LM3914 production car battery detector principle

LM3914 is a point / strip display driver integrated circuit developed by American NS company. It includes an input buffer, a 10-stage precision voltage comparator, a 1.25V reference voltage source, and a dot/strip display mode selection circuit. The non-inverting input of the 10-level voltage comparator is connected to the resistor divider. The resistor divider consists of 10 1kΩ precision resistors in series. The weights of the comparators are equal, forming a 10-level linear display driver for LEDs. Linear scale device that can drive LCD, VFD) meters. The working voltage is 3V ~ 25V (up to 48V), the output current is adjustable in the range of 2 ~ 30mA, the output end bearing capacity is ± 35V, the maximum output is limited to 30mA. The input buffer is connected to the follower form to improve input impedance and measurement accuracy. The LM3914 is internally equipped with a hysteresis circuit. The display does not jump from one LED to the male LED immediately, but is gentle and excessive, which can eliminate noise interference and improve the flicker caused by the rapid change of the input signal. Since the internal resistor divider is floating, the voltage measurement range is wide.

BRIEF broadening scale is a fixed point voltmeter, may be measured continuously for an automobile storage battery 12v state. The 4 and 6 pins of the LM3914 are the low-side and high-end of the 10-level resistor divider. R2 and RP2 are used to preset the output current of each voltage comparator, that is, the current through LED1 to LED10. This current is the reference voltage (1.25). v) 10 times the current supplied by the source. For example, if RP2 is adjusted to the uppermost end, the preset resistance is 1.2kΩ (R2). After paralleling with the on-chip voltage divider 10kΩ total resistance, the equivalent resistance between pins 4 and 6 is 1.07kΩ, 1.25V reference voltage source. The current supplied was 1.25 V, 1.07 kΩ ≈ 1.2 μA, and the current through each of the arc tubes was 1.2 mA × 10 = 12 mA. The internals of pins 7 and 8 are 1.25V reference voltage. Since R2 and RP2 provide the basic measurement range of 2.50V to 3.75V, the input signal is obtained by the positive power supply via R1 and RP1. Therefore, the reading should be the base range multiplied by the preset multiple. The display adopts red and green LEDs. When Vcc is in the normal range of 12v~14v, the green LED emits light; if Vcc is in 10V~12V or 14V~15V, the red LED emits light.

The LM3914 has a logic control network inside, which selects the moving point display or the bar display by connecting 9 signals to different signals. When the 9 and (11) feet are connected, it is the moving point display mode; when the 9 and 3 (Vcc) feet are connected, it is the bar display mode.

After all components have been installed and checked, the table can be calibrated. Methods as below:

1. Connect Vcc to 15.0v DC voltage. Adjust RP1 to make LED10 just shine.

2. Connect Vcc to 10.0v DC voltage. Adjust RP2 to make LED1 just shine.

3. After repeated adjustments several times. Connect this watch between the ground and the 12v DC contact of the ignition switch.

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