From Closed-Loop BUCK to SG3524 Flyback: Six Progressive Power Electronics Circuit Tests with PowerExpert

PowerExpert has successfully completed a series of functional tests across typical power electronic circuits. Ranging from closed-loop BUCK, closed-loop BOOST, and LLC resonant switch-mode power supplies to control IC applications integrating the NE555 and SG3524, the evaluation covers a total of six distinct circuit configurations. Each circuit underwent schematic capture, transient simulation, and key-node waveform output.

To protect project confidentiality, this article omits the identities of project stakeholders, specific industries, proprietary model files, internal file paths, and detailed parameters. It focuses exclusively on shareable test tasks, coverage boundaries, and observable outcomes.

Test Overview

Test Object: PowerExpert

Test Quantity: Six typical power electronic circuits

Closed-Loop Topologies: BUCK step-down, BOOST step-up, LLC resonant switch-mode power supply

Control IC Applications: NE555 BUCK, NE555 Flyback circuit, SG3524 Flyback circuit

Observation Focus: Schematic capture, transient execution, and key-node waveform output

Test Coverage: Successful transient execution across all six circuits

Why Evaluate These Six Circuits Together?

For power electronics simulation software, power stages comprised solely of switching devices represent only a starting point. Once feedback loops are closed, output states continuously influence control nodes and switching behavior. Furthermore, incorporating LLC resonant networks, transformers, and control ICs increases the device interdependencies and waveform dynamics within a single schematic.

Therefore, the value of these six circuits lies not in their quantity, but in establishing a step-by-step path of increasing test complexity: starting with closed-loop step-down and step-up circuits, incorporating resonant networks and transformers, and finally linking control IC models with the power stage. Completing transient execution and obtaining key-node waveforms across these designated circuits serves as a prerequisite before moving on to accuracy, performance, and project-specific model verification.

Conclusion Scope: These six circuits were utilized for functional testing. Confirmed outcomes include successful schematic capture, completed transient simulation, and observable waveforms at key nodes. This testing does not imply a precision comparison between simulation and physical measurements, nor does it guarantee that other control IC models require no independent verification.

Six-Circuit Coverage Matrix

This matrix divides the test scope into inspectable circuit structures and observable outputs, proving that testing progressed successfully from basic power topologies to combined control IC and power stage operations.

These topologies correspond directly to common power design tasks: BUCK steps down input voltage to load requirements; BOOST steps it up; LLC handles resonant isolated conversion; and Flyback is widely deployed in isolated, low-to-medium power supplies and auxiliary rails. By introducing controllers like the NE555 and SG3524, the testing scope expanded from isolated power stages to interactive workflows involving control signals, feedback nodes, and power devices.

(Note: Deions of general topology applications do not imply disclosure of any specific products or projects corresponding to this testing.)

Phase I: Closed-Loop BUCK and BOOST

Closed-loop power supplies continuously sample output states and adjust switching behavior via control stages to drive the output toward target values. Compared to open-loop baselines, feedback loops induce tight interactions between control blocks and power stages, imposing higher demands on modeling and transient execution. Phase I utilizes BUCK and BOOST configurations to examine closed-loop step-down and step-up operation.

Closed-Loop BUCK: Deriving Lower Output Voltages from Input Supplies

The BUCK topology steps down voltages. The test circuit includes switching devices, freewheeling paths, inductors, capacitors, loads, and feedback control sections. Waveforms observe the startup transient and switch control signals.

Finding: Following initial startup dynamics, the output voltage transitions into a periodic ripple interval while control nodes continuously pulse.

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From the operational results, it can be observed that the output voltage experiences startup variations before entering a periodic fluctuation interval, and the control node continuously outputs pulse signals.

Closed-Loop BOOST: Modifying Energy Transfer Pathways

The BOOST topology steps up input voltages via inductor energy storage and switching actions. Featuring a distinct power stage configuration, its feedback loop connects differently to switching elements.

Finding: Within the designated time scale, the output voltage climbs progressively from its initial state before entering a stable operating band.

