File:Undervoltage battery switch, TL431+PMOS.png
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English: The simplest battery undervoltage lockout (UVLO) circuit employs a PMOS power transistor as a switch and a TL431 as the voltage comparator. It is an RS-type latch with dual reset inputs (the analog comparator and the optional OFF button). Lowest (cutoff) battery voltage must exceed the voltage drop on the TL431 (2.5V) and the gate-source of the transistor (assume 4V min - PMOS threshold voltages are still quite high). That is, it will serve a 2S lithium pack (7.0V cutoff) but not a single lithium cell. Likewise, the reasonable upper limit for battery voltage is around 15V (4S lithium pack) due to gate-source maximum rating of the PMOS. Higher voltages are possible with additional votage dividers or zeners protecting the gate and the cathode of the TL431. R1 must be scaled to source 1..2 mA into the TL431 (e.g. 2.4 to 4.7 kOhm for a 2S lithium battery). R2 may be scaled to pass currents as low as 0.1 mA, although 0.25 mA is more reliable. Both switches must be non-latching type.
Русский: Простейшая схема защиты батареи от переразряда при снижении напряжении (UVLO) - RS-триггер на TL431 и PMOS-ключе. Работает при напряжении батареи от 7В (две литиевые банки последовательно) до 15В (четыре банки). Большие напряжения возможны при условии защитных делителей напряжении в цепях затвора и стока. Не работает с одной литиевой банкой. Величина резистора R1 должна обеспечивать ток катода TL431 порядка 1...2 мА (больше незачем, перерасход батареи) - т.е. для двух литиевых банок выбираем от R1 2.4K до 4.7К. Резистор (делитель) R2 выбирается исходя из тока не менее 0.1 мА, лучше - 0.25 мА. Обе кнопки - без фиксации. |
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| Author | Retired electrician |
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| current | 13:51, 12 October 2021 | | 1,591 × 692 (66 KB) | Retired electrician (talk | contribs) | {{Information |Description={{en|The simplest battery undervoltage lockout (UVLO) circuit employs a PMOS power transistor as a switch and a TL431 as the voltage comparator. Lowest (cutoff) battery voltage must exceed the voltage drop on the TL431 (2.5V) and the gate-source of the transistor (assume 4V min - PMOS threshold voltages are still quite high). That is, it will serve a 2S lithium pack (7.0 - 8.5V) but not a single lithium cell. R1 must be scaled to source 1 mA into the TL431 (e.g. 4.7... |
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