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UAA2016P Datasheet(PDF) 5 Page - ON Semiconductor |
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UAA2016P Datasheet(HTML) 5 Page - ON Semiconductor |
5 / 12 page UAA2016 http://onsemi.com 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 resistor. An integrated shunt regulator delivers a VEE 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 is available on Pin 4. The choice of resistor R1 connected between Pin 4 and VCC sets the 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 adjustable hysteresis. The external resistor R3 connected to Pin 2 sets the hysteresis level. Setting Pin 2 open makes a 10 mV hysteresis level, corresponding to 0.15 °C. Maximum hysteresis is obtained by connecting Pin 2 to VCC. In that 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 length is selectable by Rsync connected on Pin 8. The pulse is centered on the zero−crossing mains waveform. Pulse Amplifier The pulse amplifier circuit sinks current pulses from Pin 6 to VEE. The minimum amplitude is 70 mA. The triac is then triggered in quadrants II and III. The effective output current amplitude is given by the external resistor Rout. Eventually, an LED can be inserted in series with the Triac gate (see Figure 1). |
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