Buck Converter

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Copy of Step-Down (Buck) DC to DC Converter - Switching - on Tue, 01/28/2020 - 11:53

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Description

This design is a detailed circuit implementation of the more abstract "state-average" buck converter model shown in the companion design example: “Step-Down (Buck) DC to DC Converter - Continuous”. This example includes the low-pass voltage sense circuit, an op-amp implementation of the difference amplifier and the lead-lag compensator, as well as PWM switching control of a power MOSFET. Simulation results for the line and load transients are very similar to the results from the continuous model.This design uses a number of "datasheet characterized" components, including the power MOSFET (MCH6337), freewheel diode (NRVTS560EMFS) and op-amps (MC33272A), as well as the soft-saturation inductor (XAL6060-223) and capacitor (PEG127KA3110Q) of the power stage . The parameter values of these devices were entered directly from the datasheet for the corresponding part, including the "Maximum Ratings" information.While the simulation time for this switching circuit is significantly longer than for the abstract model, more detailed information about the circuit’s signals and components is available. This includes the component stress levels, which are monitored within all the "datasheet" models.The companion design, "TDFS Loop Stability for Step-Down (Buck) DC to DC Converter - Switching", demonstrates a method to directly assess the open-loop frequency response, and hence the stability margin, of this converter. The TDFS (Time Domain Frequency Sweep) method circumvents the need for state-average models of the switching elements.

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TDFS Loop Stability for Buck DC to DC Converter - Switching

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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 PWM Modulator Line Transient Demo

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Description

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Buck DC to DC Converter - Switching

Description

This design is a detailed circuit implementation of the more abstract "state-average" buck converter model shown in the companion design example: “Buck DC to DC Converter vs. Linear Regulator”. This example includes the low-pass voltage sense circuit, an op-amp implementation of the difference amplifier and the lead-lag compensators, as well as PWM switching control of a power MOSFET. Simulation results for the line and load transients, ripple rejection and the power consumption are very similar to the results from the abstract model.This design uses a number of "datasheet characterized" components, including the power MOSFET (MCH6337), freewheel diode (NRVBA130LT3G) and op-amps (NCV20071), as well as the passive inductor (MSS1583-105KE_) and capacitor (PEG127KA3110Q) of the power stage . The parameter values of these devices were entered directly from the datasheet for the corresponding part, including the "Maximum Ratings" information.While the simulation time for this switching circuit is significantly longer than for the abstract model, more detailed information about the circuit’s signals and components is available. This includes the component stress levels, which are monitored within all the "datasheet" models. For example, the stress indicator for the power inductor shows that the maximum RMS current level is exceeded under this simulated operating condition (i.e. stress_ratio_current_rms &gt; 1.0).The companion design, "TDFS Loop Stability for Buck DC to DC Converter - Switching", demonstrates a method to directly assess the open-loop frequency response, and hence the stability margin, of this converter. The TDFS (Time Domain Frequency Sweep) method circumvents the need for state-average models of the switching elements.

About text formats