AN557 datasheet(46/52 Pages) STMICROELECTRONICS

46 / 52 page

AN557 APPLICATION NOTE

46/52

CURRENT GENERATOR

Often it is required to generate constant current , fixed or adjustable, for various applications, such as chem-

ical process, lamp powering, battery charger for lead acids, ni-cd and ni-me-hyd batteries.

Figure 65. Constant Current Generator and battery chargers.

Figure 66.

In this paragraph some suggestions will be given for how to abtain generators of constant current, more

or less sophisticated according to the need. The examples given are time by time applicable to the differ-

ent devices of this family of regulators, with the necessary adjustement according to the current required

by the application.

The diagram of fig. 66 propose a simple solution that makes use of two esternal small signal-transistor

L4972A

R2 2.4K

STPS640

30K

330

Ω

220nF

150

µH

470

µF

Vo=12V/1A

2200

µF

≤40V

D93IN003A

10K

0.1

µF

R1 50

Ω

Rsense 100m

Ω

100K

OUTPUT

STAGE

PWM

E/A

5.1

L4972A/74A

LM358

100nF

100

4.7K

100

V+

Iomax=

V+

V+=

5.1 100

100+4.7K

~100mV

D93IN004

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