The High Voltage Protection Boards for the RICH Detectors of the LHCb Experiment

We present the protection system for the monitoring circuitry of the 20 kV high-voltage bias for the Hybrid Photon Detectors of the Ring Imaging Cherenkov detectors of the LHCb experiment. The protection system buffers the voltage lines, attenuated by about 12700 V/V in normal operating conditions, and limits the output voltage excursion to the ADCs of the monitoring system to a safe range (between -2.5 V and +5 V) in case of discharge. The circuit has been designed and tested to be radiation tolerant under the expected working conditions of LHCb. Results show that the protection boards are fully adequate for the whole LHCb lifetime.