UAA2016

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5

CIRCUIT FUNCTIONAL DESCRIPTION

Power Supply (Pin 5 and Pin 7)

The application uses a current source supplied by a single

high voltage rectifier in series with a power dropping

voltage of − 8.6 V with respect to Pin 7. The current used by

the total regulating system can be shared in four functional

blocks: IC supply, sensing bridge, triac gate firing pulses and

zener current. The integrated zener, as in any shunt

regulator, absorbs the excess supply current. The 50 Hz

pulsed supply current is smoothed by the large value

capacitor connected between Pins 5 and 7.

Temperature Sensing (Pin 3)

The actual temperature is sensed by a negative

temperature coefficient element connected in a resistor

divider fashion. This two element network is connected

between the ground terminal Pin 5 and the reference voltage

− 5.5 V available on Pin 1. The resulting voltage, a function

of the measured temperature, is applied to Pin 3 and

internally compared to a control voltage whose value

depends on several elements: Sawtooth, Temperature

Reduction and Hysteresis Adjust. (Refer to Application

Information.)

Temperature Reduction

For energy saving, a remotely programmable temperature

reduction level.

Comparator

When the noninverting input (Pin 3) receives a voltage

less than the internal reference value, the comparator allows

the triggering logic to deliver pulses to the triac gate. To

improve the noise immunity, the comparator has an

Pin 2 sets the hysteresis level. Setting Pin 2 open makes a

10 mV hysteresis level, corresponding to 0.15

°C. Maximum

case the level is set at 5

°C. This configuration can be useful

for low temperature inertia systems.

Sawtooth Generator

In order to comply with European norms, the ON/OFF

period on the load must exceed 30 seconds. This is achieved

by an internal digital sawtooth which performs the

proportional regulation without any additional components.

The sawtooth signal is added to the reference applied to the

comparator inverting input. Figure 2 shows the regulation

improvement using the proportional band action. Figure 4

displays a timing diagram of typical system performance

using the UAA2016. The internal sawtooth generator runs

at a typical 40.96 sec period. The output duty cycle drive

waveform is adjusted depending on the time within the

40.96 sec period the drive needs to turn on. This occurs when

the voltage on the sawtooth waveform is above the voltage

provided at the Sense Input.

Noise Immunity

The noisy environment requires good immunity. Both the

voltage reference and the comparator hysteresis minimize

the noise effect on the comparator input. In addition the

effective triac triggering is enabled every 1/3 sec.

Failsafe

Output pulses are inhibited by the “failsafe” circuit if the

comparator input voltage exceeds the specified threshold

voltage. This would occur if the temperature sensor circuit

is open.

Sampling Full Wave Logic

Two consecutive zero−crossing trigger pulses are

generated at every positive mains half−cycle. This ensures

that the number of delivered pulses is even in every case. The

pulse is centered on the zero−crossing mains waveform.

Pulse Amplifier

The pulse amplifier circuit sinks current pulses from Pin

then triggered in quadrants II and III. The effective output

Eventually, an LED can be inserted in series with the Triac

gate (see Figure 1).