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T2117-3AS

Zero-voltage Switch with Adjustable Ramp

Atmel Corporation 

T2117

General Description

The integrated circuit T2117 is a triac controller for zero-crossing mode. It is designed to

control power in switching resistive loads of mains supplies.

Information regarding synchronous supply is provided at pin 8 via resistor RSync. To

avoid a DC load on the mains, the full-wave logic guarantees that complete mains

cycles are used for load switching.

A fire pulse is released when the inverting input of the comparator is negative (pin 4)

with respect to the non-inverting input (pin 3) and internal reference voltage. A ramp

generator with freely selectable duration can be performed by capacitor C2 at pin 2. The

ramp function is used for open-loop control (Figure 4), but also for applications with pro-

portional band regulation (Figure 11 on page 9). Ramp voltage available at capacitor C2

is decoupled across the emitter follower at pin 1. To maintain the lamp flicker specifica-

tion, the ramp duration is adjusted according to the controlling load. One can use

internal reference voltage for simple applications. In that case, pin 3 is inactive and con-

nected to pin 7 (GND), see Figure 13 on page 11.

Figure 3. Pin 1 Internal Network

T2117

Ramp

1

control

R4

2

C2

-VS

Figure 4. Threshold Voltage of the Ramp at VS = -8.8 V

V1

-1.6 V

-7.6 V

t

Final voltage

Vmin

Initial voltage

T

Vmax

3

4768A–INDCO–11/03

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