Dimensions
Length: 12.8mm
Width: 5.8mm
Height: 7.5mm (excludes 3mm for terminals)
Arm length: 13.0mm
Features
â—† Small compact Size, high reliability
â—†Mainly used for computer mouse, car mouse, automobile electronic products, communications equipment, military product, test instrument, and general electric and wireless devices, 24 hours timer, etc.
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â—† Micro contact gap,high speed operation,high sensitivity,Micro operatizon travel.
â—† Long life & high reliability
â—† Wide Range of wiring Terminals, Variety of Levers
Analysis of the Influence of Time Offset on Measurement Results in Switching Loss Measurement
The power loss of switching devices plays a crucial role in evaluating their performance, and it is considered an advanced feature in many oscilloscopes. Although many laboratories are equipped with the necessary infrastructure for power loss measurements, the equipment and probes can be costly. However, if the time offset between channels is not properly accounted for, all test results may become unreliable or even misleading.
When measuring switching losses, one channel is typically used to capture voltage, while another measures current. The software then multiplies these two signals to obtain the power waveform, and finally integrates the area under the curve over the relevant time interval to calculate the total energy loss.
Two key factors must be taken into consideration during this process: first, ensuring that the oscilloscope and probes have sufficient bandwidth to accurately capture the fast transient waveforms during turn-on and turn-off events. Second, maintaining precise phase alignment between the voltage and current signals to ensure accurate integration.
While bandwidth is a relatively straightforward concept, ensuring the correct phase relationship between the two signals is more complex. Time offsets between the voltage and current channels can significantly affect the accuracy of the measurement, especially when dealing with high-speed switching devices.
The impact of time offset on the measurement results is significant. If there is a delay between the two channels, the calculated power loss will either be higher or lower than the actual value. The faster the switching speed, the more pronounced this error becomes. Figure 1 illustrates the effect of such an offset on the measurement of MOSFET turn-off loss. As shown, accurate results can only be obtained after proper correction. It's important to note that time offsets are common due to differences in probe design and variations in cable lengths.
To address this issue, an offset correction fixture can be used. As illustrated in Figure 2, this device helps eliminate the time delay between the voltage and current probes. The principle involves generating synchronized pulse signals on both channels and measuring the delay introduced by the probes. This allows the oscilloscope to compensate for any time difference. The fixture is USB-powered and easy to use, offering both manual and automatic correction options.
Figures 3 and 4 show the waveforms before and after correction, highlighting the importance of this step. In addition to correcting the internal offset, it’s also essential to consider the effects of extension cables. For example, when using a current clamp, the signal often needs to be routed through an extension cable, which introduces additional delay. A typical setup is shown in Figure 5.
The delay caused by extension cables can be calculated based on the material and length of the cable. For instance, a copper cable introduces approximately 33.5 ps/cm of delay. If the cable is 100 cm long, the delay would be about 3.35 ns. After using the offset correction fixture, the current channel should be adjusted to lead the voltage channel by this amount to maintain accurate timing.
In conclusion, when measuring the switching loss of high-speed devices with an oscilloscope, it's essential to not only ensure accurate voltage and current waveforms but also to account for any time delays between the channels. These delays, introduced by probes and extension cables, can cause significant errors in the final result. Therefore, always use an offset correction fixture to ensure precise power loss calculations.