Shindengen Electric MFG.CO.,LTD

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3.7 Circuit for load shorts

The MR4000 Series is designed so that voltage droop occurs under excessive load, causing the output voltage to drop, and

drain (collector) current to approximately 1/10 of its previous value. This design reduces the stress on the MR4000 Series IC

in the case of a load short and controls the short-circuit current to the secondary diode and the load circuit.

3.8 Collector pin (MR40XX Series)

The collector pin on the main switching device (Pin 7)

Depending on input conditions, the collector pin may be subject to reverse bias for a certain period during partial resonance.

This IC uses the second-generation high-speed IGBT as the main switching device. Unlike MOSFETs, this device has

no body diode structure and thus requires the connection of an external high-speed diode between the Collector and

Emitter/OCL pins (see Fig. 3.12).

3.9 Thermal shutdown circuit (TSD)

The MR4000 Series incorporates a thermal shutdown circuit. The onboard IC is latched at 150°C (typical), after which

oscillation is halted. Unlatching is achieved by momentarily dropping the voltage at the VCC pin to VUL (unlatch

voltage) or lower.

3.10 Overvoltage protection circuit (OVP)

The MR4000 Series incorporates an overvoltage protection circuit (OVP). Latching occurs when the control coil

same manner as for the overheat protection circuit.

3.11 Leading edge blank (LEB)

The MR4000 Series has the leading edge blank function. This function improves the margin of noise by rejecting

trigger signals from the drain current detection circuit for a certain time after the main switching device is turned on.

This function prevents false detections due to the gate drive current produced the moment the main switching device is

turned on or due to the discharge current of a resonating capacitor.

Fig. 3.10 Circuit for load shorts

3. Operating principles