The problem with the Fairchild monolithic offline controllers is that most of them have an internal fet with a VDS of 650V, which is less than the Power Integrations ones which are 725V rated.
Also, the Power integrations monolithic offline flyback controllers come with adjustable peak current setting. –Whereas the Fairchild ones have a fixed peak current, and this means that the transformer tends to be bigger for the Fairchild ones, because the transformer has to be able to manage the peak current.
Also, a few of the Fairchild ones have 1000V or 800v fets in them , but again these have fixed peak current limits in them which is very inconvenient. This is because as a power supply is being designed, typically the required maximum load is being repeatedly changed or adjusted. With Power Integrations flyback chips, that’s no problem, -because they have a whole family of chips that can do the job, and so you can just change to a different chip without having to vary the PCB much, whereas with Fairchild ones, they are more made for one specific power level, and certainly not the variable range of power that the families of Power Integrations chips facilitate.
Also, the power integrations chips are voltage mode chips, which means they tend to give off less audible noise in lighter loading, whereas the Fairchild ones are current mode, and one can get pulse bunching in lighter loads which can lead to audible noise.
The VIPER family is ok, but has a greater operating current draw than equivalent power integrations chips. Viper also goes into burst mode at light load so its not that good with a bias winding, as bias windings prefer regular pulses, rather than bursts interspersed with nothing.
UCC28910 again has a fixed peak current level, which of course may well not be what the design needs, and especially f if the design spec changes, as so often it does.
Also, UCC28910 has only a 700v rated fet, whereas topswitch is 725v rated.
The topswitch-jx device has a totally variable maximum fet current level, which is settable with a resistor
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Another point about the topswitch is that it uses the opto-transistor connected in common collector configuration, and there is a large capacitor connected to its emitter..therefore, the internal pole due to the high capacitance of the base-collector region of the opto-transistor is irrelevant in the design, so if you get a different batch of opto’s with much different base-collector capacitance, then it wont matter and wont bring about instability. This is a great thing about the way the topswitch has its opto connected.
The fiarchild ones have the opto connected in common-emitter mode, so this advantage is not seen, as for them, the base-collector capacitance is very significant.