Philips’ TEA 104 1T IC for Battery Voltage Monitoring:
Battery voltage monitor: The TEA 104 1T IC by Philips is well-suited for monitoring the voltage of batteries within the range of 1.8–4.0 V. Its internal trigger and timing logic play a pivotal role in preventing the circuit from reacting to brief breaks in the supply voltage, often caused by pulses in the load current. The option to use either six or two LEDs facilitates the indication of voltage drops below a preset level.
LED Circuit Configuration Using Two LEDs (Fig. 1):
Fig. 1 illustrates a circuit employing two LEDs. The potential divider R1-R2 is instrumental in determining the voltage level at which the LEDs indicate the battery’s charge status. To achieve precision, the divider should yield a voltage of precisely 1.25 V at pin 1. By assigning a value between 1 kΩ and 100 kΩ to R2, the calculation of R1 follows the equation R1 = R2 (Uth/ 1.25-1).
Setting the Desired Voltage Level (Uth):
To achieve the desired voltage level (Uth), consider the values of R3 and R4, ranging from 100 to 220 Ω, depending on the battery voltage. The TEA1041T is activated when pin 3 is at ground level. If the voltage at pin 1 falls below 1.25 V, a digital counter operates for approximately 2 seconds. Should the level at pin 1 persist below 1.25 V, the IC enters the alarm state. D1 illuminates and remains lit even when the voltage at pin 1 returns to 1.25 V. If, in this state, S1 is opened, both LEDs flash for about 4 seconds. Subsequently, the IC reverts to the standby state, drawing a minimal current of about 10 pA and placing a negligible load on the battery.
Incorporating the IC into an Existing Apparatus (Figure 2):
Figure 2 illustrates how the IC can be integrated into an existing apparatus. D2 is excluded, and pin 3 is consistently set at ground level. The monitor stays connected to the load as long as S1 is closed. The IC functions as previously described, but the LED does not flash after the reset.
Adjustments for Higher Supply Voltage:
In instances where the supply voltage exceeds 4 V, follow the connections outlined by the dashed lines in Figure 2 (R1 to R5 and D3, and C3 to earth). D3 lowers the supply voltage to 3.3 V, and the potential divider is linked to the full supply voltage.