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©2002 Fairchild Semiconductor Corporation

Application Note 7502 Rev. A1

Case 3 :Common-Source Gate Drive, Figure B-3

FIGURE B-3. COMMON-SOURCE GATE-DRIVE CIRCUIT

Turn-On 

R

O

 = R

D

(drain-to-ground capacitance of driving device adds to
C

GS

 of driven MOSFET.)

Turn Off

R

O

 = r

DS(ON)

 of driving MOSFET when

R

D

 is very much greater than R

DS(ON)

+

R

D

V

DD

R

L

10V
0V

Application Note 7502

Summary of Contents for Power MOSFET AN-7502

Page 1: ...nds Device Models The keystone of an understanding of power MOSFET switching performance is the realization that the active device is bimodal and must be described using a model that accounts for the...

Page 2: ...tate 1 MOS Off JFET Off In a power MOSFET device no drain current will flow until the device s gate threshold voltage Vgs TH is reached Dur ing this time the gate s current drive is only charging the...

Page 3: ...t5 VDK VD SAT Cx lG State 4 MOS Saturated JFET Saturated Turn Off In this state in addition to gMJVX being shorted the gMVG cur rent generator is shorted and IG is occupied with charging CX and CGS in...

Page 4: ...switching time versus 1 RO to be of the same form as those obtained for a step current drive This is exactly the case as Figure 10 is merely a vari ation of Figure 8 Using the relationships of Table 1...

Page 5: ...complexity FIGURE 10 CONSTANT GATE VOLTAGE SWITCHING TIME Using the Characterization Curve Figure 9 To estimate the switching times for an RFM15N15 power MOSFET under the conditions VG 10V VDD 75V RO...

Page 6: ...and the 90 level by another Device comparisons based on the classical switching definition can be very misleading Appendix A Analysis for Resistive Step Voltage Inputs Step Voltage Gate Drive To obtai...

Page 7: ...time The equivalent circuit then predicts State 4 Mos Saturated JFET Saturated Turn off Both equivalent circuit generators are short circuits and the gate drive is discharging CX in parallel with CGS...

Page 8: ...on Source Gate Drive Figure B 3 FIGURE B 3 COMMON SOURCE GATE DRIVE CIRCUIT Turn On RO RD drain to ground capacitance of driving device adds to CGS of driven MOSFET Turn Off RO rDS ON of driving MOSFE...

Page 9: ...ife support device or system or to affect its safety or effectiveness PRODUCT STATUS DEFINITIONS Definition of Terms Datasheet Identification Product Status Definition Advance Information Preliminary...

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