SYSTEM DESCRIPTION (see Functional Diagram)

If a heat source moves in front of the IR-detector,

the sensor delivers a quasi sinusoidal AC-signal

in the

µV to mV range. The operational amplifier

amplifies the sensor signal by 72dB.

To reject an unwanted signal, a band pass filter is

needed. If the AC-level at pin 14 exceeds the win-

dow comparator thresholds, the programmable

timer will start. To suppress short sensor signals,

a 50ms time filter is implemented between the

window comparator output and the programmable

timer. This function improves the noise immunity.

After the reset of the timer a second timer will pro-

vide a 600ms dead time to prevent retriggering of

the timer. This function avoids restarting of the

timer, when the turned off lamp temperature. de-

creases

The lamp switched by the triac can be located

close to the sensor.

To avoid circuit operation during day-time, a

photo resistor (LDR) senses the light intensity and

switches off the circuit. The capacitor at pin 2 pre-

vents circuit start-up during short shadow phases,

when a person passes by the sensor.

From the analog input pin 1 via the AD-converter

the on-time duration can be programmed in 7

teristics). The timer is clocked by the mains fre-

quency.

Two outputs for various applications are avail-

able.

Pin 5 is the trigger output for triac gate.

Pin 4 output can be used to switch a relay or

other loads.

The zero crossing detector provides the firing

pulse for the triac at the right time, shortly after

the zero crossing of the AC-signal.

The RC-network at pin 7 supplies current to the

circuit via a double wave rectification which is pro-

vided by a split power supply. Due to the capaci-

tive energy transfer into pin 7, the circuit will also

be supplied with current if the triac is fired. A short

wire for circuit supply is not needed.

The circuit works similar to a simple two-terminal

switch and can be installed in parallel with ordi-

nary mechanical pulse switches (fig. 4).

After a short supply connection via an external

pulse switch, the circuit timer will also start with-

out a sensor signal.

Therefore the circuit can also be used as an ordi-

nary light timer without the IR-moving sensor fea-

ture.

Figure 4

Figure 5: Different Possible Filter Solutions

UAA4713

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