Rev. 4.0 5/22/2010
International Rectifier
Page 10 of 16
PROPRIETARY INFORMATION - This document and the information contained therein are proprietary and are not to be reproduced, used or disclosed
to others for manufacture or any other purpose except as specifically authorized in writing by
INTERNATIONAL RECTIFIER.
4.2 AC/DC Input
The use of an isolation transformer on the AC side is highly recommended, so that all the control signals on the
test points can easily be probed by using regular scope probes
Connect a 60Hz AC power source capable of operation up to 280VAC or a 400V DC source to JP1. The
converter can keep the output regulated when the BUS voltage is in the range of 350V DC to 420V DC.
The NTC resistor limits the inrush current upon initial application of full AC line voltage. Once power is applied
to demo board, potentially lethal high voltages will be present on board and necessary precautions should be
taken to avoid serious injury.
4.3 IRS27951 DC Supply Voltage
The board is self-supplied by startup circuit and auxiliary winding of transformer. The startup circuit starts to
work once AC or DC input voltage applies to the board. However, the Vcc will be stable only when BUS
voltage is 350Vdc or above. The VCC voltage is monitored at test points VCC and COM.
If you choose to supply VCC voltage using external DC power supply (in order to study IC VCC UVLO features
etc.) then simply provide DC voltage to connector JP3 or alternatively between Test Points V
CC
and COM. You
should also dis-connect Rvcc and Rstart in order to measure the Vcc supply current from the DC source. The
minimum supply voltage recommended is 12V while a maximum voltage of 18V can be applied without
damaging the IC. The location of the DC power connector and controller IC is shown in Figure 6.
Figure 6 - VCC connector and test points
4.4 Power-up Sequence
Once all the connections are made, the system can be powered up. When using external DC supply to bias
Vcc, power-up the AC supply or 400V DC supply first and then the Vcc circuitry. This sequence is necessary to
ensure soft start operation of the DC-DC converter.
IRS27951 and control
components on
bottom layer
VCC
COM