GB2084358A

GB2084358A - Improvements in or Relating to Battery Charging Systems

Info

Publication number: GB2084358A
Application number: GB8128850A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1980-09-25
Filing date: 1981-09-24
Publication date: 1982-04-07
Also published as: FR2490890B1; JPS57116552A; GB2084358B; DE3036092A1; FR2490890A1

Abstract

A battery charging system having a permanent-magnet energized generator (11) in which the voltage is regulated by a series regulator (26a) or a parallel regulator (26b, Fig. 2) or by a combination of the two types of regulators (Fig. 3), and in which the regulators are constituted by MOSFET's. Such a battery charging system is particularly suitable for use in motor vehicles. <IMAGE>

Description

SPECIFICATION Improvements In or Relating to Battery Charging Systems The present invention relates to battery charging systems.

In battery charging systems having a permanent magnet energized generator voltage regulation can be effected in several ways. One way is that of providing a series regulator having a main current switching path connected in a series circuit, and another way is that of providing a parallel regulator having a main current switching path connected in a parallel circuit; yet another way is to provide both a series regulator and a parallel regulator. If such a system is operated without a battery, high voltage peaks which occur during switching of loads connected to the system can cause trouble.

According to the present invention there is provided a battery charging system having a permanent-magnet energized generator and a voltage regulator connected to the direct current power output of the generator, in which the voltage regulator comprises a control stage and a MOSFET controlled by the control stage, one terminal of the switching path of the MOSFET being connected to the direct current power output of the generator and the other terminal of the switching path being connected either to a connection terminal of the battery or to a common connection between the generator and the battery.

In one embodiment of the invention the switching path of the MOSFET is located in a connection lead between said direct current power output of the generator and said connection terminal of the battery, and the voltage regulator further comprises a circuit arrangement for increasing the terminal voltage of the battery and the control terminal of the MOSFET is connected to the output of said circuit arrangement.

In another embodiment of the invention the switching path of the MOSFET is connected in parallel with the direct current power output of the generator. A decoupling diode is preferably incorporated in a connection lead between the direct current power output of the generator and said connection terminal of the battery.

In a further embodiment of the invention the voltage regulator comprises a control stage and two MOSFETs which are controlled by the control stage, and the switching path of one of said MOSFETs is located in a connection lead between said direct current power output of the generator and said connection terminal of the battery, and the switching path of the other of said MOSFETs is connected in parallel with the direct current power output of the generator.

Battery charging systems embodying the present invention can have the advantage that there is only a small loss of power and that only a small amount of control power is required.

Voltage peaks occurring upon switching off loads in a system without a battery can be stabilized and isolated from the system. Moreover special switching devices for over-voltage protection are not required. A plurality of MOSFETs can readily be connected in parallel to meet the power requirements of the system without the control circuit having to be modified and without requiring additional load balancing devices.The invention will be further described by way of example with reference to the accompanying drawings in which: Fig. is a circuit diagram of a battery charging system according to a first embodiment of the invention with a series regulator, Fig. 2 is a circuit diagram of a battery charging system according to a second embodiment of the invention with a parallel regulator, and Fig. 3 is a circuit diagram of a battery charging system according to a third embodiment of the invention with both series and parallel regulators.

The circuit diagram of Fig. 1 shows a permanent-magnet energized three-phase generator 11 to the output of which is connected a three-phase bridge rectifier 12. The output power for the following electrical system is available at the direct current power output .13.

The direct current power output 13 is connected to the terminal B+ of a battery 14 by way of a lead 1 5. Loads 1 7 are connected to the battery connection terminal B+ by way of a switch 16.

The battery charging system also includes a voltage regulator 1 8. Like the recitifier 12, the battery 14 and the loads 17, the voltage regulator is also connected to the earth connection 1 9 by way of a lead. Voltage is supplied to the regulator 18 by way of a voltage supply lead 21 which is in turn connected to the connection lead 1 5 by way of a control switch 22.

The voltage regulator 1 8 includes a control stage 23 of conventional construction, and an indicator stage 24 which indicates the charging operations by way of a charging pilot lamp 25 in a known manner. An essential component of the voltage regulator 1 8 is a MOSFET metal oxide semi-conductor field effect transistor 26a disposed in the connection lead 1 5. The drain terminal D of the MOSFET 26a is connected to the direct current power output 1 3 of the generator, and the source terminal S of the MOSFET 26a is connected to the battery connection terminal B+. The substrate lis connected to the source terminal S. A circuit arrangement 27 for increasing the voltage is connected to the output of the control stage 23.

