Video apparatus for generating a conductively isolated control signal

Abstract: An input signal (R on/off ) for controlling a television power supply has "power-on" and "power-off" signal states. When the input signal is in the "power-on" state, it couples a clock signal (CK) to a primary winding (W1) of a transformer (T3) causing an alternating current voltage (V W2 ) that is conductively isolated from the input signal to be developed across a secondary winding (W2) of the transformer (T3). When the input signal (R on/off ) is in the "power-off" state, it decouples the clock signal (CK) from the primary winding (W1) so that no alternating current voltage is developed across the secondary winding (W2). The signal across the secondary winding is demodulated in a demodulator (41) that produces a control signal (S hot ) that is conductively isolated from the input signal (R on/off ). The control signal (S hot ) is coupled to a regulator (38c) of the power supply (38). A power-on state of the control signal occurs when the alternating current voltage (V W2 ) is developed at the secondary winding terminal (W2a). A power-off state of the control signal occurs when the alternating current voltage (V W2 ) is absent.

Description: The invention relates to a circuit that couples a control signal from a control circuit to a utilization circuit that is conductively isolated from the control circuit. Some television receivers have signal terminals for receiving, for example, external video input signals such as R, G and B input signals, that are to be developed relative to a common conductor of the receiver. Such signal terminals and the receiver common conductor may be coupled to corresponding signal terminals and common conductors of external devices, such as, for example, a VCR or a teletext decoder. To simplify the coupling of signals between the external devices and the television receiver, the common conductors of the receiver and of the external devices are connected together so that all are at the same potential. The signal lines of each external device are coupled to the corresponding signal terminals of the receiver. In such an arrangement, the common conductor of each device, such as of the television receiver, may be held "floating" or conductively isolated relative to the corresponding AC mains supply source that energizes the device. When the common conductor is held floating, a user touching a terminal that is at the potential of the common conductor will not suffer an electrical shock. Such electrical shock may occur if the common conductor is not held floating. Furthermore, having the common conductor floating avoids an undesirable current flow, or a current loop, among the common conductors of the devices that are, as described above, connected together. Therefore, it may be desirable to isolate the common conductor or ground of, for example, the television receiver, from the potentials at the terminals of the AC mains supply source that provides power to the television receiver. Such isolation is typically achieved by a transformer, as described below. The isolated common conductor is sometimes referred to as "cold" ground conductor. In some television receivers the AC mains supply voltage is coupled directly to a bridge rectifier for producing an unregulated direct current (DC) input voltage. The unregulated DC input voltage may be applied to a switching, or chopper, power supply having a chopper transformer that generates regulated DC voltages. The regulated DC voltages are developed, typically, from a secondary winding of the chopper transformer, relative to the cold ground conductor. The chopper transformer conductively isolates the regulated voltages, thus causing them to be floating, relative to the potentials at terminals of the AC mains supply voltage source. Circuit networks of the power supply that provide voltages that are not floating relative to the potentials at the AC mains supply voltage source terminals, such as voltages at the primary winding of the chopper transformer, are referenced to a common conductor that is, therefore, floating relative to the cold ground conductor and that is sometimes referred to as "hot" ground conductor. Some television circuits that are energized from the regulated DC voltages utilize the cold ground conductor as the common conductor. When external video devices are coupled to the receiver, the cold ground conductor that provides current return path to, for example, the video signals of the receiver is also connected to the common conductors of the external video devices. Therefore, by making each of the common conductors floating, the above-mentioned undesirable flow in a current loop among the common conductors is eliminated. Furthermore, a user who touches the floating common conductor will not suffer an electrical