![]() To reduce power, a push-to-test pushbutton is recommended. The overall current drain as shown is about 12mA with all the LEDs illuminated. This current can be adjusted simply by varying the series resistors (R9 through R13). The LEDs are biased to operate at about 1mA which is reasonably bright if high efficiency LEDs are used-mine were not of the high efficiency type. Battery Indicator high voltage indicator battery charge indicator Battery Level Indicator Battery LED Indicator Battery Level Indicator Battery Level. There is no hysteresis so the LEDs tend to flicker slightly at the threshold voltages-this is not a problem. It worked as expected and when R2 is calibrated properly, the voltage thresholds are within about 0.1V of stated values. The LM324 op amp should work OK, but the pin-out is different-and (4) LM741 op amps should also work OK. D7 protects against reverse battery connection. The comparator sections have open collector outputs that simply function as switches to operate the LEDs. U1 is an LM339 quad comparator that compares the various voltages from the two dividers. R7 & 8 form a voltage divider to that divides the battery voltage by a factor of 6. Tied to this is a string of divider resistors (R2-6) that set the various fixed voltage levels. Connecting a 33K resistor across D9 corrected this little problem without affecting anything else.24V Battery Level Indicator BOM Battery Level Indicator Circuit Operationĭ1 is the voltage reference zener. This was traced to Zener D9 dropping out of conduction thus starving the voltage divider. Testing on variable voltage turned up an interesting bug –when the voltage was turned down to about 10V, all LEDs lit again. To reduce standby power, a push-to-test pushbutton may be used. This current can be adjusted simply by varying the emitter driver resistors (R9 through R13). This circuit will work if the voltage goes about 14 v and below 10v ( you can adjust the voltage of indication using Preset ). Document Information click to expand document information. 100 (1) 100 found this document useful (1 vote) 45 views. Scribd is the worlds largest social reading and publishing site. The LEDs are biased to operate at 2.3mA which is reasonably bright for high efficiency LEDs. 36V Battery Level Indicator - Read online for free. The remaining LEDs will switch on close to the indicated voltage –accuracy of those voltages may suffer slightly, but should be close. ![]() Then adjust the calibration pot until D2 flickers. The quad comparator compares the various voltages from the two dividers.įor calibration, connect to a voltage source that can be set to the highest LED threshold (41V in this case). R7 & 8 form a voltage divider to that divides the battery voltage by a factor of 9. While this is relatively busy, it places virtually no burden on the shunt regulator.ĭ1 is the voltage reference zener. By limiting the emitter current, the LED current is automatically limited to the same value. However, the cascode transistors may drive LEDs that are tied to a much higher voltage –up to 80V using the MPS-A16. By tying the bases of these transistors to the 13V bus, the LM339 open collector drive transistors never see more than 13V. In this circuit it offers one great property –low voltage in, high voltage out. This configuration is generally used for RF amplifiers. There are two solutions for this: increase the current rating of the shunt regulator so that it can power the LEDs, or run the LEDs via a cascode amplifier arrangement –I chose the cascode amplifier.Ī cascode amplifier is a configuration where one transistor feeds a 2nd transistor that is connected in the common base configuration. ![]() However, the LM339 open collector outputs cannot drive LEDs powered from the battery bus due to the same maximum voltage limitation. Shunt regulators are very simple, inexpensive and robust –good for this application. The main component of this voltage level indicator circuit is an LM339 IC which is a quad comparator IC that has 4 comparators. The solution involves running the IC power rail off a zener shunt regulator. Through clever use of a series of resistors and the LM339 comparator, a visual indication of the state of a battery can been seen. One limiting factor is the LM339 that has an absolute maximum voltage rating of 36V –and it is not good practice to operate near that point.
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