The FC9910B is a low cost off line buck boost or buck-

boost converter control IC specifically designed for driving

enables fairly accurate LED current control without the need

multi-LED strings or arrays. It can be operated from either

universal AC line o r any DC voltage between 8~450V.

Optionally, passive power factor collection circuit can be

used in order to pass the AC harmonic limits set by EN 61000-

3-2 Class C for lighting equipment having input power less

than 25W.

The FC9910B can drive up to hundreds of

high brightness LEDs or multiple strings of HB LEDs.

The LED arrays can be configured as a series or series/

parallel connection.

The FC9910B regulates constant

current that ensures controlled brightness and spectrum

of the LEDs. and extends their life time. The FC9910B

features an enable pin(PWM_D) that allows PWM control

of brightness.

The FC9910B can also control brightness of LEDs by

programming continuous output current of the LED driver

(so called linear dimming) when a control voltage is

applied to the LIN_D pin.

The FC9910B is offered in standard SOP-8. It is also

available in a high voltage rated SOP-16 package for

applications that require Vin greater than 250V.

The FC9910B includes an internal high voltage linear

regulator that powers all internal circuits and can also

serve as a bias supply for low voltage external circuitry.

The FC9910B can control all basic types of converters,

isolated or non-isolated operating in continuous or

discontinuous conduction mode. When the gate signal

enhances the internal power MOSFET, the LED driver

stores the input energy in an inductor or in the primary

inductance of a transformer and depending on the converter

type may partially driver the energy directly to LEDs.

delivered to the output during the off cycle of the power

MOSFET producing current through the string of LEDs.

(Flyback mode of operation)

When the voltage at the Vcc pin e xceeds the UVLO

threshold the gate drive is enabled. The output current

is controlled by means of limiting peak current in the internal

power MOSFET. A current sense resistor is connected in

series with the source terminal of the MOSFET.

The energy stored in the magnetic component is further

The voltage from the sense resister is applied to the

ISEN pin of the FC9910B. When the voltage at ISEN

pin exceeds a peak current sense voltage threshold,

the gate drive signal terminates, and the power MOSFET

turn off. The threshold is internally set to 250mV, or it

can be programmed externally by applying voltage to the

LIN_D pin. When soft start is required, a capacitor can

be connected to the LIN_D pin to allow this voltage to ramp

Optionally a simple passive power factor correction circuit

at a desired rate, therefore, assuring that output current

of the LED ramps gradually.

consisting of 3 diodes and 2 capacitors, can be added as

as shown in the application circuit diagram of figure 1.

A current of 1mA is needed to start the FC9910B.

As shown in block diagram , this current is internally generated

-

in FC9910B without using bulky start up resistors typically

required in the off line applications.

Moreover, in many

applications the FC9910B can be continuously powered

using its internal linear regulator that provides a regulated

voltage of 7.5V for all internal circuits.

When the buck converter topology of Figure 1 is selected.

The peak ISEN voltage is a good representation of the

everage current in the LED. However there is a certain

error associated with this current sensing methode that

need to be accounted for. This error is i ntroduced by the

difference between the peak and the everage current in

the inductor is 150mA, to get a 500mA LED current, the

sense resistor should be 250mV/(500mA+0.5*150mA) =

0.43 ohm.

Dimming can be accomplished in two ways, seperately

or combined, depending on the application.

Light output of the LED can be controlled either by linear

change of its current, or by switching the current on and

off while maintaining it constant.

The second dimming methode (so called PWM dimming)

controls LED brightness by varying the duty ratio of the

output current.

Application Information

FC9910B

2013. 08. 29

5/10

Revision No : 1

1. LED Driver Operation

2. Supply current

3. Setting Light output

4. Dimming