shock. It is desirable to maintain isolation between the hot and cold ground conductors of the television receiver when coupling a control signal from, for example, a control circuit of the television receiver that is referenced to the cold ground conductor, to a section of the power supply circuit of the television receiver that is referenced to a hot ground conductor. In some television systems it may be advantageous to have the control section of the power supply referenced to the hot ground conductor; the on/off input signal that is generated by a remote control unit may be referenced to a cold ground conductor. In order to couple the on/off input signal that is referenced to the cold ground conductor to the control section that is referenced to the hot ground conductor of, for example, a switched mode power supply, some prior art circuits utilize a relay having a control winding that is conductively coupled to the cold ground conductor. In such prior art circuits, the on/off input signal that is referenced to the cold ground conductor is conductively coupled to the control winding of the relay. A pair of contacts that are magnetically activated by the current in the control winding are conductively coupled to the control section of the switched mode, or chopper, power supply that is referenced to the hot ground conductor. The closure and separation of the relay contacts controls the on/off operation of the power supply, in accordance with the information contained in the "cold" on/off input signal in the control winding of the relay. Both contacts of the pair of contacts are conductively isolated from the on/off input signal that is coupled to the control winding. Thus, the on/off input signal is magnetically coupled across the cold-hot barrier formed by the relay without affecting the conductive isolation across the cold-hot barrier. A disadvantage of such on/off input signal coupling arrangement is that it is bulky, not highly reliable because it utilizes the moving mechanical parts of the relay, and consumes excessive power when, for example, the relay is energized. In other television systems the on/off input signal coupling arrangement includes a photo-coupler that couples the on/off input signal by a cooperating pair of electrical-to-digital and optical-to-electrical transducers. A disadvantage of such coupling arrangement is that the level of the signal produced by, for example, the optical-to-electrical transducer is low. Such low level signal may be susceptible to noise. Another disadvantage is that such photo-coupler may be relatively expensive. Additionally, the conductive isolation in the photo-coupler between the input and output signals may not be adequate in some television applications. DE-A-2024092 relates to a power supply with a DC voltage converter and a feedback regulation arrangement for providing a constant DC output. The DC voltage output signal is fed back to control the frequency of switching of an internal circuit which chops the input mains signal into a pulse frequency, which pulse frequency is subsequently rectified. This system is relatively complex for providing a constant DC output voltage and is not concerned with the problems of hot and cold ground conductors. DE-A-3232554 discloses a remote control arrangement for a television receiver wherein the control simulates an abnormal operating condition. The present invention provides a power supply apparatus, comprising a source providing a first on-off control signal having an on-state and an off-state for providing normal operation on-off control; means responsive to said first on-off control signal for generating a first AC signal conductively coupled to said source of on-off control signal, and of constant frequency during one of said on and off-states, and not during the other of said on and off-states; a signal transformer having a first winding coupled to said first AC signal for developing, in a second winding thereof, conductively isolated from said first winding, a second AC signal of constant frequency and width during said one state and not during said other state; a source of input supply voltage; and a normal operation power supply coupled to said source of input supply voltage and to said second winding of said signal transformer for developing only during the on-state of said first on-off control signal an operating voltage. In accordance with the invention, a power supply control apparatus responsive to an input signal, that contains power on and power off control information, produces a control signal that controls the on-off operation of a power supply. A modulator produces from a first signal, that contains an alternating current (AC) component signal, a modulated signal that is modulated in accordance with the input signal. The control signal is produced from the