ACTIVATION CIRCUIT

Devices operated by solenoids and specifically to circuits for protecting the solenoid from overheating during operation.

It is known to use a solenoid for providing a mechanical operation in response to an electrical signal. Generally the electrical signal is initiated from a location remote to the device being operated by the solenoid. It is also known to initiate the electrical signal by pressing an operator interface device, such as a push button, for a period of time required to cause the desired response. This time period is usually only a fraction of a second. However, the reaction time of most people will be somewhat longer thereby causing current to be applied to the solenoid for a period of time longer than required to produce the desired response. The problem can also occur if the operator interface sticks in the closed position or is held in the closed position for a prolonged period of time thus causing current to be continuously supplied to the solenoid circuit. In other applications, the solenoid can be controlled by a programmable logic controller ("PLC") device which is programmed to initiate operation of the solenoid in response to a predetermined logical condition. If, for any

reason, the PLC device should cause a continuous current to flow in the solenoid circuit or should the PLC repeatedly attempt to initiate the solenoid operation, a heat failure of the solenoid would occur. When there are no size constraints on the solenoid, a larger solenoid capable of handling the extended current flow can be used. Small solenoids used in today's solid state devices are more susceptible to heating failures and therefore are at a higher risk of solenoid failure due to heating when current is applied to the solenoid activating circuit for an extended period of time. However, modern solid state devices generally require a small solenoid and further require that the heat dissipated by the solenoid be less than a level that will cause damage to any of the solid state components which are in close proximity to the solenoid. It is therefore desirable to provide a solid state solenoid activation circuit which will provide protection to the solenoid against heat caused failure due to extended current in the solenoid circuit and rapid repeated activation of the solenoid. It is also desirable that this circuit have few components such that it can be assembled on a small printed circuit board and be relatively inexpensive to manufacture.

If the desired operation is not performed in the expected time frame the operator will probably press the button again and again. These repeated operations cause

heat to build in the solenoid and can ultimately cause failure of the solenoid.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a simple solenoid activation circuit of few components which can be easily assembled on a small printed circuit board. It is also an object of the present invention to provide protection against solenoid failure due to heat caused by extended current flow in the solenoid circuit and rapid repeated operation of the solenoid. This protection circuit permits the use of a smaller solenoid which would normally be more susceptible to heat damage. These objects are accomplished by including a timer circuit in the solenoid activation circuit, which, after a time sufficient for the solenoid to perform its intended function, prevents further current from being applied to the solenoid as long as power continues to be applied to the solenoid activation circuit. When power is removed from the solenoid activation circuit the circuit will be automatically reset for the next solenoid operation initiated by the operator interface device or PLC device.

Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an exploded view of a solenoid operated remote mechanical operator device in accordance with the present invention.

Figure 2 is a front interior view of a solenoid operated remote mechanical operator in accordance with the present invention.

Figure 3 is a view of the back of a solenoid operated remote mechanical operator in accordance with the present invention.

Figure 4 is a sectionalized view of a solenoid operated remote mechanical operator device showing the solenoid in its normal operating position with respect to a device which it is to operate when activated.

Figure 5 is a sectionalized view of a solenoid operated remote mechanical operator device showing the solenoid in its activated position with respect to a device which it is to operate when activated.

Figure 6 is a block diagram of a first embodiment of a solenoid activation circuit in accordance with the present invention.

Figure 7 is a circuit diagram of the first embodiment of a solenoid activation circuit in accordance with the present invention.

Figure 8 is a block diagram of a second embodiment of a solenoid activation circuit in accordance with the present invention.

Figure 9 is a circuit diagram of the second embodiment of a solenoid activation circuit in accordance with the present invention.

Figure 10 is an alternate circuit diagram of the second embodiment of a solenoid activation circuit in accordance with the present invention.

Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various other ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT A solenoid operated remote resetting device 10 in accordance with the present invention is generally illustrated Figure 1. The remote resetting device 10 includes a housing 14 made from two parts which snap together to define a hollow interior. Enclosed within the housing are a solenoid 18, a solenoid plunger 22, a plunger return spring 26, a mechanical operator 30, and a printed circuit board 34. As shown in Figure 2, the solenoid 18 and printed circuit board 34 are fixedly held by portions of the housing 14 such that movement is prohibited. The solenoid

plunger 22 is normally biased to a first position as shown in Figure 2 by the return spring 26 and is linearly movable to a second position as shown in Figure 5 when current is applied to the solenoid 18. Also movably enclosed within the housing 14 is the mechanical operator 30 which is attached to an extending end 38 of the plunger 26 such that the mechanical operator 30 is also movable between a first position shown in Figure 4 and a second position shown in Figure 5.

Referring now to Figure 3, an operating side of the housing 14, generally indicated by reference numeral 42 is juxtaposed to the device being operated by the solenoid operated remote resetting device 10. A rectangular opening 46 is defined by the housing 14 such that it passes through the operating side 42. The opening 46 receives an operating arm 50 which extends outwardly through the opening 46. The operating arm 50 is an integral part of the mechanical operator 30 and therefore also moves linearly between a first position and a second position. This linear movement corresponds to the movement of the plunger 22 between its first and second positions. Also defined on the operating side 42 of the housing 14 are two generally parallel spaced apart retaining ribs 54. These ribs 54 are slidingly received in two correspondingly spaced apart generally parallel grooves provided in the enclosure of the device to be operated by the solenoid operated remote resetting device 10. The ribs 54 and corresponding grooves provide a means

for properly aligning the solenoid operated remote resetting device 10 with the device being operated. A fastener, such as a screw 58 shown in Figure 1, is used to secure the solenoid operated remote resetting device 10 to the enclosure of the device being operated.

Referring now to Figures 4 and 5 a solenoid operated remote resetting device 10 of the present invention is attached to the housing of an overload protection device generally indicated by reference numeral 62. In Figure 4 the solenoid plunger 22 is shown in its normally biased first position wherein the operating arm 50 is located immediately adjacent to a manual reset mechanism 66 of the overload protection device 62. In Figure 5, current has been applied to the solenoid 18 causing the solenoid plunger 22, mechanical operator 30 and operating arm 50 to be moved to their second position. In moving to the second position the operating arm 50 engages the manual reset mechanism 66 causing it to be moved to a reset position and thereby resets the tripped overload protection device 62.

Referring now to Figure 6, a block diagram of a solenoid activation circuit, generally indicated by reference numeral 70, is shown. Also shown in Figure 6 is an activation means 74 which includes devices such as a manually operated operator interface device, programmable logic controller or other interposing relays which provide an AC (alternating current) electrical activation signal to the solenoid operated remote resetting device 10. The

electrical activation signal is received through a pair of terminals 78 mounted on the housing 14 as shown in Figure 1. The terminals 78 are electrically connected to the printed circuit board 34. This electrical signal provides operating power to a solenoid activation circuit 70. The solenoid activation circuit 70 includes a rectifier 82, a timing circuit 86 and a solenoid power circuit 90.

Referring now to Figure 7, a first embodiment of the solenoid activation circuit 70 will be explained. In this embodiment, a full wave bridge rectifier 82 includes diodes l, D2, D3 and D4. The AC electrical signal is passed to rectifier 82 at a pair of input terminals connected to the anodes of diodes D3 and D4. A pair of output terminals located at the anodes of diodes Dl and D2 and cathodes of diodes D3 and D4 provide DC current for the timing circuit 86. The solenoid power circuit 90 is composed of resistors Rl and R2, capacitor Cl and silicon controlled rectifiers Ql and Q2. The anodes of SCR's (silicon controlled rectifiers) Ql and Q2 are electrically connected to the input terminals of the rectifier 82. The resistor R2, capacitor Cl and diode D6 are electrically connected to the output terminals of the rectifier 82 and provide gate current for SCR's Ql and Q2 which in turn controls current flow through Ql and Q2. The timing circuit 86 is composed of resistors R3, R4, R5 and R6, capacitor C2 and transistor Q3 and is also electrically connected to the output terminals of the rectifier 82. When an AC electrical signal from the

