THE PRINCIPLES OF CONSTRUCTING VOLTAGE-CONTROLLED ELECTRONIC CURRENT SOURCES

Abstract

The basic principles of construction of voltage controlled current sources (VCCS) on op- erational amplifiers (OA) are described. The schemes of VCCS designed for ungrounded and grounded loads are considered. The VCCS for ungrounded loads are the simplest in the scheme realization and basically use the following property of OA: in inverting and non-inverting am- plifiers the current flows through the negative feedback and it is independent of the resistance of this circuit, to which the load is switched. In doing so, it is preferable to use a non-inverting amplifier, since in this case, the conversion coefficient of VCCS does not depend on the inter- nal resistance of the control signal source. The VCCS for ground loads are more perfect, the load in them has a grounded clamp common with the control voltage source grounded clamp. All of them are based on the use of the Howland current source circuit. A distinctive feature of this scheme is the presence of an additional positive feedback circuit. The compensation of the current change in the load while its resistance changes is carried out through this circuit, how- ever, this happens under specified ratios of resistors. The method of determining the mathemat- ical models of all VCCS reviewed is considered, by the analysis of which their quality is eval- uated. The influence of the resistance variation of the resistors used and the imperfection of the OА on the VCCS scheme operation has been studied. The main characteristics of the best cir- cuit solutions of VCCS are given.