LED driving method and driving power source device

An LED driving power source device comprising:

• a pulse current generating means for generating pulse currents as a current signal for controlling operation of series connections of LEDs;
• a signal current allocating means for generating signal currents by switching the current signal generated by the pulse current generating means in units of a period of the current signal;
• first switching circuits each of which is turned on only during periods when a signal current produced by the signal current allocating means flows and causes an allowable forward current having a duty cycle corresponding to an allocation number of the signal current allocating means to flow through one of the series connections of LEDs;
• second switching circuits each of which is turned on only during periods when no signal current produced by the signal current allocating means flows and causes a rated forward current that does not cause destruction of LEDs to flow through the other of the series connections of LEDs;
• and
• at least one additional LED for producing a difference between respective voltages corresponding to the allowable forward current and the rated forward current as a result of flow of the rated forward current through the additional LED,
• the series connections of LEDs being driven by causing the allowable forward current and the rated forward current to flow periodically for an allowable time determined by the switching of the signal current allocating means.