Audio transistors take temperature in their stride

ThermalTrak is an innovative family of output transistors with internal bias control that provide a simplified single-device solution for audio amplifier design.

ThermalTrak is an innovative family of output transistors with internal bias control that provide a simplified single-device solution for audio amplifier design.

Featuring patent-pending technology, these devices eliminate tedious warm-up time, enable quick and precise temperature adjustment, and improve both sound quality and bias stability.

The initial devices will be ideal for use in high-end consumer audio amplifiers and receivers, as well as professional audio applications such as theatre, stadium and PA sound systems.

ThermalTrak devices simplify board design by eliminating the need for output drive compensation circuitry and costly manual bias adjustments.

"This new family of audio output devices provides a simplified, single-device design solution for audio amplifiers", said Keith Nootbaar, ON Semiconductor Director of Power Discrete Products.

"The soon-to-be patented ThermalTrak technology used to develop these devices enhances THD performance at lower power levels where it matters the most and will change the way audio amplifiers are designed".

"Additionally, this technology provides a platform on which the company plans to build a significant portfolio of audio output power solutions".

In audio output applications, transistor overheating leads to increased harmonic distortion and can potentially cause catastrophic failure of the end product.

Designers have traditionally mounted discrete bias protection circuitry to the heatsink to monitor temperature changes.

While relatively effective, this standard industry solution still results in a lag time before thermal stability is achieved.

Ultimately, it can take up to 5min for the temperature change of the heatsink to be significant enough to be recognised, creating the potential for thermal runaway of an individual transistor before any compensation is made.

More accurate bias control is needed to overcome this design challenge and eliminate both the thermal lag and bias trimming.

Rather than mounting bias transistor (or transistors) to the heatsink in close proximity to the output devices, ON Semiconductor's ThermalTrak technology thermally integrates bias compensation within an output transistor.

This provides precise detection and immediate correction of thermal changes - improving both sound quality and bias stability.

This technology establishes a superior level of bias compensation performance not previously achievable using traditional discrete biasing circuitry.

The first ThermalTrak transistors to be introduced by ON Semiconductor are the NJL1302D (PNP) and the NJL3281D (NPN).

These 230V devices offer a 200W power rating.

Following the 200W introduction, the company plans to introduce devices for 150 and 250W requirements.

Further expansion of the ThermalTrak family for lower power applications is planned for later 2005.

The NJL1302D and NJL3281D ThermalTrak devices will be offered in a standard size 5-lead, TO-264 package.

The devices are budgetary priced at $2.25 per unit in 10,000-unit quantities.

Limited advance engineering samples are currently available.

The devices are scheduled for full production early in the second quarter.

Back to top