Several clever current detection circuits

In power supplies and other equipment, current detection or feedback is usually required. Current detection usually uses a series sampling resistor to amplify the voltage on the resistor through an amplifier. If you want to improve the detection accuracy, you often need to use a more expensive instrumentation amplifier. The offset voltage of the op amp is relatively large.

Here are some ingenious and cheap current detection circuits,

1 Triode current detection circuit
 

If you simply use the transistor on and off to detect the current, the transistor should be turned on at about 0.7V. When the current is relatively small, a relatively large resistor needs to be used, and a large feedback voltage is wasted. The method shown in the figure above can be used to reduce The resistance of, the current I can be detected by consuming a very small voltage, and the sensitivity of detection can be adjusted by adjusting the resistance of the triode base machine. This circuit can be used in chargers and other places that need to show whether there is charging current.

3 High-sensitivity current detection circuit
 

This circuit uses two diodes for current sampling. The sensitivity is very high, and the current can achieve a large dynamic range. It is more suitable for high-power or high-voltage applications. The disadvantage is that the voltage needs to be damaged by about 1.4V.

3 TL431 current feedback circuit
 

TL431 is low in price and is widely used in the feedback loop of switching power supply, but its FB voltage is 2.5V. When it is directly used as current feedback, a large sampling resistor is required and voltage is wasted. In the figure, two TL431s are used to achieve current feedback, and a relatively small sampling resistor can be used to achieve precise current feedback. If there is a voltage feedback network, then the voltage feedback circuit of U3 is combined.