Automatic power-saving circuit for video recording/reproducing apparatus

An automatic power-saving circuit in a video recording/reproducing apparatus comprising:

• a key input unit for entering a user command;
• a power unit for supplying power to each element of the video recording/reproducing apparatus;
• a pre-amp for amplifying an input video signal and detecting and outputting an envelope of the amplified signal;
• a video signal discriminator for discriminating the existence of the input video signal from the envelope signal output from said pre-amp and outputting a discrimination signal according to said existence;
• a microcomputer for controlling said power unit according to said discrimination signal and said user command;
• and
• wherein said signal discriminator comprises:
• a biasing circuit having first and second resistors connected to first and second potentials, respectively;
• a first transistor having a base connected to the biasing circuit and receiving the envelope signal output from the pre-amp, a collector connected to the first potential, and an emitter connected to a second potential through a third resistor;
• a second transistor having a base connected to the emitter of the first transistor through a fourth resistor, a collector connected to the first potential through a fifth resistor, and an emitter connected to the second potential through a sixth resistor;
• a third transistor having a base connected to the emitter of the second transistor through a seventh resistor, a collector connected to the first potential, and an emitter connected to the second potential through a ninth resistor;
• and
• an integrating circuit having a capacitor connected between the emitter of the second transistor and the second potential, an eighth resistor connected between the emitter of the second transistor and the emitter of the third transistor, and a tenth resistor having one terminal connected to the emitter of the third transistor and a second terminal supplying the discrimination signal.

A method for automatically cutting-off power to a video recording/reproducing apparatus, comprising the steps of:

• determining if a video signal is present;
• outputting a cut-off signal if a key input is not present during a predetermined amount of time while said video signal is not present;
• and
• cutting-off power output from a power unit of the video recording/reproducing apparatus based on the cut-off signal;
• wherein said determining step comprises the steps of:
• discriminating the presence of an envelope signal output from a pre-amp of the video recording/reproducing apparatus;
• and outputting a logic signal having a first level if the envelope signal is discriminated, and having a second level if the envelope signal is not discriminated.