Forem: GeunWooJeon

AC 220V to DC 5V Simulation with easy circuits (And Why It Doesn't Work in Reality

GeunWooJeon — Sat, 04 Apr 2026 16:56:39 +0000

In my recent university classes, I learned about three foundational concepts in power electronics: the Buck Converter, the Full-Wave Rectifier, and the Smoothing Circuit.

quickly recap their roles:

Full-Wave Rectifier: Flips the negative half-cycles of an AC voltage into positive ones.

Smoothing Circuit: Filters this pulsating waveform to make it resemble a steady DC voltage.

Buck Converter: Steps down an input voltage to a lower output voltage.

Armed with this knowledge, a thought crossed my mind: "Wait, if I combine these, can I convert the AC 220V from my wall outlet (the standard in South Korea) directly into a DC 5V output for a smartphone charger?"

I immediately booted up my software, designed the circuit, and ran the simulation. The result? Success! I managed to get the exact DC 5V output I was aiming for. It is always incredibly satisfying to see theoretical concepts work perfectly on the screen.

The Reality Check
However, I quickly realized that a successful simulation does not necessarily mean a practical design. If I were to actually build this, there are major engineering flaws:

Physical Size
The components required for this specific topology would be incredibly bulky. There is no way this circuit could fit inside the compact smartphone chargers we carry around every day.
Extreme Duty Cycle
Stepping down from AC 220V RMS (which has a peak voltage of over 311V) directly to 5V requires an absurdly low duty cycle. In my simulation, the switch-on time was a mere 1.6%. Controlling a pulse width that narrow with any level of stability and precision is an absolute nightmare.
Massive Switching Losses
Dropping from 220V RMS to 5V using a standard buck converter topology would result in astronomical switching losses. The efficiency would be terrible, and the heat generation would be unmanageable.

This experiment was a great way to understand the limitations of basic topologies. To solve these exact issues—size, efficiency, and extreme step-down ratios—modern chargers use an entirely different approach.

Therefore, my next step is to study the Flyback Converter. It is an isolated topology perfectly designed to handle these challenges. I am excited to simulate it next and see how it improves upon my initial design. Stay tuned!

Simulation of full-wave rectifier

GeunWooJeon — Sun, 08 Feb 2026 12:29:00 +0000

A full-wave rectifier is the cornerstone of converting AC to DC. To truly understand how this is implemented and to identify the critical parameters of each component, I conducted a series of simulations using LTSpice and python.

A full-wave rectifier is a fundamental device that converts AC to DC. However, designing one is far from simple. The core challenge lies in finding the perfect "sweet spot" between stable power supply (low ripple) and circuit reliability (wide conduction angle).

The Capacitor’s Dilemma

In a rectifier circuit, the capacitor acts as a filter.
Larger Capacitance: Leads to a smaller ripple voltage and more stable power, but it narrows the conduction angle. This results in excessive peak currents and a poor power factor.
Smaller Capacitance: Increases the conduction angle (better power factor) and lowers peak currents, but results in a high ripple voltage, which leads to unstable power.

Why do Current Peaks occur only at Voltage Peaks?

If you look at the waveforms, current flows in sharp bursts rather than a smooth wave.
Charging Phase: The diode opens only when the source voltage exceeds the voltage stored in the capacitor. This happens briefly near the voltage peak, causing current to "pour in."
Discharge Phase: Once the voltage passes its peak, the diode closes, and the load relies solely on the energy stored in the capacitor.
This phenomenon is described as having a narrow conduction angle. It means the circuit "snaps" energy from the grid in short, violent bursts rather than drawing it smoothly.

The Consequences: Harmonics and Power Factor

Harmonics (The "Villains"): When the current is not a clean sine wave, it contains high-frequency noise called harmonics. These put significant stress on the power grid.
Power Factor: The more the current waveform deviates from the voltage waveform, the lower the power efficiency (Power Factor) becomes.

Ripple, Power, and the Macro Connection

This represents the change in instantaneous power (P = V * I) actually consumed by resistor R1.

The Quadratic Relationship: When resistance is constant, power is proportional to the square of the voltage (P = V^2 / R). This explains why even a minor fluctuation in voltage (the blue line) results in a much more significant "swing" or oscillation in power (the green line).
The Importance of Energy Storage: Increasing the capacitance of C1 dampens these fluctuations in both the voltage and power lines. This follows the exact same principle as installing an ESS (Energy Storage System) in a macro-scale power grid to stabilize the entire system.

System Impacts: The Cost of Instability

When power fluctuates continuously, it means the load (the device) is not receiving a steady supply of energy; instead, it is experiencing "pulsation."

