Phone

    00852-6915 1330
  • Contents

Introduction

In recent years, with the continuous development of new technologies, storage batteries as a power source not only play an important role in transportation (railroad, subway, ship), power generation, communications, aerospace, chemical, traditional automobiles, and other industries. In addition, batteries have also begun to be used in the fields of electric vehicles (EV) and hybrid electric vehicles (HEV) as power sources or power auxiliary power sources.
 
Do you know what are 2 features of batteries compared with disposable rechargeable batteries? That is multiple recycling and high efficiency and energy saving. When the car is not started, it must rely on the battery to supply power to the starter until it drives the engine to rotate. When the battery voltage is insufficient or the battery is damaged, it is difficult to provide sufficient power, thus causing the engine to fail to run.
 
Therefore, this blog proposes the design of a low-battery alarm system for car batteries based on LM741. In general, when the battery voltage drops to a certain limit, it will send out a reminder. The principle of the reminder is that the circuit judges whether the battery is working normally by installing a sound and light signal alarm system. In this way, we can recharge our car or replace the battery in time.
lm741

Catalog

Introduction

Catalog

I Description of LM741

II Design of the System

III Circuit Design

3.1 System Hardware Circuit Design

3.2 Reference Power Supply Circuit

3.3 Sampling Circuit

3.4 Output Circuit

3.5 Alarm Principle

3.6 Wiring Diagram of the System

IV Test Results of the System

FAQ

Ordering & Quantity

I Description of LM741

The LM741 series are general-purpose operational amplifiers. It is intended for a wide range of analogue applications. The high gain and wide range of operating voltage provide superior performance in integrator, summing amplifier, and general feedback applications.

LM741 has both inverting inputs and non-inverting inputs. When the voltage of the non-inverting input (+) is higher than the voltage of the inverting input (-), the output of the comparator is high. If the voltage at the inverting input (-) is higher than the non-inverting terminal (+), the output is low. The output of the operational amplifier is the product of gain and input voltage.

II Design of the System

The low battery alarm system is mainly composed of a reference power supply circuit, a sampling circuit, a voltage comparator circuit, and output circuit. The reference power supply circuit consists of a voltage regulator and a current limiting resistor, which is added to the inverting input of the voltage comparator and provides a reference voltage for it. The sampling circuit is composed of two resistors in series to form a series voltage divider, which is used as the input signal of the whole circuit, and a part of the battery voltage is compared with the reference voltage. The voltage comparator circuit judges whether the output is high level or low level by comparing the voltage of the reference power supply circuit and the voltage of the sampling circuit. The output circuit judges whether the light-emitting diode is in the conducting state by the received output voltage from the voltage comparator, thereby giving an alarm signal to indicate the battery power is too low.

design of battery alarm system

Figure 1. Structure of the System

III Circuit Design

3.1 System Hardware Circuit Design

The hardware circuit of the low battery alarm system is shown in Figure 2. The system mainly includes voltage comparator LM741, resistor, voltage regulator, and LED.

lm741 circuit

Figure 2. Hardware Circuit

3.2 Reference Power Supply Circuit

The reference power supply circuit consists of current limiting resistor R2 and voltage regulator VDZ. This system takes the stable voltage of the regulator as the reference voltage of the comparator LM741, and connects it to the inverting input of the LM741. R2 = 100k Ω. The stable voltage is 5V.

3.3 Sampling Circuit

R1 and R3 are connected in series to form a sampling circuit, which is connected to the in-phase input terminal of LM741. The resistance values of R1 and R3 are equal, taking 100k Ω to form a series partial voltage. The intermediate point is the sampling voltage, that is, taking part of the battery voltage as the detection voltage, i.e. the input voltage.

3.4 Output Circuit

The output circuit consists of R4 and LED. R4 = 1K Ω, which can limit the current. According to the voltage value at the output of the voltage comparator to determined whether the LED is on or off.

3.5 Alarm Principle

When the battery voltage is higher than 10V, that is, the voltage of sampling circuit exceeds 5V, the input signal voltage is higher than the reference voltage, then LM741 outputs high level, and the output voltage is battery voltage (10 ~ 12V). It can be seen from Figure 4 that the potential of pin 6 is higher than the potential of pin 7. LED do not emit light because of the reverse voltage. This indicates that the battery voltage is normal and the alarm function is not activated. When the battery voltage is lower than 10V and the input signal voltage (<5V) is lower than the reference voltage, the LM741 outputs a low level, that is, the output voltage is zero. At this time, the potential of pin 7 is higher than the potential of pin 6, the LED is turned on due to the forward voltage. And the light indicates that the battery power is too low. The alarm function is activated.

