When the battery is charged beyond the specified battery voltage, its life expectancy will be greatly reduced.
Here is a simple charging circuit that uses a three-terminal adjustable shunt regulator TL431 (IC1) as the main regulator. When the voltage of the non-inverting input pin (REF) is lower than its internal reference voltage (2.5V), the TL431 cathode K outputs a high potential, keeping the relay in the released state, and charging continues. on the contrary. When the battery voltage exceeds the threshold voltage of the circuit. When the REF voltage exceeds 2.5V. TL431 cathode K output low potential. The relay is closed, the charging circuit is disconnected, and charging stops. The TL431 adds several external components to form the charge control circuit. Since the TL431 is internally provided with a reference voltage. Therefore, the TL431 comparator has a hysteresis effect, that is, there is a difference between the upper and lower limits of the comparator.
The threshold voltage of the circuit is the upper limit of the charging voltage. The upper limit voltage can be calculated as follows: VT = Vref × (1 + R1/R2), where Vref is the internal reference voltage of the TL431, which is approximately 2.5V.
When the battery voltage rises above the threshold voltage, the relay RL1 pulls in, its contact N/C disconnects the charging circuit, and the indicator LED1 flashes. At the same time, R3 provides a hysteresis path to control the release voltage of the relay Vr.Vr can be calculated by the following equation: Vr = Vref × (1 + R1 | | R3 / R2). Where R1||R3 is the parallel value of R1 and R3, ie (R1xR3)/(R1+R3).
When the battery voltage is lower than the release voltage, the TL431 cathode (K) voltage is close to the battery voltage. The relay remains in the released state. Charging continues and LED1 does not fire. Until the battery voltage after recharging exceeds the threshold voltage Vt, the LED 1 flashes again and the charging stops. R5 is used to limit the charging current.
The power supply of the charger is provided by a 220V AC power supply via a step-down transformer X1 and a D1 to D4 rectifier bridge.
The circuit can be mounted on a regular PCB and enclosed in a suitable box. Use an alligator clip to connect the battery while charging.
The double-concave lens is similar to the plano-concave lens. The focal length is negative, but the parallel incident light diverges outward. The two side surfaces of the double-concave lens have the same radius of curvature, and are generally used for beam expansion and projection.
The image formed by the biconcave lens is always smaller than the upright virtual image of the object. The biconcave lens is mainly used to correct myopia. Myopia is mainly due to the deformation of the lens, which causes the light to gather in front of the retina prematurely. The double-concave lens plays a role of diverging light. The double-concave lens becomes an upright, reduced virtual image, which makes the image distance longer and just falls on the retina.
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