JPS54162950A - Current driving circuit - Google Patents

Abstract

PURPOSE:To obtain a current driving circuit which features a high-speed switching and can correspond even to the signal of the minute pulse duration by securing an isolation between the constant current source for capacitor charging use and that for switching use and then setting a higher current value to the latter than the former. CONSTITUTION:For charging of capacitor 7, the constant current source is divided 1a for switching and 1b for charging each. And these current sources supply currents i1 and i0 (i1>>i0). As a result, the current flowing to charge control transistor Tr13 is increased with the switching speed accelerated. Also, collector potential Va at the OFF-time of Tr13 is set lower than capacitor voltage Vc by voltage drop 0.7V of diode 33. Thus, the switching necessary time needs just a fixed time required for increment of 0.7V, and the switching time dispersion caused by the output level is never caused. As a result, the current corresponding to the pulse duration can be well driven even with an extremely fine pusle signal. The discharge is performed by controlling Tr14 and 15 via signal S2 and then flowing the current to constant current source 6.