Current presence indicator

There is a need to track the presence of current flowing in the circuit in two states: either there or not. Example: you charge a battery with an integrated charging controller, connected to a power source, and how to control the process? You can of course include an ammeter in the circuit, you say, and you will be right. But you won't do it all the time. It is easier to insert a charge flow indicator into the power supply unit, which will show whether the current flows into the battery or not. Another example. Suppose there is some kind of incandescent lamp in a car that you do not see and do not know if it is on or has burned out. In the circuit to this lamp, you can also turn on the current indicator and monitor the flow. If the lamp burns out - it will be immediately visible. Or there is a sensor with a filament. Tapa gas or oxygen sensor. And you need to know for sure that the filament has not broken and everything is working properly. Here and come to the aid of an indicator, the scheme of which I will give below. Applications can be mass,Of course, the basic idea is one - control of current availability.

Current indicator circuit

Current availability indicator
The circuit is very simple. Resistor with an asterisk is selected depending on the controlled current, it can be from 0.4 to 10 Ohm. To charge the lithium ion battery, I took 4.7 ohms. Through this resistor, a current flows (if it flows), according to Ohm's law, the voltage that the transistor opens on it is allocated. As a result, the LED lights up indicating the charging going on. As soon as the battery is charged, the internal controller will disconnect the battery, the current in the circuit will be gone. The transistor will close and the LED will turn off, thereby making it clear that charging is complete. The VD1 diode limits the voltage to 0.6 V. You can take any on a current of 1 A. Again, it all depends on your load. But you cannot take the Schottky diode, because it has too little drop - the transistor can simply not open from 0.4 V. Through such a circuit, you can even charge car batteries, the main diode can be selected with a current higher than the current of the desired charge.
Indicator of current availability
In this example, the LED turns on during the passage of current, and if you want to show,when there is no current? In this case, there is a scheme with the reverse logic of work.
Current Presence Indicator
All the same, only an inverting key is added to one transistor of the same brand. By the way, the transistor of any of the same structure. Domestic counterparts - KT315, KT3102. - Parallel to the resistor with LED, you can turn on the buzzer, and when there is no current when you control, say, a light bulb, a beep sounds. What will be very convenient, and not be given to display the LED is not the control panel. In general, the idea can be a lot, where to use this indicator.

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