Description:
This is a replacement
power source for 1.3V mercury cells or other small batteries. It has many uses
and I use this circuit in my computer to power a front panel multi adapter which
has a digital thermometer.
Notes:
This circuit takes it power from a PC. The power connectors have colour coded wiring, red and black are a 12V supply, black
and yellow are a 5V supply. These are extremely high current so absolute care
must be taken to avoid short circuits and an inline fuse of 100mA is
recommended.
The 1.3V is derived from a Red LED. When on and forward biased the LED's
voltage drop between anode and cathode is about 1.9V, this is too high for
mercury cell powered equipment, but fed in series with a 1N4148 signal diode
drops around 0.6V, the supply is then ideal to drive battery powered peripherals.
This is not suitable for clocks, because when the computer is turned off the 5V
supply is also switched off. It is however ideal for the independent
temperature displays often included with PC preripherals
such as case mounted usb connectors.
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