Patent Application
20080043392
Referring to the drawings and initially to
The relay 2 is electrically connected to a load 1.
The sample-hold circuit 4 includes a current mutual inductor 6 and an operational amplifier 8, such as a U2A. The current mutual inductor 6 includes a primary winding 10 and a secondary winding 12. The primary winding 10 of the current mutual inductor 6 of the sample-hold circuit 4 is electrically connected to the relay 2 and the load 1. In the preferred embodiment of the present invention, the secondary winding 12 of the current mutual inductor 6 of the sample-hold circuit 4 has a center tap and is grounded.
The compare and execution circuit 14 is used to receive the signal from the sample-hold circuit 4 and is electrically connected to the relay 2. The compare and execution circuit 14 includes a plurality of operational amplifiers U2B, U2C and U2D, and a control element 16. The operational amplifiers U2B, U2C and U2D operates the signal from the sample-hold circuit 4. The control element 16 controls operation of the relay 2 according to operation of the operational amplifiers U2B, U2C and U2D so as to turn on or turn off the relay 2. In the preferred embodiment of the present invention, the control element 16 is a silicon controlled rectifier (SCR).
The sample-hold circuit 4 further includes a RC low pass filter 5 consisting of resistors R6 and R7 and capacitors C9 and C10 to filter various entering interference signals having high frequency.
The sample-hold circuit 4 further includes a difference to operation amplifier consisting of resistors R6, R7, R8 and R9, a capacitor C11 and the operational amplifier 8. The difference to operation amplifier of the sample-hold circuit 4 can amplify a difference mode signal and suppress a common mode signal. The common mode signal includes a temperature rise, an environmental noise and the like. Thus, the difference to operation amplifier of the sample-hold circuit 4 has a higher capability to pick up weaker electric signals in the noise surroundings in a stable manner without being affected by the temperature rise.
The difference to operation amplifier of the sample-hold circuit 4 is used to receive the signal from the RC low pass filter 5 of the sample-hold circuit 4.
The capacitor C11 of the difference to operation amplifier of the sample-hold circuit 4 is a Miller capacitor to compensate a signal phase shift produced by the operation and amplification.
The electricity limit protection switch further comprises a first power supply 18 and a second power supply 20. The first power supply 18 includes an electric power of 30 VDC which is supplied to the relay 2. The second power supply 20 includes an electric power of 15 VDC which is supplied to the operational amplifiers 8, U2B, U2C and U2D.
The electricity limit protection switch further comprises a delay-action circuit 22 connected between the sample-hold circuit 4 and the compare and execution circuit 14 and including a diode D8, a resistor R10 and a capacitor C12 to receive the signal amplified by the difference to operation amplifier of the sample-hold circuit 4. The delay-action circuit 22 is used to convert an alternating current signal into a direct current signal to function as a comparison signal. In addition, the basis voltage produced by the VCC, R15, VR1, R14 and R17 of the compare and execution circuit 14 is delayed about one to four (1-4) seconds to ensure stability and reliability of operation.
In operation, when the electricity limit protection switch is electrically connected to the load 1, the secondary winding 12 of the current mutual inductor 6 of the sample-hold circuit 4 has a sensed voltage whose magnitude is responsive to that of the current passing through the primary winding 10 of the current mutual inductor 6 of the sample-hold circuit 4 is further responsive to that of the load 1. More specifically, when the load 1 is working, the current will pass through the primary winding 10 of the current mutual inductor 6 of the sample-hold circuit 4. In the preferred embodiment of the present invention, the secondary winding 12 of the current mutual inductor 6 of the sample-hold circuit 4 has a center tap and is grounded, so that the sensed voltage signal of the secondary winding 12 of the current mutual inductor 6 of the sample-hold circuit 4 is an ideal difference mode signal having the same magnitude and the opposite direction. The ideal difference mode signal is filtered by the RC low pass filter 5 consisting of the resistors R6 and R7 and the capacitors C9 and C10 to filter various entering interference signals having high frequency. Then, the filtered ideal difference mode signal is amplified by the difference to operation amplifier consisting of the resistors R6, R7, R8 and R9, the capacitor C11 and the operational amplifier 8. Then, the amplified ideal difference mode signal is sent through the delay-action circuit 22 (including the diode D8, the resistor R10 and the capacitor C12) into the compare and execution circuit 14 which includes the operational amplifiers U2B, U2C and U2D, and the control element 16. The control element 16 controls operation of the relay 2 according to operation of the operational amplifiers U2B, U2C and U2D so as to turn on or turn off the relay 2. Thus, the electricity limit protection switch can achieve an electricity limit protection purpose by sensing the magnitude of the current passing through the load 1.
In the preferred embodiment of the present invention, the working conditions of the electricity limit protection switch are set as follows. The rated input voltage is 120 VAC/60 Hz of a tungsten lamp, and the electricity limit protection switch is connected between the load 1 and the mains power supply. Thus, when the magnitude of the current passing through the load 1 is smaller than 1.625 A, the electricity limit protection switch will not shut connection between the load 1 and the mains power supply, and when the magnitude of the current passing through the load 1 is greater than 1.625 A, the electricity limit protection switch will delay about one to four (1-4) seconds to shut the connection between the load 1 and the mains power supply so as to limit the electricity.
According to the law established by the California government of U.S.A. in 2006, the maximum rated power of the load of a tungsten lamp of 120 VAC/60 Hz cannot exceed 190 W. Thus, operation of the electricity limit protection switch is set as follows.
When the power of the load is not greater than 190 W, the load 1 is turned on, and the electricity limit protection switch is disposed at an indication state. For example, a first light emitting diode D9 (see
Referring to
In practice, when the power of the load is greater than the preset rated value, the electricity limit protection switch will shut the relay 2 in the switch member 40 so as to turn off the load 1. After the overload situation is removed, the push button 34 is pressed to touch the switch member 40 to contact and conduct the relay 2 in the switch member 40 again so as to connect the load 1 and the mains power supply. When the push button 34 is pressed again at the next time, the relay 2 is shut again. In such a manner, the push button 34 is pressed successively to turn on or turn off the relay 2. Thus, the electric power between the load 1 and the mains power supply is turned off by an overload or by pressing the push button 34 manually. On the contrary, the electric power between the load 1 and the mains power supply is turned on after the overload situation is removed or by pressing the push button 34 manually. Thus, the electricity limit protection switch can achieve an electricity limit protection purpose and can function as a common switch.
Accordingly, the electricity limit protection switch can achieve an electricity limit protection purpose by sensing the magnitude of the current passing through the load 1. In addition, the electricity limit protection switch can achieve an electricity limit protection purpose and can function as a common switch, thereby enhancing the versatility of the electricity limit protection switch.
Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. It is, therefore, contemplated that the appended claim or claims will cover such modifications and variations that fall within the true scope of the invention.
