IRISMPS1 IRF [International Rectifier], IRISMPS1 Datasheet - Page 5

• Manufacturer Part Number: IRISMPS1
• Description: REFERENCE DESIGN
• Manufacturer: IRF [International Rectifier]

Note that the operating frequency has now increased, and the effect of the quasi-resonant switching is now
more pronounced. This is evident by the quarter sine wave nature of the falling edge of the drain waveform, at
the bottom of which the FET is turned on, ensuring that it is turned on at the minimum possible voltage to
reduce the switching losses. Note also the steeper ramp in the FB pin voltage when the FET is on which results
in a shorter on time.
voltage with the drain voltage showing the effect of the primary current ramp, which is seen as a voltage
generated across the current sense resistor R10. Note that this waveform shows some noise on the source
pin voltage which is smothed out by the RC filter comprising R9 and C12. The intial voltage spike at the
start of the ramp is a result of discharging the quasi-resonant capacitor C5 and the primary winding
capacitance of the transformer.
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Fig 3) shows the same waveforms as in fig 2) again with a full load output, but this time with a 72VDC input.
Fig 4) shows the waveforms for a 48V input and full load output, but this time it show the Source (S) pin
Fig 4) Drain (D) voltage of IRIS4007K (CH1) and the source(S) pin voltage (CH2) at 48VDC in/Full load
output
IRISMPS1
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