We once one straightforward procedure which elaborated in “Design Example”, may after predetermined time the automatic cutout battery, lengthens the battery life (reference 1). This “Design Example” introduced that one kind simpler can complete the same function the method (Figure 1). Four heavy double input NAND Schmitt trigger IC1 two gates to compose an improvement the trigger. When the electric circuit adds on the 9V battery voltage, the IC1A output becomes the high level, because on the C1 initial voltage is zero. The IC1B output becomes the low level, and feeds back IC1A through R2. C3 through the R3 charge. The IC1C output becomes the high level, because of the R6 earth. P trench MOSFET switch Q1 shuts off, the IC1D output becomes the high level, and through R2 to the C4 charge.
When presses down snap switch S1, because the IC1A two input ends are the high levels, its output becomes the low level, thus forces IC1B the output to become the high level. The R2 resistance number is much smaller than R3, when therefore S1 maintenance conducting state, C3 maintains the high logic level. When S1 shutdown, C3 through the R3 electric discharge.
The MOSFET switch may use two methods to shut off. When the tantalum electric capacity C2 charge imitates is lower than its threshold value V- to the IC1C input terminal voltage, the IC1C output from the low level becomes the high level; This level fluctuation causes the MOSFET switch to shut off. C2 and R6 decide this kind of automatic cutout the duration. If the C2 capacitance value and the R6 resistance number like chart shows, then shuts off probably needs 6 minutes. At the same time, IC1D output change from high to low may force IC1A and IC1B through C4 returns to the readiness for action.
Another method is, presses down S1, shuts off the MOSFET switch. Because on the C3 voltage is very low, therefore S1 closed causes IC1The output to become the high level, but the IC1B output becomes the low level. IC1B output change from high to low forces IC1C the output to become the high level, thus causes MOSFET to shut off. Because the C2 capacitance value is quite big, therefore provides a rapid discharge circuit with D1, and limits the discharging current with R4.
This electric circuit does not consume the 0.2mA electric current under the readiness for action. The MOSFET switch’s breakover resistance is very small, therefore when the load current is 100 mA, this switch only reduces 2 mV voltages. If needs a circular telegram indicating lamp, may, in load one side serially connects in a limiting resistor’s situation to increase LED.
