GB2088656A - Self-contained communication system and circuits for use therein - Google Patents

Abstract

A self-contained communications unit which includes a low power television receiver and preferably also a radio transmitter. The receiver and transmitter are powered from a storage battery 5 which is arranged to receive current from a solar array 1. The flow of current to the array is governed by a charge regulator which forms the product of a sample current ISR from the array and the output voltage of the array to derive an indication of maximum power 18 available from the array and to compare that maximum available power with the power fed to the battery, as determined by a measurement of current fed thereto. <IMAGE>

Description

SPECIFICATION Self-contained communication system and circuits for use therein The present invention relates to a self-contained communication unit, which includes a television receiver and preferably also a radio transmitter, and which has for its source of power a solar array which is preferably coupled by way of a charge regulator to a rechargeable electrical storage battery for powering the rest of the communication unit.

The invention is particularly although not exclusively intended for use in regions, such as the so-called undeveloped countries, which experience sufficient sunshine such that a comparatively small solar array can provide sufficient power to maintain the state of charge of a storage battery notwithstanding the drain on the battery by the television receiver or radio transmitter or transceiver.

The present invention has various aspects.

One aspect is the use of a charge regulator which includes means for sensing the maximum usable power from the solar array and by a comparison of that power with the mean power fed to the battery governs a series regulator of current to the battery. Another aspect of the invention is the design and operation of the aforementioned charge regulator. Further aspects of the invention include the design and operation of particular circuits, including a video amplifier and a line scan circuit particularly adapted for low power consumption.

All these aspects of the invention and further objects and aspects of the invention will become apparant from the following description of a preferred but not limiting example of a communications unit. In the following description, reference will be made to the accompanying drawings, in which: Figure 1 is a schematic diagram of the exemplary communications unit; Figure 2 is a schematic illustration of an embodiment of the unit; Figure 3 is a schematic diagram of a charge regulator coupled to a solar array and a storage battery; Figure 4 is a skeletal circuit diagram of the regulator and its connection to the battery; Figure 5 is a circuit diagram of an embodiment of a power detector and difference detector constituting part of the regulator; Figure 6 is a circuit diagram of a multivibrator forming part of the regulator;; Figure 7 is a schemtaic diagram of a television receiver adapted for use in the communication unit; Figure 8 is a circuit diagram of a preferred form of a line scan circuit; and Figure 9 is a circuit diagram of a video amplifier.

The system shown in Fig. 1 comprises a solar array which constitutes a prime source of power to a communication unit 2. The communication unit includes a rectifier 3 between the solar array 1 and a charge regulator 4, which will be described in more detail with reference to Figs. 4, 5 and 6. The charge regulator regulates the flow of power from the solar array into an electrical storage battery 5 which can provide, on closure of a series switch 6, power either to a television receiver 7, which is described in more detail with reference to Figs. 7 to 9, or a radio transmitter 8, which may have an output power of the order of 1 watt and radiate frequency modulated signals at VHF (85 to 110 MHz). The transmitter has an external microphone 9. A switch 10 is provided so that the receiver 7 and the transmitter 8 may share a common antenna 11.

It is preferred that the array 1 and the communication unit be portable; for this purpose the solar array 1 may be mounted, for example hingedly mounted on the top surface of a portable television receiver 7 which is provided with an extensible antenna 11 and which may be adapted to include all the elements of the aforementioned communications unit with the possible exception of the battery 5 which may be connected to appropriate sets of terminals provided at the back of the receiver 7.

Figure 3 shows the general arrangement of the array, the regulator 4 and the battery 5.

The main solar array 1 feeds by way of the rectifier 3 (not shown in Fig. 3) a main storage capacitor 1 2. Across the capacitor 1 2 is a voltage divider network composed of resistors 1 3 and 14, there junction being connected by way of the line 15, on which a voltage reference appears, to one input of a power product generator 16, yet to be described in detail. This generator receives a current reference from a subsidiary solar array 1 7. The output of the product generator 1 6 feed a maximum power detector 1 8 which controls a variable rate pulse generator 1 9 of which the output controls a main current switch 20 is series between the main solar array 1 and the battery 5.This switch 20 is coupled to the battery 5 by way of an inductor 21 in a manner which will be described with reference to Fig. 4.

Fig. 4 illustrates the regulator in somewhat more detail. Input terminals 22 and 23 are connected to the main storage capacitor 1 2.

The positive terminal of the capacitor is connected by way of a current sensing resistor 24 to the collector of a switching transistor which constitutes the main current switch 20. The emitter of this transistor is connected by way of the inductor 21 to the positive terminal of the storage battery 25 and by way of a freewheeling diode 25 to the negative terminal of the battery. When the switching transistor 20 is conductive a rising current is caused to flow into the inductor 21 until the transistor is turned off. The energy stored in the inductor flows into the battery, the diode 25 forming with the inductor and the battery a freewheeling path for current to flow.

The arrangement shown in Fig. 4 includes an additional input terminal 26, a line 27 from the positive terminal of the capacitor and a line 28 connected to the downstream terminal of the resistor 24, terminal 26 and lines 27 and 28 providing inputs to a control circuit 29 which governs the rate at which switching pulses are fed to the transistor switch 20. The pulse rate depends on the charge stored in the capacitor C which is, of course, renewed by the solar array and exhausted by the switching transistor.

It will be apparent that the arrangement of the transistor 20, the inductor 21 and the diode 25 and their connection to the battery is in well-known form but the control of the regulator takes no account of the output voltage of the regulator but relies on monitoring the available power from the solar array.

