SuperMESHT in RCC Cost effective Power MOSFETs for ringing choke converter battery chargers

The Ringing Choke Converter (RCC) is an essential, self-oscillating flyback topology which operates between the Discontinuous Conduction Mode (DCM) and Continuous Conduction Mode (CCM) boundaries without noticeable reverse recovery of the output rectifying diodes. RCC can be achieved through a discrete solution to control the peak current mode, so the overall cost is relatively low compared to the conventional Pulse Width Modulation (PWM) IC solution. Consequently, RCC is widely used as a simple and low cost solution for low power applications such as mobile phone battery chargers. RCC demoboard schematic

A zener-protected SuperMESH MOSFET is the ideal choice for an RCC control circuit that needs to achieve high performance. The built-in, back-to-back zener diodes are specifically designed not only to enhance electrostatic discharge (ESD) protection, but also to allow possible voltage transients (that may occasionally be applied from gate to source) to be safely absorbed. This structure provides efficient and cost-effective device protection.

Three different SuperMESH devices were subjected to thermal performance comparison. See application note AN2228: STD1LNK60Z-based cell phone battery charger design.

Under test the STD1LNK60Z and STQ1NK60ZR produced different thermal behavior because of the different package Rth values:
RthJA in IPAK was 100°C/W, while the
RthJA in TO-92 was 120°C/W

The system conduction loss was less significant than its switching losses, so the STQ1NK60ZR and STQ2NK60ZR temperatures were similar.
The better switching performance of STQ1NK60ZR, offsets the advantage of the lower RDS(on) value of STQ2NK60ZR. The best choice therefore, appears to be the STD1LNK60Z for reliability, and the STQ1NK60ZR for better cost and higher voltage (700V and 800V, for better BVDSS derating).

*Devices tested on the ST demoboards