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Clever tricks of current detection circuits

Issue Time:2006-06-22
The trick is to use the coup, today power adapter manufacturers come 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 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 relatively small, a large series of resistors are needed, and a large feedback voltage is wasted, which can be used with a relatively small resistor. The current I can be detected with a small voltage, and the sensitivity of the detection can be adjusted by adjusting the base resistance of the triode.

This circuit can be used in places such as chargers that need to display the presence or absence of charging current.

High sensitivity current detection circuit

This circuit uses two diodes for current sampling. The sensitivity is very high. The current can be used 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 has a large number of feedback loops in the switching power supply. However, its FB voltage is 2.5V. It is a large sampling resistor used for current feedback and wastes voltage.

Precise current feedback can be achieved with a small sampling resistor. If there is a voltage feedback network, then the voltage feedback circuit of U3 is connected.

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