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7
June 13, 2000 Data Device Corporation
POSITION
COMMAND
POSITION
ERROR
POSITION
AMP
VELOCITY
COMMAND
VELOCITY
ERROR
VELOCITY
AMP
TORQUE
COMMAND
TORQUE
ERROR
CURRENT
ERROR
AMP
PWM
PW-8X075P6
3-MODULE
SET
HALL SIGNALS
3
3-PHASE
MOTOR
6
TORQUE LOOP
VELOCITY LOOP
POSITION LOOP
+
-
+
-
+
-
FIGURE 6. TYPICAL POSITION AND VELOCITY CONTROL LOOP
POWER DISSIPATION (see FIGURE 7)
There are three major contributors to power dissipation in the
motor driver: conduction losses, switching losses, and flyback
diode losses. Consider the following operating conditions
VBUS = +270V
I
OA
= 40A (see FIGURE 7); I
OB
= 50A (see FIGURE 7)
ton = 50
μ
s (see FIGURE 7);T = 100μs ( period )
V
CE(SAT)
= 2.0V (see TABLE 2, I
O
= 50A, T
C
= +25°C)
ts1 = 200ns (see Figure 7); ts2 = 200ns (see FIGURE 7)
fo = 10kHz (switching frequency)
V
F
is the diode forward voltage, TABLE 2, I
o
= 50A, T
C
= +25°C
V
F
(avg) = 1.35V
1. Conduction Losses (PC)
P
C
= I
AVE
x V
CE(SAT)
x (ton / T)
I
AVE
= (I
OB
+ I
OA
) / 2
I
AVE
= (50A + 40A) / 2 = 45
P
C
= 45A x 2.0V x (50μs / 100μs)
P
C
= 45W
2. Switching Losses (PS)
P
S
= (E
ON
+ E
OFF
) x fo
E
ON
= ts1 x VBUS x I
OA
/ 6
E
ON
= 200ns x 270V x 40A / 6
E
ON
= .00045J
E
OFF
= ts2 x VBUS x I
OB
/ 6
E
OFF
= 200ns x 270V x 50A / 6
E
OFF
= .00036J
P
S
= 10000 x (.00045 + .00036)
P
S
= 8.1W
3. Flyback diode Losses (Pd)
Pd = I
AVE
x V
F
(avg) x (1- (ton / T))
Pdf = 45A x 1.35V x [1 - (50μs / 100μs)]
Pdf = 30.38W
Transistor Power Dissipation (P
T
)
To calculate the maximum power dissipation of the output tran-
sistor / diode pair as a function of the case temperature, use the
following equation.
P
Q
= P
C
+ P
S
+ Pdf
Total Hybrid Power Dissipation (P
Hybrid)
To calculate Total Power Dissipated in the hybrid add
the power dissipation of each conducting transistor / diode pair.
Typically, only two transistor / diode pairs are conducting at any
given time.
6
P
TOTAL
=
Σ
[ P
Qi
] where i = each transistor/diode pair
i = 1
I
OB
t
on
I
OA
VBUS
I
O
t
s2
t
s1
FIGURE 7. OUTPUT CHARACTERISTICS