This invention relates to a device for switching off glow of the LED (Light Emitting Diode) used as charge indicator in an alternator-battery charging system. This invention relates more particularly, though not exclusively, to automotive charging systems.

The alternator setup consists of a rotor, a stator, a regulator, a rectifier and a pre-excitation circuit. Conventionally, when the ignition switch is ON, the battery current flows through a charge indicator electric lamp, the rotor winding and voltage regulator to ground. Consequently, the rotor's magnetic field builds up as soon as current flows through the excitation winding on the rotor, inducing an alternating voltage in the stator windings providing a corresponding current for feeding the load.

The AC voltage of the alternator is rectified by a full wave bridge rectifier. However, the rectified DC output of the rectifier is not "smooth" but possesses a slight ripple.

The charge indicator lamp remains ON as long as the alternator voltage of the vehicle is below battery voltage, but the lamp goes off when the speed is reached at which rated alternator voltage is generated and the alternator starts to feed power to the vehicle electrical system.

According to the known art, the LED is presently used as a charge indicator in place of the aforementioned electric lamp not only resulting in a more durable component, but also in greater aesthetics in use.

When an LED is used as a charge indicator instead of the aforementioned electric lamp, a resistor is connected in parallel with the LED to ensure supply of sufficient current for the self-excitation of the alternator. The LED remains ON as long as the alternator voltage is below battery voltage, but goes OFF when the alternator reaches rated voltage for charging the battery and otherwise feeding the electrical load of the vehicle.

However, the drawback with the LED circuit is that the LED responds to very short voltage dips (transients) at the point of commencement of the pre-excitation circuit (indicated by the point marked A in the accompanying drawings) and gives off a mild glow even after the alternator generates full rated voltage, presenting a wrong indication to the driver that the alternator is defective. In other words, the very purpose of providing an LED charge indicator is defeated by causing confusion and needless delays involved in unnecessarily checking the charging system of the vehicle to locate an imaginary fault.

This invention therefore proposes a device which totally switches off the LED after the alternator reaches full rated voltage regardless of the voltage dips referred to above.

The device for switching off glow of the LED used as charge indicator in an alternator-battery charging system, according to this invention, comprises an alternator connected to a battery, said alternator incorporating a pre-excitation circuit, the said LED and a parallel resistor connected to form an LED circuit; a control unit connected between the LED circuit and the pre-excitation circuit, said control unit consisting of a transistor, a second resistor and capacitor whereby, with the battery switched on, current from the battery flows through the LED circuit and then to the base of the transistor through the second resistor, to switch on the transistor, for allowing flow of the said current to the pre-excitation circuit, thus causing the alternator to generate voltage. LED goes off when the speed of the alternator is reached at which rated voltage is generated and the alternator starts to feed power into the vehicle electrical system.

When the regulator is in switching mode, the transient voltage dip occurs at the point of commencement of the pre-excitation circuit. Whenever the above dip occurs, the capacitor by-passes this transient voltage, keeping transistor in OFF condition thereby preventing current flow through LED, to totally prevent any glow of the LED.

This invention will now be described with reference to the accompanying drawings which illustrate, by way of example, and not by way of limitation, one of possible embodiments of the device proposed herein

Fig. 1 illustrating the pre-excitation circuit

Fig. 2 illustrating the circuit of the LED control unit

Fig. 3 illustrating the circuit of the LED control unit of Fig. 2 incorporated in the pre-excitation circuit of Fig. 1

An alternator (with stator S) is connected to a battery B. The alternator incorporates a pre-excitation circuit (Fig.1). An LED F and resistor R1 are connected to form a LED circuit K, the LED serving as a charge indicator.

The LED circuit K is connected between a control unit (Fig.2) and the battery, the control unit itself being connected between the LED circuit and the pre-excitation circuit of alternator.

The said control unit consists of a transistor T, second resistor R2 and capacitor C whereby, with the battery ON, current from the battery flows through the LED circuit and then to the base of the transistor T, through the second resistor R2 to switch on the transistor. Once switched ON, the transistor allows flow of the said current to the pre-excitation circuit of alternator to cause the LED to go off when the speed of the alternator reaches a value at which rated voltage is generated to feed power to the vehicle electrical system.

When the regulator R is in switching mode, the transient voltage dip occurs at the point A of commencement of the pre-excitation circuit. Whenever the above dip occurs, capacitor C by-passes this transient voltage, retaining transistor T in OFF condition thereby preventing current flow through LED, so that the LED in such situations will be completely OFF without so much as even a mild glow.

It will be observed that what has been described above with regard to an automotive application will equally be applicable to other cases as well, such as, a captive generator-battery charging system.

The terms and expressions herein are of description and not of limitation, there being no intention in the use of such terms and expressions of excluding any equivalents of the features illustrated and described, but it is understood that various other embodiments of the device proposed herein are possible without departing from the scope and ambit of this invention.

We Claim:

1. 1. A device for switching off glow of the LED used as charge indicator in an alternator-battery charging system, comprising an alternator connected to a battery, said alternator incorporating a pre-excitation circuit, the said LED and a parallel resistor connected to form an LED circuit; a control unit connected between the LED circuit and the pre-excitation circuit, said control unit consisting of a transistor, a second resistor and capacitor whereby, with the battery switched on, current from the battery flows through the LED circuit and then to the base of the transistor through the second resistor, to switch on the transistor, for allowing flow of the said current to the pre-excitation circuit, LED goes off when the speed of the alternator is reached at which rated voltage is generated and the alternator starts to feed power into the vehicle electrical system, When the regulator is in switching mode, the transient voltage dip occurs at the point of commencement (Point A in pre-excitation circuit) of the pre-excitation circuit. Whenever the above dip occurs, said capacitor by-passes this transient voltage, keeping transistor in OFF condition thereby preventing current flow through LED which prevents glow of LED

2. A device as claimed in Claim 1 wherein the said system is an automotive battery charging system.

4. A device as claimed in Claim 1 wherein the said system is a captive generator-battery charging system.

5. A device for switching off glow of the LED used as charge indicator in an alternator-battery charging system substantially as herein described with reference to, and as illustrated in, the accompanying drawings.