AN1818

Optimizing your system

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Optimizing your system

Typically, when one designs a battery charger or adapter application, a target power consumption is set

for the application under no-load conditions. This target may be 500mW, or even 300mW, but until

recently, it seemed impossible to reach a no-load total power consumption of as low as 100mW.

In this section, we will look at three example systems:

a A typical secondary side configuration, as seen in Figure 1, and using a general-purpose second-

ary-side integrated circuit, such as ST’s TSM103.

b An advanced secondary side circuit schematic (see Figure 3), using an integrated circuit such as

ST’s TSM1011 which includes a self-polarizing voltage reference. The inclusion of a self-polariz-

c An advanced secondary-side schematic (see Figure 3) using a very advanced integrated circuit,

ST’s TSM1012, which draws only 150

µA under no-load conditions.

Figure3: Advanced secondary-side schematic for battery-charger/adapter application

In addition to considering the typical (Figure 1) and advanced (Figure 3) secondary side schematics,

there are now on the market optocouplers that need as little as 0.5mA. As we will see below, using such

an optocoupler can allow power consumption to drop very low indeed.

Rsense

C2

R2

R1

C1

C3

optocoupler

secondary side

Cic1

Cvc1

Ric1

Rvc1

Rlimit

2

3

4

8

6

5

28V

Vref

Vcc

CC

CC-

CC+

Gnd

CV

CV-

CV+

Out

2,5V

R4

R5

1

R3

D1

D2

Ric2

TSM1012

7

PWM

controller

optocoupler

primary side