Power-on delay is a new concept. When a power supply is first turned on, it inevitably needs a certain period of stabilization before it can provide a stable output. During this period, it is difficult to guarantee the stability of the voltage. Therefore, power supply designers allow the power supply to delay by 100ms-500ms, so that it can provide high-quality power to the computer after it has stabilized.
To set a boot delay: In the BIOS, go to Power Management Setup, change "Disabled" to "Enabled" after "WakeUP by Alarm", and enter the desired boot time after "Time (hh:mm:ss) Alarm". Save and exit.
Its delay time is determined by T=RC. Relay J is energized and remains energized T seconds after K is closed until K is opened. This circuit can be combined with other circuits to form a power-on delay circuit or a switching circuit. K can be replaced by a relay contact or an electronic switch. The working principle of this circuit is as follows:
After K is closed, since the voltage on capacitor C cannot change abruptly, the potential at point A is 0. The potentials of pins ② and ⑥ of the 555 timer are both lower than the potential of its internal comparator, and its internal RS flip-flop is set. Pin ③ outputs a high level (approximately equal to the power supply voltage Vcc), and J is not energized. +12V charges C through R. When the potential at point A rises to 1/3 Vcc, due to the characteristics of the 555 timer, pin ③ continues to maintain a high level. When the potential at point A continues to rise to 2/3 Vcc, the internal RS flip-flop of the 555 timer flips, pin ③ outputs a low level, and the relay is energized and begins to work.
What is the working principle of a time delay switch?
The time-delay switch has a metal sensor on the outside. When a person touches it, a signal is generated, triggering a transistor to conduct and charge a capacitor. The capacitor creates a voltage that keeps a field-effect transistor conducting, illuminating the light bulb. When the hand is removed, charging of the capacitor stops. After a period of time, the capacitor discharges completely, the gate of the field-effect transistor becomes low-potential, and it enters the cutoff state, turning off the light bulb.
The dotted line on the right of the touch-sensitive time-delay switch circuit represents the ordinary lighting circuit, while the left side represents the electronic switch section. VD1-VD4 and VS form the main circuit of the switch, and the IC forms the switch control circuit. Normally, VS is in the off state, and the light is off. VD1-VD4 output 220V pulsating DC power, which is current-limited by R5, regulated by VD5, and filtered by C2 to output approximately 12V DC power for the IC. At this time, the LED illuminates to indicate the switch position, making it easy to find the switch at night.
The IC is a dual D flip-flop. Using only one of the D flip-flops, it is configured as a monostable circuit. In steady state, pin 1 outputs a low level, and VS is off. When a person touches electrode M, the leakage current from the human body is divided by resistors R1 and R2. Its positive half-cycle causes the monostable circuit to flip, and pin 1 outputs a high level. This high level is applied to the gate of VS via resistor R4, turning on VS and lighting the lamp. At this time, the high level output from pin 1 charges capacitor C1 via resistor R3, gradually increasing the level at pin 4 until the transient state ends. The circuit then flips back to steady state, pin 1 abruptly drops to a low level, VS loses its trigger voltage, and the circuit turns off when the AC current crosses zero, extinguishing the lamp.
Application scope of time delay switches
Time-delay switches are mainly used in stairwells, restrooms, corridors, and other places where lights are not always on but are frequently used. Using time-delay switches avoids wasting electricity by leaving lights on unnecessarily. Features: 1. Simply touch the metal contact of the switch to activate it; it automatically turns off after a set time. 2. Application control: the switch automatically detects the insulation resistance to ground, ensuring more reliable and error-free operation. 3. Contactless electronic switch, extending the lifespan of the load. 4. The voltage across the ground wire is less than 36V, a safe voltage for humans, making it harmless to use. 5. Unique dual-system design: it can directly replace a traditional switch and power various loads.