modulated signal. In accordance with the invention, the modulated signal is magnetically coupled to the power supply such that the control signal, that is produced from the modulated signal, is conductively isolated from the input signal. In carrying out the invention, the input signal has first and second signal states. The input signal modulates a carrier signal for producing the a modulated signal in accordance with the corresponding state of the input signal. Illustratively, when the input signal is at the first signal state, the modulated signal contains the AC component signal. In contrast, when the input signal is at the second signal state, the modulated signal does not contain the AC component signal. The modulated signal is applied to a primary winding of a transformer. The signal at the secondary winding of the transformer that is coupled from the primary winding of the transformer is conductively isolated from the control circuit and from the input signal by the isolation between the secondary and primary windings. The signal at the secondary winding is demodulated in a demodulator for generating the control or output signal having, for example, first and second signal states that correspond with the first and second signals states of the input signal. The output signal is coupled to a control terminal of a power supply that is conductively isolated, by the transformer, from the input signal for controlling the power supply in accordance with the first and second signal states of the input signal. In an embodiment of the invention, the input signal is generated by a remote control circuit that is referenced to a cold ground conductor of a television receiver. When the input signal is at the first state, the television receiver power supply is turned on. When the input signal is at the second state, the power supply is turned off. When the input signal is at the first, or "power-on" state, a clock signal of a constant duty cycle is coupled to a primary winding of a transformer. On the other hand, when the input signal is at the second, or the "power-off" state, the clock signal is not coupled to the primary winding. The signal at the primary winding is thus amplitude modulated by the input signal. When the clock signal is coupled to the primary winding, the AC component signal of the clock signal is magnetically coupled to a secondary winding across a hot-cold barrier formed by the transformer. When the clock signal is not coupled to the primary winding, corresponding with the input signal being at the second state, the signal in the secondary winding does not contain the AC component signal and is illustratively at zero volts. An amplitude demodulator demodulates the signal in the secondary winding to generate the output or control signal that is conductively isolated from the cold ground conductor of the remote control circuit. The output signal is coupled to a regulator of the power supply that is referenced to the hot ground conductor. Illustratively, the output signal remains at a "power-on", or a first state, as long as the clock signal is coupled to the primary winding, and remains at a "power-off", or a second state, as long as the clock signal is not coupled to the primary winding. The first and second states of the output signal correspond with the "power-on" and "power-off" states, respectively, of the input signal of the remote control circuit for turning-on and turning-off the power supply, respectively. In this way, each state of the input signal determines the corresponding state of the output signal that is conductively isolated from the input signal. In a typical television display system, a high voltage ultor accelerating potential is applied to the final anode electrode of a picture tube to accelerate an electron beam generated at a picture tube cathode onto a phosphor screen. To ensure that the television receiver will not be operated under fault conditions at excessive ultor potential levels, a high voltage protection circuit is incorporated in the television receiver circuitry. In carrying out an aspect of the invention, the high voltage protection circuit causes the shut-down of the high voltage power supply by the output signal of the demodulator. The output signal of the demodulator is at the "power-off" state when the high voltage becomes excessive. In accordance with another aspect of the invention, a fault indicative signal that is referenced to the cold ground conductor and that is representative of, for example, excessive ultor voltage, is also coupled to the primary winding of the transformer that was described before. The fault indicative signal causes the output signal from the demodulator to assume the second, or "power-off", state that causes the shut-down of the high voltage power supply when the ultor voltage becomes excessive. In