Power source control circuit and an electronic device with such power source control circuit

Abstract: An electronic device such as a color television receiver with two kinds of power source turning on/off switches; a main switch (1) and a relay switch (4) to operate the electronic device only when both of the two kinds of switches are operated. Even if the contents of a memory (3) which stores the on/off state of the relay switch (4) indicate that the relay switch is off, detection of a change of the main switch (1) from off to on serves to turn on the device.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to power source control circuits used in electronic device such as, for example, television receivers having two kinds of power source turning on/off means; namely, a main switch provided in each of the electronic devices for necessarily turning off that device when the main switch is turned off and a remote control switch effective only when the main switch is on to turn on/off that electronic device at the same or through remote control, and more particularly to a power source control circuit which necessarily turns on the power source of the electronic device irrespective of the state of a memory circuit when the main switch is turned on and maintains the previous on/off state of the power source when power stoppage occurs. Description of the Related Art Conventional power source control circuits only operate to maintain the previous on/off state of the power source. FIG. 5 is a block diagram of a conventional arrangement known to the Applicant. In this there is a relay which turns on/off the power source of the electronic device; 9, a transistor which drives the relay 8; 11, an non-volatile memory which stores data on the state of the power source; 10, a memory reader which reads the contents of the memory 11 to control the transistor 9. The operation of the conventional power source control circuit will be described with reference to FIG. 5 in which when the main switch 7 is turned on, the reader 10 reads data from the non-volatile memory 11 to see if the previous state of the power source of the electronic device is on. If so, it drives the transistor 9 to thereby drive the relay 8 and hence to operate the electronic device. If the contents read from the memory 11 indicate that the previous state of the power source is off, the memory reader 10 does not drive the transistor 9 and hence the relay 8. By such operation, the electronic device is not operated even if the main switch 7 is turned on so long as the contents of the non-volatile memory 11 indicate that the previous state of the power source is off. SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a power source control circuit for an electronic device which necessarily operates the electronic device when the main switch is turned on. According to the present invention there is provided a power control circuit for an electronic device comprising a main switch, a non-volatile memory operative to store data indicative of the previous state of a power source for the electronic device even if the main switch is not in an "on" state; a memory reader and a drive circuit for controlling the power source of the electronic device, said memory reader being operatively associated with the memory such that it can read data from said memory even if the main switch is not in an "on" state, said control circuit including a determining circuit which is operatively associated with the main switch and the memory reader and is arranged to receive the output of the memory reader and data indicative of the state of the main switch and to determine a control signal for the power even if the main switch is not in an "on" stage, and said drive circuit being arranged to control the power source in accordance with the output of the determining circuit, the arrangement being such that the determining circuit provides a control signal to cause the drive circuit to provide power to said electronic device when the main switch is turned from an "off" to an "on" state. According to the present invention, the above arrangement permits the electronic device to be turned on by detecting a change of the main switch from off to on even if the contents of the non-volatile memory indicate that the previous state of the power source is off. The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings: FIG. 1 is a block diagram of a power source control circuit of one embodiment of the present invention. FIG. 2 is a flowchart indicative of the operation and control of the power source control circuit. FIG. 3 shows a table used for determining the operation and control of the power source control circuit. FIG. 4 is a block diagram of a determining circuit of the control circuit. FIG. 5 is a block diagram of a conventional power source circuit. DESCRIPTION OF THE PREFERRED EMBODIMENT A power source control circuit of one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a power source control circuit according to the present invention. In FIG. 1, reference numeral 1 denotes a main switch; 4, a relay which turns on/off a power source of an electronic device such as a television receiver; 6, a transistor which drives the relay 4; 3, a non-volatile memory which operates in response to application of the power source to store data on the state of the power source even if the main switch is not on; 2, a memory reader which operates in response to application of the power source to read the contents of the non-volatile memory 3 even if the main switch 1 is not turned on; 5, a determining circuit which operates in response to an application of the power source even if the main switch 1 is not on to determine the output of the memory reader 2 and the state of the main switch 1 and, if the result of the determination indicates that the previous state of the power source is on, it drives the transistor 6. In operation, if the power source is turned on (AC 100 V is applied) in FIG. 1, the memory reader 2 first operates to read the contents of the non-volatile memory 3. The determining circuit 5 reads the state of the main switch 1, and if the main switch 1 is on, drives the transistor 6 and hence the relay 4 in accordance with the state of the output of the memory reader 2 to thereby operate the electronic device. This situation includes recovery from power stoppage which occurred when the electronic device was operating. In this case, the previous state of the eletronic device is preferably maintained. If the main switch 1 is off, the transistor 6 is not driven and hence the electronic device is not operated even if the output of the memory reader 2 is on. In this case, the electronic device must not operate because the main switch is turned off even if the previous state of the electronic device was on. For example, this corresponds to turning-off of the main switch for safety's sake due to the occurrence of power stoppage. If the main switch is changed from off to on, the transistor 6 and hence the relay 4 are driven to operate the electronic device irrespective of the output of the memory reader 2. Since the main switch 1 is turned on in this case, the electronic device is preferably operated as such. FIG. 2 is a flowchart indicative of the operation and control of the power source control circuit of the present invention. First, it is determined whether the AC power source is on or off, or properly connected or not (power stoppage or the power source feed switch is on or off). If the AC power source is conencted or on, "high" or "low" memory contents A₁{H, L} corresponding to the power source on/off control signal due to remote control and stored in the non-volatile memory 3 are read out, a "low" or "high" signal B i {H, L} corresponding to the open/closed state of the main switch 1 is detected. By the memory read signal A i {H, L} and the state detection signal B i {H, L} of the main switch 1, the operation A i x B i is performed in determining circuit 5 to thereby obtain the result of the determination C i {H, L} = A i {H, L} x B i {H, L}. Since C i is the ANDing operation of A i and B i , C i = H only when A i = H and B i = H. A bias is then applied to the base of the transistor 6 to thereby render it conductive. This turns on the relay 4 and the power source. The determination in these operations and control or the results of the determination of the respective cases A i {H, L} x B i {H, L} = C i {H, L} (on or off of the relay) are illustrated as the cases I-IV on the table of FIG. 3. As will be obvious from the result of the determination of the cases I-IV of FIG. 3, "L" is stored in the memory 4 in the state of the case I or when the power source is turned off (the relay is turned off) by remote control. When the main switch 1 is further turned off, the state of the main switch 1 is "L", which is the most general case after viewing the television was terminated. As just described above, for example, when the case I state has been brought about after the television was viewed last day, the power source of the television receiver is not turned on but maintained off since the FIG. 3 case III where A i = L, B i = H is maintained and the relay 4 is maintained off even if the main switch is turned on next day. Therefore, even if the main switch 1 of the television receiver is turned on, the power source of the television receiver is not turned on. Provided in the determining circuit 5 is an edge detection circuit which feeds a "high" level signal to the base of the relay drive transistor 6 such that the relay 4 is turned on irrespective of the contents of the memory 3 when the state of the main switch 1 is changed from off to on. Detection of an edge is illustrated as a case V in FIG. 3. Determination of the edge detection is performed using the state B j {H, L} of the main switch 1 at a time t j and the state B j+1 {H, L} of the main switch 1 which has changed at time B j+1 . Namely, the operations B j (L)∩ B j+1 (H) = H, and B j (L)∩B j+1 (L) = L, B j {H, L}∩B j+1 (L) = L are performed. By this edge detection, the edge detection signal becomes "high" so as to turn on the relay 4 in correspondence to a change of the state of the main switch 1 from the case I to III of FIG. 3 and, thus, the power source is connected and fed to the electronic device. FIG. 4 illustrates a block diagram of the determining circuit 5. In FIG. 4, the operations of the cases I-IV are performed on the basis of A i {H, L} x B i (H:on, L:off) = C i (H, L} where A i {H, L} is the contents of the memory 4 and B i (H:on, L:off) is the state of the main switch 1. The operation of the case V in which the edge detection "high" is output in correspondence to the operator's operation to turn on the main switch 1 for B i (L) is performed. While, conventionally, the electronic device is not turned on even if the main switch is turned on provided that the contents of the non-volatile memory indicate that the state of the power source is off, as mentioned above, the electronic device is necessarily turned on when the main switch is turned on in the present invention. Thus, the inventive power source control circuit is easy to use. If the electronic device has operated as usual before power stoppage, it will also operate as usual even in the power stoppage. In addition, since the main switch turns on/off the relay winding current without turning on/off an AC 100 volt power in the present invention, the cost of the switch is reduced compared to the corresponding conventional switch.

