Power supply for an apparatus with standby operation

p0001The invention relates to a power supply for a device with the standby mode, also called standby mode. Devices of this type are, for example, televisions or VCRs in which certain stages, for. Example, an infrared receiver and a microprocessor, are active during standby operation to receive and evaluate infrared signals of a remote control to be able to. Since the microprocessor is already a power of about 750 milliwatts needed and switching power supplies in standby mode have poor efficiency, switch mode power supplies of this type in standby mode have a power consumption of about 5 to 10 watts or more.

p0002To reduce the power loss in standby mode is known from EP 0610700 A1 a switching power supply known that a third operation, a so-called organic farm which. In this mode, only the infrared receiver and a device connected to the output filter with operating voltage is supplied. For this purpose, a battery that is to be charged regularly again during operation.

p0003The invention has for its object to provide a power supply of the aforementioned type, which has a very low consumption in standby mode and also avoids the shortcomings of battery operation.

p0004This object is achieved by the specified in claims 1, 9 and 11 invention. Advantageous developments of the invention are specified in the subclaims.

p0005According to the invention, a separate switching power supply in addition to a main switching power supply used alone for the standby mode. Since this provides only a few components with power in standby mode, it can be very compact. It can be particularly operated at reduced operating voltage, which his own power loss is minimized.

p0006Since the separate switching power supply is designed for a nominal operating voltage of only 36 V, having a very low power and only a few components are needed, the entire power supply is cheaper than the switching power supply of EP 0610700 A1. Also a separate linear power supply for the standby mode would not be cost-effective. The separate switching power supply can also be used to transmit control signals from the secondary side to the primary side.

p0007The input voltage of the separate switching power supply is at least one current-limiting component, z. B. a capacitor is reduced, so that it has a high resistance to reduce power dissipation.

p0008In standby mode, the separate switching power supply operates only an infrared receiver on the secondary side, a downstream this circuit for detecting received infrared pulses and the start-oscillation of the main switching power supply, possibly even an LED for status display. By this measure, the entire power supply in standby mode consumes only 100 mW. The main switching power supply is maintained with only 4 mW in standby. The LED for status display requires only 3 mW, as it is powered by the high switching frequency, 100 kHz, the standby switching power supply. In this switching frequency, the light emitting diode has a very good energy utilization.

p0009Applications for this power supply type, in particular for televisions, video recorders, satellite receivers, stereos and basically all devices with standby mode and remote control. This low consumption a TV can be started even over prolonged periods in standby mode, it consumes for example, one year standby just about one kilowatt hour.

p0010During standby operation, advantageously, the oscillator and the driver stage of the main switching power supply can be kept in readiness. This achieves the main switching power supply after a short start-up phase to full operating power and can in particular provide the required for the evaluation of remote control signals microprocessor in a short time with voltage. This is advantageous in switching power supplies that operate over a wide input voltage range of z. B. 90 V to 265 V and have a long start-up phase at low input voltages.

p0011In normal operation the Hautpschaltnetzteil operates as a flyback converter and the separate switching power supply as a forward converter, wherein the switching frequency of the stand-by switching power supply is synchronized by the main switching power supply. By synchronizing the control of the secondary output voltages of the main switching power supply is ideal, as this cause small voltage fluctuations of output voltages, which are unavoidable due to the switching frequency, no parasitics. Therefore, the switching power supply has a separate oscillator operating during normal operation as a monostable multivibrator during standby operation and as an astable multivibrator. The separate switching power supply is fixed and requires no self-control information in standby mode.

