Automatic plug-in indicator dimmer

0001This invention relates to visual indicators generally and particularly to visual indicators used to indicate if an electronic apparatus is connected to an AC power source.

0002An electronic apparatus may be disconnected from an AC power source ("OFF" mode), connected to the AC power source ("STANDBY" mode) or energized for use ("ON" mode). Safety regulations in some countries require consumer electronic product such as television receivers to have at the front panel an indicator light which is illuminated as soon as the television receiver is plugged into an AC power outlet. This indicator light should be bright enough to be seen in a well-lighted room and visible from different angles to warn the owner that the television receiver is plugged in. The indicator is provided so that if, e.g., the owner leaves home for a protracted period of time, there is a reminder to unplug the receiver.

0003Various indicator systems are known. For example, in television receivers manufactured for the domestic Japanese market it is known to use a combination of red and green light emitting diode (LED) indicators to visually indicate the three modes as follows: if both LEDs are off (dark), then the receiver is in the OFF mode (unplugged); if the red LED is on and the green LED is off, then the receiver is in the STANDBY mode; and if the red LED is off and the green LED is on, then the receiver is in the ON mode. Other known techniques include illuminating a single red LED to indicate both the STANDBY and ON modes, illuminating a single red LED only in STANDBY mode, and using one segment of a seven segment LED to indicate STANDBY mode where the seven segment display normally indicates a tuned channel number in the ON mode.

0004One of the deficiencies in the above indicator systems is the fact that two LEDs may be necessary, thereby increasing the cost of the indicator system. Another deficiency is the distracting affect of an indicator to a viewer of a television system. Since the STANDBY and ON mode indicators must be visible in a well lit room, one or more of the indicators may have a distracting affect when a viewer is watching television in a dimly lit room. It is therefore desirable to implement a mode indicating system using only one indicating light source (e.g., an LED). It is also desirable to reduce the distracting influence of the mode indicator on the user of apparatus equipped with the indicator system.

0005The present invention is in part based on the recognition that, in an electronic apparatus, including a display device, a STANDBY mode (connected to an AC power source) is indicated by an LED at a first brightness level and an ON mode (apparatus energized for use) is indicated by the LED at a second brightness level, which is lower than the first brightness level.

0006The invention will be described with reference to the accompanying Drawing, in which: <ul id="ul0001" list-style="none" compact="compact"><li>Figure 1 shows a block diagram of a television receiver including the invention;</li><li>Figure 2 shows a block diagram of a television receiver including a circuit embodying the invention; and</li><li>Figure 3 shows a block diagram of a television receiver including another circuit embodying the invention.</li></ul>

0007Like reference designators in the various Figures refer to the same or similar elements.

0008The invention will be described in terms of a television receiver, however, it should be appreciated that it is applicable to any electronic equipment where a power-on indicator is desired.

0009Referring to Figure 1, a television receiver 100 receives RF signals from an antenna 12. The RF signals are coupled to a tuner 13 where they are combined with a local oscillator signal having a frequency controlled in accordance with the channel selected by a viewer to produce an IF signal. The IF signal is coupled to an IF signal processor 14. A portion of the IF signal is coupled to a sound processing circuit 16 and converted to an audio response by a speaker 18. Another portion of the IF signal is coupled to a video processing circuit 15 which includes a luminance processing section (not shown) and a chrominance processing section (not shown). The luminance processing section removes luminance signal representing picture transition and tone information from the IF signal, amplifies the luminance signal and couples the amplified luminance signal Y to a kinescope driver 19. The chrominance processing section removes chrominance signals representing picture color information from the IF signal. The chrominance signals are then amplified and demodulated to form color difference signals R-Y, G-Y, B-Y which are then coupled to the kinescope driver 19. The kinescope driver includes three amplifier arrangements (not shown) for combining the color difference signals with the luminance signal to form color signals representing red R, blue B and green G picture information. The color signals are applied to a kinescope 20 which produces corresponding electronic beams. Deflection circuitry (not shown) controls the three electronic beams to produce an image on the screen of the kinescope 20.

0010Television receiver 100 includes a controllable light source 30 which is used to indicate a mode of operation of the television receiver. As previously discussed, there are three modes of operation: OFF mode, in which the television is disconnected from an AC power source; STANDBY mode, in which the television is connected to an AC power source; and ON mode, in which the television is energized for use by the viewer. When the light source 30 is not illuminated the receiver is in the OFF mode. The STANDBY mode is indicated by the light source 30 emitting light at a first brightness level. This first brightness level is, illustratively, bright enough to be seen in a well lighted room and visible from different angles. The illuminated light source 30 warns the owner that the television receiver is plugged in and should therefore be unplugged if, e.g., the owner leaves home for a protracted period of time. The ON mode is indicated by the light source 30 emitting light at a second brightness level. This second brightness level is, illustratively, dimmer than the first level such that a television viewer will not be distracted by the light source while viewing television images. However, this second brightness level should be sufficient to indicate that the television receiver is in the ON mode even if there is no displayed image.