Claims: A power control circuit for an electronic device comprising a main switch (1), a non-volatile memory (3) operative to store data indicative of the previous state of a power source for the electronic device even if the main switch (1) is not in an "on" state; a memory reader (2) and a drive circuit (4, 6) for controlling the power source of the electronic device, said memory reader (2) being operatively associated with the memory (3) such that it can read data from said memory even if the main switch (1) is not in an "on" state, said control circuit including a determining circuit (5) which is operatively associated with the main switch (1) and the memory reader (2) and is arranged to receive the output of the memory reader (2) and data indicative of the state of the main switch (1) and to determine a control signal for the power even if the main switch (1) is not in an "on" state, and said drive circuit (4, 6) being arranged to control the power source in accordance with the output of the determining circuit (5), the arrangement being such that the determining circuit provides a control signal to cause the drive circuit to provide power to said electronic device when the main switch is turned from an "off" to an "on" state. A power source control circuit according to claim 1, wherein the main switch (1) is provided in series between the power source for feeding power to the drive circuit (4, 6) and a winding (4) of a relay of the drive circuit. A power source control circuit according to claim 2, wherein the determining circuit (5) detects the voltage at a junction point between the main switch (1) and the winding (4) of the relay of the drive circuit (4, 6) to determine the state of the main switch (1). An electronic device including a power source control circuit according to any preceding claim.

Inventors: SHIMIZU YOSHIKAZU, SHIMIZU, YOSHIKAZU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H04N5
IPC codes: H04N5, H02J1