Controller for 2switch flyback 1000V input

1. Is there any flyback controller IC that can be used for 2switch topology directly?

• No but the 2-switch topology motivation is to reduce the VDS across each primary MOSFET. Can you use a SiC MOSFET and consider a single low-side, high-voltage switch? If this is a consideration, TI has improved the UCC28C4x family of GP PWMs to include UCC28C5x-Q1 which incorporate improvements dedicated to SiC flyback topologies.. 

2. What is the most reliable way of driving the high side mosfet if I use a 1-switch flyback controller like UCC28740-q1? I am worried about reliability as i need it for automotive application. 

• Gate drive transformer because your switch node voltage is high voltage. Consider a dual gate drive transformer, so the high/low-side prop-delays are "matched" 

Regards,

Steve

1. I am restricted to use SMD and automotive SiC mosfet is not available in smd package for more than 1200V from any manufacturer. 

• ok

2. UCC28c5x-Q1 series does not have valley switching capability as its fixed frequency. Is there any such IC that supports valley switching and good light load efficiency with UVLO tuned for SiC ?

• Controllers that do have valley switching are mostly targeting consumer applications and will not be -Q1 (Automotive) rated. However, you can use any QR flyback connected to either a gate driver transformer or half-bridge driver (if you have a way to charge the high-side bootstrap capacitor) to design a 2-switch flyback as mentioned below.

3. Is there any reference design that shows how to design/select the gate drive transformer for such application and what extra circuitry could be needed? 

• For 2-switch flyback you would need a single ended gate drive transformer such as section 7.1 in this app note. However, since you are driving 2 MOSFETs that are synchronous and in-phase, you need a gate drive transformer with two secondaries. Here is a blog discussing the topic of gate drive transformer vs half bridge drivers.

Regards,

Steve