Structure design of high pressure differential probe

High voltage differential probe means that a pair of signals are input into the amplification circuit at the same time , And then subtract , Get the original signal , Differential amplifier is an amplifier composed of two transistors with the same parameter characteristics and directly coupled , If the signals with the same size and phase are input on the two input terminals respectively , The output is zero , So as to overcome the zero drift . The differential probe is used to measure the voltage difference between two test points that are not grounded , Available for up to 6000V The signal of , Due to its common mode rejection capability , Become a non-earth reference in larger parts 、 Choice of floating or isolated measurements , Any two points can be floating connected to the signal , Convert the signal to ground , To supply oscilloscope 、 Electric meter 、 Or computer use , A lot of circuits , Especially the motor circuit , It contains DC or AC compensation or even no ground circuit , At this time, rash use of the oscilloscope will cause electric shock , Or damage the oscilloscope , Or cause the wire to go off , At this time, only the differential probe is a better choice .

One of the common differential probes is for low-voltage signals , This differential signal is common in high-speed digital circuits , The common amplitude of the measured voltage of this kind of differential probe is ±8V, The bandwidth is generally at 1GHz above ; The other is for high voltage measurement , Measure the voltage up to KV, This kind of differential signal is common in the measurement of switching power supply , This kind of differential probe is called high-pressure differential probe , The measured voltage is generally at KV Level , Bandwidth in 20MHz—100MHz Common within the scope .

The differential probe is mainly used to measure the floating system , In the test of power supply system, it is often required to measure the live wire and live wire in the three-phase power supply , Or FireWire and zero （ in ） The relative voltage difference of the line , Many users directly use a single ended probe to measure two-point voltage , The probe is often burnt out . This is because ： Most oscilloscopes “ Signal common line ” The terminal is connected to the protective grounding system , Usually called “ Grounding ”.

The result is ： All applied to the oscilloscope , And the signals provided by the oscilloscope have a common connection point . The common connection point is usually the oscilloscope shell through the use of the third wire in the power line of the AC power supply equipment , Connect the probe ground wire to a test point . If a single ended probe is used to measure , Then the ground wire of the single ended probe is directly connected with the power supply line , The result must be a short circuit . In this case , We need a differential probe for floating measurement .