NTC Thermistor Circuit Diagram: Divider Wiring Basics
This reference focuses on how a measurement NTC, pull-up resistor, supply and ADC node are connected in a simple voltage divider. The wiring direction determines the resistance equation and signal polarity. It is not a substitute for the controller datasheet, sensor R/T data or circuit-level validation.
NTC Response and Measurement Inputs
An NTC’s resistance generally decreases as its temperature rises. A controller measures the divider voltage and maps the calculated resistance to temperature using the correct part-specific R/T table or model. Confirm the thermistor part, rated resistance and reference temperature, tolerance, controller ADC range, supply/reference arrangement and required temperature range before choosing resistor values.
Where Divider Wiring Is Used
Divider circuits are commonly used to read an NTC probe with an ADC in appliances and other electronic systems. The same element may also be used in a circuit for thermal compensation or over-temperature monitoring, but these functions require system-specific circuitry, thresholds and validation. An NTC measurement probe is different from a power inrush limiter; do not apply a sensing-divider example to a power circuit.
Two Common NTC Divider Orientations
NTC below the ADC node
Connect the fixed resistor from VCC to the ADC node, then connect the NTC from the ADC node to ground. The measured voltage is VADC = VCC × RNTC / (Rfixed + RNTC), so RNTC = Rfixed × VADC / (VCC − VADC). As NTC temperature rises and resistance falls, the node voltage falls.
NTC above the ADC node
Connect the NTC from VCC to the ADC node, then connect the fixed resistor from that node to ground. Now VADC = VCC × Rfixed / (RNTC + Rfixed), and resistance can be recovered as RNTC = Rfixed × (VCC − VADC) / VADC. As the NTC warms and resistance falls, the node voltage rises.
Do not combine the equation for one orientation with the wiring of the other. Use a common, correctly referenced ground, check that the ADC input stays within its absolute limits, and verify settling and noise behavior with the actual controller. The NTC circuit design guide covers divider sizing, ADC conversion, self-heating and system validation in greater depth.
Wiring and Validation Checklist
- Draw the actual connection from supply through the upper element, ADC node and lower element to ground.
- Derive the resistance equation from that exact topology and test it with known resistor values before connecting the sensor.
- Use the selected model’s R/T curve or stated Beta interval; nominal resistance alone is not a full conversion curve.
- Account for resistor tolerance, ADC reference, wiring resistance and measurement current. Check open, short and near-rail readings explicitly.
- Validate the complete probe/controller assembly against a suitable reference over its specified operating conditions.
Review the NTC R/T chart guide, browse the NTC sensor range, or request an OEM probe quotation with the wiring and installation requirements.
For component characteristics and measurement considerations, consult TDK’s NTC thermistor technical information.
