5V - Digital Camera Charger

Posted on Feb 6, 2014

You need not be disappointed next time when your digital camera shows low battery indication during a picnic trip. Just plug this digital camera adaptor into the cigarette lighter outlet of your car and connect the camera to it. The adaptor will interface the DC source and the camera battery to provide sufficient charging current to replenish the

5V - Digital Camera Charger
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battery in one hour. The Lithium ion or NiMH battery of the digital camera can be quickly charged with a nominal voltage of 5V and 300mA to 1A current. Fig. 1 shows the circuit of the digital camera adaptor. The circuit uses a differential transistor amplifier and a current amplifier to output constant voltage and the required current, respectively. npn transistors T1 and T2 form a differential amplifier just like the inputs of an op-amp in differential amplifier configuration. The base voltage of T1 is fixed to 3 volts by zener diode ZD1. T2 obtains the base voltage from a potential divider comprising R4 and R5 via the output rail. T1 and T2 compare the voltage at their base-emitter junctions and adjust the base current of current amplifier T3. pnp transistor TIP127 (T3) is used as the current amplifier to provide sufficient current for charging. It is a medium-power Darlington transistor with a current gain of 1000. That is, if 1mA current is provided to the base of T3, its collector current will be 1A maximum. T3 works in inverter mode, so when a positive voltage is applied to the base of T1, a negative pulse will drive T3 when T1 conducts. Resistor R2 (820-ohm) provides around 1mA current to the base of T3, so it can output 1A current from its collector. Resistor R3 (100-ohm) plays an important role in the working of the differential amplifier to adjust the output voltage and current. The current passing through it is...

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