Circuit and method for preheating filaments and ballast

A method for preheating filaments using a circuit for preheating filaments, the circuit comprising:

• a transistor;
• a first winding, one terminal of which being electrically connected with a collector of the transistor, and the other terminal being connected to an input of a power source;
• a second winding, one terminal of which being electrically connected with an emitter of the transistor, the other terminal being electrically connected with a base of the transistor, and the second winding being coupled with the first winding in a self-excitation mode;
• one or more load windings respectively connected with the filaments in series, each of which being coupled with the first winding in a flyback mode;
• and a delay switch, configured to change into an on state from an off state when a trigger signal with a predetermined delay is received, so as to turn off the transistor,
• the method comprising:
• setting, when power is on, the delay switch in the circuit for preheating filaments to an off state to start up the circuit for preheating filaments;
• and
• sending, after passing a predetermined delay, a trigger signal to the delay switch in the circuit for preheating filaments, and setting the switch to an on state to cut off the circuit for preheating filaments.

A ballast, comprising;

• a circuit for preheating filaments, the circuit comprising:
• a transistor;
• a first winding, one terminal of which being electrically connected with a collector of the transistor, and the other terminal being connected to an input of a power source;
• a second winding, one terminal of which being electrically connected with an emitter of the transistor, the other terminal being electrically connected with a base of the transistor, and the second winding being coupled with the first winding in a self-excitation mode;
• one or more load windings respectively connected with the filaments in series, each of which being coupled with the first winding in a flyback mode;
• and
• a delay switch, configured to change into an on state from an off state when a trigger signal with a predetermined delay is received, so as to turn off the transistor;
• and the ballast further comprising a half-bridge circuit, wherein the circuit for preheating filaments is connected with the half-bridge circuit in parallel.