VIPer22ADIP / VIPer22AS

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Figure 8 : Rectangular U-I output characteristics for battery charger

RECTANGULAR U-I OUTPUT

CHARACTERISTIC

A complete regulation scheme can achieve

combined and accurate output characteristics.

Figure 8 presents a secondary feedback through

an optocoupler driven by a TSM101. This device

offers two operational amplifiers and a voltage

reference, thus allowing the regulation of both

output voltage and current. An integrated OR

function performs the combination of the two

resulting error signals, leading to a dual voltage

and current limitation, known as a rectangular

output characteristic.

This type of power supply is especially useful for

battery chargers where the output is mainly used in

current mode, in order to deliver a defined charging

rate. The accurate voltage regulation is also

convenient for Li-ion batteries which require both

modes of operation.

This feature offers a great flexibility in design to

achieve various behaviors. In figure 8 a forward

configuration has been chosen to supply the

device with two benefits:

– as soon as the device starts switching, it

immediately receives some energy from the

auxiliary winding. C5 can be therefore reduced

and a small ceramic chip (100 nF) is sufficient to

insure the filtering function. The total start up

time from the switch on of input voltage to output

voltage presence is dramatically decreased.

– the

output

current

characteristic

can

be

maintained even with very low or zero output

voltage. Since the TSM101 is also supplied in

forward mode, it keeps the current regulation up

voltage may vary as much as the input voltage,

that is to say with a ratio of about 4 for a wide

range application.

T1

D3

C5

C4

D4

C3

T2

F1

C1

C10

-

+

-

+

Vref

Vcc

GND

U2

TSM101

R6

R9

R10

R4

C9

R7

R5

R8

C8

R3

ISO1

D2

D5

R2

C7

R1

C2

D1

FB

VDD

DRAIN

SOURCE

CONTROL

U1

VIPerX2A

C6

AC IN

DCOUT

GND