Addressing Battery-Operated Equipment Woes: Preventing Unintended Power Drain
One common frustration with battery-operated devices is the realization that shortly after turning them on, the batteries have drained. It’s highly likely that the last user, which may even be you, forgot to switch the device off.
Understanding the Switch-Off Delay Mechanism: How the Timer Operates
The operation of this timer relies on a consistently connected power source to function effectively. To trigger the timer, a signal is required at the trigger input, typically resulting from a contact closure. Usually, this signal originates from the positive or live side of the power supply that energizes the timer. Once triggered, the relay activates, and even when the trigger is removed, timing initiates while the relay remains in the energized state. Upon the lapse of the preset timing period, the relay disengages. The circuit outlined here ensures that this battery-draining mishap won’t reoccur. A simple press of the button, S1, suffices to enable the equipment to operate for a pre-defined period exclusively.
Notable Circuit Feature: Minimizing Quiescent Current Drain
An intriguing characteristic of this circuit is its ultra-low quiescent current, measuring a mere 0.00 mA. This efficiency is attained because T1 completely switches off the timer at the conclusion of each cycle. The switch-on action is facilitated by the energy stored within the power-on pulse. When S1 is depressed, the supply voltage becomes instantly accessible across C2. Due to the differentiating action of R2-C2, the supply voltage briefly connects to the V+ input of IC1 via D1.
Utilizing Stored Energy for IC Activation: IC Power Supply Initiation
Stored energy, harnessed through the power-on pulse, serves as the catalyst enabling the IC to initiate the timer’s operation. During this phase, T1 becomes active, providing the necessary energy to sustain the IC throughout the cycle. As the cycle concludes, T1 deactivates, ceasing energy supply. The duration of this cycle, denoted as “t,” is calculated by the formula:
t = (P1+R4) C3 seconds
Setting Constraints and Parameters: Controlling Current and Voltage
To ensure optimal performance, certain constraints must be adhered to. The current switched on should not exceed 350 mA, and the permissible supply voltage range lies between 5 V and 15 V. Additionally, the trigger amplitude must be at least 5 V to guarantee accurate functionality. With the component values depicted in the diagram, the switch-off time spans from 1 to 100 seconds. Notably, the circuit draws approximately 4 mA of current during the switching interval when the supply voltage is 6 V.