Control loop stability Innoswitch3-EP
Hello
We testing an Flyback 24V/60W with high line input. We saw that the device always change the operation point.
In the first part of the measument, the current could be higher, in the second part the current should be lower. The
change of the operation point is relatifly large. I couldn't find much how could we adjust the control loop. The voltage
overshoot is higher as normal (additional inductance of the current measurement). We saw a D-part parallel to the high
side resistor of the voltage divider, but no informations about it. Do you have an idea how could we optimize the control
loop.
Thank you
Ralf
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Hi Ralf Negele,
->InnoSwitch3 start-up frequency is approximately 25kHz, after that, it will ramp-up its FSW dependent on the output power.
Figure 6 in datasheet is the graph between Ilim (primary current) vs FSW of operation. The higher your FSW of operation, the higher Ilim will be.
-> INN3678C has higher RDSon vs INN3670C. INN3678C has lower Ilim vs INN3670C so it will affect that computation generated by PIexpert.
Regards,
Jedidiah
Dear Jedidiah
Thank you for your answer. At startup we have a "normal" operation without changing from continuous to discontinuous mode. I couldn't find out why the device change the mode. The test with the INN3678 was only a test, but this insn't the problem. What could influcene the operation mode at DC-Input and constant load? For the control loop we have not much informations.
Thank you and best regards
Ralf
Hi Ralf Negele,
If you have low input voltage, your flyback would most probably be in continuous mode (this depends on your KP, KP<1 can make the flyback be in CCM mode). But for high input voltage, your operation will change to discontinuous since you don't need CCM to deliver the same amount of output power at high input voltage.
Regards,
Jedidiah
I saw if I change the device from INN3678C to INNN3670C to reduce the conduction losses, this have a large influence to the design with PI Expert, why?
Thank you