Start-up and short-circuit conditions TSM1011
10/14 DocID9310 Rev 2
8 Start-up and short-circuit conditions
Under start-up or short-circuit conditions the TSM1011 is not provided with a high enough
supply 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 ensured by the primary PWM module, which
should be chosen accordingly.
If the primary current limitation is not considered to be precise enough for the application,
then a sufficient supply for the TSM1011 has to be ensured under all conditions. This means
that it is necessary to add some circuitry to supply the chip with a separate power line. This
can be achieved in numerous ways, including an additional winding on the transformer.
9 Voltage clamp
The schematic in Figure 10 shows how to realize a low-cost power supply for the TSM1011
(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 TSM1011 supply voltage is 28 V. In the aim to
protect the TSM1011 against such high voltage values an internal Zener clamp is integrated
(see Figure 6).
Equation 5
Figure 6. Clamp voltage
R
limit
I
vz
VCC V
z
–=
7[
7
3MJNJU
7$$
*W[
54.
".W
7$$
