Patent ID: 6140771
Filing Date: 2000-10-31
Classification: H05B,Y10S

Abstract:
Electronic ballast for operating at least one gas discharge lamp, said ballast comprising:an inverter;a load circuit connected to the inverter;a gas discharge lamp connected to the load circuit, said gas discharge lamp having a filament-heating transformer for preheating the filaments of the gas discharge lamp;a primary winding for said transformer being connected in series with a first resistor in parallel with the gas discharge lamp;a monitoring circuit arrangement for monitoring the current flow through the primary winding of the filament-heating transformer, or a variable that is proportionally dependent upon such current;an interconnection point between the primary winding of the filament-heating transformer and the first resistor being connected to the monitoring circuit arrangement by way of a second resistor so that the voltage drop across the first resistor and the current flow through the second resistor are fed as monitoring variables to the monitoring circuit arrangement;said monitoring circuit arrangement being arranged to assess, as a monitoring variable, the presence of a rectification effect in the gas discharge lamp in the case of a voltage drop across the first resistor which increases in a positive direction or in the case of a current flowing through the first resistor which increases, in a positive direction as a function of the voltage drop across the first resistor;said monitoring circuit arrangement further being arranged to assess, as a monitoring variable, the presence of a rectification effect in the gas discharge lamp in the case of a voltage drop across the first resistor which increases in a negative direction or a current flow through the first resistor which increases in a negative direction as a function of the current flow through the second resistor;said monitoring circuit arrangement being constructed to indicate the presence of a rectification effect in the gas discharge lamp upon a monitoring variable exceeding a predetermined limiting value.