The core of low-cost current detection circuit

Use tricks to use tricks, today to teach you the clever skills of several current detection circuits. It is necessary to know that current detection or feedback is usually required in equipment such as power supplies. Current detection usually uses a series sampling resistor to amplify the voltage across the resistor through the amplifier. If the detection accuracy is to be improved, a relatively expensive instrumentation amplifier is often used. I think the normal op amp offset voltage is relatively large.

Here are some clever cheap current detection circuits

Transistor current detection circuit

If the transistor is simply turned on and off to detect the current, the transistor should be turned on to about 0.7V. When the current is small, the resistor needs to be used in large series, and a large feedback voltage is wasted. As shown in the above figure, it can be used relatively small. The resistance can be detected by consuming a small voltage, and the sensitivity of the detection can be adjusted by adjusting the resistance of the triode base. This circuit may be used in a charger, there is no need to show where the charging current.

High sensitivity current detection circuit

This circuit uses two diodes for current sampling. The sensitivity is very high. The current can be made in a wide dynamic range. It is suitable for high power or high voltage applications. The disadvantage is that the voltage needs to be lost by about 1.4V.

TL431 current feedback circuit

The TL431 is inexpensive and widely used in the feedback loop of the switching power supply, but its FB voltage is 2.5V. It is a large sampling resistor used for current feedback and wastes voltage. In the figure, the current feedback is realized by two TL431s, and the precise current feedback can be realized with a relatively small sampling resistor. If there is a voltage feedback network, the voltage feedback circuit of U3 is connected.

N-BK7 Half Ball Lens

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