TL496C, TL496Y

9-VOLT POWER-SUPPLY CONTROLLERS

SLVS012B – AUGUST 1978 – REVISED AUGUST 1995

4–6

POST OFFICE BOX 655303

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). An internal latch is set and the output transistor is turned on. This causes the current in the external

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.