TL496C, TL496Y
9-VOLT POWER-SUPPLY CONTROLLERS
SLVS012B – AUGUST 1978 – REVISED AUGUST 1995
functional description
The TL496C is designed to operate from either a single-cell or two-cell battery source. To operate the device
from a single cell (1.1 V to 1.5 V), the source must be connected to both inputs 1C INPUT and 2C INPUT as
shown in Figure 1. For a two-cell operation (2.3 V to 3 V), the input is applied to 2C INPUT only and 1C INPUT
is left open (see Figure 2).
battery operation
The TL496C operates as a switching regulator from a battery input. The cycle is initiated when a low-voltage
condition is sensed by the internal feedback (the thresholds at terminals 1 and 8 are approximately 7.2 and 8.6 V
respectively). Aninternallatchissetandtheoutputtransistoristurnedon. Thiscausesthecurrentintheexternal
inductor (L) to increase linearly until it reaches a peak value of approximately 1 A. When the peak current is
sensed, the internal latch is reset and the output transistor is turned off. The energy developed in the inductor
is then delivered to the output storage capacitor through the blocking diode. The latch remains in the off state
until the feedback signal indicates the output voltage is again deficient.
transformer-coupled operation
The TL496C operates on alternate half cycles of the ac input during transformer-coupled operation to first
sustain the output voltage and second to recharge the batteries. The TL496C performs like a series regulator
to supply charge to the output filter/storage capacitor during the first half cycle. The output voltage of the series
regulator is slightly higher than that created by the switching circuit. This maintains the feedback voltage above
the switching regulator control circuit threshold, effectively inhibiting the switching control circuitry. During the
second half cycle, an external diode (1N4001) is used to clamp the negative-going end of the transformer
secondary to ground, thus allowing the positive-going end (end connected to V+ side of battery) to pump a
charge into the standby batteries.
4–6
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