0011Details of the arrangement for controlling the light source 30 will now be described. Television receiver 100 includes a plug 1 having two conductors for coupling AC power from an external AC power source (not shown) to a standby power supply 3 and a main or "run" power supply 11. The standby power supply 3 provides a DC standby voltage VSB, which is typically between 3 and 15 Volts. The standby power supply is energized when plug 1 is plugged into the external AC power source. The controllable light source 30 is coupled to the standby power supply 3 and is illuminated at a first brightness level when the plug 1 is plugged into the external AC power source (STANDBY mode).

0012The main power supply 11 provides various DC voltages, indicated as POWER OUT, for the circuitry within the television receiver 100. The main power supply 11 is energized in response to a control signal ON/OFF CONTROL from a controller 5. The main power supply 11 produces the various "run" (ON mode) supply voltages for the television receiver circuitry, including tuner 13, IF processor 14, sound processor 16, video processor 17, kinescope driver 19, display device 20 and other non-standby-mode circuitry. The main supply 11 is also coupled to the controllable light source 30. The controllable light source 30 is responsively illuminated at a second, lower brightness level when the main power supply is energized (ON mode). As indicated by the dashed line in Figure 2, the light source 30 may also be controlled by the controller 5 directly.

0013Referring to Figure 2, a television receiver 200 similar to the television receiver 100 described above is shown. Television receiver 200 includes an LED 6 which is used to indicate a mode of operation of the television receiver. The LED must be visible, e.g., a red LED. Television receiver 200 includes a plug 1, a standby power supply 3 and a controller 5 which operate in the same manner as previously described with respect to television receiver 100. However, in television receiver 200 a power switch 2 couples the AC power source to the main power supply 11. In addition, the power switch 2 (not the main power supply) is responsive to a control signal ON/OFF CONTROL produced by the controller 5.

0014When plug 1 is connected to an AC power source while power switch 2 is open (STANDBY mode), alternating current flows to the standby power supply which produces the standby voltage VSB. A current limiting resistor 7 is coupled between VSB and a node 10. An anode of the LED is coupled to node 10, and a cathode of the LED is connected to ground 4. The LED emits light when a current flows through it from the anode to the cathode. The brightness of the light produced by the LED is proportional to the current flowing through the LED. The current flowing through the LED, and therefore the brightness level, is limited by the limiting resistor 7 to a predetermined level.

0015When power switch 2 is closed (ON mode) in response to the control signal ON/OFF CONTROL, main power supply 11 is energized and provides the various "run" supply voltages to the television receiver circuitry. Main power supply 11 also produces a signal BYPASS CONTROL which indicates that the television receiver is in the ON mode, i.e., viewing mode.

0016The BYPASS CONTROL signal is coupled to a bypass switch 9, comprising a bipolar transistor, via base resistor 21. Bypass switch 9 is connected in series with a bypass resistor 8, and the two elements are together coupled in parallel with the LED. When the BYPASS CONTROL signal is relatively positive, bypass switch 9 is closed, thereby coupling the bypass resistor 8 in parallel with the LED. A current passes through the bypass resistor 8 from node 10 to ground 4, thereby reducing the current flowing through the LED and diminishing the brightness of the LED.

0017Referring to Figure 3, another embodiment of the invention is shown. The transistor switch 9 of television receiver 200 has been replaced by adding a third pole on a "ganged" power switch 2. When power switch 2 is closed (ON mode) in response to the control signal ON/OFF CONTROL the "ganged" switch 9 is closed at the same time, thereby connected bypass resistor 8 to ground and reducing the brightness of LED 6. This embodiment does not require the BYPASS CONTROL signal found in television receiver 200 or the base resistor 21.

0018The invention provides several advantages over the prior art. For example, the invention requires only one light source to indicate which the operating mode (i.e., OFF, STANDBY or ON) of an electronic apparatus. The invention also reduces the distracting affect of the mode indicator by providing a second (lower) brightness level during the ON mode of operation.

0019It will be apparent to those skilled in the art, that although the invention has been described in terms of specific examples, modifications and changes may be made to the disclosed embodiments without departing from the essence of the invention. For example, bypass switch 9, which is shown as an NPN transistor, may be another type of transistor, a mechanical switch or any other suitable switching device.

0020Another modification would be the use of a second current limiting resistor in series with limiting resistor 7. This second current limiting resistor could be bypassed (shorted) with a parallel-connected switch during the STANDBY mode, such that only the limiting resistor 7 affected the current flow to the LED. During the ON mode the parallel-connected switch would be open, thereby forcing the current to the LED to flow through both limiting resistors and consequently reducing the brightness of the LED.

0021Another modification would be the use of a different light source (e.g., incandescent light). The invention only requires that the light source be controllable to supply two brightness levels. Moreover, a fixed brightness level light source could be used if the brightness could be reduced by, e.g., inserting an optical filter between the light source and the viewer in response to the ON mode of the electronic apparatus.

0022It must also be noted that controller 5 may be electronic or mechanical. For example, the controller could be a microprocessor coupled to an associated keyboard (or remote control receiver) or an ON/OFF push-button switch which provides a mechanical actuation of the power switch 2.

0023These and other modifications are intended to be within the scope of the resent invention defined in the following claims.