A circuit for passive charge integration is presented. The circuit is combined with a device to suppress the noninformative part of the signal from the light-pulse detector, which is based on an SNFT3 photomultiplier tube. The charge integration time varies from units of nanoseconds to units of microseconds. The device to suppress noninformative part of the signal consists of two switches based on a 2T312B transistor and OU103B optocoupler. It enables one to reduce the sensitivity of the photomultiplier by a factor of 10(4) for greater-than-or-equal-to 500 musec after the informative part of the signal has passed through.