LeCroy HVFO103 High Voltage Fiber Optically-Isolated Probes

• 60 MHz bandwidth
• Common-mode (safety) voltage virtually unlimited (optical isolation)
• Superior Noise and Rejection
• 140 dB CMRR
• Low loop inductance
• Low attenuation

The HVFO is an affordable, optimally designed probe for measurement of small signals floating on an HV bus in power electronics designs or for EMC, EFT, ESD, and RF immunity testing sensor monitoring. It far surpasses the measurement capabilities and signal fidelity of both conventional HV differential probes and acquisition systems that rely on galvanic high voltage isolation. Furthermore, it mitigates the need to rely on dangerous test setups that require floating the oscilloscope and probe.

The HVFO provides capability to measure your signal as it truly is, in-circuit, without compromise. Upper-side gate drive signals will be faithfully reproduced without loading and distortion or mysterious ringing, overshoots and transients, providing a clear view of the Miller effect on the gate drive signal. AC and DC sensor signals floating at a high voltage or in the presence of EMC, EFT, ESD, and RF disturbance signals can be acquired with high signal fidelity and correctly correlated to in-circuit and control activities.

The HVFO architecture is simple - a single laser and fiber optic cable is used for optical isolation and modulated signal + data communication, and multiple tips achieve different operating voltage ranges. Optical isolation between the probe tip and the oscilloscope input reduces adverse loading of the DUT, provides faithful pulse response, and increases confidence in the measurement. Safety against dangerous high voltage levels can be ensured and unsafe “floating” of the oscilloscope can be avoided High CMRR (>100 dB) provides more accurate representation of the measured signal despite the presence of high dV/dt or dA/dt events elsewhere in the circuit. The test lead is optimized to limit loop inductance and radiated pickup. Tip attenuations are optimized for a wide range of signal amplitudes. The HVFO103 is small enough to fit in tight spaces, provides just enough performance for real-world needs, and is affordable enough to fit the tightest of equipment budgets.
  The HVFO is ideal for measuring low voltage (1 to 40V) signals floating on a HV bus, such as in-circuit upper-side gate drive signals and low voltage control, sensor, or sense resistor signals. The probe is also suitable for EMC immunity testing in which a device operation must be monitored in the presence of disturbance signals.

Upper-side Gate Drive Voltage Measurement

 

Upper-side Gate Drive Voltage Measurment Graph 1 ×	Upper-side Gate Drive Voltage Measurment Graph 2 ×
The HVFO (yellow trace) and a conventional HV differential probe (blue trace) capture an upper-side gate drive signal. The HVFO exhibits a classic, textbook shape while the HV differential probe has more loading and lower-side device high dV/dt signal interference.	In this upper-side gate drive measurement, the gate drive is captured when current is sinking into the half-bridge phase in a cascaded H-bridge. The Miller effect can be clearly observed.

Floating Control or Sensor Signal Measurements

The HVFO measures only the low voltage sensor voltage across its high impedance input leads. Total load on the device under test (DUT) is very small. Furthermore, the low lead loop inductance, >100dB CMRR, and low attenuation provide superior signal fidelity, noise and rejection.

Floating Control or Sensor Signal Measurements Diagram 1 ×	Floating Control or Sensor Signal Measurements Diagram 2 ×
The HVFO measures only the small signal voltage with high probe input impedance; therefore, total DUT load is very small. Low tip loop inductance and >100 dB CMRR provide superior signal fidelity, noise and rejection.	The HV differential probe measures the full common mode + sensor voltage. Therefore, the DUT load is ~100 times larger than with the HVFO. This excessive load will impact the signal fidelity and may even cause the circuit to malfunction.