Power Delivery + Sliding Mode Control Flashcards
Losses in Switching mode power supply
1) Conduction Losses
2) Switching Losses
3) Magnetic core Losses
4) Copper/Resistance Losses
5) Dielectric Losses
6) Electromagnetic Radiation Losses (EMI)
7) Gate Drive Losses
8) Control/Regulation Losses
9) Parasitic Losses
10) Heat sink Losses
11) Thermal Losses
Copper Losses
- Specifically refer to the power dissipation due to the resistance of copper conductors (wires, traces, and interconnections within the SMPS)
- Occur when current flows through these conductive elements and the resistance of the copper material causes a voltage drop
- Results in power being converted into heat.
- Sometimes called “I²R losses” because they are proportional to the square of the current (I) and the resistance (R) of the copper conductors.
Conduction Losses
- Conduction losses are a broad category of losses
- Result of limited conductance (non-zero resistance) and the current flowing through those conducting elements
- includes the losses in conducting elements within the SMPS:
- Copper Losses (Losses in traces, wires, connectors, etc)
- Forward voltage losses (Losses in diodes)
- Switching Losses (Losses in transistors)
- Turn-on Losses
- Turn-off Losses
Thermal Losses
- “Thermal losses” is a generalized category of losses
- Refers to the TOTAL power dissipation in the SMPS that results in heat generation (irrespective of the source)
- Includes anything that leads to heat generation in the device:
- conduction losses
- copper losses
- Forward voltage losses
- switching losses
- Turn-on Losses
- Turn-off Losses
- core losses in magnetic components
- dielectric losses in capacitors
- conduction losses
Switching Losses
Switching losses occur when the active semiconductor devices (transistors) switch between their on-state (conducting) and off-state (non-conducting). These losses result from the finite time it takes for the transistor to transition from one state to another and are primarily associated with high-frequency operation. There are two main components of switching losses:
Turn-off Switching Losses
These occur when the transistor turns off. During this transition, the voltage across the transistor increases from a lower level to the supply voltage, which again leads to power dissipation. The energy stored in the inductance of the circuit and parasitic capacitances is released, causing losses.
Turn-on Switching Losses
These occur when the transistor turns on. During this transition, the voltage across the transistor drops from the supply voltage to a lower level, causing power dissipation. The energy stored in the parasitic capacitances of the transistor is discharged, resulting in losses.
Ten Advantages of using SMPS over Linear regulators
1) Higher Efficiency: SMPS are generally more efficient than linear regulators. Linear regulators dissipate excess energy as heat, resulting in lower efficiency, especially when there is a significant voltage drop between the input and output. In contrast, SMPS can achieve much higher efficiency by switching the input voltage on and off rapidly, thereby minimizing heat dissipation.
2) Wider Input Voltage Range: SMPS can handle a broader range of input voltages without a significant drop in efficiency. This makes SMPS more versatile and suitable for a wider range of input voltages, which is particularly valuable in applications with variable input sources.
3) Smaller Size and Weight: SMPS are typically more compact and lighter than linear regulators with similar power ratings. The smaller form factor is especially advantageous in applications where space is limited or where portability is essential.
4) Reduced Heat Generation: Because of their higher efficiency, SMPS generate less heat compared to linear regulators for the same power output. This can simplify thermal management and reduce the need for additional heat sinks or cooling mechanisms.
5) Lower Energy Consumption: SMPS are more energy-efficient, making them a better choice for battery-powered or energy-conscious devices and systems. They can extend the battery life in such applications.
6) Better Voltage Regulation: SMPS can provide excellent voltage regulation, often with tight tolerances. They are less affected by input voltage fluctuations and variations compared to linear regulators.
7) Higher Power Output: SMPS can deliver higher power output for a given input voltage and current, making them suitable for high-power applications where linear regulators may not be feasible.
8) Isolation Capability: Many SMPS designs can provide electrical isolation between the input and output, which can be essential in applications where safety and protection against voltage spikes are necessary.
9) Customization and Optimization: SMPS designs can be tailored to specific requirements, allowing for optimization of performance, efficiency, and other characteristics.
10) Reduced Heat Dissipation: With their improved efficiency, SMPS generate less heat during operation. This is advantageous in applications where excess heat can be a concern, such as in enclosed environments or when power dissipation needs to be minimized.
Ten Advantages of using Linear Regulators over SMPS
1) Simplicity and Low Noise: Linear regulators are inherently simpler in design and generate less electromagnetic interference (EMI) compared to SMPS. They produce a smoother and quieter output voltage, which can be crucial in applications sensitive to voltage ripple or noise.
2) Minimal Output Voltage Variability: Linear regulators provide excellent output voltage stability and regulation, making them suitable for applications where a stable voltage is critical, such as analog circuitry or precision instrumentation.
