LS7234

LS7231 through LS7234 are a series of monolithic, MOS integrated circuits designed for the control of brightness of incandescent lamps. The outputs of these ICs control the brightness of a lamp by controlling the firing angle of a triac connected in series with the lamp. All internal timings are synchronized with the line frequency by means of a built-in phase-lock loop circuit. The output occurs once  every half-cycle of the line frequency. Within the halfcycle, the output can be positioned anywhere between 158°conduction angle for maximum brightness and 41° conduction angle for minimum brightness in relation to the AC line frequency. The positioning of the output is controlled  by applying a low level at the SENS input or a high level at the EXT input.

These functions of LS7234 may be implemented with very few interface components, as shown in Figure 5. When implemented in this manner, touching of the Touch Plate causes the lamp brightness to change as follows:

1. If the Touch Plate is touched momentarily (42ms to 333ms), the lamp is:
    a) turned off if it was on,
    b) turned on if it was off.
The brightness resulting is either full brightness or depending on the circuit type, a previous brightness stored in the IC memory.

2. If the Touch Plate is touched for a prolonged time (more than 342ms) the light intensity changes slowly. As long as the touch is maintained, the change continues; the direction of change reverses whenever the maximum or minimum brightness is reached.

The IC also provides an input for slow dimming. By applying a slow clock to this input, the lamp can be dimmed slowly until total turn off occurs. This feature of LS7234 can be useful at bedtime in a child's room.