Power supply measurement tips (Part 1): Component selection and characteristic analysis-EEWORLD

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The first step in any power supply design is to select components. A good power supply design is inseparable from power components and control chips. Considering all the options, choosing the right power components for the optimal design can be a bit cumbersome. Narrowing down the scope and finding the right components is tedious in itself. The product data sheets of various manufacturers provide first-hand information about the functions of components, but they cannot guarantee optimal operation in a given design. Before locking in the design, it is necessary to analyze the characteristics of the selected components in a specific application, which can significantly save time and reduce problems.

Certain key power components, such as MOSFETs and IGBTs, should be selected based on key parameters such as rated voltage and current, turn-on time and turn-off time, input and output capacitance, on-state resistance, and off-state characteristics.

Perhaps one of the most important details in a vendor's datasheet is the safe operating area (SOA) plot. Steps should be taken to understand this behavior at different voltage and current parameters. The problem is that most SOA plots provided by vendors do not provide a complete picture because they are only valid at 25°C. Relying solely on this data can introduce significant risks to implementation and design, especially thermal design. Component characteristics must be analyzed in real-world environments where power components are rarely kept below ideal ambient temperatures.

Without a prototype at this stage of the design, it is difficult to simulate the expected rated current and voltage. The best way to solve this problem is to use a source measure unit, which can drive tens of amps of current and generate a voltage that can be measured. This helps to obtain the actual IV characteristics for the application. The same equipment can be used to measure small differences in on-state characteristics, such as gate threshold voltage, gain, and on-resistance. Similarly, for low-current off-state measurements, such as leakage current, an instrument can be used to source a high voltage to generate a current that can be measured.

For breakdown voltage, make sure you are applying a voltage that is several times the device operating voltage in order to measure the breakdown voltage. When measuring device capacitance versus voltage on a simple two-terminal device or a more complex three or four-terminal transistor, be sure to use a capacitance measurement system that is capable of testing the entire range of the device's DC operating voltage. Note that a traditional LCR meter will tell you the capacitance, but not over the entire operating voltage.

Keithley source measure units can be used as four instruments in one: voltage/current source, voltage/current meter, swept analyzer, function generator, providing a perfect solution for this type of test. The source meter also includes programmable loads that can measure IV characteristics on components from a few µV to 3KV, from a few fA to 100A. A great add-on is the IVy app, which can be downloaded from Google Play for Android smartphones or tablets, and allows you to seamlessly perform voltage-voltage (IV) characteristic analysis on components.

The IVy app can be downloaded free of charge from Google Play for Android devices and makes it easy to check IV characteristics on components. Here is a link to a webinar where our experts present how to analyze and verify the performance of power semiconductors.

Once you’ve chosen your components and designed a prototype, you need to power it up. In the next post in this series, we’ll look at power-up testing of low-voltage DC circuits and provide a variety of tips to ensure you can accurately assess the performance of your design.

Reference address：Power supply measurement tips (Part 1): Component selection and characteristic analysis

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