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Company Logo NXP Semiconductors

  • Single Solar Cell Battery Charger

  • Created: Sep 03, 2014

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A battery charger is a device used to energize a secondary cell or rechargeable battery by applying an electric current through it. The charging time will depend on the size and type of battery being used. The schematic diagram shown is a battery charger circuit that utilizes a single solar cell. The main component used for the design is an HEF4093BP Quad 2-input NAND Schmitt trigger manufactured by NXP Semiconductor.

The circuit charges a 9V battery at about 30mA per input ampere at 0.4V. U1, a quad Schmitt trigger, operate as an astable multivibrator to drive push-pull TMOS devices Q1 and Q2. Power for U1 is derived from the 9V battery via D4; power for Q1 and Q2 is supplied by the solar cell. The multivibrator frequency, determined by R2-C1, is set to 180Hz for maximum efficiency from 6.3V filament transformer, T1. The secondary of the transformer is applied to a full wave bridge rectifier, D1, which is connected to the batteries being charged. The small Ni-Cad battery is a fail-safe excitation supply to allow the system to recover if the 9V battery becomes fully discharged. A CdS photocell shuts off the oscillator in darkness to preserve the fail-safe battery during shipping and storage, or prolonged darkness.

This circuit can be used to charge a pair of AA or AAA sized rechargeable battery cells from sunlight. For this circuit, the output supply voltage range is from 3VDC to 18VDC of which it can supply any portable electronic devices within that range.



I like the idea, but Q1, Q2 and T1 make the circuit very expensive for a <1W Solar cell charger. Could it be possible to use MOSFETs with lower Vds and then a cheaper TRAFO? Any suggestions?

Posted: Sep 19, 2014

PB Fortich

I think it is possible. The design only tells us the ideal components for the circuit. I will try to build that one with general purpose components. :)

Posted: Oct 27, 2014



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