Abstract: The light control with infrared sensing chip PT8A2621 the main features of pin functions, internal structure and working principle, while operating PT8A2621 made a more specific application in detail. Finally, it's typical application circuit.
  Key words: light control; infrared; override control; PIR
  1 Overview
  PT8A2621 is the PT produced using CMOS technology to produce a large-scale integrated circuit chips LSI, mainly used in infrared motion-sensing light control aspects of the human body. The output is relay control, can be used in corridors, cookroom, courtyards, meeting rooms, storage, warehouse, and other energy-efficient lighting applications.
  PT8A2621 The main features are as follows:
  includes two operational amplifiers, can be used to amplify the signal and filter out noise;
  chip has a power supply, 3.6V output voltage;
  There are three control modes: ON / AUTO / OFF;
  output level for the relay control;
  can be ultra vires override control;
  When the zero crossing ZC terminal signal disappeared more than 3 seconds, the chip automatically reset;
  PT8A2621 chip pin DIP or SOP 16 in two packages.

2 pin function
  PT8A2621 the pin function as listed in Table 1.
  Pin Function Table 1 PT8A2621
  Pin No. Name Function Description
  1GND to end
  2RELAY relay driver output, the output is high, the effective
  3OSCD external RC oscillator output end of time, through the RC adjusting the duration of the relay output driver
  External RC oscillator 4OSCS end system, is used to set the system operating frequency, the rated frequency is 16kHz
  5ZC AC (AC) zero-crossing detection side, the inner end of the Schmitt trigger
  6CDSCDS control input voltage by detecting the photosensitive resistor to determine the day or night
  7MODE mode selection input. Connected to Vcc, 2 pin output protection is ON; ground when OFF; open when AUTO
  8Vcc supply side, 5V
  9VEE internal voltage regulator output, the output voltage of 3.6V, connecting PIR (Precision Infrared tracking) sensor
  10RST chip RESET input, active low
  11OP1P first stage op-amp inverting input can be directly connected to the output of PIR sensor
  12OP1N first stage op amp inverting input
  13OP1O move put the output of the first stage
  14OP2P the second stage of the op amp inverting input
  15OP2N moving the second stage amplifier inverting input
  16OP2O the second stage of the op amp output
  3 Works
  PT8A2621 internal circuit diagram shown in Figure 1, the function of each part of the circuit is as follows:
  3.1 Comparison of input filtering and amplification circuit
  The device of the PIR sensor can be detected by the power change caused by human movement into voltage changes. The voltage through the op amp OP1 and OP2 amplified filtered into the comparator circuit, and set the threshold VTH = 2.05V VTL = 1.55V comparison, the comparator between input and output waveforms shown in Figure 2.
  PIR sensor is powered by a voltage regulator chip supply, VEE terminal voltage of 3.6V, with 4mA of load capacity. In addition, chip voltage regulator can also be compared to the same end of the op amp OP2 to provide 1.8V voltage.
  3.2 The choice of operating mode
  PT8A2621 are ON, AUTO and OFF three modes to choose from.

In the ON mode, the output RELAY pin has been high, so as to provide drive voltage relay. In OFF mode, RELAY pin has been low. In AUTO mode, RELAY pin output is usually low, and only when the PIR is triggered when the input signal is valid only within a certain time pin from the external RC OSCD output value to determine high, and then return to OFF mode.
  PIR effective trigger contains the following three conditions: first, more than 3 times within two seconds when triggered; the second is a trigger signal, but when the pulse width is greater than 340ms; the third is within the 2s 2 trigger, When one pulse width is greater than 160ms. However, the effective trigger PIR RELAY able to make pin output is high, such as the CDS pin had to be equal control constraints see Figure 2.
  Three modes of the chip by changing the MODE pin can be connected in to achieve. Table 2 shows the corresponding connection.
  Table 2 MODE pin connection
  MODE pin is connected to the position mode
  VccON
  GNDOFF
  Open AUTO
  3.3 OSCS and OSCD
  OSCS pin through an external RC circuit can generate a system frequency of 16kHz, the frequency divided by the counts added to the control circuit, but can also be used to control delay of the circuit.
  Oscillation is delayed by OSCD pin external RC circuit to obtain from the AUTO mode to ON mode the on-time.
  3.4 CDS control
  If the CDS pin through a photosensitive resistor to ground. Then, during the day when there is light, CDS pin is low; and the lack of illumination at night, CDS pin high. CDS pin inscribed with the Schmitt trigger, therefore, can be used to control and effective to enable PIR trigger, that is, when the CDS pin high, PIR RELAY effective trigger to make pin output is high, that is, The purpose of CDS is to control the difference between day and night, so during the day and control the lamp will not light. CDS pin high level has to be more than 5 seconds before enabling role. CDS if not controlled, can be connected to the CDS pin VCC.
  3.5 Initialization and Power-on RESET
  PT8A2621 chip power-on initialization time for the 40s RST pin open , if the RST pin is connected to an external capacitor CRST to the ground, you can extend the power chip initialization time. Initialization time in power, PIR trigger is disabled.
  3.6 ZC control
  As PT8A2621 the ZC pin internal Schmitt circuit, thus the input pin on the ZC signal zero-crossing detection. If the ZC signal disappears over 3s, the chip will be re-initialization, initialization time is 40s, then RST pin has no effect on the external capacitor.

Figure 3 PT8A2621 typical application circuit Click to enlarge
  Unauthorized control override 3.7
  PT8A2621 chip also has override control. The so-called ultra vires control means by switching the power switch to switch the power switch in the two 3s to change the chip mode of control. When the chip is operating in AUTO mode: If the override control mode the chip can be turned ON from AUTO mode, when the ultra vires if more control, then the chip will return AUTO mode; if there is no longer ultra vires control ON mode, the chip In the ON mode automatically after 8 hours of work to return AUTO mode. ZC pin ultra vires control is the input signal through to achieve.
  4 Application
  PT8A2621 typical application circuit shown in Figure 3. The figure, S1 control switch can be used as ultra vires, the chip VCC voltage provided by rectifier voltage regulator, relay J1 for light control, function of other parts of the circuit has already been stated no further explanation.
  As PT8A2621 more control chip, in addition to energy-saving lamps shown in Figure 3 control, but also can be used to design an infrared alarm. In addition, the work in the AUTO mode, you can also use the override control with the opening of multiple lamps with the relevant control.