The present invention relates generally to diode drive current sources, and more particularly, to a quasi-resonant diode drive current source for use in powering solid state lasers.
Current controlled quasi-resonant converters are known in the motor art and once such converter is disclosed in "A Current-Controlled Quasi-Resonant Converter for Switched-Reluctance Motor", by Hoang Le-Huy, published in IEEE Transactions on Industrial Electronics, Vol. 38, No. 5, Oct. 1991. This paper discloses a current controlled quasi-resonant converter for use with low and medium power variable speed drives employing switched reluctance motors. Zero current switching is employed to improve the switching performance and to provide effective control of the current in the motor windings.
In addition, quasi-resonant converters are also discussed in a paper entitled "Multi-Loop Control for Quasi-Resonant Converters," by Raymond B. Ridley, published in IEEE Transactions on Power Electronics, Vol. 6, No. 1, January 1991. This paper discloses a multi-loop control scheme for quasi-resonant converters, and describes various quasi-resonant buck converter topologies and circuits.
With regard to the laser art, diode pumping has become the choice for use with solid state laser systems due to its higher electrical-to-optical efficiency. Prior to the use of diode pumping, flashlamps were used as pump sources. Typical system efficiencies were in the 1% to 2% range. The low efficiency was due mainly to the low electrical-to-optical efficiency. The use of diode pumping, with its higher electrical-to-optical efficiency, can result in a laser system efficiency of 10%, to 15%. Thus, a tenfold reduction in required input power can be achieved.
Diode pumping requires high power, pulsed, regulated current sources to drive the pump diodes. Conventional current sources utilize either a series dissipative regulator or a pulse-width-modulated (PWM) converter to control output current. When used at high output currents, as is required by diode pumped lasers, for example, both of these techniques suffer from high power losses, and are thus very inefficient.
The series dissipative regulator dissipates power dropped across a series pass element, typically a transistor, and the power is given by P=(V.sub.in -V.sub.out)*I.sub.out. At high output currents, the power loss is very high. The PWM converter suffers from high switching losses in its switch transistor, particularly due to reverse recovery of a catch diode, and from switching losses in the catch diode. At high output currents, the reverse recovery currents are very large, and the resulting power losses are very high.
Therefore, it would be an advance in the art to have a current source that is relatively efficient and is capable of providing high power pulsed regulated current to solid state diode pumped lasers, and the like.