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CAT4104 LED Controller Application Example

DavidGohara
Designer199194

DavidGohara

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This is an application example for an ON Semiconductor CAT4104 Quad Channel Constant Current LED Driver. It demonstrates the part's resistor programmable and independent current control for each channel, as well as its PWM dimming capability. By choosing the value of r_set from 768 Ohm up to 12 kOhm, the current in each channel is controlled from 175 mA down to 10 mA. That is, the channel current is 100 times the current in r_set, which is driven by an internal 1.2 V source from the CAT4104 "rset" pin. The LED strings can be driven by parallel channels to reach even higher string current levels. For LED dimming, the CAT4104 "en_pwm" pin can be driven by a PWM signal. In this application circuit, that signal is provided by an LM555 timer module. The potentiometer setting controls the PWM duty cycle, and the element's total resistance value determines the PWM frequency. The initial potentiometer wiper ratio of 0.5 and resistance of 20 kOhm, gives a 50% PWM duty cycle at 500 Hz.The LED string model, for which the user can select the number of LEDs in the string as well as the individual LED operating parameters, has an internal quantity that gives the "perceived" luminous output. This includes a 15 Hz Low-pass filter, to represent the light-averaging effect of the human eye. This is shown in the dark blue waveform. The user can explore the effect of changing the potentiometer settings, which in turn change the PWM characteristics, on the perceived light output. The initial LED parameters for this example represent a CREE XPCWHT-L1-R250-009E6.

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ACME AS123 LED Driver with Dimmer Control - Application Note

docman
Designer199081

docman

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The AS123 LED Driver from ACME Semiconductor (fictional) provides fully integrated PWM dimming and a programmable current set-point. This IC is specifically for automotive rear combination (tail/stop) lighting applications. It tightly regulates the desired string current under conditions of widely varying applied DC voltage.The PWM dimming function, which switches the LED on and off at just over 300 Hz, is active when the line input pin is high and the "PWM_disable" pin is low (The AS123 supports current programming using a single external resistor (see r_iset in the schematic). The resistor value can be selected to give the desired LED string current, using the following formula:r_iset = 1.85/i_desired The AS123 is capable of regulating up to 100mA per string continuously. Therefore the value of r_iset should be no less than 18.5 Ohms.In the simulation results, note that the brake/stop signal is active (12.6V) for the first 100ms, and then low (0 V) for the next 100ms. The tail light input is active the entire time, pulsing between 11.6V and 17.6V. Note that the LED current is approximately constant, at just under 30mA during the brake/stop on-time. When the brake/stop signal goes to 0V, then the LED current begins to PWM (55% duty-cycle, 325Hz).The user can move the waveform probes around, to look at other signals both on the schematic nets and within components. For example, move a probe onto one of the LED models and select to view the "power_dissipated".If the user creates a free account on systemvision, he can make a copy of this design. Then he can make changes to it, such as adjusting the r_iset resistor value. He can then simply re-run the simulation to see the effect of that change.See a "block diagram" schematic model of the ACME AS123 here: https://www.systemvision.com/design/acme-as123-led-driver-schematic-model-------------- End of Example Application Note ------------------If you are a component supplier, this type of "Executable Application Note" can help your potential customers better understand the features and benefits of your components.

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10 LEDs em sequência

RafaelPereira
Designer198138

RafaelPereira

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120v to 36v 100W LED Driver

Cuthbert
Designer197868

Cuthbert

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Joule Thief Transformer Physical Design For LED Lighting

captain
Designer197694

captain

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Joule Thief Transformer Physical Design For LED Lighting

RobertCampbell
Designer197545

RobertCampbell

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TDFS Impedance Stability of Transmission Line Fed LED Driver - Switching

MASA
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MASA

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9 years 10 months

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Description

This example demonstrates the use of the TDFS method (Time Domain Frequency Sweep) to measure impedance stability ratio. The system is a switching DC/DC step-down power converter used for LED lighting, supplied by a battery through a long power cable.The TDFS impedance stability measurement model applies a 0.2A sinusoidal stimulus current at the point where the cable connects to the converter. The voltage at that point, as well as the stimulus current splits (toward the source and the load) are measured, and the associated source and load impedances vs. frequency are computed.The ratio of the source to load impedance is the impedance stability ratio (Tm). Similar to the open-loop frequency response requirement for closed-loop stability, Tm must not have magnitude = 1.0 at phase = 180 degrees, at any frequency.For this system, with a cable length of 400 meters and 8 AWG wire, the results show that the impedance ratio magnitude (green waveform) reaches unity (0 dB) at close to 2 kHz, where the phase (light blue waveform) is approximately 165 degress. This implies a "phase margin" of only 15 degrees, For a longer cable, this margin is further reduced. As shown in the companion example, "Transmission Line Fed LED Driver - Switching", for the cable length = 800 meters the system is unstable.This instability is the result of the "source" impedance (which includes the cable) variation over frequency, interacting with the varying load impedance. Note that at low frequency, the load effectively has a negative impedance, due to the constant power nature of the DC to DC converter.

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