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Precise temperature measurement is becoming ever more critical, especially in industrial, lighting and microcontroller based applications where products are becoming more densely packaged. TDK EPCOS surface mount precision NTC thermistors have been designed as a reliable key components for accurate temperature measurement in these applications.

Today’s electronics modules and systems with high packing densities are often operated up to their thermal limits, accurate temperature measurement is indispensable in order to initiate countermeasures in good time to prevent overheating.

The new miniaturized SMD NTC precision thermistors from TDK EPCOS permit the highly precise temperature measurements required for this purpose. Together with intelligent control circuits, they enable the design of effective thermal control systems.

The SMD NTC thermistors products are available in case sizes 0402 (B57230) and 0603 (B57330) with resistance value 10 kΩ tolerance options of ±1%, ±3% and ±5%. Their narrow tolerances are achieved utilising a new production technology as well as a rugged glass passivation, which additionally ensures high reliability and degradation stability. The slope of the R/T curves and B values with a narrow tolerance of ±1% or ±3% gives a short response time meaning these new NTC thermistors allow accurate and fast temperature measurement across a wide range.

The standard series is suitable for temperatures up to +125 °C making the B57230 (0402) and B57330 (0603) series suitable for use in a wide range of consumer and industrial markets. Automotive versions are also available, B57232 (0402) and B57332 (0603), which are suitable for temperatures up to +150°C.

Precise current control thanks to rapid temperature measurement

A typical example of where precise temperature measurement is required can be found in the charge monitoring of rechargeable batteries in mobile devices. State-of-the-art charging techniques require not only that the maximum permissible temperature of the battery cells be maintained, but also that, as far as possible, charging does not exceed the maximum permissible charging current at the maximum permissible cell temperature.

When the charge current heats the cell to its limit temperature, the current must be very accurately reduced to avoid damage to the cell. The more accurately and quickly the temperature change of the cell can be detected, the more precisely and quickly the charging current can be adjusted. Integrating a NTC thermistor into the battery pack allows charging to take place in the shortest possible time without the risk of thermal overload.

For some applications, such as rapid charging, it makes good sense to additionally measure the ambient temperature in order to avoid excessive differences between the ambient and cell temperatures. For this purpose, a second NTC thermistor can be integrated directly into the circuit board of the charging electronics.

Figure 1: Schematic diagram of a charge monitoring circuit with NTC thermistors

Protecting semiconductors from overheating

Power semiconductors, logic components, microcontrollers and processors must also be protected from excessive temperatures to ensure their reliable operation. Thanks to their compact size, 0402 and 0603, the new SMD NTC thermistors from TDK EPCOS can be integrated in close proximity to microcontrollers and other hot spots on the circuit board. The excellent thermal contact to the circuit board via the solder connections with negligible self-heating assures highly accurate thermal monitoring of sensitive semiconductors.

Thanks to the high resilience of the TDK EPCOS SMD NTC thermistors against thermal shock, they are suitable not only for reflow solder processes but also for wave soldering. Designers can consequently place the thermistors on the underside of the board, for instance, opposite microcontrollers, thus producing a very good thermal contact – even for microcontrollers with large dimensions.

Figure 2: Typical protection circuit for microcontrollers.

Extending LED operating life

In LED based solid state lighting systems, SMD NTC thermistors can be used to assure excellent luminous efficiency together with a long operating life. The efficiency and life of LED lighting depends very much on the temperature of the LED junctions. Temperature extremes must be avoided, as these lead to faster power degradation, reduced intensity, colour shifting as well as a significantly shortened lifetime. In the worst case it can even lead to failure of the product.

By integrating a SMD NTC thermistor into the LED circuit, the optimum operating temperature can be maintained leading to improved stability of light output, colour and lifetime of the lighting system.

Figure 3: Thermal monitoring of LED lighting using NTC thermistor

Anglia are offering customers FREE samples of the SMD Precision NTC Thermistors from TDK, fill in the form below to register your interest now.