GB1602977A - Voltage regulators - Google Patents

Description

(54) VOLTAGE REGULATORS (71) I, JOHN WILLIAM HERBERT FREE MAN, a British Subject of, 10 Westwood Grove, Solihull, West Midlands, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a voltage regulator for use with a generator having a field winding.

According to the invention a voltage regulator in accordance therewith comprises:- a. a first transistor connected in series with the field winding; b. a first biasing circuit normally rendering the first transistor conductive, c. a second transistor connected with its emitter collector circuit across output terminals of the generator, d. a second biasing circuit comprising a potential divider resistive branch connected between the output terminals, and a voltage sensitive device connected between the tapping point on the potential divider and the base of the second transistor and rendering the latter non-conductive for output voltages of the generator below a predetermined low value, e. connections between the first and second transistors of a configuration to render the second transistor non-conducting when the first transistor is conducting and the first transistor non-conducting when the second transistor is conducting, and including a first feed-back branch containing resistive and capacitive elements in series with each other and connecting the emitter collector circuit of the first transistor to the second biasing circuit to that side of the voltage sensitive device which is connected to said tapping point, and a second feed-back branch containing a capacitive element and connecting the emitter collector circuit of second transistor to said side of the voltage sensitive device.

The invention will now be described, by way of example, with reference to the accompanying drawings wherein:- FIGURE 1 shows the circuit diagram of a known type of voltage regulator; FIGURE 2 is a circuit diagram of an embodiment of the present invention.

The voltage regulator circuit is intended primarily for use with generators in the form of alternators as commonly employed for maintaining the state of charge of chargeable batteries on motor vehicles, although the invention is not limited to generators used for this purpose. Further, the invention is of primary application with voltage regulator circuits to generators in the form of alternators.

Referring to Figure 1, a generator in the form of an alternator ALT serves to charge a battery B.

The alternator has a field winding F, the current through which is controlled by transistor T3 connected as a Darlington pair with transistor T2 and which are rendered conductive by connection of the base of T2 through resistor R6 to the positive rail.

When the output of the alternator is low (insufficient to charge the battery), the voltage between the positive and negative rails is insufficient to apply a break down voltage across zener diode D1, and a second bias circuit R1, R2, R3, D1 and R4 remains in a condition to hold the base of transistor T 1 at or near the level of the negative rail and this transistor remains non-conducting.

As the voltage rises, however, the break down voltage of D1 is exceeded, T1 conducts causing the base voltage of T2 to fall thereby cutting off T2 and T3. This in turn causes the field current through F to be cut off, a feedback signal is fed through feed-back network C2, R5 to the base of transistor Tl, and causes this to be cut off thereby re-establishing conduction of transistors T2 and T3.

Oscillation thus occurs and the ratio of the "on" periods ofT 1 to the "on" periods of T2 and T3 is determined by the position of the slider of resistance R2 (which determines the voltage applied across zener diode D1), and also by the instantaneous speed of and load upon the generator.

When the alternator is generating power there is a ripple voltage at the output terminals and a proportion of this tends to be applied to the base of T 1 via the feed-back network C2, R5. Such a ripple voltage may cause transistor Tl to conduct prematurely thus cutting off transistors T2 and T3. Thus the ratio of charging to non-charging during a cycle of oscillation is reduced thereby impairing the efficiency of the charging operation.

In the voltage regulator of the invention of which one embodiment is shown in Figure 2, components already described are designated by like references. In this circuit, however, the feed-back network C2, R5 is connected between the emitter collector circuit of transistor T3 and the second biasing circuit at a point of connection between R2 and zener diode D2.

Any feed-back of ripple voltage merely produces division of the ripple current respectively through R 1 and the upper part of R2 on the one hand, and R3 and the lower part of R2 on the other hand. The ripple voltage is, therefore, reduced and this reduced ripple voltage, in order to cause undesirable early switching of transistor T1, must now overcome the input characteristics of not only the transistor T 1 but also the zener diode Dl The regulator is thus more stable particularly when charging operations are at a state to which oscillation of the regulating circuit commences, the tendency for premature cutoff of transistor T3 by early switching of transistor T1 is either avoided or reduced to such an extent as to be insignificant.

The capacitor C1 in Figure 1, connected between the emitter collector circuit and the base circuit of transistor T1, serves the purpose of minimising radio interference.

A further feature of the invention, as shown in the embodiment of Figure 2, is that this capacitor Cl is now connected between the emitter collector circuit of transistor TI and the point of connection of the feed-back circuit between R2 and Dl. With this configuration it serves also to assist suppression of current spikes which may occur in the zener diode under the threshold conditions just below the point of conduction of transistor T 1. If desired a further capacitor, of a value which is small compared with that of C2, may be connected between the collector of T3 and the junction of R2 and Dl.

The invention is especially useful where the battery B 1 has become discharged and it is desirable to recharge the battery as quickly as possible. Appreciable loads may be present across the battery, for example vehicle lamps, and rear window demister, and recharging is important when such loads are present.

A further advantage of the circuit shown in Figure 2 is that if either of the capacitors Cl or C2 are faulty or become faulty in a manner such that current can leak through from one "plate" to the other, the small change in the current through the feed-back circuit or through capacitor Cl is very small compared with the current flowing through resistors R1, R2 and R3.Thus the functioning of the regulator will be affected by only a negligible amount whereas the circuit shown in Figure 1, if provided with a slight increase in feed-back current, would tend to cause premature switching of transistor Tl and could, in a case where the leakage through the capacitor was sufficiently bad, cause total inoperation of the circuit by maintaining transistor T1 in an "on" condition.

