Power delay turn-on circuit

When designing electronic circuits, sometimes it is hoped that after closing the switch, the power supply will be delayed for a while before being turned on again. For example, on a device with output, it is hoped that the device will work stably before outputting. In audio amplifiers, wait for the amplifier to stabilize before turning on the speakers, etc.

Figure 1 is such a delay circuit. The time base circuit 555 is used as a timer to drive the relay. After the power switch is turned on, it delays for a period of time and then connects or disconnects the circuit. The delay time is determined by the capacitor C and the resistor R. When R=100kΩ.C=10μF, the delay time is about 1.1 seconds.

When you do not want to use a relay, a transistor can be used to delay the turn-on of the DC voltage. The circuit is shown in Figure 2.

When the circuit in Figure 1 and Figure 2 is working, as long as the manual switch K is connected to the +12V power supply, the monostable circuit composed of NE555 works, and its ③ pin outputs high level. In the circuit of Figure 1, the relay contact K and Vout are connected to the +12v power supply for external loads: In the circuit of Figure 2, when the transistor T (PNP type) is turned on, its Vout is connected to the +12V power supply for external loads. Load usage.