Precision Electronics: Pulsation creates thermal stress within the circuitry, which eventually shortens the lifespan of the components.
Motor Systems: These fluctuations become a primary source of micro-vibrations and audible noise.
Efficiency Metrics: By analyzing the gap between the average and peak values of the green power graph, we can quantify exactly how inefficiently the system is utilizing energy.

The Benchmark of Stability: "Pure DC"The smaller the amplitude of this fluctuation (ΔV), the closer the output is to "Pure DC." In AI Data Centers, this level of stability is critical. Because even a minute spike in ripple voltage can lead to system crashes or catastrophic data corruption, maintaining these ripples at an extremely low level is considered a top-tier technological requirement for modern power engineering.

Optimizing Power Stability: The Trade-off of Capacitance

By increasing the capacitance to 1000uF, the graph becomes visibly flatter, enabling a significantly more stable power supply. However, in power electronics, every choice involves a trade-off between output quality and grid health.

Large Capacitance
-Conduction Angle: Small (Narrow)
-Output Ripple Voltage: Low (Excellent)
-Current Peak: High (Risky for components)
-Power Quality: Poor (High Harmonics)

Small Capacitance
-Conduction Angle: Large (Wide)
-Output Ripple Voltage: High (Poor)
-Current Peak: Low (Safe)
-Power Quality: Good (Low Harmonics)

While a large conduction angle is much better for the longevity of the power grid and individual components, a small conduction angle is often preferred when the priority is purely output voltage stability (low ripple).

Modern Solutions

Achieving the Best of Both WorldsIn modern power electronics engineering, the goal is to achieve "Clean Output (Low Ripple)" and a "Wide Conduction Angle (High Power Factor)" simultaneously. To reach this "holy grail," we utilize the following technologies

Adding an Inductor: By placing an inductor before the capacitor, we leverage its natural property of resisting sudden changes in current (L* di/dt). This forcibly widens the conduction angle and "shaves off" dangerous current peaks.
PFC (Power Factor Correction) Circuits: This is an advanced "active" approach. By precisely controlling the switching, the circuit forces the current waveform to mimic a sine wave, fundamentally resolving the conduction angle issue at its source.Engineer's Note: You can truly master this principle by comparing the FFT (Fast Fourier Transform) graphs before and after adding an inductor. Seeing the "villainous" harmonics drop as the current waveform smoothens is a satisfying confirmation of optimized design.

python simulation

max voltage: 310.19 V
min voltage: -0.88 V
ripple voltage (V_pp): 311.07 V
avg DC voltage: 160.28 V

To go a step further and cross-validate my results, I also implemented the simulation in Python. It was rewarding to see that the Python-generated graphs perfectly matched the behavior observed in LTSpice.

Real-World Applications: Where Theory Meets Reality
Diode bridge rectifiers are an essential component in virtually every electronic device that plugs into a standard 220V AC wall outlet. Here are a few critical examples of how the circuits I simulated are used in everyday life:

Smartphone Chargers (Adapters): Wall outlets provide 220V AC, but smartphone batteries require 5V DC to charge. Inside every adapter, there is a diode bridge (either four discrete diodes or a single integrated chip) that performs the primary conversion.
Computer Power Supply Units (PSU): High-performance components like CPUs and GPUs demand extremely "clean" and stable DC power. The diode bridge sits at the very first stage of the PSU, converting the 220V input into the initial DC voltage before it is further refined for the computer's sensitive electronics.
Subways and Electric Vehicles (EVs): On a much larger scale, these systems must convert high-voltage AC from overhead lines into DC (or controlled AC) to power massive traction motors. This requires industrial-grade, high-capacity power diodes—components produced by industry giants like Mitsubishi Electric or Fuji Electric.

What I Learned
Although I am a sophomore and haven't officially covered this in my curriculum yet, diving into this as "pre-study" was an eye-opening experience. The most fascinating part was observing how changing component values directly impacts the output:

Capacitance Trade-offs: Increasing capacitance significantly reduces ripple voltage, creating a more stable power supply. However, I observed that this also narrows the conduction angle, which can lead to undesirable peak currents.
The Inductor Solution: To mitigate this, I designed a Low-Pass Filter (LPF) by adding an inductor. It was thrilling to watch the inductor "smooth out" the current and widen the conduction angle, effectively balancing the circuit.
Real-world Connection: It’s incredible to realize that these rectifier circuits are practically right behind our wall outlets—constantly processing and supplying power so it's ready whenever we need it.
Looking Ahead: As technology continues to advance, I believe the ability to run and analyze such simulations is a vital competency for any engineer. Most importantly, I realized that I truly enjoy the process of circuit design and troubleshooting.

I’m already looking forward to my next challenge—what circuit should I explore next?

