UM0575
Board performances
9/20
The two resistors which are mainly dissipating power at standby are:
●
R2 - used to provide T2 with gate current during the e-STARTER on state
●
R3 - used to sense the voltage level across the PTC
As R2 is connected just behind the diodes’ bridges, the V
AK
voltage is applied across it, in
full-wave mode. R3 senses only half the voltage across the PTC and T1. This voltage is also
equal to V
AK
as T1 is OFF, and so no current is circulating through the PTC.
We can neglect the voltage drops of M1 and of C1, which are lower than 0.6 V and 16 V
respectively. The power losses, dissipated by the two resistors, are given by the following
equations:
Equation 1
An example with R2 = 470 k
Ω
and R3 = 510 k
Ω
gives:
●
For a 230 V / 50 Hz application using a run capacitor, V
AK
can reach up to 350 V RMS.
The overall power losses then equal 380 mW.
●
For a 100 V / 60 Hz application using or not a run capacitor, V
AK
stays around the line
voltage, i.e at worst 115 V RMS. The overall power losses then equal 41 mW.
2.3 Fast
transient
voltages
Immunity tests, as described by the IEC 61000-4-4 standard, have been performed with the
schematics of
Figure 5
, connected in series with a compressor without a RUN or START
capacitor. e-STARTER spurious triggerings have not been detected with spikes up to 2 kV.
This high immunity level has been reached thanks to:
●
the high dV/dt capability of the ACST6
●
the improved dV/dt capability of the very sensitive SCR X0202M (20 µA < Igt < 50 µA)
thanks to the fact that its gate is short-circuited to the cathode via M1 in OFF state, and
also thanks to the R6-C4 snubber circuit
●
the R
GK
(R7) resistor which is added on the ACST6 device to derivate the current
provided by R2 when M1 is ON
●
the immunity provided by the layout of the printed circuit board (refer to
Figure 15
)
It should be noted that spurious triggering of the e-STARTER is not a problem as such
behavior is not seen by the end user, and as these turn-ons do not lead to any component
failure.
2.4 Surge
voltages
The ACST6 device is an overvoltage protected device which means that it can be used
without any varistor in parallel with its terminals. If a high energy surge is applied to the
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⎩
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⋅
=
=
3
R
V
2
1
P
2
R
V
P
2
AK
3
R
2
AK
2
R
