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Disable INN3366C on primary

Posted by: ex on Sun, 06/27/2021

Dear Sir or Madame,

is there any recommendation how to switch off INN3366C on the primary side. We need some kind of second level protection that switches of the primary side if there is a output voltage higher than allowed. We know that this feature is implemented in the INN3366C as well using the reflected voltage but to have a redundant switch-off feature, we have to use an independent monitoring circuit in parallel. 

The idea is to have an optocoupler triggered from the seconary side that switches off the primary if the voltage on the secondary is too high. With some hysteresis it will reactivate the primary if the voltage falls back to a defined values. If this functionality has to be latching (till secondary voltage falls below the minimum voltage powering the latching circuit) or toggling is today not defined.

Is the only way switching off the AC input voltage or is it an option shorting BPP to GND as it's the supply voltage of the MOSFET driver?


Thanks and Regards



Submitted by PI-Martok on Tue, 06/29/2021

Hi Etatronix,

     Thank You for using Power Integrations Innoswitch-3 controller. Please see attached suggested circuit to enable or disable the primary switching.  You can use the  CE side of the optocoupler in place of Q3 to drive Q2 . Hope this will help. 

Attachment Size
Primary Side Enable Disable Circuit 75.85 KB
Submitted by ex on Fri, 07/02/2021

Thanks for your great feedback. Using the OVP feature at the V-pin will be a good option to switch off Innoswitch-3. 

Allow me to share some thoughs. For a safety relevant application we are not sure if this is the safest way. Let's construct the unlikely issue that the IC is broken and is permanently switching with high duty cycle. With a broken IC, OVP will not work. Unfortunately this argument is more or less the same for grounding the BPP pin. If we pull it to GND, the internal start circuit may power the broken ICs internal circuit and allow in worst case switching of the MOSFET...

I know, unlikely circumstances that will never happen but maybe the only safe option is switching of the positive or negative rectifier output? What do you think about that?

Submitted by ex on Fri, 07/09/2021

Hi again,

by using the V pin your example simulates an over voltage event. Do you think simulating an under voltage event by shorting V to S will be an option as well? In this case, an opto-coupler from V to S will be an easy option.  

Submitted by PI-Spark on Wed, 07/21/2021

Hi ex,

Yes, you can use the under voltage brown-out protection feature in the V pin to disable switching of the InnoSwitch3 device.