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IRS29831PBF Datasheet(PDF) 11 Page - International Rectifier |
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IRS29831PBF Datasheet(HTML) 11 Page - International Rectifier |
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11 / 17 page  IRS29831PBF 11 www.irf.com © 2014 International Rectifier September 10, 2014 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 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. t ts V(t) VOUT(t) VCS(t) 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. |
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