Standby circuit for an electrical device

#The invention relates to a standby circuit, an electrical device with a standby circuit, a method of controlling an electrical device and a power supply module.

#A great number of electrical devices, such as video recorders, satellite receivers, television sets, set-top boxes, computer monitors, etc., have a so-termed standby mode. These devices are supplied with electric energy from the electricity mains. For this purpose, they have corresponding power supply units. In addition to 50 Hz transformer-based power supplies, SMPSs (switched-mode power supplies) are also very often used in this case. Switched-mode power supplies work with a stabilized or unstabilized D.C. input voltage, which is usually drawn from the mains by means of a rectifier. One or more electronic switches are used to convert this D.C. voltage into an A.C. voltage or A.C. current, whose frequency is usually high (i.e. greater, often even many times greater than the mains frequency). The A.C. voltage or A.C. current is used for further voltage transformation and power transmission, respectively, for the generation of one or more D.C. and/or A.C. voltages. A distinctly higher switching frequency in comparison to the mains frequency makes possible the use of very much smaller magnetic components. Control of the output voltage is possible by means of a suitable switch control method (e.g. frequency control, pulse duty factor control or other methods known to the expert).

#Devices such as televisions are often equipped with a circuit breaker by which the power supply unit is completely isolated from the mains and in this way the device is switched off “hard”, i.e. electrically completely isolated from the mains, by means of a mechanical switch, for example. In this off position the device does not consume any electrical energy. However, a device can also be switched to the standby mode, for example, by pressing the “off” button on a standard wireless remote control, e.g. a radio or infrared remote control. Then the functional units of the device (here for example the picture tube, the receiver element, etc.) are switched off, usually with relays or electronic switches or through drastic reduction in the secondary side supply voltage. In standby mode, however, the power supply unit is not isolated from the mains, because at least one unit of the device, here designated “standby circuit”, remains active in the standby mode.

#In the drawings:

#FIG. 1 shows a schematic diagram of a first embodiment of a standby circuit;

#FIG. 2 shows a block diagram of the components of an electrical device including a standby circuit;

#FIG. 1 shows a switching module ZPS including a standby circuit 20. The switching module ZPS has 14 external terminals 1 to 14. The standby circuit has a power supply assembly 22 with a linear voltage regulator 24. Also provided are a clock 26, a control unit 28 and a store 30.

#The terminals 1 and 2 of the module ZPS are used for the power supply. The power supply assembly 22 here has a linear voltage regulator 24, to which the constant voltage Vref is fed as a reference and which holds a constant, linearly regulated supply voltage ready for the control unit 28 and (not shown), as appropriate, the other components. In this way the circuit module can be operated across a broad range of input voltages from approximately 2 to 15 V. The power supply assembly 22 has a voltage divider formed from resistors R1, R2, R3 and R4, the voltage level of each stage of the voltage divider being connected to one of three comparators U0, U1 and U2. These comparators U0, U1 and U2 compare the respectively divided fraction with the fixed reference level Vref.

#The reference voltage, as shown, can for example be supplied by a power source I1 and a zener diode 30. In this way Vref remains independent of the input voltage, with constantly low power consumption.