Radio power automatic shutdown circuit ---- Radio Auto Power Off

Author: Temple With battery powered equipment, if you forget to turn off the power. The battery's electrical energy will be exhausted unconscious; and dry batteries are often leakage, corrosion circuit boards after exhaustion. Figure 1 The circuit can be at a certain period of time. Automatically turn off the power supply of the device. The circuit uses a CMOS type time-based integrated circuit ICM7555 for a one-time action. Taking radio power control as an example. First press the start switch SW1, at the time of the 2 foot voltage of the time base IC to achieve 1/3 of the power supply voltage below 1/3. The time base IC internal trigger is flipped, and the output pin 3 transitions into a high level "H" MOSFET tube TR1 drain-source is turned on, and the power source is turned on. At the same time, the 7 foot of the time base IC becomes a high impedance, and the capacitor C1 is charged by the resistor R1, and the voltage Vx of the two ends rises until 2/3 of the power supply voltage Vcc, this time T can be expressed: Vx = VCC [L-E- (T / R1C1)]] When the 6 foot voltage reaches 2/3 of the power supply voltage, the time base IC internal trigger is turned again, so that the 7 foot and ground (GND) is connected, the Vx instantaneously turns 0V, 3 foot transition to low "L", TR1 As close, turn off the power supply. From the power supply to the power switch, the VX can be replaced with 2 / 3VCC in the above calculation to obtain the following formula: T = LOGE3R1C1 ≈ 1.1R1C1 so. The time to maintain the power supply is determined by the product of R1C1. If the set time is 60 minutes, R1 takes 327μF capacitance of 10MΩ.c1, which requires minimal as possible to the leakage current of the capacitor; but the large capacity, low leakage capacitor is more difficult to obtain. Therefore, the circuit of Figure 1 is suitable for working hours. Be Be For the above problems, the circuit structure is changed, and the output count of the low-frequency RC oscillator is turned off, and the power is turned off when a value is reached. Be The circuit is shown in Figure 2. There is no steady multi-resmicker with time base IC. When working between VCC1 / 3 and VCC2 / 3 - segment. Cycle: Τ = 0.69C1 (2R1 + R2) The output of the low frequency oscillator is sent to the input of a divider. The divider selects asynchronous 14 binary counters TC4020B. Maximum can be used for 213. At this time, if you want to get a 60-minute delay, the cycle of the input pulse = 0.44 seconds. It can be seen that the time constant of the RC is small, and a small capacity of the film capacitor can be used. Avoid unstable phenomena due to leakage current. The four door circuits with non-door TC4001BP constitute an RS trigger, and the other two doors circuit constitute an inverter. Reset to IC1 and IC2. And drive TR1 shutdown. The output of the TC4020B selects Q14.