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When designing a temperature measurement circuit using NTC thermistors, one key detail often goes unnoticed — their essential partners: pull-up and pull-down resistors.Together, they form a voltage divider that converts the NTC’s resistance change with temperature into a measurable voltage signal for MCUs or ADC modules.

1.Why NTC Needs Pull-Up or Pull-Down Resistors?

NTC thermistors are analog devices that only change resistance with temperature.Digital circuits, however, can only read voltage — not resistance.So, a resistor (either pull-up or pull-down) is paired with the NTC to create a divider circuit that outputs a variable voltage corresponding to temperature.

The basic voltage divider formula is:

where:

 V_out = voltage across NTC (or across the fixed resistor, depending on configuration).

 V_CC= supply voltage (e.g., 5 V or 3.3 V).

 R_NTC = thermistor resistance (decreases as temperature increases).

 R_pull-up= pull-up or pull-down resistor.

2.Pull-Up vs Pull-Down: Different Connections, Same Purpose.

They ensure stable voltage levels, suppress electrical noise, and protect sensitive ICs from current surges.

3.Understanding Voltage–Temperature–Logic Relationship.

Using the divider formula:

• At low temperature:R_NTC is high → V_out increases → MCU reads a higher voltage (logic HIGH).
• At high temperature:R_NTC drops → V_out decreases → MCU reads a lower voltage (logic LOW).

This makes it easy for an MCU to detect temperature thresholds or continuously measure analog temperature through ADC input.

4.Temperature Switch Example Using Comparator.

For simple thermal control (no MCU), a comparator circuit can directly interpret NTC voltage levels:

• Comparator “+” input → fixed reference voltage (e.g., 2 V).
• Comparator “–” input → NTC divider output.

When Vout crosses the reference threshold:

• Low temperature (RNTC high): Vout > V_ref  → output HIGH → “Normal Temperature”
• High temperature (RNTC low): Vout< V_ref  → output LOW → “Overheat Warning”

Advantages:Low cost, fast response, no MCU needed — ideal for over-temperature protection in power supplies, chargers, or industrial modules.

5.Selecting Proper Resistor Values.

Choosing the right resistor ensures balance between power consumption, sensitivity, and noise immunity.

6.Why Partner with Shiheng Electronics?

With over 20 years of manufacturing experience, Shiheng Electronics offers:

•  Full NTC thermistor and temperature sensor product line.
•  High precision, fast response, excellent stability.
•  Multiple encapsulation options for embedded and industrial use.
•  Expert guidance on voltage divider design, resistor pairing, and circuit optimization.

Our MF52 series thermistors and precision sensors are widely used in:

•  Smart home appliances.
•  EV and battery thermal systems.
•  Medical electronics.
•  Industrial automation.

Looking to Design a Reliable Temperature Sensing Circuit? Contact Shiheng Electronics today for expert engineering support and custom NTC solutions.

Web:www.ntcshiheng.com；Email:Globalsales@shiheng.com.cn.