The control circuit samples the available power from the solar array by finding the product of the output voltage of the array and the short-circuit current. The sample array (17) is required for finding the short-circuit current because the variation of maximum power is non-linear. The mean charging current to the battery (which is represented by a signal representing the load current and appearing on the line 28) is compared with the power available from the array, as represented by the voltage across the capacitor 1 2 and an input current (at terminal 26) from the sample array. The comparison is performed by a defferential amplifier, the output of which causes the production of pulses for operating the switching transistor 20 to increase the load current until the maximum available power is fed to the storage battery.

The particular arrangement of the control circuit is shown in Figs. 5 and 6. In the circuit shown in Fig. 5, the multiplication of the signals available at the terminal 26 and the line 27 (shown as the line 1 5 in Fig. 3) is performed by a field effect transistor 29 which feeds by way of an appropriate input resistor the non-inverting input terminal of difference amplifier 30. The line 28 is coupled by way of another appropriate input resistor to the inverting terminal of the difference amplifier 30. The output line 31 from the difference amplifier maintains, if the maximum available power is greater than the power fed to the battery the multivibrator 32 (Fig. 6) in oscillation, output pulses being fed out on a line 33 to the base of the switching transistor 20.

Normally the switching transistor would be operated at between 20 and 30 kilohertz. The frequency of the output pulses from the multivibrator 32 is the function of the signal applied on its input line 31, the output from the multivibrator being pulses of fixed length but at a variable rate, the rate depending on the difference between the inputs to the difference amplifier 30.

Fig. 7 is a schematic diagram of the television receiver. The arrangement of the receiver is generally of known form. The antenna 11 is coupled to a tuner unit 34 and the receiver includes an intermediate frequency amplifier 35, a detector 36, a sound filter 37 for the separation of the modulated audio carrier from the composite television signal, an audio system 38 for the demodulation of the audio carrier, the sound system 38 feeding a loudspeaker. The detector 38 also feeds a class B video amplifier 39 feeding the video input terminal of a cathode ray television display tube 40. The detector 36 also feeds a signal processing circuit 42 which provides signals for a frame scan integrated circuit 43 and a line scan circuit 44, which provides drive signals for the tube 40 and also drive signals for an EHT rectifier 45 coupled to the tube 40.The receiver includes a regulator 46 having an input switch 47 coupled to the battery 5 and output lines 48 which provide a regulated ten volt output to all the various stages of the receiver.

As has been mentioned, for the most part the receiver is of known form. However, the line scan circuit 44 and the amplifier 39 are particularly designed for low power consumption and will be described further with reference to Figs. 8 and 9 respectively.

As is known, the line scan circuit in a television receiver consumes most of the total power consumed by the receiver. Normally the transistor which generates the line scan signals is a high power, high voltage device which operates in Class C. It is either turned off or turned on and saturated. At saturation the current gain of the device tends to be quite low, of the order of two or three, and the device requires a large drive current, typically between 0.2 and 0.3 amps. Hence a Class C driver stage is required, scanning at a power level of about 1 watt.

In the circuit shown in Fig. 8, the transistors 45 and 46 constitute a power Darlington connection. The collector of the transistor 46 is connected to one end of the primary of a flyback transformer 47. One end of the secondary of the transformer 47 is coupled by way of a rectifier to an output terminal 48 which provides the scanning signals for the cathode ray tube; the other end of the secondary is coupled by way of rectifiers to an output 49 which provides the high anode voltage for the cathode ray tube. The collector of the transistor 45 is taken to a second tap on the primary of the transformer, so as to provide between the end tap and the second tap a signal of about 2 volts when the collector-emitter voltage of the transistor 46 is 0.6 volts.

In the circuit shown the power transistor (46) draws 0.7 amps only of the required scan current and at saturation its current gain (in grounded emitter) is between 2 and 4. The drive transistor (45) of the Darlington pair thus supplies 0.2 amps of the base drive to the transistor 46 when its collector-emitter voltage is 0.6 volts but its current gain is between 1 5 and 30. Accordingly the base drive required to the Darlington is now only 20 to 30 milliamps at 10 volts which may be supplied from a lower power line oscillator (which would be coupled to the input terminal 50 shown in Fig. 8).

Thus the conventional drive stage and its concomitant power loss of about 1 watt may be eliminated, all the drive power now being used in the line scan circuit. A saving of about 10% of the power required for scanning may be saved. The Darlington pair has a high gain by virtue of a tap on the main transformer, the collector-emmitter voltage of the transistor 45 being maintained even though the collector emitter voltage of the transistor 42 is very low. In the normal Darlington stage the current gain suffers if the collectors are common, as in the usual arrangement.

Reference will now be made to Fig. 9. The video amplifier of an ordinary television receiver produces, for example, a 60 volt video signal for the cathode ray tube by means of a linear Class A bias stage. The current requirement at this stage is high because the cathode capacitance of the cathode ray tube has to be driven via the load resistor. Fig. 9 illustrates a Class B video amplifier which can operate on 2 milliamps (for a blank screen) up to 10 milliamps for a complex test pattern. The maximum power is about 1 watt but averages about 60 % of that value during ordinary transmission.

In a circuit shown in Fig. 9, the Class B pair is constituted by the video transistors 51 and 52 connected between the 140 volt line (48) and the high tension line (49). They provide at terminal 53 a video output to the cathode ray tube's beam limiter. The input video signal is received at the base of a transistor 54 which is connected in cascode with a transistor 55, which feeds the Class B stage. The transistor 54 is a low voltage high gain transistor and the use of the transistor 55 in cascode prevents large voltages from appearing at the collector of the transistor 54. This expedient improves the black level stability of the receiver.

Claims (1)

1. A communication unit comprising a solar array a television receiver fed from an electrical storage battery and a charge regulator which is arranged to govern the flow of current to the storage battery in accordance with the maximum power available from the solar array.