Power supply with battery backup for DMM -
This is a simple charger circuit which will work for
a light load like a DMM, the Battery can be a sealed
maintenance free battery of 9V-2AH or better. The
circuit will work best if the Unit is powered on
many times daily on regular use, else battery will
Regulators LM7812 and LM317
The 555 Astable is used to generate a AC signal from
which a negative voltage is generated, A 79L05 which
is a low power TO92 equivalent of 7905 a negative -5
volts regulator is used as -5 volts load is less. A
TO220 7805 is used for the +5V supply.
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with battery backup for DMM - del20010
Many dual supplies are derived from one DC Source. A
SMPS solution is the best. A Series Regulator is
simple to troubleshoot in comparison to Switching
Types, there is no EMI-RFI too.
to -5 using a 555 Astable Multivibrator
This simple circuit is ok only for Low Current
gadgets, Whereas SMPS is green and efficient. In
SMPS a greater care for Product Safety is required.
In a Linear Supply with Step-Down Mains-Frequency
Transformer. The Transformer is the only place,
where you look into safety the most. In SMPS it is
the PCB, the feedback components and also The
High-Frequency (200 kHz) Mains Ferrite Transformer.