Knowledge
Advantages of high-voltage differential probes and limitations of passive probes
Using high-voltage differential probes is a routine task for power electronics engineers, but there are many differences between their use and that of standard passive probes. Choosing the correct measurement method is key to ensuring both safety and accuracy.
1. Three Methods for High-Voltage Power Supply Measurement
- Floating Ground Measurement Method
Directly float the oscilloscope’s ground lead to measure high-voltage signals.
This approach is neither safe nor accurate. Due to the parasitic capacitance between the oscilloscope casing and ground, it can easily cause signal ringing, leading to severe
waveform distortion, and is not recommended for practical use.
2. AB pseudo-differential method
Use two passive probes to measure the voltage of two points relative to ground separately, and then use the oscilloscope's math function to subtract and obtain the differential value.
Although relatively safe, avoiding the danger of direct grounding short circuits, the measurement accuracy is relatively poor. Due to the delay and gain inconsistencies
between the two channels, the system's common-mode rejection capability is weak, and the results are easily affected by common-mode noise, making it unsuitable for
high-precision scenarios.
3. High-voltage differential probe measurement method
A specialized high-voltage differential probe is used to directly measure the voltage difference between two points.
This is currently the safest and most accurate method. The probe has built-in high-voltage isolation and a high common-mode rejection ratio design, allowing direct
measurement of signals with high voltage to ground. It is also suitable for differential systems that are not grounded together (such as CAN buses), preventing the risk
of short circuits caused by improper grounding.
4. High-Voltage Differential Probe
High-voltage differential probes use a differential input mode and are mainly used in situations that require high-voltage floating measurements. This high-performance
high-voltage differential probe features audible and visual alarms, a 5 MHz bandwidth limit function option, and better common-mode noise suppression capability.
Its bandwidth reaches up to 100 MHz. The input terminal has high input impedance and low input capacitance, allowing accurate and high-speed measurement of differential
voltage signals, meeting the needs of most testing systems.
