Understanding the Design and Function of SMPS Circuit Board

Introduction

In today’s high-speed, high-tech society, electronic devices are essential. Electronic devices are present everywhere, from homes to public workplaces. For these devices to work smoothly, they need a power supply that’s both reliable and consistent. Have you ever wondered why your electronics work so efficiently? Well, one of the reasons behind this is the use of SMPS (Switched Mode Power Supply) circuit boards. The switching regulator on an SMPS circuit board transforms high-voltage AC input into low-voltage DC output, which protects electronic devices. SMPS circuit boards are designed to supply electronic devices with a consistent and controlled output DC voltage.  

Figure 1 SMPS Circuit Board

There would be no exaggeration to say that SMPS circuits have significantly advanced power electronics by providing a highly efficient and adaptable solution to convert power. These circuits are widely used in modern electronics, providing power to devices such as laptop chargers, set-top boxes, smartphones, and portable devices. 

The significance of SMPS circuit boards has grown as our demand for electronic devices has increased. Many different types of electronic devices can benefit from the stable, efficient power supplied by SMPS circuit boards. They are a crucial part of current technology like smartphones, computers, laptops, and LEDs because of the following features:

• Efficiency ≥ 85%
• Reliable 
• Lightweight
• Compact
• Cost saving
• Long Lifespan
• Reduce heat dissipation.
• Protect from voltage fluctuation.
• Environmentally friendly

The requirement for smaller and more efficient designs in power electronics is increasing daily. This means that SMPS circuit boards will continue to be a must-have for the next generation of cutting-edge tech.

SMPS Circuit Board Components and Working

Switched-mode power supplies are a circuit type known for their complexity. High-frequency switching devices efficiently transfer power from the source to the load in these circuits. The utilization of cutting-edge technologies and careful component design provides such efficiency. The result is a power supply that is both reliable and effective. 

1. Filters: The purpose of the input filter is to protect the power supply from being damaged by harmful voltage fluctuations and surges that may be present in the input. The filter prevents switching circuit-generated electromagnetic interference (EMI) from reaching the AC mains. Capacitors, inductors, and resistors are used to reduce the fluctuating AC input voltage. They also protect the SMPS board from electrical surges and fluctuations in voltage.
2. Transformer: An SMPS circuit board’s transformer reduces the AC input voltage to a more acceptable level. Electromagnetic induction powers the transformer’s primary and secondary windings. Power is subsequently sent throughout the circuit through the secondary winding.
3. Rectifier: A bridge rectifier setup converts the filtered alternating current input voltage to a pulsing direct current. Output rectification components smooth the pulsating DC output voltage
4.  to provide a consistent power supply. 
5. Switching Devices: These devices rapidly turn on and off the current to convert energy efficiently. IGBTs and MOSFETs are typical SMPS circuit board switching devices.
6. Control circuitry: An SMPS circuit board monitors the output voltage and adjusts the switching frequency to keep it stable. This is achieved by employing feedback control loops that monitor the output voltage and react accordingly. Control circuitry modulates switching frequency to compensate for output voltage variations, delivering a consistent and dependable power supply.
7. A schematic of the SMPS’s components is given in Figure 1 to see how the SMPS functions. 

 

Due to the higher complexity of an SMPS’s circuit, its operation is broken down into five steps:

• During the initial phase, the AC power input undergoes rectification and filtration processes to generate a direct current output.
• The SMPS operates at a higher frequency, requiring a high-frequency switch to generate a pulsating DC signal.
•  The high voltage DC signal is stepped down when passed through the transformer and converted into the allowable DC signal level.
•  The reduced DC signal undergoes rectification and filtration to achieve a stable, constant DC output voltage.
•  Finally, the control circuitry supervises the output voltage and dynamically adjusts the high-frequency switch to maintain a consistent output stream of the desired voltage.

SMPS Circuit Board Topologies

As was previously mentioned, switching mode power supplies (SMPSs) may change the DC/AC input voltage into a different DC output voltage based on the circuit configuration. A switch mode power supply’s (SMPS) topology categorizes the many SMPS circuit configurations. Non-isolated switch mode power supplies (SMPS) and isolated switch mode power supplies (SMPS) are the two most general types of SMPS.