p0012Another way of looking at the invention is as follows: A working as a forward converter transformer has second during a working period of three phases. During the first phase, the so-called trace period, the switching transistor is conductive, and the energy is brought through the transformer and the rectifier circuit to the load capacitor on the secondary side. During the second phase, the so-called retrace period, the switching transistor on the primary side and the rectifying circuit on the secondary side are locked. However, the magnetizing current in the trace transformer must be dismantled. Of the amplitude of the degaussing current the amplitude of the voltage pulse depends, ie by changing the degaussing current on the secondary side of the pulse voltage changes on the primary side. The third phase, the so-called rest period is the period after the demagnetization of the transformer until the renewed switching on of the switching transistor. In the invention, the fact is exploited that the trace time and the return time for the transmission of different sizes can be used, as these times always clearly defined by the impulse response of the transformer and separated controllable and evaluable. Said second small transformer is thus in one direction and the return time for transmitting control or control variables in the other direction exploited advantageously during the trace for the transmission of energy in standby mode while. It is for the transfer of energy from the primary to the secondary one hand, and for the transfer of control or controlled variables from secondary to primary the other hand, no longer two components required. The second transformer may still be implemented in compliance with all requirements for dielectric strength with a volume of, for example, 5 cc.

p0013The transmitted via the second transformer control variable is preferably used on the primary side of the transformer for switching the power supply between various operating modes such as standby mode, search mode and normal mode. This is achieved by varying the amplitude of the pulse voltage during the retrace period. In normal operation a controlled variable for controlling the duty cycle of the switching transistor is preferably transmitted via the second transformer for the purpose of stabilizing the operating voltages generated on the secondary side

p0014Preferably, the second transformer is part of a second, opposite the main switching power supply small switch mode power supply. The second switching power supply includes an oscillator which oscillates freely in standby mode and is synchronized in normal operation by the first switching power supply. This synchronization a stable operation of the control loop is ensured. The second switching power supply preferably effected in the standby mode, a shutdown of the main switching power supply.

p0015The invention is illustrated by way of example with reference to schematic drawings. Show it:<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>a block diagram of the complete power supply;</dd><dt>Fig. 2A</dt><dd>a diagram of the separate switching power supply;</dd><dt>FIG. 2b</dt><dd>a circuit diagram of the main switching power supply.</dd></dl>

p0016In FIG. 1, the AC voltage VAC of 230 V network is applied to a first rectifier G1, supplies power to the main circuit power supply via a capacitor C50 with a smoothed DC voltage. This is due to a primary winding W4 of a first transformer L50, and a series-connected switching transistor T85. The first transformer L50 includes secondary windings W7, W8 and W9 for generating operating voltages V_sys, Vx and Vs +/-, and on the primary side a feedback winding W6 and an auxiliary winding W5 to the primary-side voltage generation. The switching transistor T85 is driven in the Nomalbetrieb of a driver circuit DR, which is connected to the feedback winding W6. On the primary side, a circuit OVP overvoltage protection and an oscillator STO for the start-up operation of the main switching power supply are also still arranged. The oscillator STO runs at a frequency of approximately 1 kHz, causing a gentle start-up of the power supply after power on. In Nomalbetrieb the main switching power supply oscillates depending on the load with a frequency of approximately 60-150 kHz.

p0017For the standby mode, a separate switching power supply is provided, which is connected via two capacitors C1, C2 to the AC voltage VAC. These act as lossless reactances and reduce thereby the input voltage for a rectifier G2 and for the subsequent switching power supply. Therefore, D5 and D6 connected in series for generating operating voltages of 36 V and 6 V. directly to the output of the rectifier G2 two Zener diodes The separate switching power supply further includes a second transformer L1 with primary windings W1 and W3 and a secondary side winding W2 , The to winding W1 lying in series switching transistor T21 is driven by an oscillator OSC, the fixed vibrates in standby mode with a frequency of 100 kHz. It operates both as a forward converter and as a flyback converter, and generates via the connection 8 of the secondary side winding W2 a Vorsorgungsspannung of 5 V for an infrared receiver IE and the other terminal 5 is a power supply voltage for a variable gain amplifier IS10. The control amplifier IS10 is used for transmitting control information and a control information from the secondary side to the primary side of the second transformer L1. This information is passed on via a control stage SEC and a compound 6 to the driver DR of the main switching power supply.

p0018At the exit of the infrared receiver IE a passive filter circuit STS is connected, which is matched to remote control pulses a corresponding infrared remote control. In recognition of remote control pulses, it outputs a signal on, which turns on the main switching power supply through the control amplifier IS10 and the control stage SEC.