the Drawing: FIGURE 1 illustrates a block diagram of a television receiver power supply system that includes an on/off control signal generator embodying an aspect of the invention; FIGURE 2 illustrates a first detailed embodiment of the on/off control signal generator of FIGURE 1, embodying another aspect of the invention; FIGURE 3 illustrates a second detailed embodiment of the on/off control signal generator of FIGURE 1, embodying a further aspect of the invention; and FIGURE 4 illustrates a circuit, embodying an additional aspect of the invention, that includes a microprocessor for generating the on/off control signal of FIGURE 1. FIGURE 1 illustrates a power supply system of a television receiver. In FIGURE 1, an AC mains supply 30 provides a voltage V AC that is conductively coupled to a pair of input terminals of a bridge rectifier 31. Bridge rectifier 31 produces, in a conventional manner, an unregulated DC voltage V INNR at an output terminal 31a that is referenced to a current return terminal 31b of rectifier 31. Terminal 31b provides the potential of a first common conductor, referred to as a hot ground conductor 27. Voltage V AC is also magnetically coupled by a transformer T1 to a bridge rectifier 32 that similarly produces an unregulated DC voltage V INSB at an output terminal 32a that is referenced to a current return terminal 32b. Terminal 32b provides the potential of a second common conductor, referred to as a cold ground conductor 25. Voltage V INSB is conductively isolated from voltage V INNR because of the conductive isolation provided by the transformer T1. Voltage V INSB energizes a conventional standby power supply 33 that provides a regulated DC voltage V SB to a conventional remote signal processor 34 even when the television receiver does not produce a raster. Remote signal processor 34 is referenced to cold ground conductor 25 and receives an input signal RM. Signal RM is indicative of "power-on" and "power-off" user commands that are initiated when such user wishes to turn on and turn off the display operation, respectively. Signal RM is conventionally generated by, for example, an infrared remote receiver, not shown in FIGURE 1. Signal RM is used in processor 34 for generating an on/off signal R on/off . A first state of signal R on/off is used for turning on a normal operation power supply 38; whereas a second state of signal R on/off is used for turning off power supply 38. Processor 34 may include a microcomputer that processes signal RM for generating signal R on/off and that receives a clock signal CK1 for its operation. Clock signal CK1 is generated by a clock generator 35. Clock generator 35 includes, illustratively, an oscillator that provides an input signal to a frequency dividing chain, not shown in FIGURE 1. Clock signal CK1, that is obtained from the frequency dividing chain, provides a conventional clock signal to the circuitry of remote signal processor 34. Clock generator 35 also generates, for example, a 32 KHZ clock signal CK, obtained from the frequency dividing chain, that is not shown in FIGURE 1, used for generating a signal S cold . In carrying out an aspect of the invention, clock signal CK and on/off signal R on/off are coupled to first and second input terminals, respectively, of an "AND" gate 36. Signal S cold , developed on a line 37e at an output terminal 36a of "AND" gate 36 is referenced to cold ground conductor 25. When signal R on/off is at logical "TRUE", that is representative of the first, or "power-on", state of signal R on/off , "AND" gate 36 causes signal S cold to toggle alternately between logical "TRUE" and logical "FALSE" states at the frequency of clock signal CK. On the other hand, when signal R on/off is at logical "FALSE", that is representative of the "power-off", or second, state, signal R on/off prevents the clock pulses of clock CK from appearing on line 37e. Therefore, signal S cold is continuously at logical "FALSE" state. Thus, "AND" gate 36 produces from clock CK signal S cold that is modulated in accordance with signal R on/off . Signal S cold is coupled to an input terminal 37a of an on/off control signal generator 37, embodying yet another aspect of the invention. Generator 37 is energized by a DC voltage V XP that is referenced to cold ground conductor 25 and that is generated by standby power supply 33. Generator 37 includes a transformer T3 that magnetically couples, under normal operating conditions, the signal component at the frequency of clock signal CK that is contained in signal S cold when signal R on/off is at the "power-on" state, for generating a corresponding "power-on", or first, state of an on/off input signal S hot at terminal 37d. Signal S hot , that contains only on/off control information, is referenced to hot ground conductor 27. When signal S cold is at the logical "FALSE" state, occurring when signal R on/off is at the "power-off" state, signal S cold does not include the signal component at the frequency of clock signal CK. Illustratively, as long as signal S cold , that is coupled to transformer T3, does not contain a signal component at the frequency of clock signal CK, control signal S hot is caused to be at a corresponding "power-off", or second, state. Control signal S hot , that is conductively isolated from cold ground conductor 25 by the magnetic coupling of transformer T3 of generator 37, is coupled to an on/off control terminal 38a of a conventional chopper switch regulator control section 38c of normal operation switching power supply 38. Control section 38c is referenced to hot ground conductor 27. Control section 38c may include, illustratively, a driver transformer 38e that provides the drive signal to a chopper switch, not shown in FIGURE 1. Each winding of transformer 38e may be referenced to hot ground conductor 27. When signal S hot is in the "power-on" state, chopper regulator control section 38c generates, in a conventional manner, an alternating current voltage V W3 that is developed across a primary winding W3 of a chopper transformer T4 that is powered by unregulated DC voltage V INNR . An induced voltage V W4 across a secondary winding W4 of transformer T4 is coupled to a conventional rectifier and filter unit 38d that generates, by rectifying voltage V W4 , a regulated voltage B+ that is referenced to cold ground conductor 25. Isolation between hot ground conductor 27 and voltage B+ is obtained in a conventional manner by the conductive isolation between windings W3 and W4 of transformer T4. On the other hand, when signal S hot is in the "power-off" state, that occurs when signal R on/off is at the "power-off" state, power supply 38 is turned off by signal S hot causing a voltage B+ to be zero. Thus, windings W3 and W4 are located on the opposite sides of a hot-cold barrier that isolates signals S hot from signal R on/off . In accordance with an aspect of the invention, the regulation of voltage B+ that is referenced to cold ground conductor 25 is performed on the "hot" side of the hot-cold barrier. Signal S hot , that is referenced to hot ground conductor 27, turns on and off, respectively, voltage B+. Advantageously, driver transformer 38e need not serve as an isolation transformer, thereby simplifying the transformer design. Voltage B+ provides power to a conventional horizontal deflection circuit 39 that produces horizontal deflection current cycles in a deflection winding, not shown in FIGURE 1, in accordance with timing information derived from a horizontal sync signal H s . Deflection circuit 39 includes a flyback transformer T2, partially shown in FIGURE 1, having a tertiary winding W6 that provides at a terminal 39c of circuit 39 a deflection rate retrace pulse V HV . Terminal 39c is coupled to a high voltage or ultor circuit 40 that produces an ultor voltage U at a level that is determined according to, for example, the positive peak value of pulse V HV . A secondary winding W5 of flyback transformer T2 produces a deflection rate retrace pulse V LV . Each pulse V LV has a positive peak of, for example, 20 volts at a terminal 39b of circuit 39. Because of the tight magnetic coupling of transformer T2, the positive peak voltage of pulse V LV is also representative of the level of ultor voltage U. Pulse V LV is coupled to an input terminal 37b of on/off control signal generator 37. When the positive peak of pulse V LV exceeds a predetermined threshold voltage, representative of a corresponding level of ultor voltage U, pulse V LV causes signal S hot to be at the second, or "power-off", state, regardless of the state of signal R on/off . When signal S hot is in the second state, power supply 38 causes voltage B+ to become zero. When voltage B+ is zero, ultor voltage U becomes zero, because retrace pulse V HV at terminal 39c of transformer T2 is no longer produced. When the positive peak of pulse V LV does not exceed the predetermined threshold level, pulse V LV does not affect signal S hot . Thus, in accordance with a further aspect of the invention, the information in pulse V LV is coupled to generator 37 for establishing high voltage or X-ray protection. FIGURE 2 illustrates detailed schematic diagram of on/off control signal generator 37 of FIGURE 1, embodying aspects of the invention. Similar numbers and symbols in FIGURES 1 and 2 indicate similar items or functions. In FIGURE 2, energizing voltage V XP , supplied from standby power supply 33 that is referenced to cold ground conductor 25, is coupled through a current limiting resistor R1 to the cathode electrode of a zener diode CR1 that develops a voltage V E of 10 volts. Voltage V E is coupled to the emitter electrode of a transistor Q1. The