Electric Industry Operation

GeunWooJeon — Mon, 12 Jan 2026 11:08:03 +0000

01/11/2026

I learned about electric power industry, covering the essential stages of Generation, Transmission, Distribution, and Load. Understanding these systems is not just about formulas; it’s about understanding the backbone of modern civilization. I can’t wait for my Financial Aid to be approved so I can unlock the rest of the course and continue my studies.

1. Electric industry tech:

More Than Just Moving Electrons. While we view electricity as a continuous flow in our macroscopic world, it is essentially the coordinated movement of individual electrons at the micro-scale.

Energy Versatility: Electricity is the ultimate energy carrier because it is "clean" at the point of use and easily convertible into other forms (heat, light, motion).
Physics of Power: I revisited the core units:
1[A] = 1[Coulomb/sec]
1[V] = 1[Joule/Coulomb] Voltage is the potential energy that provides the "pressure" and direction for current.
Lenz’s Law in the Real World: One of the most fascinating realizations today was the application of Lenz’s Law. When the electrical load increases, the generator faces higher magnetic opposition, making the turbine mechanically harder to rotate. This requires more fuel to maintain frequency, directly linking physical resistance to energy consumption.

2. Electricity Generation:

The Heart of the GridMost power plants (except solar) rely on turbines.

Combined Cycle vs Simple Cycle: A Simple Cycle uses one turbine. A Combined Cycle plant is far more efficient; it uses a gas turbine for primary generation and then captures the exhaust heat to boil water for a secondary steam turbine.

Key Performance Metrics:
- Efficiency: (Electrical Output / Fuel Input). Always < 1.
- Heat Rate: The inverse of efficiency.
- Capacity Factor: Measures how consistently a plant runs (e.g., nuclear plants have high capacity factors as they run 24/7, even if their thermodynamic efficiency is moderate).

3. Transmission & Distribution (T&D):

The Science of Stepping Up To minimize energy loss during long-distance transport, we use Step-up Transformers. Why High Voltage? Since P(loss) = (I^2)R, we must lower the current I to reduce loss. By stepping up the voltage V, we can deliver the same power (P=VI) with much lower current. Since line resistance is a fixed factor, reducing current is the most effective way to minimize power loss. To achieve this, we step up the voltage for long-distance transmission, allowing us to deliver power efficiently at a lower current.

Step-down Transformers: Near residential areas, we use step-down transformers (fewer coils on the output side) to bring the voltage down to safe levels (e.g., 120V or 220V).

4. Load & Safety:

Creating a Closed Loop: Residential power typically uses a Single-phase system (Two hot lines and one neutral).

The Neutral Line: It completes the circuit. Even though it is grounded and near 0V, it carries the same current as the hot line. If the grounding fails, it becomes extremely dangerous.
Safety Layers:
- Ground Line: An emergency path for current to the earth.
- Polarized Plug: Ensures the switch always cuts the high-voltage "Hot" side.
- GFCI (Ground Fault Circuit Interrupter): Instantly cuts power if it detects a current imbalance (leaking).
- Breaker: Prevents fires by cutting off overcurrent.5.

Deep Dives & Industry InsightsT

The Governor: Much like a car's cruise control, the governor automatically adjusts the turbine's speed to keep the frequency constant despite fluctuating loads.
Japan’s Unique Grid: Japan is divided between 50Hz (East) and 60Hz (West). This requires massive Frequency Converter Stations to exchange power. For an engineer, this highlights the importance of SMPS (Switching Mode Power Supply) designs that can handle both frequencies—something companies like Yamaha excel at.
Energy Storage: Since electricity is hard to store, we use Pumped-storage Hydro (the world's "giant battery") or Hydrogen Conversion (electrolysis) to manage supply and demand.

[New Vocabulary & Concepts]

SMPS: Switching Mode Power Supply – Highly efficient DC power conversion.
HVDC: High Voltage Direct Current – The future of long-distance, low-loss transmission.
PCS / BMS / ESS: Essential acronyms for the modern grid (Power Conversion, Battery Management, and Energy Storage Systems).

[Final Thoughts]
The systematic design of the power grid is breathtaking. Every stage is engineered to maximize efficiency and safety. Learning about HVDC and the unique frequency challenges in Japan has solidified my goal: I want to design stable power circuits and noise filters that can perform flawlessly in any global environment. It was a deeply meaningful time for me. Even though the subject matter is introductory, the 'aha' moments and new knowledge I gained made me feel more passionate about engineering than ever. It really made me feel alive. Now, I am more determined than ever to gain practical experience. I want to see and experience for myself how everything I’ve learned is being put into practice in the industry.

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GeunWooJeon — Fri, 09 Jan 2026 11:55:33 +0000

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