Ixan0009 24 need protection for undervoltage in

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: of –ve bias during turn-off is ensured. IXAN0009 2.4 NEED PROTECTION FOR UNDERVOLTAGE In Transfer Characteristics (I D vs. VGS ) of a MOSFET, one can see that for values of VGS below VGS(th), the drain current is negligible, but in this vicinity, the device is in its linear (Ohmic) region and concurrent application of large values of V DS could cause considerable amount of localized heating of the junction. In short, when a MOSFET is being used as a switch, any operation in its linear region could cause overheating or device failure. Bringing the MOSFET quickly into its saturation from its offstate is the Driver’s job. And, if Vcc is below the minimum required value, linear operation can ensue to the detriment of MOSFET. I hasten to add, however, that most PWM ICs, controller ICs and microcomputer ICs have this protection feature built-in and, if sharing the same Vcc bus, the Driver IC gets the benefit of this function being implemented elsewhere in the subsystem. Nevertheless, Driver ICs having this feature is an added benefit. The need of UV protection applies equally well to IGBTs. 2.5OVERLOAD/SHORT CIRCUIT ROTECTION Any operation of MOSFET/IGBT outside the Safe Operating Area (SOA) could cause overheating and eventual device failure and should be prevented by an electronic active monitoring and corrective arrangement. Load or current sensing could be done by either a Hall Effect Sensor or by a Shunt resistor in series with source/emitter terminal. The voltage picked up, which is proportional to current, is low pass filtered and then compared to a preset limit. The comparator output could initiate turnoff of MOSFET/IGBT. A circuit to detect overload/short circuit is shown in Fig. (12), where the output FAULT will go low when it occurs. All IXDD series of Drivers have an ENABLE pin, which, when driven low, say, by the FAULT output from this comparator, puts the final NChannel and P-channel MOSFETs of the IXDD Driver in its TRISTATE mode. This not only stops any output from the Driver, but also provides an envi...
View Full Document

This note was uploaded on 01/15/2014 for the course ECE 624 taught by Professor Staff during the Winter '08 term at Ohio State.

Ask a homework question - tutors are online