3) Low Output Voltage Drop: Linear regulators have minimal voltage drop between the input and output. This is advantageous when the input voltage is only slightly higher than the desired output voltage, as there is very little power dissipation.
4) Low Quiescent Current: Linear regulators typically have low quiescent (idle) current consumption, making them suitable for battery-powered devices that require efficient standby modes.
5) No High-Frequency Switching Noise: Linear regulators do not produce high-frequency switching noise or “switching losses” associated with SMPS, making them well-suited for applications that require a clean power supply.
6) Lower Cost for Low Power Applications: For low-power applications, linear regulators can be more cost-effective because the components required are relatively simple and inexpensive compared to SMPS.
7) Ease of Design: Designing with linear regulators is generally simpler and requires fewer external components than SMPS. This can result in quicker development times and lower design complexity.
8) Linear Behavior: Linear regulators exhibit a linear relationship between input and output, making them predictable and easier to work with in some applications.
9) No Electromagnetic Interference (EMI) Issues: Linear regulators do not generate EMI, which can simplify electromagnetic compatibility (EMC) testing and reduce the need for additional filtering components.
10) Low Output Voltage Noise: Linear regulators have lower output voltage noise compared to some SMPS designs, which is important in sensitive analog or audio applications.
Efficiency Calculation
Efficiency (%) = (Output Power)/(Input Power)*100
Where:
Efficiency (%) is the efficiency of the SMPS expressed as a percentage.
Output Power is the power delivered to the load (usually measured in watts) and is calculated as the output voltage multiplied by the output current.
Input Power is the power consumed from the input source (usually measured in watts) and is calculated as the input voltage multiplied by the input current.
Efficiency in SMPS
Efficiency is a critical parameter in SMPS design and evaluation, as it reflects how well the power supply minimizes losses (such as conduction losses, switching losses, and other types of losses) and converts electrical energy from the input source into useful output power. Higher efficiency indicates that the SMPS is better at converting input power into output power and is typically desired to reduce energy consumption and heat generation in various applications.
It’s important to note that the efficiency of an SMPS can vary with the load and input voltage. Therefore, it’s common to calculate efficiency at different load and input voltage conditions to assess the SMPS’s performance over a range of operating conditions.
Efficiency Factors in a SMPS
1) Load Current: Efficiency can vary with the load current. SMPS designs are typically most efficient at specific load levels, and efficiency may decrease at very light or very heavy loads. Selecting the right SMPS design for the expected load range is essential.
2) Input Voltage: The efficiency can also vary with the input voltage. SMPS designs often have an input voltage range within which they operate most efficiently. Efficiency may decrease when operating near the extremes of the input voltage range.
3) Switching Frequency: The switching frequency used in the SMPS design can impact efficiency. Higher switching frequencies can reduce the size of passive components but may lead to increased switching losses. Lower frequencies reduce switching losses but may require larger components.
4) Components: The quality of components used in the SMPS can impact efficiency. Higher-quality components often have lower losses and better performance. The choice of components, such as high-efficiency diodes, low-loss capacitors, and magnetic components with low core losses, plays a significant role in overall SMPS efficiency.
5) Control Circuitry: The control and regulation circuitry of the SMPS should be designed for efficiency. Efficient control algorithms and feedback mechanisms help maintain stable output voltage while minimizing power losses.
6) Topology: The choice of SMPS topology (e.g., buck, boost, buck-boost, flyback, forward, etc.) can affect efficiency. Each topology has its own strengths and weaknesses, and selecting the right one for a specific application is important.
7) Operating Conditions: Environmental factors such as temperature, humidity, and altitude can affect SMPS efficiency. Operating within specified environmental limits is important for optimal performance.
8) PCB Considerations: The layout and design of the SMPS circuit, including proper grounding, component placement, and the use of filtering and shielding techniques, can influence efficiency.
9) Electromagnetic Compatibility (EMC): Proper design for electromagnetic compatibility can prevent radiated and conducted interference that may lead to energy losses.
Component Selection Criteria for a SMPS
1) Component Material and Quality: Choose high-quality components from reputable manufacturers. Reliable components with known performance characteristics are essential for long-term reliability. The choice of material used in components can significantly impact efficiency. For example, inductors and transformers with high-quality magnetic core materials have lower core losses, resulting in improved efficiency. Similarly, capacitors with low equivalent series resistance (ESR) and equivalent series inductance (ESL) are more efficient.
2) Component Tolerances: Components with tighter tolerances can lead to better accuracy and performance, contributing to higher efficiency. For example, using resistors, capacitors, and inductors with precise values can help reduce errors and improve efficiency.
3) Operating Temperature: Determine the expected operating temperature range for your SMPS. Select components that can operate reliably within this temperature range without significant performance degradation. The temperature at which components operate can affect their efficiency. Some components may exhibit improved efficiency when operated within a specific temperature range. Thermal management is essential to maintain efficiency in high-temperature environments.
