</a>led" title="led">led" title="led">led by externally pulling the voltage at the CT/SD pin below its enable voltage threshold.

IRS27951/2主要特性:

· Simple primary-side control solution for fixed and variable frequency DC-DC resonant converters.

· Max 500kHz per channel output with 50% duty cycle

· Floating channel bootstrap operation up to +600Vdc

· Programmable minimum and maximum switching frequency

· Programmable soft start frequency and soft start time

· Programmable dead time

· Micropower start-up & ultra low quiescent current

· Over-current protection using low side MOSFET Rds(on)

· User initiated micropower “Sleep mode”

· Under-voltage Lockout

· Simple design with minimal component count.

· Lead-free

IRS27951/2典型应用:

· LCD & PDP TV

· Telecom SMPS, PC SMPS

· Home Audio Systems

图1. IRS27951/2功能方框图

图2. IRS27951/2典型应用电路图

IRAC27951-220W IRS27951评估板

The evaluation board consists of a front-end AC-DC rectifier stage cascaded with a half-bridge resonant DCDC converter with multiple output voltage rails (24V and 12V). The front end is a conventional rectifier stage with a rectifier bridge and an EMI filter.

The downstream converter is a multi-resonant half bridge LLC converter whose control is implemented with the IRS27951 (U1) controller HVIC. The controller drives the two half-bridge MOSFETs with a 50 percent fixed duty cycle with dead-time, changing the frequency according to the feedback signal in order to regulate the output voltages against load and input voltage variations. As described earlier, in addition to current protection, all the critical functions needed to control resonant converter designs can be externally programmed using this 8 pin controller IC.

The transformer uses the magnetic integration approach, incorporating the resonant series and shunt inductances in the power transformer. The transformer configuration chosen for the secondary winding is center-tap, and the output rectifiers are Schottky diodes. The feedback loop is implemented by means of a classical configuration using a TL431 (U3) to adjust the current in the optocoupler TLP621 (U2). Weighted resistive dividers from both voltages are summed at the reference node of the TL431 in order to achieve a better overall output voltage regulation. The optocoupler transistor modulates the current from the RT pin of the controller IC to modulate the switching frequency, thus achieving output voltage regulation.


图3. IRAC27951 220W 评估板外形图

IRAC27951 220W 评估板主要指标:


图4.IRAC27951 220W 评估板电路图
IRAC27951 220W 评估板材料清单:



图5.IRAC27951 220W评估板PCB布局图(顶层)

图6.IRAC27951 220W评估板PCB布局图(底层)
详情请见:
http://www.irf.com/product-info/datasheets/data/irs27951s.pdf
和
http://www.irf.com/technical-info/refdesigns/irac27951-220w.pdf