Method and steps for testing switching power supply using a digital oscilloscope
Oscilloscope and power supply measurement
For those accustomed to using an oscilloscope for high-bandwidth measurements, power measurement may be simple because its frequency is relatively low. In fact, there are also many challenges that high-speed circuit designers never have to face in power measurement.
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 all vary. It is necessary to capture and analyze the waveform truthfully and detect any abnormalities in the waveform. The requirements for oscilloscopes are demanding. Multiple probes - simultaneously requiring single ended probes, differential probes, and current probes. 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 significant amplitude differences in one acquisition.
Fundamentals of Switching Power Supply
The mainstream DC power supply architecture in most modern systems is a switching power supply (SMPS), which is well-known for its ability to effectively cope with changing loads. The electrical 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 device also has a control part, which includes components such as pulse width modulation regulator, pulse frequency modulation regulator, and feedback loop 1. The control section may have its own power supply. Figure 1 is a simplified schematic diagram of a switching power supply, which shows the power conversion part, including active devices, passive devices, 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 a short switching time and can withstand unstable voltage spikes. Equally important, they consume very little energy in both open and closed states, with high efficiency and low heat generation. Switching devices largely determine the overall performance of switching power supplies. The main measurements of switching devices include: switching loss, average power loss, safe working area, and others.
