Nickel Hydride No. 5 batteries

　　Circuit design to prevent Nickel Hydride No. 5 batteriesreverse connection protection

　　Users often mistakenly install the Nickel Hydride No. 5 batteriesupside down when using battery-powered products (of course, engineers will not make such a mistake). Damage to the circuit can be avoided by using a single diode or a diode bridge, but that wastes power and reduces the available supply voltage by putting one or two diode drops in series between the Nickel Hydride No. 5 batteriesand the system supply. Here we introduce an alternative solution, which not only solves the protection problem of reverse-connected batteries, but also automatically corrects reverse-connection errors (see the figure below). To eliminate the tube voltage drop of the discrete diode, a DPDT (Double Pole Double Throw) switch with low on-resistance is selected and used as a full-wave rectifier. When the Nickel Hydride No. 5 batteriesis connected correctly as shown in the figure, the upper switch (S1) is in a normally closed state because its control pin is low. The connection from Pin 2 to Pin 10 provides a low-resistance path from the Nickel Hydride No. 5 batteriesto VCC. Conversely, the lower switch (S2) closes its normally open contact (not shown) because its control pin is high. Connecting pins 7 to 6 connects the negative terminal of the Nickel Hydride No. 5 batteriesto system ground.

　　The ESD protection diode inside IC1 ensures that the circuit is turned on normally and acts like a full-wave rectifier. When the Nickel Hydride No. 5 batteriesvoltage is higher than 1V, the MOSFET inside the analog switch is turned on. Its conduction time is less than 20ns, and it can quickly switch the connection polarity between the Nickel Hydride No. 5 batteriesand the system when the Nickel Hydride No. 5 batteriespolarity is reversed, ensuring the normal operation of the circuit. Circuit on-resistance is related to Nickel Hydride No. 5 batteriesvoltage. When powered by 4 NiCd, NiMH or alkaline batteries, the resistance at each end of the rectifier is 2.5Ω (the total resistance is 5Ω). When powered by 2 batteries (2.4V to 3V), the total resistance is 10Ω. IC1 is rated for operating voltages up to 5.5V and allows a continuous current of 30mA, making this circuit ideal for cordless phones, portable audio equipment, handheld electronics and other low to medium current applications. IC1's ultra-small 10-pin µMAX package occupies less space than the four leaded small-signal diodes required for discrete diode solutions and is nearly the same size as two SOT-23 dual diodes.

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