US3440519A - Constant current regulator with moving coil transformer - Google Patents

Description

April 22, 1969 I J,M CEMO'N 3,440,519

CONSTANT CURRENT REGULATOR WITH MOVING COIL TRANSFORMER Filed NOV. 16. 1966 United States Patent 3,440,519 CONSTANT CURRENT REGULATOR WITH MOVING COIL TRANSFORMER Herbert J. Macemon, Hendersonville, N.C., assignor to General Electric Company, a corporation of New York Filed Nov. 16, 1966, Ser. No. 594,911 Int. Cl. Gf l /16 US. Cl. 323-6 5 Claims ABSTRACT OF THE DISCLOSURE A constant current regulator to control lighting systems or heating devices. The regulator has a moving coil transformer wherein the primary winding or a main secondary winding connected to the load are movable relative to each other. An auxiliary secondary winding has a controlled rectifier switching circuit connected across it to control the current in the main secondary winding.

The present invention relates to a constant current regulator, and particularly a constant current regulator of moving coil transformer type.

It is an object of the invention to provide a constant current regulator of the above type which provides for stepless control of the constant current produced thereby.

Another object of the invention is to provide a constant current regulator of the above type which is compact and lightweight, is reliable in operation, has low losses, and which automatically limits short circuit current.

It is a particular object of the invention to provide a constant current regulator of the above type which provides for control of the output current by controlling a circulating current in an auxiliary winding of the moving coil transformer.

Other objects and advantages will become apparent from the following description and the appended claims.

With the above objects in view, the present invention relates to a constant current regulator comprising, in combination, a moving coil constant current transformer having main primary and secondary windings, at least one of the windings being movable relative to the other for maintaining a constant current in the secondary winding, the main primary winding having terminals connected thereto for connection to a source of alternating current, load means connected to the main secondary winding, control circuit means associated with the main secondary winding for varying the level of current supplied to the load means comprising an auxiliary secondary winding adjacent the main secondary winding, and means connected across the auxiliary secondary winding for controlling the current flow therein and thereby in the main secondary winding, whereby the current to the load means may be controlled by the control circuit means.

In the preferred embodiment of the invention, the means connected across the auxiliary secondary winding is a phase control means comprising controlled rectifier means.

The invention will be better understood from the following description taking in conjunction with the accompanying drawing, in which:

The single figure is a circuit diagram of an embodiment of the improved constant current regulator of the invention.

Referring now to the drawing, there is shown a circuit arrangement energizing at a constant current a load 1, such as an illuminating means. The illuminating means may be constituted by one or more lamps such as incandescent, gaseous discharge or fluorescent-type lamps. The circuit includes a movable coil constant current transformer 3 comprising a main primary winding 3a connected to terminals 2 of a source of alternating current and a main secondary winding 3b across which load 1 is connected. In such a movable coil transformer 3, either primary coil 3a or secondary coil 3b may be made movable on the core relative to the other, or both coils may be movable with respect to each other and the core. In such a device, the magnitude of the output current is controlled by the effective weight of the moving coil structure. In operation, this weight is exactly balanced by the repulsion forces produced by the currents flowing in the primary and secondary coils. These repulsion forces are proportional to the square of the secondary ampereturns. Variations in either input voltage or output load result in the moving coil seeking a new position relative to the other coil so that again the Weight of the moving coil assembly and the repulsion forces between coils are balanced, resulting in maintaining a constant output current over the designed range of travel of the moving coil. With a constant output current and a fixed number of turns in the secondary coil, the total ampere-turns in the secondary is a constant. In the regulator circuit employed in the invention, a control device is incorporated for varying in stepless fashion the level of the constant output current which would otherwise be fixed. In accordance with the principles of the invention, such control is achieved by providing a control circuit comprising an auxiliary secondary winding on transformer 3 and a means for controlling the flow of current in the latter winding. When current flows in the auxiliary winding, the ampere-turns in the auxiliary winding directly subtract from the total constant ampere-turns available to the main secondary coil (output) circuit, and hence the magnitude of the output current is reduced to a lower constant level. Preferably, current flow in the auxiliary winding should be controlled without introducing significant additional losses. In the embodiment shown in the drawing, the control device comprises auxiliary second ary winding 4, adjacent the main secondary winding 3b and in fixed spatial relation thereto. Connected across auxiliary secondary winding 4 is a controlled rectifier switching circuit 5 which serves to provide a phase controlled current of desired amount in winding 4 to thereby vary the ampere-turns of main secondary coil 3b, thus resulting in the desired adjustment of the constant current supplied to load 1. Controlled rectifier circuit 5 includes a paralleled pair of oppositely poled controlled rectifiers 7 and 8, which are typically silicon controlled rectifiers (SCRs) having controlled (gate) electrodes 7 and 8 by means of which the SCRs are rendered conductive for unidirectional flow of current when a signal pulse is applied to the respective control (gate) electrodes.

Control electrodes 7' and 8' are connected respectively to secondary windings 9a, 9b of coupling transformer 9. Transformer 9 serves to isolate the controlled rectifier circuit 5 from the trigger pulse generating circuit described below. The signal generating or actuating circuit 23 comprises a variable resistance 10 in series with a charging capacitor 11 connected across auxiliary winding4.

