YX8018 Solar Light DC-DC Booster IC

Description

YX8018 Solar Light DC-DC Booster IC comes in a 4 pin transistor style TO-94 package and the pin configuration and block diagram is shown in figure below. A low voltage near the negative battery voltage (GND) on the CE input of the YX8018 gates off the oscillator. A high voltage near the positive battery voltage (V_DD) conversely gates the oscillator on.

The gated oscillator in the YX8018 runs at approximately 200 KHz driving an open drain NMOS switch ( output on LX pin1 ). The circuit pulses the inductor to step up the voltage to drive the LED.

To reduce the component count the application of the YX8108 chip is rather ingenious. They use the internal ESD diode between the CE ( chip enable ) input and ground for charging the NiCd cell from the solar panel, but also use the voltage ( or lack thereof ) from the solar panel to detect when it is dark enough to turn the LED on. The CE input includes a small pull-up current (30 uA with 1.25 volts on V_DD). This small current will pull pin 3 high gating on the oscillator if the solar panel is not generating more than 30 uA of current.

Typical YX8018 Circuit

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