base electrode of transistor Q1 is supplied, under normal operating condition of ultor voltage U, with sufficient base current to maintain transistor Q1 turned-on so as to couple voltage V E to the collector electrode of transistor Q1. The voltage at the collector electrode of transistor Q1 is coupled through a current limiting resistor R3 to an end terminal W1a of a primary winding W1 of transformer T3. A filter capacitor C Q1 is coupled between terminal W1a and cold ground conductor 25. The other end terminal W1b of winding W1 is coupled to the collector electrode of a transistor switch Q2. The emitter electrode of transistor switch Q2 is coupled to cold ground conductor 25. Control signal S cold , that is referenced to cold ground conductor 25, is coupled through a resistor R4 to the base electrode of transistor switch Q2. Control signal S cold provides, through resistor R4, a train of base electrode current pulses i b , at the frequency of clock signal CK of FIGURE 1,that flows in the base electrode of transistor switch Q2 of FIGURE 2 throughout the period in which signal R on/off of FIGURE 1 is at the "power-on" state. The train of base electrode current pulses i b of FIGURE 2 causes the alternate switching-on and switching-off of transistor switch Q2, that is coupled between terminal W1b and cold ground conductor 25. The alternating switching of transistor switch Q2 at the frequency of clock signal CK of FIGURE 1 causes an AC voltage V W1 of FIGURE 2 to be developed across primary winding W1. Capacitor C Q1 maintains voltage V W1 at a substantially constant level when switch Q2 is conductive, for developing an upramping current in winding W1. AC voltage V W1 across primary winding W1 is coupled by transformer action of transformer T3 to a secondary winding W2 for developing an AC voltage V W2 between a terminal W2a and a terminal W2b that is coupled to hot ground conductor 27. A demodulator or detector 41 includes a diode CR2. The anode electrode of diode CR2 is coupled to terminal W2a of transformer T3. One plate of a capacitor C3 is coupled to both output terminal 37d of generator 37 and to the cathode electrode of diode CR2. The other plate of capacitor C3 is coupled to hot ground conductor 27. Diode CR2 rectifies signal V W2 in winding W2, that is conductively isolated from cold ground conductor 25, for developing signal S hot at terminal 37d. In carrying out another aspect of the invention, diode CR2 may be coupled to winding W2 by a passive coupling arrangement such that, for example, signal V W2 appears at the anode of diode CR2. Thus, the energy for generating signal S hot may be supplied entirely by signal V W2 across winding W2. Signal S hot that is referenced to hot ground conductor 27 is at a level that is substantially equal to the peak positive voltage of signal V W2 that is developed across capacitor C3. The input resistance that is not shown in FIGURE 2, from terminal 38a of power supply 38 to hot ground conductor 27, provides a discharge trickle current path to the charge in capacitor C3 so that signal S hot can change state from the first to the second state when signal S cold is continuously at the "FALSE", or "power-off" state. Thus, when transistor switch Q2 is alternately turned on and off by pulsed signal S cold , corresponding with the "power-on" state of signal R on/off , AC signal V W2 is developed at secondary winding W2 causing signal S hot to be at the "power-on" state. On the other hand, throughout the period in which input signal S cold is continuously at the "FALSE" state, occurring when signal R on/off of FIGURE 1 is at the "power-off" or second state, transistor switch Q2 of FIGURE 2 is turned-off. Because switch Q2 is nonconductive in the "power-off" state, voltage V W1 is zero in the "power-off" state. Voltage V W1 being of zero volts causes signal V W2 to be at zero volts; therefore, the resulting signal S hot is at zero volts. As long as signal S hot is at zero volts, power supply 38 stays turned-off. Thus signal S hot , that is conductively isolated from signal S cold , contains the "power-on" and "power-off" information of each of signals R on/off and S cold . The positive portion of each retrace pulse of voltage V LV is coupled by a series arrangement of a resistor R5 and a diode CR3 to develop across a capacitor C4 a DC voltage V C4 that is equal to the positive peak of voltage V LV . Voltage V C4 across capacitor C4 is coupled across series coupled resistors R4 and R6. A junction terminal J R4 between resistors R4 and R6 is coupled to the base electrode of transistor Q1. Under normal operating conditions of both voltages V HV and L LV of FIGURE 1, the voltage developed at junction J R4 is lower than voltage V E , developed at the emitter electrode of transistor Q1 of FIGURE 2. Transistor Q1, therefore, stays continuously