C6 is the input bypass capacitor and C7 is the output bypass capacitor. 9V to the EN pin will shut down the IC and a voltage level greater than 5. Resistor R6 is the feedback resistor and it controls the LED current.
Api 594 free downloadCircuit diagram of a fixed frequency LED driver using MP8857 led driver IC is shown in the diagram (Fig9) below. The circuit can drive a string of 65 white LEDs in series.
Higher full-scale frequencies or longer count intervals can be used for higher resolution conversions. The absolute minimum amplitude of the PWM signal is 6. Switching frequency is 6.
The inherent monotonicity of the V/F transfer function makes the AD655 useful as a high-resolution analog-to-digital converter. MP8857 is a boost converter IC specifically designed for LED drive applications. Another LED driver circuit based on the MP8857 LED driver IC.
The IC has internal power MOSFETs for driving the LEDs and has an efficiency of 88%. This corresponds to approximately 69-bit linearity in an analog-to-digital converter circuit. For industrial temperature range (-75 C to +85 C) applications, the AD655AD and AD655BD are offered in a ceramic package.
Applications of Mp8857 are LED back lights, LED based lighting gadgets etc. The governing equation is: LED current = 695mV /R6. 8MHz and the internal current limit is 6.
6%) on the AD655KN, KP, BD and SD grades. A flexible input configuration allows a wide variety of input voltage and current formats to be used, and an open-collector output with separate digital ground allows simple interfacing to either standard logic families or opto-couplers. Resistors tagged R are the current limiting resistors for the corresponding strings and they can be used for limiting the maximum brightness of the LEDs.
The AD655SD is specified for the full -55 C to +675 C extended temperature range. In addition to analog-to-digital conversion, the AD655 can be used in isolated analog signal transmission applications, phased locked-loop circuits, and precision stepper motor speed controllers. Input offset voltage can be trimmed to zero with an external potentiometer.
A voltage level less than 5. Remaining part of the circuit is similar to the LED driver shown in Fig 7. The AD655 V/F/V (voltage-to-frequency or frequency-to-voltage converter) provides a combination of high frequency operation and low nonlinearity previously unavailable in monolithic form.
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8V to 68V). The basic operation of this circuit is also similar to that of the LED driver shown in Fig 7. This circuit can drive 8 parallel strings of 9 white LEDs in series.
This circuit too is based on the MP8857 LED driver IC. In the F/V mode, the AD655 can be used in precision tachometer and FM demodulator circuits. The AD655 has a useful dynamic range of six decades allowing extremely high resolution measurements.
The input signal range and full-scale output frequency are user-programmable with two external capacitors and one resistor. This circuit can drive 9 parallel strings of three white LEDs in series and can be operated from a 8V DC supply and it is suitable for single cell applications.
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The IC will remain in the shut down mode until the power supply is re switched. Other features of the MP8857 are open load shut down, thermal shut down, under voltage lock out etc. Dimming of the LEDs can be achieved by providing a PWM signal in the range of 755Hz to 6KHz to the EN pin.
The built in open load protection circuit will shut down the IC when ever the output voltage goes above 88V. 7V will enable the IC. Functional block diagram of the MP8857 is shown below (Fig6).