GB2049329A

GB2049329A - Electrical load control system

Info

Publication number: GB2049329A
Application number: GB8011424A
Authority: GB
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1979-05-14
Filing date: 1980-04-03
Publication date: 1980-12-17
Also published as: DE3018026A1

Abstract

A two wire load control system for controlling the energization of a load by a source, the system comprising a switch (16) in series connection via a terminal (10) with the load (14) and source, a control circuit such as an oscillator (20) for controlling the operation of the switch and hence energization of the load, a capacitor (18) providing the supply voltage for the control circuit, and means (17) for connecting the capacitor to the terminal (10) whereby energy is stored in the capacitor when the switch is in an OFF state. <IMAGE>

Description

SPECIFICATION Electrical load control system This invention relates to the energization of a load upon actuation of a switch or other input.

This particular invention is useful, for example, when a load is to be actuated in response to a sensing switch. In these types of applications, if a mechanical switch is used directly to control current flow through the load, the contacts become black with carbon deposits because of the high heat built up across the contacts and will eventually open circuit. Since these switches are not themselves capable of handling the high load currents which are necessary to drive the load, it is necessary to use the switch actuation to energize an electronic control circuit for controlling the flow of current through the load instead of using the switch to control load current directly. The electronic approach is desirable to provide long life of the sensing system.

Circuits, particularly in direct current applications, for providing this type of operation have all involved the use of at least three wires. One wire connects the source of voltage to the load, a second wire connects the source of voltage to the control which controls the flow of current through the load and a third wire acts as a return for both the control circuit and the load. It is an aim of the invention to reduce the number of wires necessary to connect the control circuit to the source of voltage, thereby materially reducing the installation costs of such systems.

According to the invention, there is provided a two wire load control system for controlling the energisation of a load buy a source, the system comprising a switch for series connection via a terminal, with the load and source; a control means for controlling operation of the switch and hence energisation of the load, energy storage means for supplying energy to the switch control means; and means connecting the energy storage means to the terminal whereby energy is stored in the storage means when the switch is in an OFF state.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an overall schematic diagram of a two wire load control system, according to the invention, connected to a load and source, Figure 2 shows a detailed circuit of the oscillator of the system of Figure 1, Figure 3 shows an alternative supply circuit for the energy storage device of the system of Figure 1; and, Figure 4 shows a device which may provide the enable signal to the oscillator.

Referring to the drawings, the load control system is connected in series with positive source 11 and load 14 via line 12 and terminals 13 and 15. Load terminal 15 of the system is connected to the drain of VMOS field effect transistor (FET) 16 the source and substrate of which is connected to ground. Load terminal 15 is also connected through diode 17 to capacitor 18 the other side of which is connected to ground. The junction of capacitor 18 and diode 17 forms a voltage supply terminal 19 which is connected to oscillator 20. Oscillator 20 has an input terminal 21 and is connected to ground by line 22.

The output of oscillator 20 is connected by line 23 to the gate of FET 16. Oscillator 20 may have a variable duty cycle so long as output 23 of oscillator 20 is high long enough for energy to transfer to capacitor 18 through load 14. The duty cycle of oscillator 20 will control through FET 16 the average power delivered to load 14 when an input is received to terminal 21 of oscillator 20. When an input is received at terminal 21, oscillator 20 is energized to supply its output over line 23 to the gate of FET 16.

During the time FET 16 is on, current flows from source 11 through load 14 and switch 16to ground.

During the time that FET 16 is off, current flows from source 11 through load 14 and diode 17 to charge capacitor 18. Capacitor 18 then provides the power for oscillator 20. Thus, as switch 16 is repetitively turned on and off to supply power to load 14, capacitor 18 is charged while 16 is off. When the input is taken away from terminal 21, the load will deenergize and while switch 16 is off, capacitor 18 will charge through diode 17.

Figure 2 shows one form of the oscillator 20. This oscillator has input terminal 19 also shown in Figure 1 and receives its voltage from capacitor 18. Terminal 19 is connected through resistor 31 to terminal 21 which provides the input to oscillator 20. The junction of resistor 31 and terminal 21 is connected both to ground through capacitor 32 and to the input of an inverting gate 33 which has a further terminal connected to ground. The output of inverting gate 33 is connected through the reverse junction of diode 34 to line 23 which is connected to the gate of FET 16.

Terminal 19 is also connected to the power supply terminal of inverting gate 35 which has an input connected to ground through capacitor 36. The input of inverting gate 35 is also connected through diode 37 and resistor 38 to its output and is further connected to its output through resistor 39. The output of inverting gate 35 is connected through resistor 40 to line 23. The ratio of resistor 38 and 39 are selected to determine the percent duty cycle of oscillator 20, and resistors 38 and 39 as well as capacitor 36 are selected to determine the frequency of oscillator 20.

Terminal 21 shown in Figure 2 may be connected to the device shown in Figure 4. This device shown in Figure 4 is a tilt responsive switch and comprises a conductive pendulum arm 42 which has a terminal 21' connected to terminal 21 in Figure 2, the arm 42 extending through the center of a circular wire 43 which is connected to ground. When the device shown in Figure 4 is tilted sufficiently, pendulum arm 43 will contact circular contact 43 and connect the input to inverting gate 33 to ground. When this occurs, oscillator 20 will begin providing an oscillating output signal over line 23 for energizing FET 16 to energize load 14.

Figure 3 shows an alternative approach for supplying energy to capacitor 18 particularly useful when load 14 is inductive. Terminal 10 is connected through the forward junction of diode 51 and resistor 52 to capacitor 18. The junction of resistor 52 and capacitor 18 is connected to the ground through zener diode 53. Zener diode 53 provides a regulated voltage to capacitor 18.

It will be apparent from the above described embodiments that only two wires are necessary to install the present system comprising diode 17, capacitor 18, oscillator 20 and switch 16. The system only needs one wire to connect it to the load and a second wire to connect it to return. No third wire needs to be run from source 11 to terminal 19 for supplying power to oscillator 20. Instead, capacitor 18 is connected to the load circuit for storing energy for providing the power necessary to operate oscillator 20.

Claims

1. A two wire load control system for controlling the energization of a load by a source, the system comprising a switch for series connection via a terminal, with the load and source; a control means for controlling operation of the switch and hence energization of the load; energy storage means for supplying energy to the switch control means; and means connecting the energy storage means to the terminal whereby energy is stored in the storage means when the switch is in an OFF state.

2. The system of Claim 1, wherein the switch control means is an oscillator responsive to an enabling input signal and operable to supply an oscillating gating signal to the switch.

3. The system of Claim 1 or 2, wherein the source is a direct current source and the connecting means includes a diode connected between the terminal and energy storage means.

4. The system of Claim 1,2 or 3, wherein the switch is a field effect transistor with its gate connected to the output of the switch control means, and wherein the energy storage means is a capacitor.