Synchronous rectification in ACF / QR flyback

Hello Jack, 

Thank you for your interest in TI controllers.  

For your ACF and QR applications with SR, I suggest that you review the UCC24612 SR controller datasheet https://www.ti.com/lit/gpn/ucc24612 .  This is probably your best bet. 

Another option to consider is UCC24636, although it does have a limited frequency range https://www.ti.com/lit/gpn/ucc24636 .  

The difference between the two is that the -612 uses Vds-sensing to determine when to turn off the SR-FET, while the -636 use volt-second balance timing to turn off the SR-FET.

Regards,
Ulrich. 

Hello Jack, 

As I mentioned, the UCC24612 uses Vds-sensing to determine when to turn off (open) the SR FET.  
Section 7.1 of the datasheet states in the second sentence that the MOSFET is turned off when the drain-to-source voltage "V_DS" falls below the turn-off threshold "V_THVGOFF".  V_THVGOFF is typically -9mV, so when the UCC24612 detects that VD is 9mV below VS, it turns off the VG signal and pulls charge out of the SR-FET gate.  

When the source-to-drain current drops low enough, the voltage developed across RDS(on) falls to the turn-off threshold.
Figure 17 illustrates the gate-drive voltage with respect to V_DS and I_SD, and the IC's turn-on and turn-off thresholds. 

The UCC24612 can be used for SR control in an ACF power supply the same way as in any other flyback power supply, in both high-side and low-side arrangements.  Sections 8.1 and 8.2 of the UCC24612 data sheet discuss these implementations.  https://www.ti.com/lit/gpn/ucc24612 

The UCC28782 data sheet section 10 discusses some design points for the output rectifier (whether diode or SR) to consider when used in the ACF application.  https://www.ti.com/lit/gpn/ucc28782 

Regards,
Ulrich

Hi Jack, 

The Simplis model for UCC24612 can be obtained at this link:  https://www.ti.com/lit/zip/slum597

found on this product page UCC24612 data sheet, product information and support | TI.com .

Regards,
Ulrich