SLUAAE5 June   2022 TL2842B , UCC2813-2 , UCC28600 , UCC28704 , UCC28730 , UCC28740 , UCC28742 , UCC28781 , UCC28782 , UCC28C42


  1. 1Application Brief

Application Brief

Flyback controllers are inherently isolated topologies which are ideal for offline (AC/DC) conversion. Flyback controllers are available with two control methods. The first is Primary-Side Regulation (PSR) which use the information from the auxiliary transformer winding to regulate the output and the other is Secondary-Side Regulation (SSR) which uses an optocoupler to provide more accurate feedback.

What are the pros and cons of Primary Side Regulation (PSR) vs. Secondary Side Regulation (SSR)? The following is a simple summary and a short list of popular controllers for each:

Figure 1-1 SSR Control
Figure 1-2 PSR Control

Pro – Tighter output voltage regulation (~2%) and faster load transient response

Con – Requires Opto-coupler and shunt regulator

Pro – No Opto-coupler and shunt regulator

Con – Less accurate voltage regulation (~5%) and slower load transient response

Are you wondering when to choose Continuous Conduction Mode (CCM), Discontinuous Conduction Mode (DCM), or Transition Mode also known as Critical Conduction Mode (TM/CrM)? Table 1-1 highlights the pros and cons of each.

Table 1-1 Pros and Cons of CCM, DCM, or TM/CrM
Operating Mode Pros Cons TI Product Family
CCM Lower conduction and switching losses
Improved cross regulation
Smaller filtering solution
Low light-load efficiency
Higher diode reverse recovery loss
More difficult to compensate and stabilize
General Purpose PWM Controllers
DCM No diode reverse recovery loss
Improved stability
Potentially smaller transformer size
Higher ripple currents
Higher conduction and switching losses
Larger filtering solution
TM (CrM) No diode reverse recovery loss
Valley or Quasi Resonant (QR) switching
Improved stability
Higher ripple currents
Higher conduction and switching losses if not used with valley switching or QR mode
Larger filtering solution
Dedicated Flyback Controllers

Texas Instruments has Flyback controllers to support a wide variety of applications ranging from low power bias to high power density supplies. Our dedicated Flyback controllers combine our advanced control law to minimize switching losses and EMI by adjusting their switching frequency as a function of load. For high-power density or if you want to use a flyback more than 100 watts, check out our Zero-Voltage Switching (ZVS) and Active-Clamp Flyback (ACF) controllers.

Figure 1-3 is a quick selection guide for our controllers. To see more visit Flyback Controllers.

Figure 1-3 Flyback Selection Guide