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Conventional ballasts

Due to the current-voltage characteristic of mercury lamps, a current-limiting ballast is required that is connected in series to the UV lamp.
In the UV application, high-power mercury lamps with a power output
of several kilowatts are currently operated on inductive or capacitive power switching ballasts.

The simplest arrangement consists of a choke and the UV lamp connected in series. If different power outputs are required, a step circuit can be used. Several chokes are connected in parallel; the lamp current is increased by activating them one after the other.

Transductors enable dimming of up to approx. 50% of the rated power. With lamp arc voltages of more than 280 V, a sufficiently stable operation using a choke and the 400 V mains is no longer possible. UV lamps with an arc voltage of 280 to 450 V are in practice mostly operated on a combination of autotransformer and choke or transductor.

As far as the ballasts described so far are concerned, an ignitor is required to ignite the UV lamp. In these cases, additional ignition devices operating at a maximum ignition voltage of 4 kV are used.

For arc voltages of more than 450 V, leakage-field transformers are employed. Their leakage inductance has a current-limiting effect and at the same time, their ratio of turns provides the higher voltage for the operation of the UV lamp. Choke circuits or transductor power stages are also possible.