TLE 4729 G

Data Sheet

22

V1.2, 2008-03-18

Calculation of Power Dissipation

The total power dissipation

Saturation losses

Quiescent losses

(quiescent current times supply voltage) and

Switching losses

(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.

where

=

P

q

V

S

T

-------

i

D

t

DON

×

2

-------------------------

i

D

i

R

+

ON

×

4

--------------------------------------

I

N

2

-----

t

DOFF

t

OFF

+

()

++







≅

= Nominal current (mean value)

= Quiescent current

= Reverse current during turn-on delay

= Peak reverse current

= Conducting time of chopper transistor

= Turn-ON time

T

= Cycle duration

d

= Duty cycle

= Forward voltage of free-wheeling diode (DX1, DX2)

= Supply voltage