TLE 4726
Calculation of Power Dissipation
The total power dissipation Ptot is made up of
saturation losses Psat (transistor saturation voltage and diode forward voltages),
quiescent losses Pq
switching losses Ps
(quiescent current times supply voltage) and
(turn-ON / turn-OFF operations).
The following equations give the power dissipation for chopper operation without phase
reversal. This is the worst case, because full current flows for the entire time and
switching losses occur in addition.
Ptot = 2 × Psat + Pq + 2 × Ps
where
Psat IN { Vsatl × d + VFu (1 – d ) + VsatuC × d + VsatuD (1 – d ) }
Pq = Iq × VS + IL × VL
iD × tDON iD + iR × tON
VS
------
T
IN
----
PS
--------------------- + ----------------------------- + tDOFF + tOFF
2
2
4
IN
Iq
= nominal current (mean value)
= quiescent current
iD
iR
tp
= reverse current during turn-on delay
= peak reverse current
= conducting time of chopper transistor
= turn-ON time
tON
tOFF = turn-OFF time
tDON = turn-ON delay
tDOFF = turn-OFF delay
T
d
= cycle duration
= duty cycle tp/T
Vsatl = saturation voltage of sink transistor (T3, T4)
VsatuC = saturation voltage of source transistor (T1, T2) during charge cycle
VsatuD = saturation voltage of source transistor (T1, T2) during discharge cycle
VFu
VS
VL
IL
= forward voltage of free-wheeling diode (D1, D2)
= supply voltage
= logic supply voltage
= current from logic supply
Data Sheet
19
1999-09-15
INFINEON [ Infineon ]
