Basic mirror constant current source circuit
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Basic mirror constant current source circuit
A mirrored constant current source is a standard component commonly found in power adapter analog integrated circuits. Its controlled current is equal to the input reference current, that is, the input-output current transmission ratio is equal to one. It is characterized by an output current that is "replicated" in proportion to the input current and used to generate bias current and as an active load. There are many places in the scientific experiment and various technical fields that need to stabilize the current. For example, a highly stable electromagnetic field with constant plating current, a constant charging current for charging the battery, a constant starting current for starting the motor or the resistance furnace, etc., should be supplied by a constant current source circuit. Constant current source circuits are also required for the measurement of contact resistance of certain component devices in measurement techniques (eg, testing and grading of bulk resistor values). In electronic circuits, particularly in integrated circuits, there are many applications where a small DC drop is required but the dynamic resistance is large. For example, the current limiting resistor in the Zener voltage regulator circuit, the collector load resistance in the amplifier, the two emitter common resistors in the differential amplifier, and the emitter resistance in the emitter output are all these resistors. Both are replaced by constant current source devices or constant current source circuits. In industrial automation instruments, constant current source circuits are also often used.
The constant current source is a current source whose output current is kept constant, and the ideal constant current source should have the following characteristics:
a does not change due to load (output voltage) changes;
b does not change due to changes in ambient temperature;
The internal resistance of c is infinite (so that its current can flow out to the outside).
A circuit capable of providing a constant current is a constant current source circuit, which is also called a current mirror circuit.
The temperature coefficient of the output current Io is zero, that is, Io does not change with temperature.
Actual constant current source circuits are of course difficult to achieve these ideal values, but they can be approached
If the load resistor B can remain constant at all times, B can be directly connected across the two outputs of the regulated power adapter to obtain a constant current. However, many actual loads that require a constant current source such as transistors, batteries, and coils of electromagnetic fields, and the like. Their equivalent load resistance is constantly changing. Therefore, in this case, you cannot use the above simple method to obtain constant current from the regulated power adapter, but you must create some constant current source devices with or without the help of a regulated power adapter or Constant current source circuit.
The mirrored constant current source is a current controlled current source, and the mirrored constant current source can have multiple output currents. The concerns of the image constant current source are its output resistance, the accuracy of Io versus IR, and its sensitivity to supply voltage and temperature. In traditional voltage mode op amp designs, a mirrored constant current source is used to generate the bias current and act as an active load. In the design of new current mode analog integrated circuits, in addition to generating bias current, mirrored constant current source is widely used to achieve the replication or multiplication of current signals. The mirrored constant current source with complementary polarity can also achieve differential A single-ended current signal transformation. A mirrored constant current source is the basic unit circuit for designing an integrated circuit.