Class-E RF Generator with a Three-Layer Safety Architecture
Description
A high-efficiency RF power generator for a medical application, running Class-E switching at 500 kHz. Class-E is chosen when efficiency matters more than simplicity — the switch turns on at zero voltage, so losses drop sharply, but the topology is unforgiving about component tolerance and timing.
Stack
- Class-E switching topology at 500 kHz
- ESP32 using its MCPWM peripheral for gate timing
- TC4420 high-current gate driver
- Three independent layers of safety supervision
Why Three Layers
RF energy delivered to a patient is not a system where a single interlock is acceptable. Any one protection mechanism can fail, and the failure is often silent.
The architecture uses three independent layers so that no single fault removes protection: hardware limiting that acts without software, firmware supervision that monitors operating conditions, and a watchdog path that shuts the stage down if the controller stops behaving.
Each layer assumes the others may already have failed. That assumption is the design.
Engineering Constraints
Zero-voltage switching depends on timing. Class-E only stays efficient while switching lands in the correct part of the resonant cycle. Gate timing came from the ESP32 MCPWM peripheral, which gives hardware-accurate edges rather than software-timed ones — deterministic timing is a safety property here, not just a performance one.
Gate drive at 500 kHz. The TC4420 supplies the current needed to move gate charge fast enough to keep switching losses low. Slow edges at this frequency turn efficiency into heat.
Thermal behaviour is a safety property. In a Class-E stage, thermal runaway and efficiency loss are the same failure progressing.
Deliverables
- Schematic, layout, and fabrication package
- Safety architecture documented layer by layer with failure assumptions stated
- Firmware for gate timing and supervision
- Design review against the intended operating envelope
Published without client, project name, or location under NDA. Topology, silicon, and safety architecture are unchanged.