CA1098961A - Battery charging and emergency supply circuit - Google Patents

Abstract

BATTERY CHARGING AND EMERGENCY SUPPLY CIRCUIT

ABSTRACT

A circuit provides a regulated voltage from a primary source of power to a load and maintains the charge on a battery for standby use. A Zener diode paralleling the battery provides clamping during charging, when batteries are cold, or if the battery should fail open. Power from the primary source is supplied through a transistor having the load in the emitter circuit and having the battery coupled to its base. A lamp, chosen to provide the desired charging current, is coupled across the collector-base junction for forward biasing of the transistor and also provides a visual indication that the primary source is operative.

Description

Back round of the Invention g _ _ This invention relates to the field of power supplies and particularly to a supply which provides DC power for electronic apparatus from an external source and maintains the charge on a standby battery which, in turn, supplies power for the apparatus during loss of the external source.
There are many applications for electronic apparatus, ranging from medical monitoring to remote radio repeater stations, in which it is desirable or imperative to have standby power available in the event of failure of a primary power source. It is likewise desirable to have the standby power supplied automatically and without a break in service.
While it is known in the art to provide these capabilities, it would also b~ desirable to add, wi~h a minimum of addi-tional components, limiting of the charging current and the output voltage of the standby power source. A visual status indicator is also a needed feature in many applications.
,~ ~"~ ' .

-~

:: : ~,: : . :
, . ~ ., ;
;.

: ` , -C~-76332 ~un~ary of the Invention It is, therefore, an object of this invention to provide an improved means of supplying both normal and emergency power for an electronic apparatus which is at the same time simpler and less expensive than the prior art and includes a visual indicator.
These objectives are provided in accordance with the invention by a supply circuit which has an input connected to a primary power source and an output connected to the apparatus. The primary source may be any suitable supply having a DC output. ~ transistor is connected between the input and the outpu~ ~ resistive element which is also a visual indicator is coupled to provide forward biasing for the transistor and also to provide charging current for a battery which, in turn, supplies power to the apparatus in the event of failure of the primary source. A Zener diode is coupled across the battery ~or clamping the battery at the appropriate voltage level and limiting the voltage applied to the load even in the case o~ an open battery circuit.

Brief Description of the Drawing Fig. 1 is a perspective view of an electronic apparatus - embodying the invention.
Fig. 2 is a schematic diagram of a circuit in accord-ance with the invention.

Detailed Description of a Preferred Embodiment In Fig. 1 of the drawing an electronic apparatus 10 is shown with an associated power supply 11. The apparatus 10 represents any piece of electronic equipment which is required to be operative in the event of failure of its primary power CM-76332 ~9~

source. This type of equipment would include stationary apparatus normally supplied from ~C power line as, for example, computers wherein loss of power could mean the permanent loss of data, and mohile radio communication equipment normally powered by the battery of a vehicle, wherein vehicle battery failure could cause a dangerous lack of communication. The power supply 11 may be a separate unit as shown in Fig. 1, but might equally well be integrally housed with the apparatus 10~ A lamp 12 indicates tha~ the primary source of power is operative. Other functions of the lamp 12 will be discussed hereinafter with respect to Fig. 20 Fig. 2 shows a preferred embodiment of a circuit accord-ing to the invention. The load 10 represents the apparatus 10 of Fig. 1 which is to be supplied power under both normal and emergency conditions. The remaining circuit elements of Fig. 2 would comprise at least part of the power supply 11.
If the supply 11 is connected to an AC power line, the supply could also include (not shown) the customary trans-former, filter and rectifier circuitry well known in the artfor changing AC at one voltage to filter DC at possihly a different voltage. For purposes of the present invention, ~ Pvr it is only required that there be connected to an e~
terminal 13 an appropriate DC primary power source.
transistor 14 has its collector 15 coupled to the terminal 13~ and its emitter 16 coupled to ~he load lQ. The load 10 may be connected by means of a plug-in connector 17, but could as well be wired in with an intervening on-off switch (not shown). The lamp 12 is connected between the transistor collector 15 and -the transistor base 21. Coupled in parallel from the base 21 to ~round are a battery of rechargeable cells 22 and a Zener diode 23.

In ~ormal operation, i.e., with power being supplied from the primary power source to the terminal 13, current will flow through the lamp ~ lighting the lamp as a visual indication of normal operation. The voltage drop across the lamp ~ will forward bias the transistor 14, causing current to be passed through the collector-emitter path to the load 10. If the battery 22 is less than fully charged, a charging current will flow through the lamp to the battery. If insuficient power or no power is being supplied to the terminal 13, load current will be supplied by the battery until the stored energy is exhausted or until primary power is restored. In the emergency mode~ the lamp ~ will not be illuminated.
The Zener diode is chosen to provide a reference voltage equal to or slightly higher than the nominal value of voltage on the battery 22. The load voltage will then be the refer-ence voltage less one diode drop, even when the battery is cold and would tend to supply a higher refer~nce voltage if not clamped. If the voltage on the terminal 13 should increase for any reason, the voltage on the transistor base 21 would be held at the reference voltage. The emitter voltage would be held at the reference voltage less one diode drop, negating the effect of the voltage rise at the terminal 13. The transistor 14 is chosen for its current carrying and power dissipation capabilities. The lamp is chosen to provide the appropriate charging current to the battery and forward bias to the ~ransistor.
Thus there has been provided an improved means of supplying power to electronic equipment in both normal and emergency modes of operation.

What is claimed is~

Claims (4)

CM-76332 The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A circuit arrangement for supplying power to elec-tronic apparatus having a primary source of power and having normal and emergency modes of operation, the circuit arrange-ment comprising:
input means coupled to the primary power source;
output means connected to the electronic apparatus;
transistor means coupled between the input means and the output means for supplying power to the apparatus in the normal operating mode;
resistive indicator means coupled to the input means and to the transistor means for forward biasing the transistor;
rechargeable cells coupled to the indicator means for receiving charging current from the indicator in the normal mode, and to the apparatus for supplying power to the apparatus in the emergency; and voltage limiting means coupled across the recharge-able cells for limiting the voltage across the cells.

2. A circuit arrangement according to claim 1 wherein the resistive indicator means comprises a lamp bulb.

3. A circuit arrangement according to claim 1 wherein the resistive indicator means is connected across the collector-base of the transistor means.

4. A circuit arrangement according to claim 1 wherein the voltage limiting means comprises a Zener diode.