Used for: High power voltage conversion with isolation
Pros:
- Basic building block for all high power converters
- Small transformer
- Low input and output ripple
- Outpu ripple can be arbiraritly low, set by output inductor
- relatively easy to implement synchronous rectification for high efficiency
Cons:
- Requires output choke
- Can be complex to stabilise optimally under all load and line conditions
- Transformer must be 'reset' each cycle which can limit duty cycle
Basics:
- Q1 switches on and transfers current to the output directly in the turns ratio
- Output inductor charges during this period and transformer magnetising current rises
- Q1 switches off and third winding on transformer resets the magnetising current
- Other reset mechanisms are possible including resonant reset and active reset
- In off period Df conducts keeping current circulating through output inductor
- Regulation achieved by feddback controlling duty cycle
- Vo = Vin.D. Ns/Npri