【Iprober 520 Current Probe】Evaluation Report (Part 3) Practical Circuit Application

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【Iprober 520 Current Probe】Evaluation Report (Part 3) Practical Circuit Application [Copy link]

This test content: For a circuit board in the laboratory, try to test the switch tube current, cooperate with the voltage probe to obtain the switching loss waveform, and summarize the usage experience.

1. Test content

The current passing through the MOSFET in a switching power supply is measured as follows.

The drain and source trace width of the MOSFET in the PCB board is 3mm . First, adjust the sensitivity of the Iprober 520 current probe so that the peak-to-peak value of the corrected AC power output is 3V , as shown below.

Then measure the drain-source current of the MOSFET as follows

The blue one is the PWM signal, the switching frequency is 20k , and the duty cycle is 0.93 . The green one is the measurement of the inductor current by A622 , which is used as a reference for the MOSFET trace current. The orange one is the current measured by the Iprober 520 current probe. Theoretically, the current measured by the Iprober 520 current probe only measures the circuit corresponding to the high duty cycle. There is no current at the low duty cycle because the MOSFET is turned off.

The test for the other route is as follows:

As can be seen from the two figures, the Iprober 520 current probe can reflect the changing trend of the MOSFET drain-source circuit, that is, the inductor current. The inductor current flows when the switch is turned on and becomes 0 when it is turned off . Compared with the inductor current measured by A622 , the current value is slightly lower. In the first figure, it seems to be interfered by the switching noise.

In general, the current waveform (orange) obtained by the Iprober 520 current probe when measuring the MOSFET drain-source current at a switching frequency of 20kHz has low noise and fast response, and the current change trend of the drain-source current at the switching moment can be clearly seen. More importantly, the current is obtained without the use of clamp accessories. After calibration, the measurement is completed by simply placing the probe in the center of the 3mm PCB trace. This provides great convenience for many pure PCB board-level current tests.

2. User experience and a major drawback

In general, through the previous review post and this review post, as a current probe, I think it basically achieves the performance of nominal 5MHz and 6mA noise and 10A range. It can be said that for its price range of 5,000 yuan, such performance is already competitive.

On this basis, the probe also comes with a PCB trace measurement function. By placing the probe directly on the trace, it is possible to measure the current of PCB traces with a line width of less than 6.5mm . It is full of gimmicks and a sense of futuristic technology. However, from our actual experience, this function is not just a pie in the sky, but a real function.

However, there were many minor problems in our experience, which can be summarized as quality control. The evaluation team received a total of three trial samples, and one of them was broken; the laboratory received the goods and began to evaluate in the first week. According to the test instructions, the AC current test was performed on the 2.5mm PCB trace, and it was found that the AC current reading was directly 30% smaller ; in the second week, it was tested on the laboratory DC/DC board, and it was found that no matter whether it was the conductor or PCB trace measurement mode, whether or not the clamp accessories were added, the measured current DC bias would change significantly with the change of probe position or rotation, and the positive and negative deviations were about 0.1A .

I plan to contact the supplier to see if I can get a better probe. The current probe has too many deviation and offset problems, so I dare not use it directly.