Tips for Choosing Online Engineering Calculators and Design Tools for Power Supplies

Author : By Mark Patrick, Mouser Electronics

01 August 2023

Figure 1: Alternating current from wall outlet
Figure 1: Alternating current from wall outlet

Every electronic system needs a power supply to convert the available power (AC or DC) to the type and voltage required. This blog looks at a range of tools for selecting and designing power supplies.

Types of power converter
Power converters can be categorised as unregulated or regulated. 

Figure 2: Full wave rectified
Figure 2: Full wave rectified

An unregulated supply relies on a transformer to reduce AC input to the desired voltage. If necessary, this is rectified to DC and a capacitor is used to smooth the output to produce an approximately constant voltage. Some power is dissipated in the transformer, so efficiency will not be optimal.

Table 1: Advantages and disadvantages of unregulated supplies

Advantages          Disadvantages
Simple                 Efficiency
Robust                 Designed for specific input and output voltages
                               Residual ripple        
                               No noise filtering
                               Voltage varies with changes in both the input supply and the output loading

Figure 3: Full wave rectified (with capacitor included)
Figure 3: Full wave rectified (with capacitor included)

Some systems are sensitive to variations in supply voltage and will require a regulated supply. This uses an electronic circuit to provide a more accurate and stable output. It can also implement other functions - such as variable output or protection from excessive current.

Voltage regulators can be used within a system to provide the supply voltages required by different subsystems. Regulated supplies can be further divided into linear and switched mode.

Linear regulators
A linear voltage regulator (see Figure 4) can be added to an unregulated supply. A pass transistor acts as a variable resistor to control the output voltage, correcting any changes caused by variations in supply voltage or output load. This transistor always dissipates some power.

Figure 4: Block diagram of simple linear regulator
Figure 4: Block diagram of simple linear regulator

Switched-mode regulators
In a switched-mode power supply, a pass transistor rapidly switches the input voltage on and off. The proportion of time that the transistor is on controls how much charge is transferred and, therefore, the output voltage. This eliminates the need for a transformer. Because the pass transistor is either fully conducting or completely switched off, it dissipates very little power. Consequently, switched-mode regulators are very efficient.

Table:2: Comparison of linear and switched-mode regulators

Figure 5: Coilcraft (Source: Coilcraft)
Figure 5: Coilcraft (Source: Coilcraft)

                                                 Advantages                                 Disadvantages
Linear                                      Simple and reliable                         Low efficiency
                                                 Low residual ripple                         Large /heavy
                                                 Low noise                                      Can require large heatsinks
                                                 Good line and load regulation      More expensive
Switched mode                     Small size/lightweight                    More complex circuitry
                                                 Wide input voltage range              Radiate electrical noise
                                                High efficiency (> 80%)
                                                Low cost

Power supply parameters
Typical parameters for specifying a power supply are:

1.Physical form factor: Standalone unit or component to be integrated into a circuit 
2.Input voltage type (AC or DC) and range
3.Output voltage and current range
5.Acceptable level of ripple or noise
6.Stability of the output for variations in load and input

Figure 6: EE-Sim Solution Finder (Source: Analog Devices)
Figure 6: EE-Sim Solution Finder (Source: Analog Devices)

Using these requirements, you can decide if an unregulated, linear, or switched-mode power supply is most appropriate and start the design process.

Power supply selection, design and simulation tools

Design tools for power supplies allow you to choose components and design a circuit around them. Simulation tools can be used to evaluate the performance of the circuit. These will report factors such as efficiency, ripple, and transient response. The design can be exported in various forms including, in many cases, a complete bill of materials (BoM).

CoilCraft (Figure 5) is a supplier of magnetic components. They have a set of online tools to help design and optimise your power supply design by choosing the most appropriate transformers and inductors. You can use these to identify the best components for a given reference design.

Figure 7: onsemi WebDesigner+ Power Supply design tool (Source: onsemi)
Figure 7: onsemi WebDesigner+ Power Supply design tool (Source: onsemi)

They also have links to simulation tools from the semiconductor companies that provide relevant power supply components. 

Analog Devices 
Analog Devices have a suite of Windows-based tools for designing power systems and circuits. LTpowerCAD is a DC-DC power supply design and simulation tool that provides recommendations for component values and performance estimates specific to your application. The final design can be exported to LTspice® for further simulation.

Figure 8: STMicroelectronics Power Supply Design Tool (Source: STMicroelectronics)
Figure 8: STMicroelectronics Power Supply Design Tool (Source: STMicroelectronics)

The EE-Sim Solution Finder (Figure 6) is an online selection tool for switch-mode power converters. You can find devices based on input and output voltage and other features. The selected device can then be used in the EE-Sim® DC-DC Converter Tool to generate a complete design. Finally, you can simulate the design to ensure it meets your requirements. 

The WebDesigner+ Power Supply design tool (Figure 7) helps you select the best onsemi products and create a design for your application. You can select ICs, MOSFETs, and diodes using comprehensive filters to design AC/DC and DC/DC converters. The tool will model your design to generate reports of circuit behaviour.
STMicrolectronics (Figure 8) has a set of tools for power supply design. Its Power Supply Design Tool supports the development of DC/DC and AC/DC supplies plus supporting circuitry for solar-powered battery chargers. Based on input and output voltages, you can select components for a switched-mode design.

Texas Instruments
The TI WEBENCH Power Designer (Figure 9) creates customised power supply circuits based on your requirements. You can create a design with AC or DC input up to 500V.

Figure 9: Texas Instruments WEBENCH Power Designer (Source: Texas Instruments)
Figure 9: Texas Instruments WEBENCH Power Designer (Source: Texas Instruments)

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