The output of the circuit arrangement 27 is connected to the gate terminal G of the MOSFET 26a. Finally, the voltage regulator 18 also includes a voltage limiting device 28 which is connected to the direct current power output 13 of the generator 11. Instead of a single MOSFET 26a, a plurality of MOSFETs can be connected in parallel with the connection lead 1 5 according to the maximum current flowing in the lead 1 5.

The blocking voltage of the switching path D S (drain to source) of the MOSFET 26a must exceed the maximum output voltage occurring during switching. The voltage limiting device 28 is not essential for suppressing the voltage peaks caused by the current inductance of the generator 11, although it is advantageous, and can be realized by, for example, a Zener diode.

Advantageously, the control stage 23 obtains its control voltage from the battery connection terminal B+. The control stage 23 need only supply a very low control power and can thus be an IC circuit or a hybrid circuit having a corresponding control IC. The circuit arrangement 27 for increasing the voltage is required in the case of a series regulator owing to the fact that a control voltage of approximately 10 V is required between the gate terminal G and the source terminal S of the MOSFET for the purpose of triggering the latter.

By actuating the control switch 22, the battery voltage is applied by way of the voltage supply lead 21 to the control stage 23 and to the circuit arrangement 27 for increasing the voltage. The control stage 23 controls the MOSFET 26a into its conductive state when the voltage of the electrical system on the battery connection terminal B+ lies below the prescribed regulating voltage. Current commences to flow to the battery 14 by way of the connection lead 15 when the generator 11 is in operation and has exceeded its starting speed. When the voltage of the electrical system on the battery connnection terminal B+ then exceeds the regulating voltage, the control stage 23 renders the MOSFET 26a non-conductive by way of the circuit arrangement 27 and thus isolates the generator 11 from the battery 14.The voltage across the switching path D-S of the MOSFET 26a can be superimposed by a voltage peak caused by the current inductance of the generator 11. The voltage peak of this kind can be clamped by the voltagelimiting circuit 28 on the drain terminal D of the MOSFET 26a.

Fig. 2 shows a battery charging system having a parallel regulator. Components which are the same as those illustrated in Fig. 1 are provided with the same reference numerals. In this embodiment, the output of the control stage 23 is connected to the gate terminal G of a MOSFET 26b whose switching path D-S is connected in parallel with the direct current power output 13, 19 of the generator and earth 19. In this embodiment also, a plurality of MOSFETs 26b can be connected in parallel as required. In this embodiment, and in contrast to the first embodiment, the blocking voltage of the switching path D-S of the MOSFET 26b must only exceed the maximum occurring voltage of the electrical system, that is to say, the output voltage of the generator 11 at the terminal 1 3.A circuit arrangement for increasing the terminal voltage of the battery 14 is not required in this embodiment, since, by virtue of the terminal voltage of the battery 14, a potential of adequate magnitude relative to earth is available. Here also, the voltage regulator 23 can be an IC circuit or a hybrid circuit having a control IC. In this second embodiment, a decoupling diode 29 must be provided to decouple the switching path D-S from the battery 14.

In this second embodiment also, the electrical system is protected against over-voltages when the system is operated without a battery 14 and a load 1 7 is switched off, without requiring additional switching devices.

The supply voltage is applied to the regulator 1 8 when the control switch 22 is actuated. The switching path of the MOSFET 26b remains nonconductive when the voltage of the electrical system, that is to say, for example, also the terminal voltage of the battery 14, is lower than the prescribed regulating voltage. When the generator 11 reaches its starting speed, current commences to be supplied to the battery 14.If the voltage of the electrical system then exceeds the regulating voltage, the control voltage at the gate terminal G of the MOSFET 26b increases to a value which renders the switching path D-S conductive and thus virtually short-circuits the generator output 13, 19. Only a small residual voltage remains across the switch path D-S of the MOSFET 26b, and the decoupling diode 29 is blocked. The generator 11 is thus isolated from the connection lead 1 5 and thus from the electrical system.

A voltage peak cannot occur at the output 13, 1 9 of the generator 11 when loads are switched off when a battery 14 is not connected, since it is virtually short-circuited by way of the switching path D-S of the MOSFET 26b.

Fig. 3 shows a third embodiment in which both series regulation and parallel regulation are included. The MOSFET 26b connected in parallel with the output 13, 1 9 of the generator 11 is controlled directly by the control stage 23, and the MOSFET 26a located in the connection lead 1 5 between the direct current power output 13, 1 9 of the generator 11 and the battery 14 is controlled by the control stage 23 by way of a circuit arrangement 27 for increasing the terminal voltage of the battery 14. In this embodiment also, a plurality of MOSFETs 26 can be connected in parallel in each case. In this embodiment, it is e advantageous that the values of the blocking voltages of the series MOSFET 26a and the parallel MOSFET 26b need only to be chosen such that they lie above the normal voltage of the electrical system. Compared with MOSFETtypes having a higher blocking voltage, MOSFET types having a lower blocking voltage have higher continuous current with a lower load resistance.

