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Single-chip Temperature Control Schematic Circuit Diagram

Proportional Mains-Operated Temperature Control with UAA2016

The UAA2016, designed by Motorola, is exceptionally suited for creating a mains-operated temperature control system with proportional regulation. This component is specifically engineered for driving triacs using the zero-voltage technique. Enabling precise power regulation for resistive loads without causing radio frequency interference (RFI). Its primary application involves the precise regulation of electrical heating systems like panel heaters or irons, which function directly on the AC power line.

The UAA2016 incorporates a built-in digital sawtooth waveform. Enabling proportional temperature regulation within a 1°C range around the designated set point. It also features a programmable temperature reduction function for energy efficiency, along with a failsafe mechanism that inhibits output pulses if the sensor connection is disrupted, enhancing security. Additionally, it allows for predetermined temperature applications, such as defrosting, and offers the flexibility to adjust hysteresis values within 5°C of the set point. All these functionalities are achieved with a minimal number of external components.

Temperature Sensor and Heating Element Setup

A negative temperature control (NTC) resistor, denoted as R3, with an approximate value of 100 ohms at 25°C, acts as the sensor in this configuration. In the provided diagram, the heating element is represented by a 100 W light bulb, generating sufficient heat for applications like greenhouses or climatic chambers used for electronic equipment testing. The triac has the capacity to switch up to 3 A when equipped with an appropriate heat sink.

Single-chip temperature control Schematic diagram

Setting Temperature Range with Resistors

The regulator’s characteristics are defined by the resistors connected to pins 1-4. Resistors R1 and R2 determine the temperature range achievable with P1. In the current setup, the range spans from 0 to 70 °C.

Temperature Drop Adjustment

Activating S1 leads to a temperature decrease of approximately 2 °C. The extent of the temperature drop is influenced by R4: a 100 KΩ value results in a reduction of around 5°C.

Hysteresis Control

Resistor R5 plays a crucial role in determining the regulator’s hysteresis, which is approximately 150 mV in this configuration. The translation of this value into degrees Celsius depends on the specific type of Negative Temperature Coefficient (NTC) used and the prevailing temperature. It’s important to note that NTCs possess non-linear temperature characteristics.

Safety Considerations

Given the circuit’s connection to the mains, the utmost caution must be exercised in adhering to safety regulations. The regulators should be meticulously constructed, ensuring compliance with safety standards. Ideally, the circuit should be housed in a well-insulated, grounded metal case to enhance safety measures.

 

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