4) Reliability and Lifespan: Ensure that selected components have the necessary reliability and lifespan for your application, considering factors like MTBF (Mean Time Between Failures). Over time, the performance of some components may degrade, affecting their efficiency. For example, electrolytic capacitors may experience increased ESR as they age, leading to reduced efficiency. Regular maintenance or component replacement can mitigate this issue.
5) Frequency and Voltage Range: Some components may be optimized for a specific frequency or voltage range. Deviating from these specifications can lead to efficiency losses. Careful selection of components suitable for the desired operating conditions is important.
6) Component Interactions: Ensure that the selected components are compatible with each other and with the overall SMPS design. The interaction between different components within the SMPS circuit can affect efficiency. Component selection and design should consider how different elements work together to minimize losses and improve overall performance.
7) Component Packaging and Mounting: The way components are packaged and mounted on the circuit board can influence their thermal performance, parasitic effects, and overall efficiency. Proper design and layout considerations are crucial. Consider size and form factor constraints in your design. Smaller and compact components may be necessary for space-constrained applications, while larger components might be suitable for higher-power applications.
8) Coil and Wire Resistance: The resistance of the coil or wire used in inductors or transformer windings can impact efficiency. Lower resistance materials and techniques, such as using thicker wires or litz wire, can reduce losses.
9) Inductor and Transformer Characteristics (Core Saturation): Specify inductance values, saturation current ratings, and core materials for inductors and transformers. Ensure that these components can handle the required current levels without core saturation. Magnetic components like transformers and inductors can experience core saturation at high currents or voltages, leading to efficiency degradation. Selecting components with appropriate saturation characteristics is important.
10) Capacitor Type, Material, and Voltage Rating: Choose the appropriate type of capacitors (e.g., ceramic, electrolytic, tantalum, film) based on the specific requirements of your design. Ensure that the selected capacitors have adequate voltage ratings for the application. The type of dielectric material used in capacitors also affects efficiency. Different dielectric materials have varying characteristics, and some are better suited for high-frequency applications with lower losses.
11) Diode Recovery Time: In applications that use diodes for rectification, the diode’s recovery time can impact efficiency. Fast-recovery diodes or Schottky diodes are often chosen to minimize recovery time and conduction losses.
12) Switching Transistor Characteristics: Select appropriate transistors (e.g., MOSFETs or IGBTs) for the switching elements. Consider factors such as on-resistance (Rds(on), voltage ratings, and switching speed. Transistors, such as MOSFETs and IGBTs, have different characteristics that can influence efficiency, including on-resistance (Rds(on), voltage ratings, and switching speed.
13) Parasitic Capacitance and Inductance: Parasitic capacitance and inductance of components can also affect efficiency. Minimizing these parasitics is important to maintain high efficiency.
14) Operating Frequency: Determine the required operating frequency for your SMPS. This choice will impact the selection of components such as inductors, capacitors, and transistors. High-frequency SMPS designs require components with lower parasitic elements, while low-frequency designs may require larger components.
15) Input and Output Voltage Range: Define the input voltage range and the required output voltage for your SMPS. The voltage range will determine the selection of components such as voltage regulators, inductors, and capacitors.
16) Output Power and Current: Determine the maximum output power and current your SMPS must deliver. This information will help in choosing components with the appropriate current and power handling capabilities.
17) Efficiency: Set efficiency targets based on your application requirements. Efficient components, such as low ESR capacitors and low Rds(on) transistors, should be selected to minimize power losses.
18) Ripple and Noise Requirements: Identify the allowable output voltage ripple and noise levels. Select capacitors, inductors, and output filters that can meet these specifications.
19) Component Tolerances: Consider the tolerances of critical components like resistors, capacitors, and inductors. Tighter tolerances may be necessary for applications requiring high precision.
20) Compliance with Standards: Ensure that components meet relevant safety and compliance standards for your application, especially if it’s for a regulated or safety-critical environment. This often includes EMC standards
21) Output Filter Selection: Determine the type and values of output filter components (inductors and capacitors) required to meet output voltage and noise specifications.
22) Protection Features: Some components offer built-in protection features, such as over-temperature protection or over-current protection. Consider whether these features are necessary for your application.
23) Cost and Availability: Assess the cost and availability of components. It’s essential to balance performance requirements with budget constraints and ensure that components are readily available from suppliers.
24) EMI Considerations: Components should be selected with consideration for electromagnetic interference (EMI) and electromagnetic compatibility (EMC) requirements. EMI filters and shielding may be necessary.
13 steps in Selecting the Optimal Load Current for a SMPS
Step 1) Understand the Application Requirements:
Start by thoroughly understanding the requirements of your application. Consider the desired output voltage, power consumption, and any voltage or current constraints.
