Design of constant current source circuit

Design of constant current source circuit

Recently due to job needs and personal interests, want to learn the constant current source of circuit design, and make a reliable constant current source.
Search from the Internet a bit of information, found that not too much, only a few links have reference value, here want to summarize.

First select a few of the original rational circuit reference:
Http://bbs.21ic.com/icview-390818-1-1.html
Constant current circuit has a lot of occasions not only need the situation of zero output impedance constant current source, but also the input impedance is an infinite constant current source, the following are several unipolar constant current circuit:

Type 1:
Features: Use op amp, high accuracy
Output current: Iout=vref/rs

Type 2:
Features: simple and high accuracy with shunt regulator
Output current: Iout=vref/rs
Detection voltage: Different depending on vref (1.25V or 2.5V)

Type 3:
Features: Use of transistors, simple, low-precision
Output current: Iout=vbe/rs
Detection voltage: approx. 0.6V

Type 4:
Features: Reduced temperature variation of VBE of type 3, low, medium accuracy, low voltage detection
Output current: Iout=vref/rs
Ultra-low noise output current using Jeft: determined by Jeft
Detection voltage: Related to Jeft
Where type 1 is the basic circuit, when operating, the input voltage Vref is proportional to the output current of the detection voltage Vs (vs=rsxiout) equal, 5,

Figure 5
Note: is=ib+iout=iout (1+1/HFE) where 1/HFE is the error
If the output stage uses a transistor then the current detection will produce a base current component of the error, when this is not allowed, the same as shown in Figure 6, the FET tube can be used

Figure 6
Is=iout-ig
Type 2, which is an integrated shunt regulator circuit using op amp and Vref (2.5V), since the vref of this circuit is up to 2.5V, the power supply is used in a narrower range
Type 3, which is a transistor instead of op amp Circuit, due to the use of the transistor VBE (approximately 0.6V) to replace the VREF circuit, therefore, the VBE temperature changes in the output without change, resulting in less than the desired accuracy
Type 4, this is the use of the Tube compensation VBE with temperature changes in the circuit, because the detection voltage is also less than 0.1V, should be, the power supply range is wide
Type 5, this is the use of J-FET circuit, change the RGS can make the output current reaches the drain saturation current IDSS, because the noise is also very small, therefore, in the noise becomes a problem when using this circuit also has certain value, in this circuit does not connect the RGS, then the current value becomes IDSS, thus, The J-fet diode form becomes a "constant current diode"
The above circuit is a current absorption circuit, but in addition to type 2, if you change the Vref polarity and the use of semiconductor components, it can be turned into a current-discharge circuit.

Constant current source, AC constant current source, DC constant current source, current generator, large current generator, also known as current source, steady current source, is a wide spectrum, high-precision AC power supply, with fast response, constant current accuracy, long-term stability, suitable for all kinds of load (resistive, perceptual, capacitive) and other advantages. Mainly used for the detection of thermal relays, molded case circuit breakers, small short-circuit breaker and the need to set the rated current, action current, short-circuit protection current and other production situations.
The simplest constant current source is the use of a constant current diode.　In fact, the application of constant current diode is relatively small, except because constant current diode constant current characteristics is not very good, the current specification is relatively small, the price is more expensive is also an important reason. 　　The most common simple constant current source with two transistors, using the transistor's relatively stable be voltage as a benchmark, the current value is: I = vbe/r1. The advantages of this constant current source are simple, and the numerical value of the current can be freely controlled, and no special components are used, which helps to reduce the cost of the product. The disadvantage is that different models of the pipe, its be voltage is not a fixed value, even the same model, there are certain individual differences. At the same time different operating currents, this voltage will also have a certain fluctuation. 　　Therefore, it is not suitable for precise constant current demand. To be able to accurately output current, a op amp is usually used as feedback, and the FET is used to avoid errors caused by the transistor's be current. If the current does not need to be particularly precise, the FET can also be replaced with transistors.

The essence of constant current source is to use the device to feedback the current, dynamically adjust the power supply state of the equipment, so that the current tends to constant. 　　As long as the current can be obtained, feedback can be effectively formed to establish a constant current source. A device capable of conducting current feedback, as well as a current transformer, or using a hall element to provide feedback on the magnetic field of certain devices on the current circuit, or using a light emitting device (such as a optocoupler, a light emitting tube, etc.) on a return path. These methods can form an effective constant current source, and it is more suitable for special occasions such as high current.

The basic constant current source circuit is mainly composed of input stage and output stage, the input stage provides the reference current, and the output stage output needs constant currents. ① constitutes the basic principle of constant current source circuit: constant current source circuit is to be able to provide a stable current to ensure the stability of other circuits. That is, the constant current source circuitry is required to output constant currents, so the device as an output stage should be a volt-ampere characteristic with saturated output current. 　　This can be achieved using a BJT or MOSFET that is operating at an output current saturation. In order to ensure the current stability of the output transistor, it is necessary to meet two conditions: a) Its input voltage to be stable-input stage needs to be constant voltage source; b) output transistor output resistor as large as possible (preferably infinite)-the output stage needs to be constant current source.
② requirements for input-level devices: Because the input stage needs to be a constant voltage source, it is possible to use a device with a voltage saturation volt-ampere characteristic as an input stage. 　　The General PN Junction Diode has this characteristic--exponential rise of the Volt-ampere characteristic, moreover, the enhanced MOSFET's source-drain short-form diode, also has a similar volt-ampere characteristics-parabolic rise of the Volt-ampere characteristics. When diodes are used as input-level devices in an IC, they are generally integrated diodes that are properly connected using transistors, as they can accommodate both IC processes and special advantages. For these transistors, it is required to have a certain amplification performance, which can make its corresponding diode has a good constant voltage performance.
③ Requirements for output-stage devices: If using a BJT, in order to increase its output resistance, it is necessary to try to reduce the evarly effect (the base width modulation effect), that is, to maximize the early voltage. If the MOSFET is used, in order to increase its output resistance, it is necessary to try to reduce its channel length modulation effect and the liner bias effect. For this reason, long-channel MOSFETs are generally chosen instead of short-channel devices