conductive. On the other hand, when voltage V LV of FIGURE 2 exceeds the predetermined threshold level, that was mentioned before, the voltage developed at the base electrode of transistor Q1 is sufficiently high so as to cause transistor Q1 to turn off. When transistor Q1 is turned-off, the collector voltage of transistor Q1 is zero. Therefore, the switching operation of transistor switch Q2 does not produce voltage V W1 between terminals W1a and W1b of primary winding W1 of transformer T3. It follows that signal V W2 at terminal W2a is zero and signal S hot is forced to be at the second, or "power-off" state. When signal S hot is at the second or, "power-off", state power supply 38 of FIGURE 1 is turned off, causing voltage B+ to become zero. Voltage B+ at zero volts causes voltage V HV and ultor voltage U to become also zero. Thus, when ultor voltage U becomes excessive, generator 37 generates signal S hot at the second, or "power-off" state that causes ultor voltage U to disappear. A generator 37′ of FIGURE 3, embodying another aspect of the invention, is a second embodiment of generator 37 of FIGURE 1. Similar numbers and symbols in FIGURES 1, 2 and 3 indicate similar items or functions. Generator 37′ of FIGURE 3 is similar to generator 37 of FIGURE 2 and operates similarly except that in generator 37′ of FIGURE 3, signal S cold at output terminal 36a of "AND" gate 36 of FIGURE 1 is coupled directly to terminal W1b of transformer T3. When generator 37′ of FIGURE 3 is used in the system of FIGURE 1, it is desirable that "AND" gate 36 of FIGURE 1 have sufficient sinking current capability at terminal 36a when signal S cold is at logical "FALSE" for sinking the current that flows in winding W1 of FIGURE 3. Also, it is desirable that "AND" gate 36 at terminal 36a have sufficiently high breakdown voltage so as to be able to withstand the flyback voltage that is developed at the collector electrode of transistor switch Q2. FIGURE 4 illustrates a second embodiment of the function performed by the arrangement of remote signal processor 34, "AND" gate 36 and clock generator 35 of FIGURE 1. Similar numbers and symbols in FIGURES 1 and 4 indicate similar items or functions. In carrying out yet further aspect of the invention, processor 34 of FIGURE 4 may include a microcomputer 34a that generates under program control a signal S′ cold that is coupled to line 37e of FIGURE 1. Signal S′ cold of FIGURE 4 is substantially equivalent to signal S cold at output terminal 36a of "AND" gate 36 of FIGURE 1.

Claims: A power supply apparatus, comprising: a source (34) providing a first on-off control signal (R on/off ) having an on-state and an off-state for providing normal operation on-off control; means (36) responsive to said first on-off control signal (R on/off ) for generating a first AC signal (S cold ) conductively coupled to said source of on-off control signal, and of constant frequency during one of said on and off-states, and not during the other of said on and off-states; a signal transformer (T3) having a first winding (W1) coupled to said first AC signal (S cold ) for developing, in a second winding (W2) thereof, conductively isolated from said first winding, a second AC signal (V W2 ) of constant frequency and width during said one state and not during said other state; a source (30) of input supply voltage (V AC ); and a normal operation power supply (38) coupled to said source (30) of input supply voltage and to said second winding (W2) of said signal transformer (T3) for developing only during the on-state of said first on-off control signal (R on/off ) an operating voltage (B+). Apparatus according to claim 1 characterized in that said normal operation power supply (38) includes a regulator control section (38c) responsive to said second AC signal (V W2 ) and conductively nonisolated from said input supply voltage (V AC ), and wherein said first on-off control signal (R on/off ) and said first AC signal (S cold ) are conductively isolated from said input supply voltage (V AC ), the first (W1) and second (W2) windings of said signal transformer (T3) providing an isolation barrier. An apparatus according to Claim 2 characterized by a demodulator (41) responsive to said second AC signal (V W2 ) for producing therefrom a second on-off control signal (S hot ) having a first state during one of said on and off-states of said first on-off control signal (R on/off ) and a second state during the other one of said on and off-states of said first on-off control signal (R on/off ). An apparatus according to Claim 3 characterized in that said second on-off control signal (S hot ) is conductively nonisolated from said input supply voltage (V AC ) and wherein said first on-off control signal (R on/off ) is conductively isolated by said transformer (T3) from said second on-off control