Bulk is used to protect the photodiodes from damage. A safety package containing the photodiodes is provided for their protection. When the photodiodes are reverse-biased, the voltage should never exceed 40V. A photodiode has a pin number of 2. There was the possibility that photodiodes in a circuit would emit 150mW heat. The reverse anode voltage for the photodiodes should be 40V. In order for a photodiode to pass current, you need a voltage of 800mV. During reverse-bias operation, the photodiodes were able to supply voltages of 40V. The current in a photodiode is 1nA even when there is no light input.