Transient response improvement in isolated DC-DC converter with current injection circuit

Converter transient response is mainly limited by filter LC delay time, controller delay time and propagation delay time. It is a tradeoff between efficiency and transient response in the design. In isolated DC/DC converter, the bandwidth of opto-coupler has an extra strong effect on the system bandwidth improvement. This paper presents current injection method, switching mode current injection circuit only engaged in transient periods operating in high frequency at the secondary side to improve the bandwidth for better dynamic response while the main topology can operate in lower frequency for good efficiency. Simple voltage control for fixed switching frequency and stable operation, instead of hysteretic control, is carried out for current injection circuit. Finally, experimental results are given to verify the theoretical analysis.