The third embodiment is provided with a further switching stage 31 which ensures that the parallel MOSFET 26b is non-conductive when the series MOSFET 26a is conductive, and that, when the series MOSFET 26a is non-conductive, the parallel MOSFET 26b is switched to its conductive state only when the voltage across its switching path D-S has exceeded a predetermined value.

An input of the control stage 23 of the voltage regulator is connected to the direct current power output 1 3 of the generator 11 by way of a sensing lead 32.

After actuation of the control switch 22, the supply voltage is applied to the control stage 23, the indicator stage 24, the circuit arrangement 27 for increasing the voltage and the switching stage 31. When the voltage of the electrical system lies below the regulating voltage, the parallel MOSFET 26b is switched to its non-conductive state and the series MOSFET 26a is switched to its conductive state. The series MOSFET 26a is switched to its non-conductuve state if the regulating voltage exceeds the predetermined value as a result of delivery of current by the generator 11. The parallel MOSFET 26b remains non-conductive when, and for as long as, the potential on the drain terminal D of the two MOSFETs 26a, 26b is lower than the maximum admissible blocking voltage.If the rotational speed of the generator is very high and thus the no-load voltage of the generator lies above the maximum admissible blocking voltage of the two MOSFETs 26, that is to say, when the series MOSFET 26a is non-conductive, the voltage regulator 23 switches to parallel regulation by way of the sensing lead 32 and switches the parallel MOSFET 26b to its conductive state.

MOSFETs 26 having a low blocking voltage can also be used in the third embodiment. The MOSFETs having a low blocking voltage have a higher maximum admissible continuous current and a lower forward resistance than MOSFETs having a higher blocking voltage. The voltage regulator 1 8 can thus operate with a low power loss and only a few power components are required. Furthermore the total power loss of the generator system can be very low, since the voltage regulator 1 8 operates as a series regulator up to a predetermined blocking voltage.

Claims

1. A battery charging system having a permanent magnet energized generator, and a voltage regulator connected to the direct current power output of the generator, in which the voltage regulator comprises a control stage and a MOSFET controlled by the control stage, one terminal of the switching path of the MOSFET being connected to the direct current power output of the generator and the other terminal of the switching path being connected either to a connection terminal of the battery or to a common connection between the generator and the battery.

2. A battery charging system as claimed in claim 1, in which the voltage regulator comprises a MOSFET with its switching path connected in series between the direct current power output of the generator and the connection terminal of the battery and/or a MOSFET with its switching path connected in parallel across the output of the generator.

3. A battery charging system as claimed in claim 1 or 2, in which the generator comprises a permanent magnet energized three-phase alternator and a three-phase bridge connected rectifier.

4. A battery charging system as claimed in claim 1, 2 or 3, in which the switching path of the MOSFET is located in a connection lead between said direct current power output of the generator and said connection terminal of the battery, and the voltage regulator further comprises a circuit arrangement for increasing the terminal voltage of the battery and the control terminal of the MOSFET is connected to the output of said circuit arrangement.

5. A battery charging system as claimed in claim 4, in which a voltage limiting device is connected in parallel with the direct current power output of the generator.

6. A battery charging system as claimed in claim 1, 2 or 3, in which the switching path of the MOSFET is connected in parallel with the direct current power output of the generator.

7. A battery charging system as claimed in claim 6, in which a decoupling diode is incorporated in a connection lead between the direct current power output of the generator and said connection terminal of the battery.

8. A battery charging system as claimed in claim 1,2 or 3, in which the voltage regulator comprises a control stage and two MOSFETs which are controlled by the control stage, and in which the switching path of one of said MOSFETs is located in a connection lead between said direct current power output of the generator and said connection terminal of the battery, and the switching path of the other of said MOSFETs is connected in parallel with said direct current power output of the generator.

9. A battery charging system as claimed in claim 8, in which the voltage regulator further comprises a circuit arrangement for increasing the terminal voltage of the battery, and the control terminal of said one of said MOSFETs is connected to the output of said circuit arrangement.

1 0. A battery charging system having a permanent-magnet energized generator, and a voltage regulator constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustruted in Fig. 1 of the accompanying drawings.

11. A battery charging system having a permanent-magnet energized generator, and a voltage regulator constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 2 of the accompanying drawings.

1 2. A battery charging system having a permanent-magnet energized generator, and a voltage regulator constructed and arranged and adapted to operate substantially as hereinbefore particularly described with reference to and as illustrated in Fig. 3 of the accompanying drawings.