Charger Failure Alarm Circuit

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Introduction:

The failure alarm circuit simply produces an alarm when there is a power supply that fails. The battery charger failure alarm is a similar kind of failure alarm that indicates the disconnection of the battery from the charger using an insightful signal such as a LED or a buzzer indicator. The failure can occur due to the reasons such as loss of input supply or discontinuity in the circuit, failure of the rectifier circuit, etc.

This post describes the simple and easy build a circuit of charger failure alarm with minimum hardware. Two transistors BC557 are used as the main components acting as a switch for the buzzer and LED that will indicate the failure of the battery charger or the disconnection. The working of the circuit is described in detail below.

Hardware Components

The following components are required to make Charger Failure Alarm Circuit

S.no	Component	Value	Qty
1.	Resistor	1KΩ, 10KΩ	2, 1
2.	Diode	1N4007	1
3.	Switch	–	1
4.	Buzzer	–	1
5.	LED	–	1
7.	Transistor	BC557	2
6.	Screw jacks	–	2

BC557 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 555 Timer BC557

Charger Failure Alarm Circuit

Working Explanation:

The circuit is easy to build and uses transistors BC557, diode, LED, resistors and capacitors. The buzzer and LED are used to indicate the disconnection of the battery from the charger and the transistors are used as a switch for the buzzer.
The base of the transistor Q1 is connected between the resistor R2 and the collector of the transistor Q2. As the battery charger is connected, there is a current flowing through the charger to the battery and thus diode D2 conducts and there is a voltage drop of 0.7 volts across the diode and Q2 conducts and the transistor Q1 is off.

When the battery is disconnected, the diode will not conduct and the transistor Q1 will conduct that will make LED and buzzer operate indicating the disconnection of the battery.