Low Noise IGBT Dimming – Making the Silicon Scream

This dimmer is a microprocessor design used primarily to control dimming of cove lighting. It is a very flexible design that provides several control interfaces. The use of IGBTs allows leading edge dimming along with control of the turn off time. The resolution of the Programmable Output Generator makes it easy to consistently and accurately control the dimming of multiple lights. A monitor program and the ability to boot different versions of software from the FLASH enhance troubleshooting and development of custom software.

This device would be used where it is necessary to control many lights or interfacing to existing control systems. Serial channel 1 of the Z183 interfaces with an RS-422 driver/receiver to allow connection to the industry standard DMX512 protocol. This protocol consists of sending packets that contain a byte of data for each light. The packet begins with a BREAK followed by a control byte and then up to 512 bytes of channel data. The bytes of data are standard 8 bit asynchronous serial data at 250K baud. The size and repetition rate of the packets are user defined. Each dimmer uses it’s node address to retrieve it’s 8 assigned data channels from the DMX512 packet. The 8 analog inputs also allow Interfacing to the industry standard 0 to 10V control signals. The analog interface also has enough control signals to be controlled through a parallel port. The RS232 Monitor on serial channel 0 provides another control path.

The IGBT drivers allow up to 500 watts to be dimmed, typically eight 60 watt lights would be individually dimmed. However it can drive two 250 watt lights or one 500 watt light. By using IGBTs to control the lights instead of the typical SCR the dimming can start on the leading edge of the power cycle. This allows for a smooth turn on. The turn off is also smooth thereby eliminating the rapid rise times that produce noise. This design eliminates costly noise filtering and improves the life of the light by reducing thermal shock. The characteristic ringing of a dimmed light is greatly reduced.