INN3672C Difference between RDR-611 & RDK-611

5 posts / 0 new

Hi.

 

We've just received a RDK-611 kit and realized the InnoSwitch pin FWD is connected to the 12-V negative transformer pin instead of the 5-V one, as showed in RDR-611 schematic...

 

We noticed that so soon because this was the main reason to buy the kit: to verify the minimal positive voltage on the FWD pin (i. e., during the primary mosfet conduction) which allows the InnoSwitch to start-up. So, what is this minimal voltage in fact? And, once started, what is the minimal value to keep the InnoSwitch away from the auto-restart entering? Was this the reason to use the 12-V transformer pin in RDK-611?

 

This is a special concerning point in our project because it must operate from 36 Vdc primary voltage. Thus, with the most suitable turns ratio options, the FWD pin positive voltage may be too low.

 

Regards,

Christos

Hi.
Could anyone please answer this question?
Christos.

Hi Christos,
InnoSwitch3 requires minimum 50Vdc drain to source voltage to start-up. It wont' work on 36Vdc.
Regards,
Jedidiah

Thank you, Jedidiah!
.
In principle, the minimum Vdrain strict question must have been solved according the chat in "https://ac-dc.power.com/forum/low-power-design/2015/innoswitch-minimal-vdrain/".
.
The only remaining question is related to the resulting positive voltage on the FWD pin. I suspect that, in DK-611 kit, this voltage would be too low at 85 Vac input voltage if the 5-V negative transformer had been used (according the RDR-611 schematic), and this was the reason to use the 12-V pin instead.
.
This issue is more difficult to overcome at 36 Vdc input voltage, but we have a possible solution. I just wonder if my analysis above is correct and if there is a known minimum positive voltage on FWD pin I can count on, to allow the internal InnoSwitch regulator on generating the proper VBPS at start-up.
.
Regards,
Christos