signal (S hot ). An apparatus according to claim 3 or claim 4 characterized in that said regulator control section (38c) regulates said operation voltage (B+), wherein said regulator control section (38c) is conductively nonisolated from said second on-off control signal (S hot ) and said input supply voltage (V AC ) and wherein said operating voltage (B+) is conductively isolated from said regulator control section (38c). An apparatus according to claim 5 characterized in that said regulator control section (38c) includes a driver transformer (38e) such that each winding of said driver transformer (38e) is conductively nonisolated from said input supply voltage (V AC ) and said second on-off control signal (S hot ). An apparatus according to any one of Claims 3 to 6 characterized in that said demodulator (41) comprises a peak detector that produces said second on-off control signal (S hot ) by peak detecting said second AC signal (V W2 ) in said second winding (W2). An apparatus according to any one of claims 3 to 7 characterized in that said demodulator (41) comprises a two-terminal rectifier (CR2) that is coupled to said regulator control section (38c) only via a passive coupling arrangement. An apparatus according to any one of Claims 3 to 8 characterized in that said operating voltage (B+) energizes a deflection circuit (39) of a video display apparatus and wherein said second on-off control signal (S hot ) is capable of turning on and of turning off said operating voltage (B+), in accordance with said on and off-states, respectively, of said first on-off control signal (R on/off ). An apparatus according to any one of claims 3 to 9 characterized by means (Q1) responsive to a third signal (V LV ) and coupled to said demodulator (41) for bringing said second on-off control signal (S hot ) to a state which causes said normal operation power supply (38) to be in its off state irrespective of said first on-off control signal (R on/off ). An apparatus according to claim 10 characterized in that said means responsive to the third signal (V LV ) comprises a transistor (Q1) having a main current conducting electrode (collector) that is coupled to a first terminal (W1a) of said first winding (W1) for coupling a source (V E ) of energizing current to said first winding (W1), and wherein said third signal (V LV ) is coupled to a control terminal (base) of said transistor (Q1) for decoupling said source (V E ) of energizing current from said first winding-when said third signal (V LV ) is outside a predetermined range. An apparatus according to Claim 11 characterized by a second transistor (Q2) having a main current conducting electrode (collector) that is coupled to a second terminal (W1b) of said first winding (W1) and having a control electrode (base) that is responsive to said first AC signal (S cold ). An apparatus according to any one of claims 1 to 11 characterized by a second transistor (Q2) having a control electrode (base) that is responsive to said first AC signal (S cold ), wherein said first winding (W1) of said signal transformer (T3) has a terminal (W1b) that is coupled to a main current conducting electrode (collector) of said second transistor (Q2) such that said second transistor (Q2) generates in said first winding (W1), a current at said constant frequency in accordance with said first AC signal (S cold ). An apparatus according to any one of the preceding Claims characterized in that said first on-off control signal (R on/off ) is generated by a remote control circuit (34), in accordance with a user initiated command (RM). An apparatus according to any one of the preceding Claims characterized in that said first AC signal generating means comprises a switch (36) that couples a third AC signal (CK) to an output terminal (36a) of said switch (36) when said first on-off control signal (R on/off ) is at one of said on and off states and that decouples said third AC signal (CK) from said output terminal (36a) of said switch (36) when said first on-off control signal (R on/off ) is at the other state. An apparatus according to any one of Claims 1 to 14 characterized in that said first AC signal generating means comprises a microcomputer (34a) that generates said first AC signal (S' cold ) such that said first AC signal has a substantially rectangular waveform when said first on-off control signal (R on/off ) is at one of said on and off-states and at a substantially constant level when said first on-off control signal (R on/off ) is at the other state.

Inventors: FERNSLER RONALD EUGENE, FITZGERALD WILLIAM VINCENT, NORTRUP KEVIN EUGENE, FERNSLER, RONALD EUGENE, FITZGERALD, WILLIAM VINCENT, NORTRUP, KEVIN EUGENE
Applicants: RCA THOMSON LICENSING CORP, RCA THOMSON LICENSING CORPORATION
Application year: 1987
Main classification: H04N5
IPC codes: H02M3, H04N3, H04N5