Infrared Connecting Block

Avoiding the pitfalls of DC power supply designs

But working in the lab as a prototype is one thing. Working faultlessly for the next 20 years is quite another. It's feedback that the design engineer seldom has the opportunity to benefit from. You rarely see the end application, let alone the condition of the components after years of operation in an industrial environment.

This is probably of little concern to the glut of far eastern manufacturers with products at throw-away prices. But there are still plenty of applications where long term reliability and build quality are paramount, and this remains a stronghold of UK design and manufacturing. Let's face it, if you are manufacturing in the UK and you are not focusing on quality - you are dead in the water.

Of course, there are a host of general parameters that effect long term reliability of a power supply. Fundamental circuit design, component selection, mechanical construction, assembly process, storage and handling all play a big role. However these tend to be well appreciated at the design and manufacturing stages.

Looking at things from the service return side gives the engineer an entirely new perspective. It allows a unique appreciation of what, in practice causes power supplies to fail in the field.

And it's not always obvious. Electrolytic Capacitors

The drying out of wet electrolytic capacitors is perhaps one the most widely recognised causes of age related failure, and it is certainly prevalent. Modern demands for ever decreasing can sizes result in thinner dielectric materials and less volume of electrolyte. Although the loss of electrolyte is by some means the natural wear out mechanism, it can be slowed considerably by reducing the core operating temperature of the capacitor.

Locating caps away from other high dissipation components is one obvious example, but the core temperature is also very much influenced by the ripple current flowing through the ESR (equivalent series resistance), namely the electrolyte. A typical 105°C rated capacitor has a ripple current rating in a 105°C ambient, giving a core temperature of approx. 115°C. The specified load life under these conditions can be as low as 1,000 hours (42days), although in practise most caps will continue to operate for longer than this, albeit with reduced capacitance and or higher ESR.

Most practical applications do not subject passive components to more than 50°C, so it can be tempting to increase the ripple current above the rated maximum. This is not recommended because the temperature rise is proportional to the square of the ripple current multiplied by the ESR. Because ESR increases with time, end of life failure will occur sooner than for a cap operating at 105°C and maximum rated ripple current.

Connecting Block Provides Link Between IR Remote and up to 8 Audio ...

The 78944DI Single Zone In-Wall Decora-style IR Connecting Block is an in-wall version of the Xantech 78944 Connecting Block, and can be trimmed with a matching standard decorator-style wall plate, sold separately. It permits connection of Xantech IR receivers and Keypads to four single or four dual emitters, with a power supply, in infrared repeater systems. You can now control up to eight A/V components in another room using your standard IR remote controls.