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Within the illustrated time range, the output voltage gradually rises from its initial value and enters a relatively stable interval in the later stage.

Phase II: Integrating Resonant Networks and Transformers in LLC

The LLC switch-mode power supply leverages a resonant inductor, magnetizing inductor, and resonant capacitor to share energy transfer responsibilities. The circuit also incorporates a switch bridge, transformer, rectification, and load elements. Compared to Phase I, device types and interactive complexity are noticeably higher.

Finding: The output node rises rapidly during the startup phase before settling into a relatively stable region.

In the operational results, the output node rises rapidly during the startup phase and subsequently enters a relatively stable interval.

Phase III: Integrating Control ICs into Power Circuits

After completing the three types of closed-loop topologies, the testing proceeds to incorporate control ICs and their respective models. At this stage, circuit operation involves not only the power stage and feedback network, but also handling the connection relationships among control IC outputs, peripheral components, and switching devices.

The three application circuits are as follows:

• NE555 BUCK: Uses the NE555 to generate control pulses to drive the BUCK step-down circuit;

• NE555 Flyback Circuit: Integrates the NE555 control section into a flyback switch-mode power supply;

• SG3524 Flyback Circuit: Constructs a flyback switch-mode power supply using the SG3524 pulse-width modulation control IC.

The NE555 BUCK connects timing control with the step-down power stage; the two Flyback setups further incorporate transformer coupling, secondary rectification, and feedback mechanisms. All three circuits completed transient execution and output the corresponding node waveforms.

NE555 BUCK Operation Results

The control node of the NE555 BUCK outputs continuous pulses after startup, and the output node decreases along with the transient process before entering a relatively stable interval.

NE555 Flyback Circuit Operation Results

The NE555 flyback circuit simultaneously output the waveforms of the output, control, and feedback nodes.

SG3524 Flyback Circuit Operation Results

The output node of the SG3524 flyback circuit undergoes an upward process and then enters a platform interval, with the oscillation amplitude of the differential observation quantity gradually decreasing as the transient progresses.

At this point, the testing has progressed from closed-loop step-down and step-up circuits to resonant power supplies and control IC applications. All three stages of circuits completed transient execution, and relevant output nodes can be observed. This is the extent of what can be confirmed by this test, and it does not replace model checking and result verification tailored to specific projects.

Moving from "Able to Start" to "Able to Observe"

The ability to construct a schematic only proves that the modeling entry point has been established. Only when a circuit completes transient execution and allows key nodes—such as output, control, and feedback—to form observable waveforms can engineers proceed to examine startup processes, steady-state intervals, and timing relationships among different nodes.

These six circuits completed this functional workflow. For teams evaluating power electronics simulation tools, it provides a more concrete starting point for judgment: first use typical closed-loop topologies to check the power stage and feedback loop, then add control ICs along with flyback and resonant circuits, observing how the tool operates as structural complexity increases incrementally.

Tool evaluations typically need to answer another question: Once models and analysis settings are unified, can the output results be compared against existing reference workflows? The previously published [Multi-Type Circuit Comparative Testing] focused on this aspect, whereas this six-circuit test supplements functional coverage ranging from typical closed-loop topologies to control IC applications. These two types of tests answer "whether execution can be completed" and "how results compare," respectively, collectively forming a more complete evaluation pathway.

Existing public information does not provide quantitative errors and execution time consumption, so this set of test results does not bear conclusions on accuracy and performance comparisons. Different teams utilize varying control methods, device models, and judgment criteria; therefore, before a tool enters a specific R&D workflow, it should still be verified using authorized, representative circuits.

If your team is currently evaluating power electronics simulation tools, you can use this progressive path as the starting point for functional verification: first select the closed-loop topologies that are most frequently used and most prone to exposing issues, and then gradually overlay the specific topologies, control strategies, and device models from your project.

PowerExpert supports targeted evaluation testing based on authorized circuits and models, progressing step-by-step from typical topologies to project models to verify the tool's applicability within the target design workflow.