AN4205

Output stage setting

Doc ID 023929 Rev 1

17/23

Figure 11.

The bipolar Q1, operating in forward active mode, guarantees the linear region for the

to Equation 1. The Q1 transistor is basically a common-emitter amplifier where the base

terminal serves as the input and the collector terminal as the output. The voltage gain

The R1 resistor in Figure 10 and the Vz voltage of DZ3 Zener fix the collector variations in

regulation signal. On the other hand, the R3 and R19 resistors in Figure 10 set the feedback

time of the bipolar Q1 and Power MOSFET M2.

To summarize, Figure 12 clarifies the linear current regulation of this simple and innovative

solution.

+

-

Vcc

R4

R6

R5

R2

C8

8

.

41

)

2

.

1

49

1

(

)

1

(

4

6

2

≅

Ω

Ω

+

=

+

=

k

k

R

R

G

V

mV

V

G

V

R

o

1

.

5

120

*

8

.

41

2

2

≅

=

=

2

R

V

o

V

AM16377v1

V

ec

V

eb

---------

g

=