User manual

CD5.121
CD–Series
DC/DC Converter; 12V, 8A
Jan. 08 / Rev. 1.1 DS-CD5.121-EN / All parameters are specified at 12V, 8A and 24Vdc input at 25°C ambient unless otherwise noted.
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25. APPLICATION NOTES
25.1. PEAK CURRENT CAPABILITY
Solenoids, contactors and pneumatic modules often have a steady state (sealed) coil and a pick-up coil. The inrush
current demand of the pick-up coil is several times higher than the steady state current and usually exceeds the
nominal output current (including the PowerBoost) The same situation applies, when starting a capacitive load.
Branch circuits are often protected with circuit breakers or fuses. In case of a short or an overload in the branch
circuit, the fuse needs a certain amount of over-current to trip or to blow. The peak current capability ensures the
safe operation of subsequent circuit breakers.
Assuming the input voltage is turned on before such an event, the built-in large sized output capacitors inside the
DC/DC converter can deliver extra current. Discharging this capacitor causes a voltage dip on the output. The
following two examples show typical voltage dips:
Fig. 25-1 Peak load 16A for 50ms, typ. Fig. 25-2 Peak load 40A for 5ms, typ.
10ms/DIV
Output
Voltage
Output
Current
12V
1A
16A
8.3V
1ms/DIV
Output
Voltage
Output
Current
12V
1A
40A
4.3V
Peak load 16A (resistive) for 50ms
Output voltage dips from 12V to 8.3V.
Peak load 40A (resistive) for 5ms
Output voltage dips from 12V to 4.3V.
25.2. BACK-FEEDING LOADS
Loads such as decelerating motors and inductors can feed voltage back to the DC/DC converter. This feature is also
called return voltage immunity or resistance against Back- E.M.F. (Electro Magnetic Force).
This DC/DC converter is resistant and does not show malfunctioning when a load feeds back voltage to the DC/DC
converter. It does not matter, whether the DC/DC converter is on or off.
The maximum allowed feed back voltage is 16Vdc. The absorbing energy can be calculated according to the built-in
large sized output capacitor which is specified in chapter 7.
25.3. INDUCTIVE AND CAPACITIVE LOADS
The unit is designed to supply any kind of load, including unlimited capacitive and inductive loads.