International Radiation Detectors, Inc.

BT-250 Bias Tee

When measuring energy of light pulses with the SXUV/UVG series photodiodes, it is recommended that a reverse bias be used. These photodiodes will saturate for pulse energies greater than 10 µJ/cm² if used without bias. Applying a reverse bias will raise the saturation threshold to higher levels. The BT-250 is a low noise bias insertion tee with a DC blocking capacitor that was designed specifically for use with the SXUV/UVG series photodiodes. The BT-250 is rated for up to 250V applied bias and an optional BT-500 is available with voltage rating up to 500 V.

The BT-250 has 3 ports that should be connected with BNC cables to an oscilloscope, DC power supply and photodiode. The BT-250 can be connected to a common ground with a banana plug. Be sure the detector is reversed biased. To check if the detector is reverse biased, slowly increase the bias voltage and verify that the current is not rapidly increasing. If it is, switch the polarity on the power supply. (Note: the detector may be damaged by a forward bias.) The amount of bias should not exceed the breakdown voltage of the detector.

It is estimated that the measured output of the BT-250 is approximately 5% less than the actual output of the diode due to the loss in the bias tee.