Step 2) Estimate the Maximum Load Current:
Determine the maximum load current your SMPS must support. This value is typically the highest current that the application will draw during normal operation.
Step 3) Consider Peak and Transient Loads:
Account for peak or transient loads that the application may experience. These short-duration surges in current may occur during startup, sudden load changes, or other dynamic conditions. Ensure that the SMPS can handle these variations.
Step 4) Safety Margin:
It’s advisable to include a safety margin when specifying the load current. A safety margin ensures that the SMPS operates comfortably within its rated specifications, reducing the risk of overheating or component stress. A common practice is to use a safety margin of 10-20% above the estimated maximum load current.
Step 5) Review Efficiency Requirements:
Determine the efficiency requirements for your SMPS. In some cases, improving efficiency may involve operating the SMPS at a specific load level. Consider the relationship between efficiency and load current when selecting the optimal load.
Step 6) Select SMPS Specifications:
With the load current in mind, select an SMPS that can provide the required output voltage and power at the specified load. Check the SMPS’s datasheet and specifications to ensure it can handle the load current and operating conditions.
Step 7) Component Suitability:
Ensure that the components within the SMPS, such as transistors, inductors, and capacitors, are rated to handle the selected load current without exceeding their limitations. Pay attention to factors like current ratings, thermal characteristics, and voltage ratings.
Step 8) Dynamic Load Response:
Evaluate the SMPS’s ability to respond to dynamic load changes. If your application experiences rapid changes in load current, consider the transient response and stability of the SMPS under these conditions.
Step 9) Test and Validation:
Verify your load current selection through testing and validation. Measure the actual load current under various operating conditions to ensure it aligns with your expectations.
Step 10) Long-Term Considerations:
Consider the long-term reliability of your SMPS under continuous operation at the selected load current. Components and materials should be chosen with an eye on durability and expected lifespan.
Step 11) Efficiency Optimization:
If energy efficiency is a critical factor, you may need to perform efficiency analysis at different load levels and optimize the load current to achieve the best overall efficiency.
Step 12) Regulatory and Safety Compliance:
Ensure that the chosen load current complies with relevant regulatory and safety standards for your application. Some industries and applications have specific requirements for load profiles.
Step 13) Environmental Considerations:
Take into account the environmental conditions in which the SMPS will operate, as temperature and altitude can influence component performance and load current requirements.
13 Steps for finding the optimum voltage range for a SMPS
1) Understand Application Requirements:
Start by thoroughly understanding the voltage requirements of your application. Identify the desired output voltage and any constraints or limits on the input voltage.
2) Determine Output Voltage Requirements:
Define the required output voltage of the SMPS. This voltage level should meet the needs of the connected load or device. Consider the load’s voltage tolerance and any specific voltage standards applicable to your application.
3) Account for Voltage Drops:
Consider any voltage drops that may occur in your system due to factors like transmission losses in wires or cables. Ensure that the output voltage of the SMPS, when accounting for these losses, still meets the load’s voltage requirements.
4) Allow for Tolerances:
Take into account component tolerances and variations. Some components, such as voltage regulators or voltage references, may have tolerances that can affect the output voltage. Ensure that your selected components can meet the specified output voltage within acceptable tolerances.
5) Safety Margin:
Include a safety margin to provide some buffer for voltage variations. This margin helps ensure that the SMPS operates reliably even under less-than-ideal conditions. The safety margin typically ranges from 5% to 10% above the minimum required voltage.
6) Consider Input Voltage Variations:
Analyze the input voltage conditions the SMPS will experience. If the input voltage can vary due to factors like fluctuations in the power source, select a voltage range that accommodates these variations.
7) Peak Voltage and Transients:
Account for peak voltage and transient conditions. In some applications, you may need to consider short-duration voltage spikes or transients that the SMPS must handle without damage.
8) Efficiency and Design Requirements:
Consider the impact of voltage range on efficiency. Some SMPS designs may be more efficient within specific voltage ranges. Ensure that your selected voltage range aligns with efficiency and design constraints.
9) Protection Circuits:
If the SMPS includes overvoltage or undervoltage protection circuits, ensure that the voltage range accommodates these features without unnecessary triggering.
10) Regulatory and Safety Compliance:
Ensure that the chosen voltage range complies with relevant regulatory and safety standards for your application. Some industries and applications have specific requirements for voltage tolerances and ranges.
11) Component Suitability:
Verify that the components used in the SMPS, such as voltage regulators and input filters, can operate within the selected voltage range without exceeding their limitations.
12) Environmental Conditions:
Consider the environmental conditions in which the SMPS will operate, as temperature and altitude can affect component performance and voltage range requirements.
13) Validation and Testing:
Confirm the selected voltage range through testing and validation. Measure the actual input voltage under various operating conditions to ensure it remains within the specified range.
