Multiple Position Power Switch

I. Field of the Invention

The invention relates to a multiple position power control switching system and more particularly to a power control system employing capacitors to change the power level at which a load such as a fan motor is operated.

II. Description of the Prior Art

It has been known to provide a series connection of a load with a capacitor in order to change the phase angle and thus power level at which a load is operated. Prior art systems required a large number of capacitors to achieve a full range of operational power levels, thus increasing cost.

It is an object of the invention to provide a multiple position power control switch system in which the number of capacitors utilized is minimized yet four distinct operational power levels may be provided to a load such as for a fan motor to be operated at four distinct speeds.

According to the invention, a five position single pull, throw switch has its common terminal connected to one side of the line. One of the five positions functions as an "OFF" position. Of the remaining four positions, a first provides direct operation of the fan across the power source. In a second position, four diodes are employed to parallel connect two capacitors which themselves are series connected with the fan across the power source. In a third position, one of the capacitors is connected in series with the fan across the power source. In a fourth position the other of the two capacitors is connected in series with the fan across the AC power source.

With the invention, four distinct operational power levels are achieved with only two capacitors. Maximum versatility at minimum cost is achieved.

FIG. 1 is a schematic diagram of the multiple position power switching system of the invention; and

FIGS. 2a, 2b and 2c are equivalent circuit diagrams for three of the switch positions of the power control switch system of the invention.

As generally shown at 10 in FIG. 1, a multiple position power control switch system of the invention is employed to operate a load 11, preferably a fan, at four distinct power levels or speeds. A power source is connected at terminals 12a, 12b. One side of the load 11 at terminal 11b connects to terminal 12a. The other power source terminal 12b connects through output terminal 9 to the common terminal 13' of a five position switch 13. Preferably switch 13 is a rotary switch although other designs may also be employed. Switch position 13a corresponds to "OFF" operation and is not connected. Switch position 13b corresponding to a first power level position connects directly to terminal 11a of the load 11. Position 13c corresponding to a second operational power level position connects to the cathodes of diodes 16 and 17 whose anodes respectively connect to switch position 13e and 13d. The anode of diode 17 further connects to the series circuit of power level control capacitor 20 and surge resistor 19. A bleeder resistor 18 is connected across the series combination of resistor 19 and capacitor 20. The anode of diode 16 further connects to a series circuit formed by power level capacitor 21 and surge resistor 22. Bleeder resistor 23 is connected in parallel across this series circuit.

Switch position 13d connects to the anode of diode 17 and to capacitor 20.

Switch position 13e connects to the anode of diode 16 and also to capacitor 21.

The anodes of diodes 14 and 15 connect to the common terminal 13' of switch 13. The cathodes respectively connect to capacitor 20 and capacitor 21. Resistors 23, 22, 19 and 18 all are commonly connected through output terminal 8 to terminal 11a of load 11.

FIGS. 2a, 2b and 2c respectively show the equivalent circuits for the switch power level positions 2, 3 and 4 corresponding to switch terminals 13c, 13d and 13e.

With the invention, when switch 13 is in position 13a, no power is supplied to fan 11. In switch position 13b, the fan operates at full speed. In switch position 13c, the two capacitors are paralleled and AC current flows through them as shown in FIG. 2a since diode pairs 15, 16 and 14, 17 are connected back to back to permit full wave AC operation. This corresponds, for example, to 3/4 speed operation of fan 11. In switch position 13d, capacitor 20 and surge resistor 19 permit 1/2 speed operation of fan 11. Capacitor 21 is effectively isolated from the circuit by diode 15 which, after charging of capacitor 21, is no longer forward biased.

In switch position 13e, capacitor 21, which typically has a smaller capacitance than capacitor 20, permits the fan 11 to operate at 1/4 speed, for example. In this switch position, capacitor 20 is isolated from the circuit by diode 14 which is substantially non-conducting.

Accordingly, with the invention only two capacitors are employed, yet four speed operation is attained. By provision of surge limiting resistors 19 and 22, switch contact arcing is reduced and high switch contact reliability is achieved.

Although the invention has been described as applicable to the control of loads such as fan motors, it can also be used to control heater elements such as water heaters, ceiling heating elements, lights, ventilation mechanisms or any other type of apparatus to which power is to be selectively controlled.

Although various minor modifications may be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon, all such embodiments as reasonably and properly come within the scope of my contribution to the art.