GB889026A - Improvements in or relating to voltage regulators - Google Patents

Abstract

889,026. Automatic voltage-control systems. MINNEAPOLIS - HONEYWELL REGULATOR CO. Feb. 13, 1958 [Feb. 14, 1957], No. 4764/58. Class 38 (4). The output voltage of a self-excited D.C. generator for use on a motor vehicle (or, it is stated, an A.C. generator and rectifier) is stabilized, and the output current limited, by control of a bi-stable pair of transistors, one of which has the field winding as the collector load. The generator 10 supplies a battery 17 and an external load through a main rectifier 23 which replaces the conventional cut-out. The generator field 11, shunted by a rectifier 47 to reduce switching surges, forms the collector load of a transistor 26. The base of transistor 26 is directly coupled to the collector of a control transistor 27 and the two are cross-connected by a resistor 67 shunted by a capacitor 71 to form a bi-stable pair. The base of transistor 27 is connected through a Zener diode 77 to a point on a potential divider across the output terminals-the potential divider consisting of the resistors 75, 73 and the low impedance of a normally conductive transistor 30. When the portion of the output voltage tapped off the potential divider exceeds the break-down voltage of the Zener diode 77, the base of transistor 27 becomes more negative, and the resulting emitter/collector current cuts off the transistor 26. The non-linearity of the diode 43 included in the emitter circuit of the transistor 26 ensures that the transistor is cut off.. The resulting fall in output voltage reverses the above action, causing the transistor 26 to again become fully conducting and the cycle repeats. Current limiting is effected by controlling the transistor 30 in accordance with the voltage drop across a resistor 21 carrying the load current, so that as the load current increases, the transistor 30 passes less current and the regulating point of the potential divider 73, 75, 30 is lowered. Conversely, the voltage drop across the main rectifier 23 is applied via a diode 96 to the emitter of transistor 27 to increase the output voltage to compensate for the drop across the rectifier. The base of transistor 27 is also biased via a diode 91 to ensure that it is cut-off when the generator is building up. In a modification, Fig. 2 (not shown), the load current measuring resistor 21 is omitted, and the voltage drop across the rectifier 23 is applied to the emitter of the transistor 30 (now connected in a common base circuit) to adjust the regulating point of the voltage measuring circuit, which is slightly re-arranged. In a further modification, Fig. 3 (not shown), the current control transistor 30 is omitted, and a portion of the voltage drop across the rectifier 23 is applied directly to the base of transistor 27. The diode 43 in the emitter circuit of transistor 26 is replaced by a biasing potentiometer.