Three independent TEC zones in a lab instrument, each needing bidirectional drive (heat and cool) with tight temperature regulation.
The Solution
Each channel gets its own synchronous buck converter in H-bridge configuration for bidirectional current. Synchronous topology minimizes heat in the driver board itself. Independent PID loops per channel with precision RTD feedback. TEC thermal response is slow and nonlinear, but the tuning achieves fast setpoint transitions with no overshoot.
Results
Holds ±0.05°C at setpoint once settled. The three zones don't interact thermally, which simplified tuning considerably.
How the three zones stay independent
Three complete loops side by side. Each zone has its own RTD, PID loop and synchronous bidirectional bridge, so it can heat or cool on its own, and the synchronous stages keep the driver board itself cool.Fast without overshoot. A TEC and its load behave like two slow thermal lags plus a short delay, and every extra degree of phase they take away brings the loop closer to ringing. The PID is tuned so the loop crosses unity gain where the derivative term still adds phase back, leaving about 77° of phase margin, which is what lets each zone move quickly to a new setpoint and settle without crossing it.
Have a Similar Challenge?
Precision temperature control with PID tuning is part of the regular work.
