Power-supply controller always at optimum efficiency
ON Semiconductor’s NCP1351 is a current-mode
controller that automatically
adjusts its operating frequency to
optimise efficiency at all loadings
from zero to maximum.
By using a quasi-fixed on-time with variable
off-time, the NCP1351 decreases its switching
frequency as the load becomes lighter. This
reduces standby power to 140mW, while also
ensuring optimum efficiency in other loading
conditions. When the frequency decreases,
the peak current is gradually reduced to
approximately 30% of the maximum peak
current. This also prevents transformer
mechanical resonance and thereby
avoids audible noise.
Featured for ultra-low-cost
applications, the device includes
natural frequency jittering to
minimise EMI and simplify design.
Protection features include over-current
protection featuring a dual
threshold to accommodate large
power-output transients such as in
printer power supplies. There is also
a dedicated Latch input for over-voltage
and over-temperature
protection, as well as the option of
latched or auto-restart short-circuit
protection.
As a further value-added feature,
negative-current sensing allows
designers to adjust the maximum
sensed voltage by selecting the sense
resistor, and also improves noise
immunity.
FEATURES
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- >80% efficiency from 2W to 40W output power
- 28V maximum supply voltage
- 350mA sink/source capability
- Primary- or secondary-side regulation
- Low EMI signature with bulk input ripple
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APPLICATIONS
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- Auxiliary power supplies
- Off-line battery chargers
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The NCP1351 has lower start-up current than most alternative
devices, to assist designers building low-standby power supplies.
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