A discharge loop in actuating circuit 23 for discharging capacitor 11 includes transformer primary 9c and a voltage sensitive device 12, typically a neon-glow lamp, which is a bi-laterally conducting diode, and is also referred to herein as a voltage sensitive symmetrical switch means, which becomes conductive only upon the application of a predetermined voltage thereto. Other symmetrical switch devices which could alternatively be used are a diac, a symmetrical Shockley device, or the like. Voltage sensitive switch 12 is connected in parallel with charging capacitor 11 but is eifectively connected in series discharge relation therewith and with transformer primary 9c as shown. An auxiliary discharge capacitor 13 is also preferably arranged inseries with these components of the discharge loop' as shown, so as to provide a residual charge additive to the voltage appearing across capacitor 11 on each half cycle, as more fully explained in the patent to Nuckolls 3,249,807.

In-the above described circuit arrangement, on each half cycle of the alternating current input derived from auxiliary secondary winding 4, one of the controlled rectifiers 7 and 8 will have a positive anode and the other a positive cathode. Therefore, a control signal applied to control electrode 7' and 8' will place only one of the controlled rectifiers in a conduction mode on each half cycle. A delay in the point in the alternating current input cycle at which the control signal impulse is applied to render the rectifier conductive is known as phase control. The characteristics and function of SCR switching circuit and its actuating circuit 23 are more fully described in the aforementioned Nuckolls patent, the disclosure of which is incorporated herein by reference.

As there described, voltage sensitive switch 12 becomes conductive as a result of the voltage buildup on capacitor 11, capacitor 11 partially discharges and a signal pulse is applied to the transformer primary 9c which induces a current pulse of a particular duration and at a particular time in the half cycle. The controlled rectifier 7 or 8 which has an anode positive with respect to cathode will then be triggered to conduction by the pulse current applied to control electrode 7', 8' and the voltage which has built up across the rectifier falls substantially to zero. The controlled rectifier 7 or 8 then permits current to flow, consequently circulating current through auxiliary secondary winding 4 for the remainder of that half cycle. On the next half cycle as the anode voltage becomes negative, the controlled rectifier 7 or 8 which was conductive becomes nonconductive and no current is transmitted through winding 4 until the signal generating circuit fires the other controlled rectifier. The time in the half cycle at which the rectifier is gated is adjustable by the level of resistance 10.

For the purpose of protecting rectifier circuit 5 from transient voltages, a thyrector 16, or double Zener diode device, may be connected in parallel with the rectifiers, as shown.

By suitable adjustment of variable resistance 10, which may be employed as a manually operated control means for the lighting circuit or other load, the current circulating in auxiliary secondary coil 4 may be varied by means of the described SCR phase control device. As indicated previously, the change in current thus produced in coil 4 results in variation of the ampere-turns in that coil, which subtract from the total ampere-turns in main secondary coil 3b, thus effecting a change in the load current in the latter circuit.

While a phase control arrangement as described above is preferred in accordance with the invention, other means may be substituted for SCR circuit 5 and actuating circuit 23 for short circuiting or controlling current flow in auxiliary winding 4. For example, a variable impedance device such as a variable resistor, a variable capacitor, or a variable inductance may simply be connected across auxiliary secondary winding 4 to control the current circulating therein. r

While the described constant current regulator device has been disclosed as applicable for use in the control of lighting systems, it will be understood that it may also be found useful for control of other types of apparatus which is designed to operate at varying levels of constant current, as for example electric ovens and other heating devices.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A current regulator device comprising, in combination, a moving coil constant current transformer having main primary and secondary windings, and having terminals connected to said main primary winding for connection to a source of alternating current, load means connected to said main secondary winding for energization thereby at a substantially constant current, and control circuit means associated with said main secondary winding for varying the level of constant current supplied to said load means comprising an auxiliary secondary winding adjacent to said main secondary winding.

2. A device as defined in claim 1, said control circuit means including phase control means connected to said auxiliary secondary winding for controlling the current in the latter winding.

3. A device as defined in claim 2, said phase control means comprising bi-directional conducting controlled rectifier means connected across said auxiliary secondary winding and being normally non-conductive to block current flow through said auxiliary secondary winding and having electrode control means to render it conductive in either direction depending on the polarity of the alternating current supply, and means for applying a control signal to said electrode control means including a capacitance and a resistance connected together in series across said auxiliary secondary winding, and voltage sensitive switch means and transformer means connected across said capacitance in series discharge relation therewith.

4. A device as defined in claim 3, wherein said resistance is a variable resistor.

5. A device as defined in claim 1, said control circuit means comprising variable impedance means connected to said auxiliary secondary winding for controlling the current in the latter winding and thereby elfecting control of the output current.

References Cited UNITED STATES PATENTS Trigger Circuits, third edition, 1964, p. 139.

JOHN F. COUCH, Primary Examiner.

A. D. PELLINEN, Assistant Examiner.

US. Cl. X.R.

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