Datasheet





SLLS025A − JULY 1986
3−8
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
POST OFFICE BOX 1443
• HOUSTON, TEXAS 77251−1443
APPLICATION INFORMATION
driving power MOSFETs
The drive requirements of power MOSFETs are much lower than comparable bipolar power transistors. The
input impedance of a FET consists of a reverse biased PN junction that can be described as a large capacitance
in parallel with a very high resistance. For this reason, the commonly used open-collector driver with a pullup
resistor is not satisfactory for high-speed applications. In Figure 12(a), an IRF151 power MOSFET switching
an inductive load is driven by an open-collector transistor driver with a 470-Ω pullup resistor. The input
capacitance (C
iss
) specification for an IRF151 is 4000 pF maximum. The resulting long turn-on time due to the
combination of C
iss
and the pullup resistor is shown in Figure 12(b).
5 V
7
4
8
3
5
1
2
6
V0H − VOL − Gate Voltage − V
V
OH
TLC555P
1/2 SN75447
470 Ω
48 V
M
V
OL
t − Time − µs
(b)
(a)
IRF151
4
3
2
1
0
0 0.5 1 1.5 2 2.5
3
Figure 13. Power MOSFET Drive Using SN75447