p0019The oscillator OSC of the separate switching power supply is connected via electrical connections 5 and 6 with the main switching power supply, through which it is synchronized in normal operation. This will be explained in more detail below with reference to Figures 2a and 2b.

p0020In Fig. 2a, the separate switching power supply is shown with its individual components. It is via electrical connections 1-8 with the main switching power supply, shown in Fig. 2b, respectively. Identical components are in the Fig. 1 and Figs 2a and 2b refers to the same.

p0021The switching transistor T21 in FIG. 2a is driven by an operational amplifier IP1, which is wired as an oscillator and has a very low energy consumption. The function of the error amplifier IS10 has been described above already, further reference is made to the earlier applications 19616115 and 19645926, in which the latter and a further exemplary embodiment of an error amplifier will be described.

p0022Via the connection 8 of the second transformer L1 a smoothed DC voltage of 5 volts is generated for the operation of the infrared receiver IE. Its output signals are passed to a terminal via a IR to a microprocessor not shown and serve simultaneously to turn on the main switching power supply, if there is the power supply in standby mode.

p0023In standby mode, the transistor T31 is conducting. Upon detection of infrared signals from the infrared receiver IE emits at its output OUT signals by switching the transistor T40 and thus also off the transistor T31. This provides a signal to the main switching power supply is passed through the transformer L1, which turns on this. Check-off signals can also be other connections on / off, connected for example with a video recorder or a Scart socket, supplied. About a terminal 7 is applied during normal operation of the main switching power supply of a voltage to the cathode of the error amplifier IS10, which maintains the normal operation to continue.

p0024Next, the operation of the main switching power supply circuit with reference to FIG. 2b will be described. It is operated self-oscillating, where it receives a positive feedback on the winding W6 of the first transformer L50. The amplitude of the collector current of the switching transistor T85 is controlled via a resistor R85 to the output voltages V_sysTo keep Vx and Vs +/- constant. The switching frequency of the main switching power supply circuit varies due to the output-side load, the applied voltage VAC or due to magnetic properties of the first transformer L50. The switching transistor T85 is operated in a mode in which it is locked, when its collector voltage is at a minimum. In this way, switching losses are greatly reduced. This mode is described in earlier applications DE 44 31 783 A1 and 196 19 751 in detail and will therefore not be explained here in detail. This operation also a complete energy transfer is achieved in the flyback converter mode, so that automatically overload protection is achieved through the power control.

p0025The base current of the switching transistor T85 via a choke L80 is limited in such a manner that it is proportional to its collector current. The operation of this reactor L80 is already described in the previous application 196 02 556 and is therefore not discussed here. Through this control very efficient and fast switching action is effected that is reliable up to switching frequencies of 150 kHz.

p0026When the switching transistor T85 is switched through, so transistor T77 and inductor L80 of the base current for the switching transistor T85 is connected via a terminal 6 of the winding W6 is generated. Through a capacitor C78, ​​the switching on of the switching transistor T85 is supported. The locks of the switching transistor T85 is effected via a capacitor C75 and transistors T74, T72 and T77. When the transistor T77 is steep flanks blocked a negative base current is generated via the inductor L80, which blocks the switching transistor T85.

p0027The oscillator STO of Fig. 1 is implemented in Fig. 2b by means of a wired operational amplifier IP2. In start-up operation after turning it switches the transistor T77 by a switching frequency of about 1 KHz until the main switching power supply goes into the higher frequency, self-oscillating Normal engines.

p0028The main switching power supply is turned off during standby operation, since a consumption of less than one watt is to be managed in a slightly larger-sized switching power supply hardly. The on and off commands for this purpose be tapped off at the winding W2 of the second transformer L1 from the transistor stage T30 and passed on via the connection 4 to the driver stage DR, Fig. 1, and capacitor C75, Fig. 2b. . Specifically, in this case, the transistor T74 in Figure 2b is controlled: this is an out signal (level: high) is switched through, thereby also transistor T72 is turned on, then the drive transistor T77 is blocked.