1. Non-isolated converters: Their input and output are present in the same circuit. Buck, Boost, and Buck-Boost are the most common examples. No device separates the output from the switching circuit in these switch-mode power supplies. Inductors are energy storage components in these circuits.

2. Isolated converters: The input and output circuits are separated. Forward Converter and Flyback Converters are the most common. A transformer separates the input switch from the output in these SMPS. In these, the SMPS transformer stores energy in its secondary winding.

• Buck Converter 

A buck converter (SMPS) functions by reducing the high input voltage to produce a lower output value.

When the switch is turned on, current flows through the inductor L, storing energy in its magnetic field. The flow of current is shown in green in the circuit. When the switch is turned off, the inductor releases this stored energy, which is then transferred to the output capacitor and load. During this time, the diode allows current to flow through it in a loop. The flow of current is shown red in the circuit. This cycle repeats continuously, allowing the buck converter to regulate the output voltage.

• Boost Converter 

This type of SMPS steps up the input voltage to a higher output voltage.

Using a boost converter, a switch-mode power supply (SMPS) may increase the input voltage to a higher output voltage. When the switch is activated, current passes into the inductor, which is stored as magnetic energy before being returned to the input supply. The green arrows show the current flow when the switch is on. The energy stored in the inductor is discharged when the switch is switched off and transmitted to the output capacitor and load. As a forward bias, the diode prevents current from reversing direction and returning to the power supply. The red arrows show the current flow when the switch is off. 

• Buck-Boost Converter

This SMPS may either boost or drop the output voltage depending on the input voltage. It combines the features of a buck converter and a boost converter into a single device. 

When the switch is turned on, current flows through the inductor, storing energy in its magnetic field, as the green arrows show. When the switch is turned off, the inductor releases this stored energy, which is then transferred to the output capacitor and load, as red arrows show. During this time, the diode blocks current from flowing back to the input voltage source. The buck-boost converter can regulate the output voltage by adjusting the duty cycle of the switch, which changes the amount of energy stored in the inductor during each cycle.

• Flyback Converter

This type of SMPS uses a transformer to step up or down the input voltage to a different output voltage by using two isolated circuits.

When the switch is turned on, current flows through the primary winding of the transformer, storing energy in its magnetic field. The current is also induced in secondary winding but in opposite direction, as shown by green arrows.

When the switch is turned off, the energy stored in the magnetic field is transferred to the secondary winding of the transformer, which then supplies the output voltage and current to the load. During this time, the diode D allows current to flow through it in a loop. The red arrows show the current flow when switch is off. The flyback converter can regulate the output voltage by adjusting the duty cycle of the switch, which changes the amount of energy stored in the transformer during each cycle.

• Forward Converter

This type of SMPS also uses a transformer to step up or down the input voltage to a different output voltage but uses an inductor.

Figure 8 Forward Converter Circuit Diagram

When the switch turns on, it allows current flow in the transformer’s primary winding L1. Secondary winding will also experience voltage induction due to the current flow. Because of the secondary winding’s opposite polarity, the diode, D, is biased in the opposite direction given in the green arrows. The charge is stored in a capacitor which later provides power to load. 

When the switch is turned off, no current flows through the transformer’s primary winding during the low input pulse. The secondary winding now begins to discharge energy and change its polarity. Current can pass through the diode is forward bias, as red arrows show. This allows power to the load to continue while the capacitor is being charged.

An overall comparison of the advantages and disadvantages of SMPS isolated and non-isolated converters is given in the table.

SMPS advantages over Linear Power Supplies

Switch-mode power supplies (SMPS) are known to be more complex than linear regulated power supplies, as they have several advantages. 

One of the main benefits of SMPS is its efficiency, which is due to the use of high switching frequencies. This allows for much smaller magnetic and filtering components. This makes SMPS designs much more compact and lightweight. 

On the other hand, linear power supplies rely on a main transformer and a dissipative serial regulator. This results in large and heavy 50/60 Hz transformers and lower power conversion efficiencies, making them less desirable in specific applications. An overall comparison of the main features of SMPS and Linear PS is given below:

Design Considerations for SMPS PCB Board

Designing an SMPS circuit board requires careful consideration of various factors to ensure reliable and efficient operation. Here are some design considerations to consider when designing SMPC PCB board.

