InnoSwitch3-EP PWM waveform

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Hi everyone,

I want to look at PWM waveform before plug in to variac. I used RDR-611 documantation form PI website. And I used INN3672C. But it is possible that giving around 5V to BPP pin, can I observe pwm in Drain pin?

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Hi Alimutlu1,

The INN3672 IC is not based on PWM scheme. It follows a mechanism which is somewhat similar to PWM but is different in some ways. If you probe the drain current waveform then you can see the pattern of the mechanism. You can refer in page 4 of the data sheet in the Current Limit Operation section which says as follows - 'The primary-side controller has a current limit threshold ramp that is linearly decreasing to the time from the end of the previous primary switching cycle (i.e. from the time the primary MOSFET turns off at the end of a switching cycle).

This characteristic produces a primary current limit that increases as
the switching frequency (load) increases (Figure 6). This algorithm enables the most efficient use of the primary switch with the benefit that this algorithm responds to digital feedback
information immediately when a feedback switching cycle request is received.

At high load, switching cycles have a maximum current approaching 100% ILIM. This gradually reduces to 30% of the full current limit as load decreases. Once 30% current limit is reached, there is no further reduction in current limit (since this is low enough to avoid audible noise). The time between switching cycles will continue to increase as load reduces.'