 1 Ohm until 500 us, then it jumps to 10 kOhm for 100 us, then back to 1 Ohm. The soft-start operates normally, but during the high resistance operation of the load transient, a single pulse-skip interval is observed. You can zoom in on the PWM signal and see that only two 500 kHz pulses were applied during the “burst” interval, but it will generate 3 pulses under other operating conditions. You can also see that the PWM frequency is spread-spectrum after the soft-start is complete, by measuring the clock frequency (as a waveform) in the main waveform viewer.To test the “GH continuous ON” behavior, you can select the “DC” option in the load resistance function generator to set the value to a fixed 1 Ohm, and set the input voltage to 5.5V. In the simulation you'll observe several long periods of "continuous GH" operation, with 200 ns boost recharge windows every 16 us, after soft-start has finished.To test SYNCI operation, set the input voltage to 12V and the load resistance to “Pulse” (i.e. back to their original values), and then change the synci source delay to 10 ns (instead of 10 ms). Then the device will operate in forced PWM mode, with negative inductor currents allowed during the high load resistance period (i.e. not diode-emulation), and no pulse-skip. Other features can also be tested (high voltage frequency fold-back, output voltage select, LDO bypass jumper removed, etc.). In addition, you can force abnormal operating states using the two fixed logic sources available in the lower left corner of the schematic. For example, if the controller signal “d_spread_spectrum” is disconnected right at the input to the oscillator, and then a new net is connected from “d_set0” to that open input port, then the oscillator's spread-spectrum function will be disabled regardless of the normal controller commanded behavior.Notes: (1) Because a simplified version of the resistor divider network and compensation is used, the model will regulate above the target output voltage at light loads. The the real IC will regulate within specifications. (2) In order to reduce the simulation time, the softstart capacitor value has been adjusted to reduce the softstart time. The value used in this project does not reflect the suggested value from the evaluation board schematic. The desired capacitor value should be selected based on the equation provided in the datasheet.

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NCV891930MW00 Virtual Demo Board

Pawel_1
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Pawel_1

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Description

This version of the NCV891930MW00 "Virtual Evaluation Board" represents most of the features of the 3.3 V/5.0 V output part. By changing various input stimulus and loading conditions, you can test these capabilities in the context of their intended usage.For the nominal configuration, the input voltage is set to 12V, the synci source is delayed for 10 msec (well beyond the simulation end-time), and the load resistance is fixed at 1 Ohm until 500 us, then it jumps to 10 kOhm for 100 us, then back to 1 Ohm. The soft-start operates normally, but during the high resistance operation of the load transient, a single pulse-skip interval is observed. You can zoom in on the PWM signal and see that only two 500 kHz pulses were applied during the “burst” interval, but it will generate 3 pulses under other operating conditions. You can also see that the PWM frequency is spread-spectrum after the soft-start is complete, by measuring the clock frequency (as a waveform) in the main waveform viewer.To test the “GH continuous ON” behavior, you can select the “DC” option in the load resistance function generator to set the value to a fixed 1 Ohm, and set the input voltage to 5.5V. In the simulation you'll observe several long periods of "continuous GH" operation, with 200 ns boost recharge windows every 16 us, after soft-start has finished.To test SYNCI operation, set the input voltage to 12V and the load resistance to “Pulse” (i.e. back to their original values), and then change the synci source delay to 10 ns (instead of 10 ms). Then the device will operate in forced PWM mode, with negative inductor currents allowed during the high load resistance period (i.e. not diode-emulation), and no pulse-skip. Other features can also be tested (high voltage frequency fold-back, output voltage select, LDO bypass jumper removed, etc.). In addition, you can force abnormal operating states using the two fixed logic sources available in the lower left corner of the schematic. For example, if the controller signal “d_spread_spectrum” is disconnected right at the input to the oscillator, and then a new net is connected from “d_set0” to that open input port, then the oscillator's spread-spectrum function will be disabled regardless of the normal controller commanded behavior.Notes: (1) Because a simplified version of the resistor divider network and compensation is used, the model will regulate above the target output voltage at light loads. The the real IC will regulate within specifications. (2) In order to reduce the simulation time, the softstart capacitor value has been adjusted to reduce the softstart time. The value used in this project does not reflect the suggested value from the evaluation board schematic. The desired capacitor value should be selected based on the equation provided in the datasheet.

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