M51995AP/AFP

REJ03D0835-0201 Rev.2.01 Nov 14, 2007

Page 39 of 40

Driver Circuit for Bipolar Transistor

When the bipolar transistor is used instead of MOS FET, 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).

VCC

−V

SS

(

−2 V to −5 V)

VOUT

M51995A

Emitter

GND

VCC

Collector

Figure 45 Driver Circuit Diagram (1) for Bipolar Transistor

For the low current rating transistor, type M51995A can drive it directly as shown in figure 46.

VOUT

GND

VCC

M51995A

Emitter

Collector

Bipolar

transistor

Figure 46 Driver Circuit Diagram (2) for Bipolar Transistor

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.