T
treez
Guest
Hello,
Fig43, pg 22 of the following PFC app note has a PNP (U3) turn off circuit for the boost fet M1.
Do you agree that the 27R resistor in this circuit is incorrect, since a gate drive current of >200mA could end up resulting in the abs max Vbe of the PNP being exceeded?
Also, its certainly interesting to see the 4R7 resistor in the emitter of the PNP U3. Is this placed so as to speed up the gate discharge of M1? Presumably, the tying of the PNP (U3) collector to the sub-circuit common rail means the PNP can switch on faster?
(When I was at a major TV manufacturer, they had a 1k base resistor in the turn-off PNP, and a 10R in the collector of the turn-off PNP, but no resistor in the emitter of it….and certainly no resistor in series with the diode that goes across the BE of the PNP.)
I would like to review the maximum base current of the MMBT2907 before avoiding a base resistor for it. Do you agree :???:
PFC App note:
https://www.fairchildsemi.com/application-notes/AN/AN-9738.pdf
Fig43, pg 22 of the following PFC app note has a PNP (U3) turn off circuit for the boost fet M1.
Do you agree that the 27R resistor in this circuit is incorrect, since a gate drive current of >200mA could end up resulting in the abs max Vbe of the PNP being exceeded?
Also, its certainly interesting to see the 4R7 resistor in the emitter of the PNP U3. Is this placed so as to speed up the gate discharge of M1? Presumably, the tying of the PNP (U3) collector to the sub-circuit common rail means the PNP can switch on faster?
(When I was at a major TV manufacturer, they had a 1k base resistor in the turn-off PNP, and a 10R in the collector of the turn-off PNP, but no resistor in the emitter of it….and certainly no resistor in series with the diode that goes across the BE of the PNP.)
I would like to review the maximum base current of the MMBT2907 before avoiding a base resistor for it. Do you agree :???:
PFC App note:
https://www.fairchildsemi.com/application-notes/AN/AN-9738.pdf