IRPLLED1 International Rectifier, IRPLLED1 Datasheet - Page 14

• Manufacturer Part Number: IRPLLED1
• Description: BOARD EVALUATION FOR IRS2540PBF
• Manufacturer: International Rectifier

Specifications of IRPLLED1

• Current - Output / Channel: 1.5A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 24V
• Features: Dimmable
• Voltage - Input: 50 ~ 170V
• Utilized Ic / Part: IRS2540PBF
• Core Chip: IRS2540, IRS2541, IRS25401
• Topology: Buck (Step Down)
• No. Of Outputs: 1
• Output Current: 1.5A
• Output Voltage: 500mV
• Dimming Control Type: PWM
• Development Tool Type: Hardware - Eval/Demo Board
• Lead Free Status / RoHS Status: Contains lead / RoHS compliant by exemption

Fig. 19 Low side FET vs. low side diode comparison, Vin = 100V, Iout = 1.5A, Vout = 17V
Fig. 20 Low side FET and low side diode comparison, Vin = 100V, Iout = 1.5A, Vout = 17V
The bus voltage is also of importance since it will determine how long the lowside MOSFET or the freewheeling
diode will be conducting. If the bus voltage is very large in comparison to the output, the lowside MOSFET or diode
will conduct for the majority of the switching period. A MOSFET has much lower on-state losses due to the low
RDSon where as high voltage diodes have forward drops of approximately 1V. If the load current is in the order of
1A or 1.5A a MOSFET may have low on-state losses, where as a diode may experience larger conduction losses. If
the load current is only a few hundred milliamps the losses observed in the diode may not be a concern. For system
efficiency the forward conduction losses of a diode can also be compared to the reverse recovery losses with a low
side MOSFET. For this evaluation board, it was found that conduction losses were less than reverse recovery losses
when running at 1.5A and therefore uses and freewheeling diode.
The most efficient solution would be to put the MOSFET in parallel with the diode in the lowside position. In this
case, during the deadtime, instead of the body diode freewheeling the additional diode would be conducting. This
will always be the case as long as the forward drop of the external diode is less than that of the body diode.
RD-0608
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