p0029In standby mode, only the operational amplifier wired IP2 and the transistor stage T74 via the connection 3 and 4 into operation. The components of these stages are dimensioned such that the total power consumption of the main switching power supply in the standby mode is only 4 milliwatts. - The particular reference to the F . Ig explained 2b embodiment is only a preferred embodiment in order to keep the power consumption minimal. Other embodiments of this are conceivable, in particular, for example, to optimize the start-up time of the main switching power supply.

p0030In normal operation, the operating voltage V_sys stabilized, which may for example be used for deflection in a television set. This voltage is tapped off via the connection 8, and through a voltage divider to the control input of the error amplifier IS10, in this embodiment, a variable zener diode TL431 created. The higher the voltage V_sys is, the higher the current from the cathode to the anode and correspondingly higher is the "flyback" current for the transformer LS1. At terminal 5 of transformer LS01 is the "flyback" a voltage which is charged more or less strongly by the error amplifier IS10 according to the operating voltage V_sys, This load can be tapped off on the primary side at the winding W2, the higher the secondary-side load, the lower is the "flyback" voltage on the winding W2. This control signal is passed on through the stage transistor T30 and compound 4 as described above to the main switching power supply. Via the switching transistor T85 and the transformer L1 then the control loop is closed. This direct control a very high loop gain is achieved.

p0031In order to obtain a very stable control gain, the switching frequency of the separate switched mode power supply during normal operation, is synchronized by the main switching power supply. About terminals 5 and 6, both the switching frequency and the pulse width ratio in the separate switching power supply is controlled. Compound 6 via the transistor T11 is turned on, whereby the output of the operational amplifier IP1 to high voltage is (5.6 V). When the switching transistor T85 of the main switching power supply circuit occurs at the terminal 5 of the winding W6, a positive voltage pulse, which is passed on via connection 5 to the negative input of the operational amplifier IP1 and its output switches to zero.

p0032For switching power supplies a protective circuit in terms of overvoltage is required. This is realized by a Transistsorstufe TP90, Fig. 2b, (OVP in FIG. 1), which monitors the voltage of the primary-side winding W5 and acting in the event of an overvoltage to the driver stage of the switching transistor T85. When the normal stress of the winding W5 to 10% is too high, the switching transistor T85 turned off completely for a short time. Thereafter, the main switching power supply is running again and will return to normal operation when the surge had occurred only briefly. There is a surge, however, further, the switching transistor TP85 is switched off again if the above threshold voltage is reached, and this shutdown cycle will be maintained as long as the overvoltage condition exists. This circuit has the following advantages over known circuits that limit the output voltage at a high level: Through the cyclic turning on and off the load on the components is kept low, also the effective consumptive power is greatly reduced in the event of overvoltage. For example, if the output voltages at a higher voltage level of 10% is limited, so certain safety conditions must be met for this voltage value. This leads to unnecessary se costs.

p0033The operation of the protection circuit will be explained in more detail below, if an error in case the output voltages V_sys, Vx and Vs increases, the voltage would also increase at a capacitor C95 to the primary side. At a certain value defined by the Zener diode D90 and the voltage divider in parallel with C95, the transistor T90 turns on and sends a rapid surge in the base of the PNP transistor T77. This locks and thus prevents switching on of the switching transistor T85 again. Once the first transformer L50 has swung, the skin switching power supply can turn only about the start oscillator (IP2) again. Therefore, this starting oscillator is controlled so at the non-inverting input over a larger time constant, that it for a certain time (defined by capacitor C90) is not oscillating, thus preventing start up of the main switching power supply.

p0034Through this long interruption drop all output voltages at the first transformer L50 correspondingly far from, so that the transistor T90 blocks again and is discharged after a certain time of the capacitor C91. By using only one transistor stage T90 of the cost of materials for highly effective protection circuit is very low. Since it is located on the primary side, and acts on the driving transistor T77 directly via transistor T72, it speaks to the very rapidly.

p0035The reference to the Figures 2a and 2b is explained in detail power supply is particularly suitable for applications in a television set, which is operated with 230V. For other applications, such as in a VCR, or for other input voltages, corresponding modifications are conceivable.