• Placement of components, routing of traces, and placement of vias should be followed for SMPS PCB layout. The layout must be optimized to minimize the length and impedance of the high-current paths to reduce losses and minimize EMI (Electromagnetic Interference).
• The sense line should connect directly to the sensor to reduce the error introduced by resistance. This connection is known as the Kelvin connection.
• The current loops are as small as possible and minimize the impedance of the ground plane to reduce ground bounce in SMPS PCB layouts.
• The IPC (Association Connecting Electronics Industries) guidelines for PCB design and manufacturing should be followed to meet the necessary quality standards.
• Using thermal management techniques while designing, such as using thermal vias, heat sinks, and keeping high-current traces short, can help dissipate heat and ensure reliable operation.

Applications of SMPS Circuit Board

Due to their efficiency, switching-mode power supply (SMPS) circuit boards have a wide range of applications in modern electronics.

Consumer Electronics: SMPS circuit boards may be found in many devices, including smartphones, laptops, TVs, and stereos. The job of SMPS PCB board is to power these devices reliably and efficiently with little energy waste and heat production.

Industrial Equipment: Power reliability is crucial for industrial equipment, including robots, CNC machines, and motor controllers. SMPS circuit boards’ excellent efficiency and sizeable current capacity make them a common choice for these uses.

Renewable Energy Systems: SMPS PCB boards are widely applied in renewable energy systems like solar and wind generators. A dependable and efficient power supply is essential for these systems, as is the ability to transform DC power from renewable energy sources into AC power compatible with the grid.

SMPS Circuit Board Common Issues and Solutions

SMPS circuit boards can experience issues that can affect their performance and reliability. Some common issues that can arise with SMPS circuit boards are:

1. Overheating: SMPS circuit boards can produce heat when high-frequency currents are switched. The prolonged exposure to heat may gradually affect the components on the board, which could result in performance problems and eventual malfunction. Incorporating appropriate cooling and thermal management methods like heat sinks, fans, or temperature sensors can help to address this problem.
2. Electromagnetic Interference (EMI): It sometimes occurs due to the high-frequency noise generated by SMPS circuit boards, which could potentially affect other electronic devices. One could reduce this by using shielding and filtering techniques, such as ferrite beads or capacitors.
3. Component failures occur due to various factors such as heat, voltage spikes, or aging of electronic components over time. Components such as capacitors, diodes, and transistors may sometimes experience failures. Regular inspection and testing can help find and replace faulty parts before they cause a breakdown.
4. Design issues: Poor filtering, insufficient component selection, and sloppy layout are just a few examples of how SMPS circuit boards may go wrong. These design flaws can cause inefficient operation, unwanted sound, and even component failure. Guidelines should be followed to avoid this issue.
5. Voltage Surges: Instability in the output voltage affects the functionality or damages devices plugged into it. Pulse-width modulation (PWM) and voltage feedback are two examples of feedback control techniques that may be used to help ensure steady voltage regulation.

Troubleshooting SMPS Circuit Boards

Understanding the circuitry of SMPS boards and their usual failure mechanisms is essential for troubleshooting them. Specific troubleshooting equipment is required for each problem faced in SMPS circuit boards.

• Troubleshooting SMPS circuit boards requires a multi-meter, which is a must-have instrument. Voltage, current, and resistance all can be measured using it.
• Oscilloscope can inspect circuits and identify issues based on waveform analysis.
• A soldering iron is required to repair the SMPS circuit board and replace any defective components.
• A desoldering pump is used to remove malfunctioning components from the SMPS board.
• A power supply tester verifies that the SMPS circuit board delivers the specified voltage and current at its output.

Conclusion

Switched-mode power supply (SMPS) circuit boards have become crucial in contemporary electronics, offering a dependable and steady power source. Their remarkable efficiency and adaptability have led to significant advancements in power electronics. In the SMPS circuit board technology field, the future is anticipated to prioritize compact and high-performance designs in response to the growing need for state-of-the-art technology. Regarding electronic devices, it is crucial to prioritize the quality and reliability of the SMPS circuit boards. Staying up-to-date with the latest trends and advancements in SMPS circuit board design and technology is highly recommended.