3.6 Wiring Diagram of the System

Figure 3 shows the wiring structure of low battery alarm system. The automobile battery is connected to the voltage comparison device through the car key switch, and provides power for the automobile circuit load (lighting system, instrument system, etc.) When the battery voltage is normal, the load voltage is normal. And the vehicle can start normally. The instrument system can display and work normally. When the battery voltage is too low, the voltage comparison device will send out a light alarm signal. At the same time, if the power supply voltage can not reach the required voltage level of the system, the corresponding lighting, instrument and other systems will not operate.

wiring diagram of battery alarm system

Figure 3. Wiring Diagram of the System

IV Test Results of the System

It can be seen from table 1 that when the battery voltage is lower than 10V, the alarm indicator is on; when the battery voltage is higher than 10V, the alarm indicator is off. Therefore, the circuit can give an alarm when the battery voltage is lower than 10V, and stop when the battery is recharged to above 10V again. The alarm system does not work when the output voltage of the battery is above 10V. It fully shows that the design scheme of the circuit is correct and feasible.

Test Results of the System

Battery voltage(V)

Battery voltage status

Alarm indicator status

6.8

too low

on

8.1

low

on

9.6

low

on

10.3 (After charging)

normal

off

12.8 (After charging)

normal

off

13.6 (After charging)

too hight

off


FAQ

  • What is lm741 op amp?

An LM741 operational amplifier is a DC-coupled high gain electronic voltage amplifier. It has only one op-amp inside. An operational amplifier IC is used as a comparator which compares the two signal, the inverting and non-inverting signal.

  • Why Opamp is called 741?

The 741 Op Amp IC is a monolithic integrated circuit, comprising of a general purpose Operational Amplifier. It was first manufactured by Fairchild semiconductors in the year 1963. The number 741 indicates that this operational amplifier IC has 7 functional pins, 4 pins capable of taking input and 1 output pin.

  • How does a 741 op amp work?

The most common Op-Amp is the 741 and it is used in many circuits. The OP AMP is a 'Linear Amplifier' with an amazing variety of uses. Its main purpose is to amplify (increase) a weak signal - a little like a Darlington Pair. The OP-AMP has two inputs, INVERTING ( - ) and NON-INVERTING (+), and one output at pin 6.

  • How do you calculate lm386 gain?

Voltage Gain Analysis:
Without any external components, it has a gain of Gv = 2x15K/(150+1350) = 20 (26 dB).
With a capacitor (or shortcutting) between pins 1 and 8 , it has a gain of Gv = 2x15K/150 =200 (46dB).

  • Why does the IC 741 require dual power supply?

Operational amplifiers have two power supply rails because they usually need to swing bipolar - output voltages that go either positive or negative in response to the normal range of input signals. ... Without the dual supplies the output signal would clip at the ground potential.

  • How do I check my 741 IC?

Testing a 741 IC
The circuit is commonly called as voltage follower. A voltage is applied to pin3 of the op-amp through the variable resistor (10K). All we need to do is to verify whether the voltages V1 and V2 are exactly same or not. Check them using a multi-meter.

  • What is IC 741?

An op amp is a complex electronic device, which consists of resistors, capacitors, transistors and diodes. It is commercially available in integrated circuit form. Most commonly available and used op amp IC is IC 741. The IC 741 is a small chip. It comprises eight pins.

  • What is gain bandwidth product of 741?

Gain-Bandwidth Product: For an Op-Amp the gain, G is defined as the gain when a signal is fed differentially into the op-amp and no feedback loop is present. ... It is generally given in V/μs, and for the 741 op-amp is something close to 1v/μs.

  • What are the features of IC 741?

Short circuit and overload protection provided.
In theory, the dc output voltage will be zero if both the inputs of the 741 IC are connected to the ground. …
Low power consumption.
Large common mode rejection ratio (CMRR) and differential voltage ranges.
No external frequency compensation is required.

  • Which op-amp (LM356 or LM741) is the better choice for higher frequency applications?

Um, the LM356 is an audio power amplifier with a 300 KHz bandwidth. The LM741 is an operational amplifier with a typical unity gain bandwidth of 1 MHz.
In other words, they are entirely different sorts of things and not at all interchangeable.
Neither is very good at higher frequencies.
You might be thinking of the LF356, which is a JFET input operational amplifier with a unity gain bandwidth around 5 MHz. Much better part in almost every dimension than the LM741.

  • Can we use an LM324 instead of an LM741 for constructing an op-amp integrator?

Yes. It will likely perform slightly better too as it has a slightly better specification (frequency, slew rate, etc), plus you get four identical op amps in a single 14 pin package.

Kynix

Kynix was founded in 2008, specializing in the electronic components distribution business. We adhere to honesty and ethics as our business philosophy and have gradually established an excellent reputation and credibility in our international business. With the accurate quotation, excellent credit, reasonable price, reliable quality, fast delivery, and authentic service, we have won the praise of the majority of customers.

Join our mailing list!

Be the first to know about new products, special offers, and more.

Leave a Reply

We'd love to hear from you! Feel free to share your thoughts and comments below. Rest assured, your email address will remain private.

Name *
Email *
Captcha *
Rating:

Kynix

  • How to purchase

  • Order
  • Search & Inquiry
  • Shipping & Tracking
  • Payment Methods
  • Contact Us

  • Tel: 00852-6915 1330
  • Email: info@kynix.com
  • Follow Us

authentication

Kynix

© 2008-2026 kynix.com all rights reserved.