TK75050DITL データシートの表示（PDF） - Toko America Inc
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TK75050DITL Datasheet PDF : 12 Pages
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TK75050
APPLICATION INFORMATION (CONT.)
ADDITIONAL OVERLOAD PROTECTION IN PEAK-
CURRENT-CONTROLLED CONVERTERS
Figure 5 shows the TK75050 in a current-mode-controlled
forward converter, with optically isolated feedback. In this
application the TK75050 helps to achieve a tightly controlled
current-limit-characteristic. A tight current limit cannot
usually be achieved with only current-mode control due to
the presence of the stabilizing ramp. The lack of the
stabilizing ensures that the knee current (i.e., the output
current where the limiting begins) is only slightly lower than
the short-circuit current. The difference between the knee
current and the short-circuit current is about one-half of the
ripple current in the filter inductor. If a stabilizing ramp were
added to the current-sense signal, the difference would be
significantly higher.
VIN
+
+12 V
OC
TK75050
CURRENT-MODE
PWM
CONTROLLER
VIN
+12 V
TK75050
-
+
+
-
+
FEEDBACK
FIGURE 6: TK75050 IN A CONVERTER WITH
AVERAGE CURRENT CONTROL
FLOATING DRIVE WITH OVERLOAD PROTECTION
The TK75050 can be used as a driver and current limiter
for a floating power switch. Figure 7 shows the IC in a buck
converter with transformer-isolated drive.
VIN
FIGURE 5: TK75050 IN A PEAK-CURRENT-
CONTROLLED CONVERTER
ADDITIONAL OVERLOAD PROTECTION IN AVERAGE-
CURRENT-CONTROLLED CONVERTERS
+
TK75050
In converters with average current control the peak current
information is lost and the response of the current-control
loop slows down. The speed of the current-control loop
may not be sufficient to provide effective protection against
sudden overload or saturation of an inductor or transformer.
Figure 6 shows an average-current-controlled boost
converter where the TK75050 provides additional fast
overload protection.
FIGURE 7: TK75050 AS A FLOATING DRIVER IN A
BUCK CONVERTER
DEMO BOARD
The purpose of the board is to demonstrate the high-speed
current-limit capability of Toko's TK75050 smart MOSFET
driver. In the board a 2-A/500 V MOSFET switch is turned
on directly (i.e., without any series impedance) into a DC-
bus with up to 400 V, at a frequency of 30 kHz. By removing
the short across a 3.3 µH inductor in series with the
MOSFET, it is also possible to investigate the effect of the
wiring inductance between the switch and the load. In
January 1999 TOKO, Inc.
Page 9
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