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IRISMPS3

Fig 7) shows the same details as in fig 6), but at 230VAC input, in this case you can see the on time is even

shorter as it takes very little time to get the energy required into the transformer. Again the circuit is operating in

PRC mode with an input power of 825mW which again meets the Energystar and Blue Angel requirements for

no load standby power.

Fig 8)Drain (D) voltage of IRIS4013K (CH1)/Vcc Voltage (CH2)/ FB pin voltage (CH3)/Load Current (CH4)

at 120VAC in/no load output

Fig 8) shows the circuit changing from Quasi-resonant mode to PRC mode due to a load change. The load

change can be seen by the drop on CH4, as this occurs we see the quasi-resonant info on the FB pin (CH3)

disappear after a short time due to the drop in voltage at the bias winding. This is a result of a high feedback

current from the opto ISO1 as the output voltage tries to go higher to compensate for the drop in load current. At

this point we see the feedback level is high enough to stop the drain from switching as can be seen by the flat

part of the waveform on CH1. Eventually the circuit stabilizes and the circuit starts operating again in the PRC

mode with a reduced Vcc and no quasi-resonant info on the FB pin.

Efficiency

In this section we will show the efficiency of the circuit under various conditions. Fig 9) shows a graph of the

efficiency vs AC input voltage for a full load output. This shows the efficiency well above the 85% level for most

of the input range.

Fig 10) shows the efficiency vs load current for various input voltages.