TSM1051

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connected in parallel with another capacitor

Cvc2=22pF.

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.

When the Vcc voltage reaches 12V it could be in-

teresting to limit the current coming through the

output in the aim to reduce the dissipation of the

device and increase the stability performances of

the whole application.

An example of a suitable Rout value could be

330

Ω in series with the opto-coupler in case

Vcc=12V.

3. Start Up and Short Circuit Conditions

Under start-up or short-circuit conditions the

TSM1051 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 TSM1051 has to be ensured

under any condition. It would then be necessary

to add some circuitry to supply the chip with a sep-

arate power line. This can be achieved in numer-

ous ways, including an additional winding on the

transformer.

The following schematic shows how to realize a

low-cost power supply for the TSM1051 (with no

additional windings).

Please pay attention to the fact that in the particu-

lar case presented here, this low-cost power sup-

ply can reach voltages as high as twice the volt-

age of the regulated line. Since the Absolute Max-

imum Rating of the TSM1051 supply voltage is 14

V, this low-cost auxiliary power supply can only be

used in applications where the regulated line volt-

age does not exceed 7 V.

Figure 10 :

D

+

CS

R2

R1

Rsense

Rvc1

470K

Cvc1

2.2nF

Ric1

22K

To primary

OUT+

OUT-

+

TSM105

Cic1

2.2nF

Cvc2

22pF

IL

IL

Vsense

DS

+

Rs

Vcc

+

-

+

-

1.210V

200mV

Ictrl

Gnd

Vsense

Vcc

Out

Ric2

500

Rout