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Notes:
This simple charger uses a single
transistor as a constant current source. The voltage across
the pair of 1N4148 diodes biases
the base of the BD140 medium power transistor. The base-
emitter voltage of the transistor and the
forward voltage drop across the diodes are relatively stable. The charging
current is approximately 15mA or 45mA with the switch closed. This
suits most 1.5V and 9V rechargeable
batteries.
The
transformer should have a secondary rating of 12V ac at 0.5amp, the primary
should be
220/240volts for Europe or 120volts ac for North America.
WARNING:
Take care with this circuit. Use a voltmeter to
observe correct polarity. Nicads
can explode if
short circuited or connected with the wrong polarity.
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