WHAT I CLAIM IS: 1. A voltage regulator for use with a generator having a field winding and comprising a circuit including:- a. a first transistor connected in series with the field winding, b. a first biasing circuit normally rendering the first transistor conductive, c. a second transistor connected with its emitter collector circuit across output terminals of the generator, d. a second biasing circuit comprising a potential divider resistive branch connected between the output terminals, and a voltage sensitive device connected between a tapping point on the potential divider and the base of the second transistor and rendering the latter non-conductive for output voltages of the generator below a predetermined low value, e. connections between the first and second transistors of a configuration to render the second transistor non-conducting when the first transistor is conducting and the first transistor non-conducting when the second transistor is conducting, and including a first feed-back branch containing resistive and capacitive elements in series with each other and connecting the emitter collector circuit of the first transistor to the second biasing circuit to that side of the voltage sensitive device which is connected to said tapping point, and a second feed-back branch containing a capacitive element and connecting the emitter collector of second transistor to said side of the voltage sensitive device.

2. A voltage regulator according to claim 1 wherein the circuit a third branch containing a capacitive element, a capacitor connected between the emitter collector circuit of the first transistor and said side of the voltage sensitive device.

3. A voltage regulator substantially as herein described with reference to and as shown in Figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. network C2, R5. Such a ripple voltage may cause transistor Tl to conduct prematurely thus cutting off transistors T2 and T3. Thus the ratio of charging to non-charging during a cycle of oscillation is reduced thereby impairing the efficiency of the charging operation. In the voltage regulator of the invention of which one embodiment is shown in Figure 2, components already described are designated by like references. In this circuit, however, the feed-back network C2, R5 is connected between the emitter collector circuit of transistor T3 and the second biasing circuit at a point of connection between R2 and zener diode D2. Any feed-back of ripple voltage merely produces division of the ripple current respectively through R 1 and the upper part of R2 on the one hand, and R3 and the lower part of R2 on the other hand. The ripple voltage is, therefore, reduced and this reduced ripple voltage, in order to cause undesirable early switching of transistor T1, must now overcome the input characteristics of not only the transistor T 1 but also the zener diode Dl The regulator is thus more stable particularly when charging operations are at a state to which oscillation of the regulating circuit commences, the tendency for premature cutoff of transistor T3 by early switching of transistor T1 is either avoided or reduced to such an extent as to be insignificant. The capacitor C1 in Figure 1, connected between the emitter collector circuit and the base circuit of transistor T1, serves the purpose of minimising radio interference. A further feature of the invention, as shown in the embodiment of Figure 2, is that this capacitor Cl is now connected between the emitter collector circuit of transistor TI and the point of connection of the feed-back circuit between R2 and Dl. With this configuration it serves also to assist suppression of current spikes which may occur in the zener diode under the threshold conditions just below the point of conduction of transistor T 1. If desired a further capacitor, of a value which is small compared with that of C2, may be connected between the collector of T3 and the junction of R2 and Dl. The invention is especially useful where the battery B 1 has become discharged and it is desirable to recharge the battery as quickly as possible. Appreciable loads may be present across the battery, for example vehicle lamps, and rear window demister, and recharging is important when such loads are present. A further advantage of the circuit shown in Figure 2 is that if either of the capacitors Cl or C2 are faulty or become faulty in a manner such that current can leak through from one "plate" to the other, the small change in the current through the feed-back circuit or through capacitor Cl is very small compared with the current flowing through resistors R1, R2 and R3.Thus the functioning of the regulator will be affected by only a negligible amount whereas the circuit shown in Figure 1, if provided with a slight increase in feed-back current, would tend to cause premature switching of transistor Tl and could, in a case where the leakage through the capacitor was sufficiently bad, cause total inoperation of the circuit by maintaining transistor T1 in an "on" condition. WHAT I CLAIM IS:

1. A voltage regulator for use with a generator having a field winding and comprising a circuit including:- a. a first transistor connected in series with the field winding, b. a first biasing circuit normally rendering the first transistor conductive, c. a second transistor connected with its emitter collector circuit across output terminals of the generator, d. a second biasing circuit comprising a potential divider resistive branch connected between the output terminals, and a voltage sensitive device connected between a tapping point on the potential divider and the base of the second transistor and rendering the latter non-conductive for output voltages of the generator below a predetermined low value, e. connections between the first and second transistors of a configuration to render the second transistor non-conducting when the first transistor is conducting and the first transistor non-conducting when the second transistor is conducting, and including a first feed-back branch containing resistive and capacitive elements in series with each other and connecting the emitter collector circuit of the first transistor to the second biasing circuit to that side of the voltage sensitive device which is connected to said tapping point, and a second feed-back branch containing a capacitive element and connecting the emitter collector of second transistor to said side of the voltage sensitive device.

2. A voltage regulator according to claim 1 wherein the circuit a third branch containing a capacitive element, a capacitor connected between the emitter collector circuit of the first transistor and said side of the voltage sensitive device.

3. A voltage regulator substantially as herein described with reference to and as shown in Figure 2 of the accompanying drawings.