Amypaul LED flashlight



Amypaul Light

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2014 LED flashlight newest driver


1 Introduction
MAX16801A / B for universal AC input LED flashlight driver, and MAX16802A / B are designated for low-voltage (10.8 ~ 24 V) DC input LED driver. By the MAX16801A / B and MAX16802A / B consisting of HB LED driver circuit control IC is mainly used for LCD TV and LCD display monitor RGB backlighting, commercial and industrial lighting, decorative and architectural landscape lighting and other fields.
2 Key Features
MAX16801A / 8 and MAX16802A / 8 the main features are as follows LED flashlight:
Suitable for use as component Buck (Buck), boost, fly back (Fly back), SEPIC and other circuit topology; direct output of 50 W or greater power; internal error amplifier with 1% accuracy; PWM or linear dimming; 262 kHz (1 ± 12%) of the fixed switching frequency operation; provides thermal shutdown and digital soft-start, input start voltage programmable; startup supply current is typically 45μA, operating supply current is typically 1.4 mA; slim 8-pin μMAX package.
3 pin functions and internal structure
MAX16801A / B and MAX16802A / B pin arrangement shown in Figure 1. Listed in Table 1 for each is pin function. MAX16801A / B and MAX16802A / B integrates a 1.23 V bandgap reference, digital soft-start, UVLO, regulator, 262 kHz oscillator, error amplifier, CPWM comparator, current limit comparator, thermal shutdown and MOS gate drives and other cell circuit shown in Figure 2.
4 Application circuit and working principle
4.1 MAX16801 offline using non-isolated LED flashlight LED driver
MAX16801 offline using non-isolated LED flashlight HB LED driver circuit is shown in Figure 3.
4.1.1 Input-start circuit
MAX16801 pin UVLO / EN wake-up threshold voltage is 1.28 V, the pin voltage is just over 1.28 V, the circuit can begin work. Resistor divider (R2 and R3) can be used as programming input start voltage.
MAX16801 built with a large bootstrap UVLO hysteresis circuit, the design of high-voltage HB LED driver is useful. When VIN exceeds 23.6 V threshold level, the circuit starts. During startup, UVLO circuit keeps CPWM comparator, ILIM comparator, oscillator, and output driver turned off to reduce current consumption. Once VIN reaches 23.6 V, CPWM with ILIM comparator and oscillator opened, and allows the output drivers switch. 
4.1.2 start operation
When the circuit is started, the tertiary winding of the transformer T1 (P3) no energy is delivered to the IN terminal of the control IC. After power-up, the current through R1, C1 charges, while the internal regulator charging C2, the maximum current through R1 is 45μA. When VIN exceeds 23.6 V wakeup level, VQ1 began to move, the transformer winding to the secondary and tertiary transmission of energy. The capacity C1 and third transformer winding connection configuration determines the start time. MOSFET (VQl) gate current is:
If the line LED driver start time is less than 500 ms, and C1> C2, R1 by equation (3) and (4) calculation.
4.1.3 LED current is determined
Therefore, ILED = VREF/R7 = 1.23 V/R7. If the HB LED forward current rating is 750 mA, then R7 = 1.23 V/0.75 A = 1.64 Ω
4.1.4 Output short circuit protection
Tertiary winding of the transformer also provides output short circuit hold function. As long as the voltage on the tertiary winding down to 10 V or less. It will turn off the external MOSFET gate drive.
4.2 HB LED driver circuit
Figure 4 shows the low-frequency PWM dimming with universal AC input isolated LED flashlight HB LED driver circuit turn. Among them, an inverting logic PWM signal directly added to MAX16801B the DIM / FB terminal can be realized on a wide range of low-frequency HB LED PWM dimming. Provide safety isolation transformer T1, T1 lower secondary winding grounded through a capacitor C5.
4.3 MAX16802 typical application circuit
Figure 5 shows the dimming capability with using MAX16802B buck (Buck) type HB LED driver circuit. The circuit operates in continuous conduction mode (CCM), the linear dimming signal is applied to MAX16802B pin CS. R5 is a current sensing resistor, R4 and C1 form a low-pass filter. Driver circuit DC input voltage range of 10.8 ~ 24 V. MAX16802B can also form a discontinuous conduction mode (DCM) fly back under HB LED driver circuit topology shown in Figure 6. In Figure 6, LED string may be lower or higher than the total voltage of the input voltage VIN.
5 Conclusions
MAX16081A / B and MAX16802A / B is the general lighting and backlighting applications HB LED driver offline and DE-DE controller, they can build Buck, boost, LED flashlight, SEPIC topology, etc., starting voltage programmable with PWM or linear dimming, digital soft-start and thermal shutdown protection, output power directly to 50 W or more.
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