Motors are everywhere in the modern world - especially in HVAC equipment, light industrial drives and small appliances. Inverter-based variable-speed motor drives are well established in high-power systems and bring clear energy saving benefits. Now, vendors of lower power systems are now seeking to implement this architecture to improve efficiency.
However, the traditional discrete design approach (often bulky current sense transformers or energy-dissipating sense resistors) are significantly less than optimal in these systems which are inevitably smaller and driving at lower cost points.
At their simplest level these systems consist of a controller, a driver and a motor. Like many electro-mechanical devices, motors can develop faults. If not designed correctly, these faults can easily propagate back to the controller and affect the whole system - sometimes catastrophically.
Within this miniaturization trend, the protection becomes the responsibility of the integrated smart gate-driver - this is the only viable way to achieve the smaller sizes and lower costs essential for success:-
Over-current protection and photo isolation ensure that the system is protected if the motor fails and draws too much current - or is simply misconnected. The controller receives an error signal and shuts down the motor. The photo isolation (previously discrete photo-isolators) provides another layer of protection to the controller, eliminating critical fault propagation.
Another concern within these systems is shoot-through where a combination of noise and parasitic capacitance (Miller Capacitance) in the system can lead to unwanted device turn-on. This can be addressed by introducing a Miller clamp around the lower IGBT in the driver, thus preventing spurious turn-on.
Toshiba's TLP5214 implements IGBT over-current using the fast, efficient desaturation-detection method, and also overcomes shoot-through by integrating an active Miller clamp by integrating these functions alongside isolated gate-drive and feedback circuitry, this device delivers a straightforward and cost-effective solution to the four most important aspects of controlling the inverter of a low-power variable-speed drive.
To find out more about this solution that saves the significant amount of engineering effort needed to design a solution using discrete components please click here: