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Dimmer, IGBT

A transistorized dimmer that uses Insulated Gate Bipolar Transistors as the power device. This type of dimmer operates in either reverse phase control or forward phase control mode, and does not require a large filter choke to control filament buzz. Reverse phase control offers some reduction in filament noise over forward phase control, but can only be used with resistive loads or capacitive loads (typically electronic low voltage transformers for architectural applications) , never with inductive loads.

Unlike a thyristor (SCR or Triac), which can only switch ON when current is flowing, an IGBT can switch ON or OFF, and also operate in "linear mode", which produces a controlled transition from OFF to ON, or vice-versa, with risetime or fall time. This mode is used to simulate the effect of a choke in a Phase Control dimmer for reducing filament noise. However, an IGBT dissipates the most power when operated in linear mode.

"IGBT" dimmers are sometimes confused with sine wave dimmers, since a sine wave PWM dimmer can also use an IGBT as its power device. The difference is that "IGBT" dimmers produce a line-frequency switched waveform just like a normal thyristor phase-control dimmer, while a sine wave dimmer switches at a high frequency (typically 40-50 kHz) and produces a pure sine wave output.

For absolute noise reduction of filaments, only sine wave dimmers are 100% effective.

IGBT dimmers produce harmonics just like thyristor phase-control dimmers.

IGBT Dimmers deal with rise time in a different manner than Thyristor phase-control dimmers, which use filter chokes to create rise time.

IGBT dimmers operate in the "linear" region of their power transistor during the transition from off to on (forward phase control) or on to off (reverse phase control--now it's called "fall time"). Thus, an IGBT dimmer simulates the effect of a filter choke in a thyristor phase-control dimmer, by causing the IGBT transistor to not switch instantaneously, but in a controlled rise or fall time. This causes the IGBT to dissipate additional power and causes additional heating. Thus, some IGBT dimmers must reduce their rise or fall time (causing more filament noise) as temperature increases.

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