M51995 Mitsubishi, M51995 Datasheet - Page 26

• Manufacturer Part Number: M51995
• Description: SWITCHING REGULATOR CONTROL
• Manufacturer: Mitsubishi

Driver circuit for bipolar transistor
When the bipolar transistor is used instead of MOS-FIT,the
base current of bipolar transistor must be sinked by the
negative base voltage source for the switching-off duration,in
order to make the switching speed of bipolar transistor fast one.
In this case,over current can not be detected by detecting
resistor in series to bipolar transistor,so it is recommended to
use the CT(current transformer).
For the low current rating transistor,type M51995A can drive it
directly as shown in Fig.48.
Attention for heat generation
The maximum ambient temperature of type M51995A is
+85°C,however,the ambient temperature in vicinity of the IC is
not uniform and varies place by place,as the amount of power
dissipation is fearfully large and the power dissipation is
generated locally in the switching regulator.
So it is one of the good idea to check the IC package
temperature.
The temperature difference between IC junction and the surface
of IC package is 15°C or less,when the IC junction temperature is
measured by temperature dependency of forward voltage of pin
junction,and IC package temperature is measured by "thermo-
viewer",and also the IC is mounted on the "phenol-base" PC
board in normal atmosphere.
So it is concluded that the maximum case temperature(surface
temperature of IC) rating is 120°C with adequate margin.
As type M51995 has the modified totempole driver circuit, the
transient through current is very small and the total power
dissipation is decreased to the reasonable power level.Fig.49
shows the transient rush (through)current waveforms at the rising
and falling edges of output pulse,respectively.
(-2V to -5V)
-Vss
Vcc
GND
Fig.47 Driver circuit diagram (1) for bipolar transistor
Vcc
M51995A
EMITTER
COLLECTOR
V
OUT
(
26
/ 27 )
GND
Vcc
M51995A
Fig.48 Driver circuit diagram (2) for bipolar transistor
Fig.49 Through current waveform of totempole driver
H-Axis : 20ns/div
V-Axis : 50mA/div
H-Axis : 20ns/div
V-Axis : 10mA/div
EMITTER
circuit at no-load and Vcc of 18V condition
SWITCHING REGULATOR CONTROL
AT RISING EDGE OF OUTPUT PULSE
AT RISING EDGE OF OUTPUT PULSE
COLLECTOR
V
OUT
M51995AP/FP
BIPOLAR
TRANSISTOR