HV9910P データシートの表示（PDF） - Supertex Inc

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HV9910P

Universal High Brightness LED Driver

Supertex Inc 

HV9910

example, a potentiometer connected between VDD

and ground can program the control voltage at the

CS pin. Applying a control voltage higher than

250mV will not change the output current setting.

When higher current is desired, select a smaller

sense resistor.

The PWM dimming scheme can be implemented by

applying an external PWM signal to the PWM_D

pin. The PWM signal can be generated by a

microcontroller or a pulse generator with a duty

cycle proportional to the amount of desired light

output. This signal enables and disables the

converter modulating the LED current in the PWM

fashion. In this mode, LED current can be in one of

the two states: zero or the nominal current set by

the current sense resistor. It is not possible to use

this method to achieve average brightness levels

higher than the one set by the current sense

threshold level of the HV9910. By using the PWM

control method of the HV9910, the light output can

be adjusted between zero and 100%. The accuracy

of the PWM dimming method is limited only by the

minimum gate pulse width, which is a fraction of a

percent of the low frequency duty cycle.

Some of the typical waveforms illustrating the PWM

dimming method used with the application circuit of

Figure 1 are given below. CH1 shows the MOSFET

Drain voltage, CH2 is the PWM signal to pin

PWM_D and CH4 is the current in the LED string.

33% PWM Ratio at 500Hz Dimming

95% PWM Ratio at 500Hz Dimming

0.4% PWM Ratio at 500Hz Dimming

Programming Operating Frequency

The operating frequency of the oscillator is

programmed between 25 and 300kHz using an

external resistor connected to the ROSC pin:

FOSC = 25000/(ROSC [kΩ] + 22) [kHz]

Power Factor Correction

When the input power to the LED driver does not

exceed 25W, a simple passive power factor

correction circuit can be added to the HV9910

application circuit of Figure 1 in order to pass the

AC line harmonic limits of the EN61000-3-2

standard for Class C equipment. The typical

application circuit diagram shows how this can be

done without affecting the rest of the circuit

significantly. A simple circuit consisting of 3 diodes

and 2 capacitors is added across the rectified AC

line input to improve the line current harmonic

distortion and to achieve a power factor greater

than 0.85.

5

C110504

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