The 13.51 step relay dimmer from Finder can operate both as a simple step relay and as a sophisticated dimmer to offer flexible control of lighting. Step relay dimmers are smart lighting circuit components that can either be used as part of a wall-mounted dimmer unit, or more flexibly, as one of several controllers in a lighting console for a larger room or small building.
The 13.51 is based on MOSFET devices, which offers a softer transition when turning the light on or off, and also has a memory feature which returns the lighting level to a preferred value each time it is switched on. Additional benefits compared with conventional triac-based dimmers include a 54% reduction in power switching losses and the elimination of the familiar buzzing noise caused by EMC suppression filters.
The step relay dimmer is a three terminal electronic lighting control module for use on a 230V AC supply. One terminal connects to the live supply (Live In), another connects to the lamp load (Live Out) and the third terminal connects to a controlling push-button. The other connection from the push button can be returned to either the L or the N of the mains supply.
When the 13.51 is used as a step relay, the lamp load is alternately turned on and off by a succession of short pulses on the push-button control. Within this function there are two possible modes of operation. In ‘With memory’ mode a short pulse on the button causes the load to alternate between the OFF state and the previously memorised ON state, allowing the preferred lighting level to be set using the dimmer and memorised, removing the need for the level to be adjusted each time the light is turned on. In ‘Without memory’ mode, a short pulse on the button causes the load to toggle between the full ON state and full OFF state in the manner of a conventional light switch. The desired mode can be selected using a simple 'set-up' routine.
By exerting pressure on the push-button control for a longer interval the dimmer function can be activated, causing the lamp output to progressively increase or decrease alternately from the previous level, over a maximum of 10 incremental light levels between fully off and fully on. However, for safety reasons the dimmer is not able to reduce the level to complete darkness: prolonged pressure on the button when decreasing the lighting level will only reduce it to the 10% level. However, a subsequent momentary pulse on the button will then turn the light off completely, if that is required.

Note to Editors
The step relay dimmer uses MOSFET switches to achieve the lighting control. These devices have the advantage that, unlike conventional triacs, they can be triggered to conduct at the zero voltage point in the waveform, and triggered to open after an appropriate time delay - a feature known as 'trailing edge switching' or 'reverse phase control'.
Trailing edge switching gives the MOSFET dimmer a number of advantages over triac-based designs, including:

•  Lower electromagnetic emissions, avoiding the need for large EMC suppression inductors (which can often cause an annoying buzzing noise).

•  The ability to control alternative types of lighting load, such as low-voltage halogen bulbs operated through a transformer. Triac-based dimmers are restricted to use incandescent lamps and specifically exclude use with inductive loads.

• Lower power dissipation - for a 1.5A load, a typical triac design will dissipate approximately 1.95W, while the MOSFET design dissipates just 1.05W.

• Full output regulation - the output can be controlled over the full 0% to 100% span, in contrast to a triac design which has a restricted lower limit, and also demands a minimum load.

• Higher OFF state - with higher loads, the triac design will permit a significant leakage current in the OFF state.

• Better reaction to gate disturbance - any momentary disturbance on the gate of a triac will affect the whole of that cycle, while a similar disturbance on the MOSFET gate will only affect it for the duration of the disturbance.