Internal Boost Power Supply - National Instruments NI 9751 User Manual

Internal Boost Power Supply

The NI 9751 contains an internal boost power supply that can maintain a voltage level from
battery voltage up to 190 V. You can use software to enable or disable boost power supply at
any time. The internal booster power supply is disabled automatically whenever critical faults
occur and can only be enabled by clearing the faults. Internal capacitors store the high voltage,
which is used to drive the high-voltage phases of the injector current profile.
High Voltage
extreme care to protect against shock. Even when the NI 9751 is completely powered
off, allow approximately three minutes for the internal high voltage to dissipate. Do
not touch any of the module screw terminals or injector terminals while the NI 9751
is powered on.
Internal Boost Power Supply Performance
The following critical factors determine how well the internal boost power supply will perform
for a particular injector solenoid application:
• Injector solenoid resistance
• Injector solenoid inductance
• Peak current required to open the injector valve
• Working voltage requirement (HVTarget)
• Frequency of injection events
• Injector solenoid back-boost time (BackBoostTime)
Injector Solenoid Resistance
Typical common rail diesel injector solenoids will have a resistance of 1 Ω or less. This
resistance wastes, as heat, a portion of the energy supplied to the solenoid and affects the
maximum current achieved in the coil, which depends on the drive voltage applied. In general,
lower solenoid resistances are better for common rail solenoid injector applications.
Injector Solenoid Inductance
Typical common rail injector solenoids have an inductance of 1 mH or less. Inductance acts to
resist current change through the coil. As inductance increases, more time is required to achieve
the required peak current level, given a constant drive voltage. When you use the internal high
voltage to drive current, energy transfers from the internal high voltage capacitance to the
injector solenoid. Longer drive times deplete energy from the internal high voltage capacitance.
The internal boost supply works harder to maintain the high voltage target. Inductance is
proportional to the magnetic force generated for opening the injector valve.
Peak Current Requirement
Higher peak-currents require more energy from the internal boost power supply because the
internally stored high voltage depletes at a higher rate.
The NI 9751 normally operates at voltages up to 190 V. Take
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