Warm-up circuit for CCFLs
A warm-up circuit adjusts the brightness of a CCFL through using PWM technique for a scanner. The warm-up circuit has an inverter connected to the CCFL for supplying power, and a PWM controller connected to the inverter for outputting a first control signal to the inverter in a warm-up time and outputting a second control signal to the inverter to control the inverter supplying power to the CCFL in a scan time.
1. A warm-up circuit for CCFLs disposed in a scanner for controlling the brightness of a CCFL according to a reference voltage, said warm-up circuit comprising:
an inverter connected to said CCFL and providing a drive power to said CCFL; and
a PWM control unit connected to said inverter and outputting a first control signal to said inverter in a warm-up time and outputting a second control signal to said inverter to control said inverter supplying power to said CCFL in a scan time;
wherein said inverter includes:
a transformer connected to said CCFL via a secondary side coil for conversion of said drive power; and
at least a transfer switch connected to said PWM control unit, said reference voltage and a primary side coil of said transformer, said transfer switch being controlled by said first control signal and said second control signal in order to perform on/off switching actions and transfer said reference voltage to the primary side coil of said transformer in an alternating way.
2. The warm-up circuit for CCFLs as claimed in claim 1 , wherein said first control signal and said second control signal control said inverter to provide a first lamp current and a second lamp current of said drive power for said CCFL, respectively.
3. The warm-up circuit for CCFLs as claimed in claim 1 , further comprising an RC circuit connected to said PWM control unit and adjusting said warm-up time by adjusting resistance and capacitance values of said RC circuit.
4. The warm-up circuit for CCFLs as claimed in claim 2 , wherein a duty cycle of said first control signal is longer than that of said second control signal.
5. The warm-up circuit for CCFLs as claimed in claim 2 , wherein said first lamp current is higher than said second lamp current.
6. A warm-up circuit for CCFLs disposed in a scanner for controlling the brightness of said CCFL according to a reference voltage, said warm-up circuit comprising:
an inverter connected to said CCFL and providing a drive power for said CCFL; and
a PWM control unit connected to said inverter and outputting a first control signal and a second control signal to said inverter to control said inverter supplying power to said CCFL;
wherein said inverter includes:
a transformer connected to said CCFL via a secondary side coil for conversion of said drive power; and
at least a transfer switch connected to said PWM control unit, said reference voltage and a primary side coil of said transformer, said transfer switch being controlled by said first control signal and said second control signal in order to perform on/off switching actions and transfer said reference voltage to the primary side coil of said transformer in an alternating way.
7. The warm-up circuit for CCFLs as claimed in claim 6 , wherein said first control signal and said second control signal control said inverter to provide a first lamp current and a second lamp current of said drive power to said CCFL, respectively.
8. The warm-up circuit for CCFLs as claimed in claim 6 , further comprising an RC circuit connected to said PWM control unit for adjusting a time for said PWM control unit to output said first control signal by adjusting the resistance value and capacitance value of said RC circuit.
9. The warm-up circuit for CCFLs as claimed in claim 7 , wherein a duty cycle of said first control signal is longer than that of said second control signal.
10. The warm-up circuit for CCFLs as claimed in claim 7 , wherein said first lamp current is higher than said second lamp current.