TSM1012

6/8

The current-control trans-conductance operation-

al amplifier can be fully compensated. Both of its

output and negative input are directly accessible

for external compensation components.

An example of a suitable compensation network is

shown in Fig.2. It consists of a capacitor

Cic1=2.2nF and a resistor Ric1=22K

Ω in series.

3. Start Up and Short Circuit Conditions

Under start-up or short-circuit conditions the

TSM1012 is not provided with a high enough sup-

ply voltage. This is due to the fact that the chip has

its power supply line in common with the power

supply line of the system.

Therefore, the current limitation can only be en-

sured by the primary PWM module, which should

be chosen accordingly.

If the primary current limitation is considered not to

be precise enough for the application, then a suffi-

cient supply for the TSM1012 has to be ensured

under any condition. It would then be necessary to

add some circuitry to supply the chip with a sepa-

rate power line. This can be achieved in numerous

ways, including an additional winding on the trans-

former.

4. Voltage clamp

The following schematic shows how to realize a

low-cost power supply for the TSM1012 (with no

additional windings).Please pay attention to the

fact that in the particular case presented here, this

low-cost power supply can reach voltages as high

as twice the voltage of the regulated line. Since

the Absolute Maximum Rating of the TSM1012

supply voltage is 28V. In the aim to protect he

TSM1012 against such how voltage values a in-

ternal zener clamp is integrated.

Rlimit = (Vcc-Vz)Ivz

Figure 4 : Clamp voltage

Figure 5 :

Vz

28V

Vcc

Rlimit

cc

Ivz

TSM1012

Rsense

C2

R2

R1

C1

C3

optocoupler

secondary side

Cic1

2,2nF

Cvc1

2,2nF

Ric1

22K

Rvc1

22K

Rlimit

R4

R5

R3

D1

D2

OUT+

OUT-

Ric2

1K

PWM

controller

optocoupler

primary side

TSM1012

28V

Vref

Vcc

CC

CC-

CC+

Gnd

CV

CV-

CV+

Out

1,25V

3

4

8

5

1

7

2

6

C4

47nF