IRS29831 查看數據表（PDF） - International Rectifier

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IRS29831

LED FLYBACK CONTROL IC

International Rectifier 

Application Information and Additional

Details

The IRS29831 is a switched mode controller IC

with an integrated high voltage MOSFET designed

for use in Flyback and Buck-Boost converters. An

internal high voltage regulator is included to supply

the IC low voltage VCC supply allowing operation

directly from a DC input voltage up to 600V with

rapid startup at low and high AC line inputs.

Internal high voltage startup

In order to begin operating, the IRS29831 requires

its VCC supply to be raised above the under

voltage lockout positive threshold (VCCUV+) and

to continue operating requires VCC to be

maintained above the under voltage lockout

negative threshold (VCCUV-).

The internal high voltage start up circuit provides

the initial VCC voltage until an auxiliary winding

from the converter transformer takes over. A

series resistor RVCC and 18V zener clamp

DZVCC or other voltage limiting scheme is

necessary in line with VCC to prevent damage to

the IRS29831 if the auxiliary winding voltage

exceeds the internal clamp voltage (VCLAMP).

The HV regulator enables the IRS29831 based

LED driver to start up very rapidly and deliver light

within 0.5s of switch on at any line input voltage.

When the converter reaches steady state and

VCC can be supplied through the auxiliary winding

the HV regulator switches off for zero power

dissipation.

The IRS29831 is primarily targeted at LED driver

applications up to 25W using isolated or non-

isolated Flyback converter or Buck-Boost

topologies. The auxiliary winding is also used to

detect output voltage and zero-crossing point. In

the event of a short circuit at the output, the VCC

supply from the auxiliary winding collapses

causing the IRS29831 to enter under voltage

lockout and shut down. The startup sequence is

then re-initialized continuing in “hiccup” mode until

the short circuit is removed. Short circuit protection

is therefore auto-recovering enabling the driver to

tolerate the condition without damage to the

components. A capacitor in the order of 10pF at

the ZX may be required for correct operation.

Primary power regulation

To eliminate feedback circuitry and opto-isolators

where the load consists of a fixed number of

11 www.irf.com © 2014 International Rectifier

IRS29831PBF

LEDs, the IRS29831 is capable of regulating the

output current indirectly by calculating and

controlling the input power of the converter. Since

an LED load has an approximately fixed voltage

the power consumed is proportional to the current.

In practice there are variations in LED forward

voltage drop due to tolerance and temperature,

however perfect accuracy is not usually required in

such applications. For a fixed number of LEDs the

current will be approximately proportional to the

input power allowing output current regulation of

+/-5% over line input from 120VAC to 230VAC.

Power regulation has been shown to provide

slightly less Lumen output variation than current

regulation.

The IRS29831 senses input voltage and current

then averages and multiplies these quantities to

determine the input power. This is then regulated

against an accurate fixed reference to control the

LED current.

The line input voltage is sensed through a resistor

divider (RIN and RDC) to provide a voltage within

the range from 0V to VDCMAX. Primary current is

sensed through shunt resistor (RCS) connected

from the source of the Flyback MOSFET switch to

the DC bus return. This waveform is a high

frequency ramp rising from zero at the beginning

of each switching cycle to reach a peak level at

the point the MOSFET is switched off, remaining

at zero during the off time.

V(t)

VOUT(t)

VCS(t)

t

ts

Figure 1: Current sense waveform

A transconductance error amplifier (OTA) uses an

external capacitor (CCOMP) referenced to 0V to

realize an integrator that provides a stable error

voltage used to control the PWM on time. A

response time of several AC line cycles is

normally used as in typical power factor correction

circuits to enable high power factor and low THD.

September 10, 2014

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