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
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.
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.
Data sheets and info useful to study and build this