activation means 74 is received at the input of the rectifier 82, a DC current begins to flow from the output terminals of the rectifier 82. If a positive half cycle is starting at the anode of D4, the voltage will be increasing with respect to the voltage at the anode of D3. As soon as the voltage is greater than the sum of the residual voltage on Cl, the forward-bias voltages of D4 and D6 and the gate- bias voltage of Q2, current will begin to flow through D4, R2 and Cl. At this time Q3 in the timer circuit is in a high impedance state which causes the current to flow through D6 thereby gating Q2 into conduction until the end of the half cycle and thereby activating the solenoid 18. The process is repeated such that Ql is gated into conduction thereby continuing the activation of the solenoid 18. During this same time interval, current is also flowing in the timer circuit 86. As the charge on C2 increases, the voltage at the base of transistor Q3 increases until Q3 is biased "ON". When Q3 is "ON" it is in a low impedance state and begins to conduct. When Q3 is in full conduction the gate voltage of Ql and Q2, is not sufficient to turn them on, thus current flow to the solenoid 18 is stopped. Q3 will remain in conduction as long as an AC electrical signal is received from the activation means 74. The component values chosen for the timing circuit 86 will determine the length of time for an active phase in which the solenoid is activated. A blocking phase in which the solenoid is not activated starts as soon as Q3 is in full conduction and

continues until the AC electrical signal from the activation means 74 is discontinued. After the blocking phase is discontinued, R6 allows the voltage at the base of Q3 to bleed off, thereby resetting the active phase time for the next AC electrical signal from the activation means 74. Thus, as soon as the AC electrical signal from the activation means 74 is discontinued, the solenoid activation circuit 70 is immediately ready to receive and process the next AC electrical signal from the activation means 74.

Figure 8 is a block diagram of a second embodiment of a solenoid activation circuit generally indicated by reference numeral 94. In this embodiment the activation means 74 and rectifier 82 are comprised of the same elements as those in the first embodiment. As shown in Figure 9, a timer circuit 98 is electrically connected to the outputs of rectifier 82 comprises resistors R2, R3 and R4, capacitor Cl and transistor Q2. A solenoid power circuit 102, including resistors Rl, R5, R6 and R7, free wheeling diode D5 and a silicon controlled rectifier Ql, is also electrically connected to the outputs of the rectifier 82 and to the timer circuit 98. When an AC electrical signal is received from the activation means 74, current flows through resistors Rl, R5, and R6 biasing the gate of Ql such that Ql goes into conduction, thereby causing current to flow through the solenoid 18. Current is also flowing through resistor R2, causing capacitor Cl to charge. As the charge on C _l increases, the base-bias voltage on Q2 also increases.

When the base-bias voltage is sufficient, Q2 will conduct, causing current to flow through Q2, thereby decreasing the gate current of Ql and causing Ql to become ungated. Current will continue to flow through Ql until the free wheeling current of solenoid 18 and free wheeling diode D5 has dropped to zero. The values of the timing circuit 98 components are chosen such the time required for the base- bias voltage of Q2 to cause conduction of Q2 is sufficient for the solenoid 18 to perform its intended duty.

An alternate solenoid activation circuit 104 is shown in Figure 10. This embodiment is the same as shown in Figure 9 except that an enhancement mode MOSFET Q3 replaces the SCR Ql of Figure 9. The MOSFET Q3 provides an immediate shutoff of power to the solenoid 18 when transistor Q2 starts conducting. The SCR of Figure 9 will continue to conduct for a short time until free wheeling current has dropped to zero.