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circuit diagram and analysis of six common constant current sources

Constant current source is a high precision and efficient controllable power supply. The use of special chip, DSP, power module as the core device, combined with intelligent and efficient software algorithm design, mainly used in time-delay, standard, instantaneous, automatic assembly lines and other equipment, integrated with the current generation, motion control, timing, test products and other functions of judging count, with good stability, high precision, high efficiency, Fast and convenient control features
Compared to several v/i circuits, there is no transistor, such as one-way devices, can achieve AC constant current, add the transistor can only do one-way DC constant current. Of course, the output current can be extended with a power amplifier. The IV and fifth are built on the basis of positive and negative feedback equilibrium, the error of the resistor loses its balance, which affects the constant current output characteristics, that is, the output current will vary with the load. The error of the resistor in several other circuits only affects the value of the output current without affecting the output characteristics. If the output current is large, or the collector current and emitter current is not equal to the transistor, the transistor can be replaced with a MOSFET.
In the work of the need to use constant current source circuit, emergency in the circuit diagram to build a, the following is six common constant current source circuit analysis:
These circuits are capable of obtaining constant current output on the load resistor RL
The first due to RL floating, generally rarely used
The second RL is a virtual ground and is not very used
The third, although RL floats, but the RL one end of the positive supply side, more commonly used
The fourth type is positive feedback balance, is due to load RL grounding and people's favorite
The fifth and fourth principles are the same, only to enlarge the output capacity of the current, people often use the resistor R2 more than the load RL, and omit the follower op-amp
The fifth kind is I think of the circuit, is also the ground load
The sixth kind is the v/i conversion circuit which I designed to the ground load;

The back two kinds are constant current source circuit
Compared to several v/i circuits, there is no transistor only one-way device, can achieve AC constant current, add the transistor can only do one-way DC constant current
The four and five are based on the positive and negative feedback balance, if the loss of balance due to the error of the resistance, will affect the constant current output characteristics, that is, the output current will vary with the load
The error of several other resistors only affects the output current value, without affecting the output characteristics
If the output current is large, or the collector current and emitter current of the transistor is not equal, the transistor can be replaced with a MOSFET

2014-8-8 Update
A slightly calculated 1c This connection, il= (1+2r/rsample)/(2R+RL) *vinput, so when the RL is much smaller than R, that is, R1 can be constant current. The Multisim simulation results in good agreement with the calculated result.

There is a lot to study, online information seems to be a lot of links posted here, another day to get:
Http://blog.chinaunix.net/uid-26085866-id-3214411.html

Http://bbs.ednchina.com/BLOG_ARTICLE_3026192.HTM

Http://wenku.baidu.com/link?url= H5visg0fmeu3mzfvxnv6kuslads4bvkyqda0cfykbopp2cbxqo6cr9cdnuicf-mcn1da1x2synvoi3m7_2p4clq_ltialaqut4fko1lrkrw

Http://zhidao.baidu.com/link?url=rQrJ2TySdFhO9sqqjzocctK0ftCMiE10EA0I4msoTGxCT_hH4vZ_eEEJeffjtVycX1Wi0TQTWqF-xdBM38EvUq

Http://bbs.yleee.com.cn/thread-34081-1-1.html

http://diagram.eepw.com.cn/diagram/circuit/cid/18/cirid/74012

http://bbs.dzsc.com/space/viewspacepost.aspx?postid=90403

Http://www.crystalradio.cn/thread-169582-1-1.html

Http://bbs.elecfans.com/jishu_482597_1_1.html
This is mentioned in a constant current source chip can refer to the following: TSM1052

http://www.dianziaihaozhe.com/lilunxuexi/2285/

Http://bbs.ednchina.com/BLOG_ARTICLE_2133022.HTM

Http://wenku.baidu.com/link?url= Gomiryhlscpq63zm08tx6okwpokdvjn3yqcepdpir2wpio1npphnjycusgnea2nuyvdtweo4yjbg6hkf92yzt7tvgh4ujzzhi8mvxv1jbbc

Http://www.amobbs.com/forum.php?mod=viewthread&tid=5500737&highlight= constant Current source

Http://www.amobbs.com/forum.php?mod=viewthread&tid=3780880&highlight= constant Current source

Http://www.amobbs.com/forum.php?mod=viewthread&tid=5635562&highlight= constant Current source

Http://www.amobbs.com/forum.php?mod=viewthread&tid=4682918&highlight= constant Current source

Http://www.amobbs.com/forum.php?mod=viewthread&tid=5004970&highlight= constant Current source
There's a circuit diagram in the comments

Http://www.amobbs.com/forum.php?mod=viewthread&tid=4282110&highlight= constant Current source

Http://www.amobbs.com/forum.php?mod=viewthread&tid=5610315&highlight= constant Current source
This is absolutely dry paste, there is information, and the landlord to do the finished product

Http://www.amobbs.com/forum.php?mod=viewthread&tid=4866287&highlight= constant Current source
The 28 floor here mentions AD620 AD705.

Design of constant current source circuit