Frequently Asked Questions
Frequently Asked Questions
Can Power Integrations drivers be used for direct series connection of IGBTs?
In principle, Power Integrations drivers with multilevel capability can be used for series circuits. The following points should be noted: even with synchronous driving of series-connected IGBTs, due to parameter fluctuations of the IGBTs, symmetrical voltage division and voltage limitation can only be achieved by additional measures, such as dv/dt limiting, active clamping or snubbers. Another problem is the necessary high insulating strength of the driver’s power supply.
Can Power Integrations drivers be used for multilevel converters?
As a rule, current Power Integrations plug-and-play drivers allow operation in multilevel topologies; see the relevant driver documentation.
In this operating mode, the drivers acknowledge any faults that occur but do not switch off automatically. The optimum turn-off sequence of the individual IGBTs is then determined by the user electronics.
Can Power Integrations drivers safely protect multilevel converters in the event of a short-circuit?
In multilevel converters a certain switching order of the power devices has to be maintained. For instance in a 3-level topology during a short-circuit event first the outer power switch of a half-bridge has to be turned-off prior the turn-off of the inner switch. Otherwise, the inner power switch would be damaged / destroyed by excessive overvoltage. The control of the right switching sequence is handled by the microcontroller stage. To enable this control sequence the driver stage is not allowed to turn-off the power switch on its own after detection the short circuit. The driver stage shall only inform the microcontroller. This requirement can be met by Power Integrations’ drivers.
A further feature, called Advanced Active Clamping, allows even that the driver is allowed to switch of the power device directly after detection of the short circuit.
I use a Power Integrations driver core for a matrix converter (quasi-resonance converter etc). Why does the desaturation detector (short circuit protection) trigger regularly in the absence of a short circuit?
With converter topologies in which power semiconductors that are already turned on initially remain currentless and are then supplied with a high di/dt current, a short-term dynamic overvoltage occurs across these semiconductors in the forward direction. If this overvoltage exceeds the desaturation threshold of the driver, the desaturation detector may trigger.
This problem can be corrected by increasing this threshold by the resistance Rth. It should be checked that the response time does not exceed the maximum permissible short-circuit duration for the power semiconductor used.
Furthermore, it is recommended for these applications to use a resistor chain instead of high-voltage diodes for the Vce detection circiuit to avoid false tripping.
Please refer also to Application Note AN-1101.