High-frequency time-ratio control with insulated and isolated inputs

Fast-responding amplifiers are needed in many industrial and defense systems. Systems using power amplifiers with one to 1000 watts of output dc power require high performance. The requirements often include high efficiency, light weight, compactness, high reliability, economy, and simplicity, along with fast response and insulated multiple inputs. These performances are required in applications such as controls for high-power inverters and converters, motors, generators, light, heat, dc-to-ac inverters, power supplies, servo systems, etc. This paper presents a transistor-magnetic power amplifier with multiple insulated and isolated inputs (Fig. 1) with characteristics in Fig. 2. The technique of time-ratio control [1] is used to provide light weight, compactness, high efficiency, and high reliability. High-speed power transistors (0.1 μs) combined with a tunnel diode circuit permit high chopping frequency (50 kc). The base current of the power transistor is switched in-less than 0.02 μs. Insulated and isolated inputs are provided by a small saturable transformer the size of a TO-5 transistor case. Transistor inputs are used on the saturable transformer. Germanium power transistors (such as 2N1907) are used to provide economy, but silicon transistors can be used for applications at high ambient temperature. The circuit of Fig. 1 is used to fire controlled rectifiers for inverters and converters. A pulse transformer in series with a resistor replaces the load of Fig. 1 when needed in firing circuits. A simple time-ratio control (TRC) circuit is presented that controls the output [Fig. 2(a)] by varying the chopping frequency from 50 kc to 5 kc. The multiple inputs are illustrated. A constant frequency (50 kc) TRC is presented that controls load voltage from zero to the supply voltage [Fig. 2(b)]. The output responds to the control signal in 40 μs. The tunnel diode switching circuit is also presented.