![]() ![]() ![]() This is an especially desirable characteristic for CCFL control, where lamp intensity must remain constant with shifts in line voltage. The circuit has none of the line rejection problems attributable to the hysteretic voltage control loops typically found in low voltage micropower DC/DC converters. Current mode operation combined with the Royer’s consistent waveshape vs input results in excellent line rejection. #COLD CATHODE FULL#When V A is set to zero, the I LIM pin’s bias current forces about 100μA bulb current.Ĭircuit efficiency ranges from 80% to 88% at full load, depending on line voltage. The LT1301 regulates L1’s current to equalize Q3’s average collector current, representing 1/2 the lamp current, and R1’s current, represented by V A/R1. The LT1301’s I LIM pin acts as a 0V summing point with about 25μA bias current flowing out of the pin into C1. On negative half-cycles the lamp’s current flows through Q3’s collector and is filtered by C1. On positive half-cycles the lamp’s current is steered to ground via D1. Alternating current flows through the 22pF capacitor into the lamp. T1 furnishes voltage step-up and about 1400Vp-p appears at its secondary. The 0.068μF capacitor combines with T1’s characteristics to produce sine wave voltage drive at the Q1 and Q2 collectors. The 1N5817 diode maintains L1’s current flow when the LT1301’s switch is off. LT1301 driven L1 sets the magnitude of the Q1-Q2 tail current, hence T1’s drive level. The Royer converter oscillates at a frequency primarily set by T1’s characteristics (including its load) and the 0.068μF capacitor. L1’s current is deposited in switched fashion to ground by the regulator’s action. Current flows from T1’s center tap, through the transistors, into L1. ![]() When power and intensity adjust voltage are applied the LT1301’s I LIM pin is driven slightly positive, causing maximum switching current through the IC’s internal switch pin (SW). The circuit uses an LT1301 micropower DC/DC converter IC in conjunction with a current driven Royer class converter comprised of T1, Q1 and Q2. Low Power Cold Cathode Fluorescent Lamp Supply Is Optimized for Low Voltage Inputs and Small Lamps Infact, the device out performed the design by a huge margin, giving a factor of 5 lower electric field, because it was found that the space charge in the well gives rise to additional lowering of the work function, by eV SC, where V SC is the potential from the space charge ρ sc.įigure 35.9. Electrons emerge from the n + – GaN tunnel resonantly into the vacuum providing a high current, as well as lowering the work function, because the quantum state is flat across the potential profile allowing the effective work function to be lowered by ∼E1/2 where E1 is the quantum state involved. With a field at the surface, the vacuum is transformed into a triangular barrier at the surface. The QW structure consists of a GaAlN barrier, a GaN well, and a second barrier, the vacuum. Recently, a new type of cold cathode has come on the scene: field emission with resonant tunneling (FERT), a scheme that involves placing a QW structure at the surface of a semiconductor with a fairly low work function such as the GaN. High-power high-frequency devices such as the TWT are still the backbone of the high-power amplifier. The cold cathode is a device for electron field emission replacing the hot filament in vacuum electronics. Raphael Tsu, in Superlattice to Nanoelectronics (Second Edition), 2011 Publisher Summary The only way to ensure peak efficiency in a given situation is to optimize the circuit to the display. In fact, it is quite possible for “inefficient” circuits to produce more light than “more efficient” versions. The optimum waveshape for emissivity may or may not coincide with the circuit’s electrical operating peak. This is primarily due to the lamp’s emissivity dependence on waveshape. It is quite significant that the electrical and optical peak efficiency operating points do not necessarily coincide. The electrical and optical losses are lumped together in this measurement to produce a luminosity vs power specification. ![]() It is simply the ratio of display luminosity to DC power into the CCFL circuit. The optical efficiency is perhaps more meaningful to the user. The electrical efficiency is the ability of the circuit to convert DC power to high voltage AC and deliver it to the load (lamp and parasitics) with minimum loss. Jim Williams, in Analog Circuit Design, 2013 EfficiencyĬCFL backlight efficiency should be considered from two perspectives. ![]()
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