Board performances

UM0575

8/20

2

Board performances

2.1

Maximum current

During e-STARTER conduction, the power losses are similar to those of the standard PTC

solution as the same current circulates through this resistor. The only difference is that a

small part of the voltage is also held by T1.

In the case of an ACST6, its forward voltage drop can be considered to be a constant

even with a 10 A peak current, the voltage drop is less than 1 V.

This forward voltage drop should be taken into account mainly to evaluate the junction

temperature elevation of the semiconductor switch.

For an ACST6 in the TO220AB package, without any heatsink, this junction temperature

elevation is equal to:

●

30° C after a 5 A RMS current during 3 s (worst case of typical 100 V/60 Hz

compressors)

●

50° C after an 11 A RMS current during 0.5 s (worst case of typical 230 V/50 Hz

compressors)

75° C initial temperature. Figure 8 gives the maximum repetitive RMS current that the

ACST6-7ST can withstand without any heatsink. This curve is given for 40° C and 75° C

ambient temperatures. As with the e-STARTER solution, the heating time of the PTC is not

long enough to warm the electronic devices, so the 40° C curve is closer to the real

e-STARTER operating conditions.

2.2

Standby power losses

During e-STARTER standby, the losses are caused only by the resistors, which are still

connected to the mains voltage. Indeed, the ACST leakage current is in practice very much

lower than 20 µA so that the resulting losses can be neglected.

Figure 8.

e-STARTER maximum current versus conduction time