Introduction to the method of using digital oscilloscope to test switching power supply
Oscilloscope and power measurement
For those accustomed to using oscilloscopes for high bandwidth measurements, power measurement may be simple due to its relatively low frequency. In fact, there are many challenges in power measurement that high-speed circuit designers never have to face.
The voltage of the entire switchgear may be high and 'floating', meaning it is not grounded. The pulse width, period, frequency, and duty cycle of the signal will vary. It is necessary to accurately capture and analyze the waveform, and detect any anomalies in the waveform. The requirements for this oscilloscope are strict. Multiple probes - requiring single ended probes, differential probes, and current probes simultaneously. The instrument must have a large memory to provide recording space for long-term low-frequency acquisition results. And it may require capturing different signals with significantly different amplitudes in one acquisition.
Fundamentals of Switching Power Supply
The mainstream DC power supply architecture in most modern systems is switch mode power supply (switch mode power supply), which is well-known for its ability to effectively cope with changing loads. The power signal path of a typical switching power supply includes passive components, active components, and magnetic components. Switching power supplies should minimize the use of lossy components such as resistors and linear transistors, and mainly use (ideally) lossless components such as switching transistors, capacitors, and magnetic components.
The switching power supply equipment also has a control part, which includes components such as pulse width modulation regulator, pulse frequency modulation regulator, and feedback loop 1. The control part may have its own power supply. Figure 1 is a simplified schematic diagram of a switching power supply, showing the electrical energy conversion section, including active components, passive components, and magnetic components.
Switching power supply technology uses power semiconductor switching devices such as metal oxide field-effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs). These devices have short switching times and can withstand unstable voltage spikes. Equally important is that they consume very little energy, with high efficiency and low heat generation, whether in the open or closed state. Switching devices largely determine the overall performance of switching power supplies. The main measurements of switching devices include: switching losses, average power losses, safe working area, and others.
