Datasheet
QTD20.241
Q-Series
24V, 20A, DC INPUT
21. APPLICATION NOTES
21.1. REPETITIVE PULSE LOADING
Typically, a load current is not constant and varies over time. This DC/DC converter is designed to support loads with a
higher short-term power demand (=BonusPower
®
). The short-term duration is hardware controlled by an output
power manager and is available on a repeated basis. If the BonusPower
®
load lasts longer than the hardware
controller allows it, the output voltage will dip and the next BonusPower
®
is available after the BonusPower
®
recovery
time (see chapter 5) has elapsed.
To avoid this, the following rules must be met:
a) The power demand of the pulse must be below 125% of the nominal output power.
b) The duration of the pulse power must be shorter than the allowed BonusPower
®
time. (see output section)
c) The average (R.M.S.) output current must be below the specified continuous output current.
If the R.M.S. current is higher, the unit will respond with a thermal shut-down after a period of time. Use the
maximum duty cycle curve (Fig. 21-2) to check if the average output current is below the nominal current.
d) The duty cycle must be below 0.75.
Fig. 21-1 Repetitive pulse loads, definitions Fig. 21-2 Max. duty cycle curve
100%
P
PEAK
T
PEAK
P
0
T
0
max.
125%
125%100
0
0.2
0.4
0.6
0.75
Duty Cycle
105 110 115 120
P
PEAK
P
0
=
1
0
%
P
0
=
5
0
%
P
0
=
7
5
%
P
0
=
1
0
0
%
P
0
Base load (W)
P
PEAK
Pulse load (above 100%)
T
0
Duration between pulses (s)
T
PEAK
Pulse duration (s)
D
uty
C
ycle
T
0
=
T
peak
-
(D
uty
C
ycle
x T
peak
)
T
peak +
T
0
T
peak
D
uty
C
ycle
=
Example: A load is powered continuously with 240W (= 50% of the rated output load). From time to time a peak
power of 600W (= 125% of the rated output load) is needed for 1 second.
The question is: How often can this pulse be supplied without overloading the DC/DC converter?
- Make a vertical line at P
PEAK
= 125% and a horizontal line where the vertical line crosses the P
0
= 50%
curve. Read the max. duty cycle from the duty cycle-axis (= 0.37)
- Calculate the required pause (base load) length T
0
:
21/27
- Result: The required pause length = 1.7s
- Max. repetition rate = pulse +pause length = 2.7s
More examples for pulse load compatibility:
P
PEAK
P
0
T
PEAK
T
0
P
PEAK
P
0
T
PEAK
T
0
600W 480W 1s >25s 600W 240W 0.1s >0.16s
600W 0W 1s >1.3s 600W 240W 1s >1.6s
540W 240W 1s > 0.75s 600W 240W 3s >4.9s
D
uty
C
ycle
T
0
=
T
peak
-
(D
uty
C
ycle
x T
peak
)
0.37
1s
-
(0.37 x 1s)
==1.7s
Oct. 2016 / Rev. 2.0 DS-QTD20.241-EN
All parameters are specified at 24V, 20A, 600Vdc input, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.
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