Amin1372, I'm sorry but you have asked this question twice before and both times I have answered but you have not given any more information about your requirements. There is no simple answer to the question you ask in the way that you have asked it. It does not give enough information to be able to give a meaningful or useful answer. * Do you want a link to `4 - 20mA current source` on the web? * Do you want a link to a chip that you can buy from a supplier? * Do you want a schematic for a circuit that has a 4 - 20mA current source as an output? * Do you want to stick something that behaves like a 4 - 20mA current source into a simulation schematic so that you can simulate some other circuit driven by such a source? * Do you want a simple schematic symbol for a box labelled `4 - 20mA current source`? **If you want a circuit then:** * What input power supply does it have? * What output voltage compliance does it need? * Does it need to be galvanically isolated? * How fast does it need to be able to respond to an input? * What input signal is fed into it? * What input impedance does it require? **If you want a simulation model then**: * Does it need power supply? * Do you care about output compliance? * How much like a real circuit does it need to behave in a simulation? There are many more questons like that and information that you could supply when asking for help on an open forum such as this. It is considered polite when doing so to demonstrate that you have made some effort to answer the question you are asking before you post to the forum. If you post back when you can frame your question in such a way that it can be answered then it will save everyone a lot of time. Thanks.

@andyfierman I'm sorry.I want to have a circuit that its output is 4-20 mA And manageable. I can give a 4-20 mA current to various loads. I do not know what the circuit should be used.

Need more info. A lot. A Requirements Specification would be a really good idea. :) Is the output continuously variable from 4mA to 20mA or is it switched between two levels? What accuracy do you require? How do you want to control the output current? Is it controlled by a voltage source or another current? What is the range of the input? What is the scaling of the output in terms of the input i.e. for a voltage input it would be in mA/V What is the output compliance (what range of voltages does the output have to work over? For example 20mA into a 1k load reqires and output compliance of at least 20V. That compliance may also determine the supply voltage needed for the circuit.)? Are the loads floating? If not, what voltage are the loads connected to? Are they grounded? Are they connected to a fixed or variable voltage? What frequency response/rise/fall time do you need for the current output? Cost? Environmental requirements? Temperature? Humidity? EMC? Safety? Is it to be used in Medical applications? Explosive atmospheres?

Need more info. A Requirements Specification would be a good idea. Have you searched on the web for ideas and circuits? Does the output have to source or sink current or both? What does the load look like? Is it tied to ground? Is it floating? Do you need a single ended or a differential current output? What voltage does the output have to handle (e.g. 20mA into a 1k load tied to a +5V supply needs to be able to swing up to at least 25V)? What controls the current? What's the output vs input scaling? For example for a voltage input it might be 1mA/V? Is the output continuously variable or does it just switch between 4mA and 20mA? What accuracy? A voltage? A knob? A DAC? What rise/fall times do you need for the output? What supply voltage do you have available? What is used for? Are there any environmental requirements? Temperature? EMC? Safety? Used in an explosive atmosphere? Medical usage?

Oops, Didn't mean to double post. My first post didn't show up when I expected it to so I thought I must have accidentally deleted it. But you get the idea. :)

use varable resistor

`use varable resistor` Sorry Acrix but that is unlikely to be a good solution for a 4mA - 20mA current source. Try it and see what happens to the current in a load as the load resistance or the source voltage varies. :)

Amin1372, In the absence of any further information from you about your requirements, does this do what you want? https://easyeda.com/andyfierman/High_side_4mA_20mA_current_source-Va86G2oXV

@andyfierman yo i need help please

@mohsinkhan135, Please read this: [https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a](https://easyeda.com/forum/topic/How-to-ask-for-help-and-get-an-answer-71b17a40d15442349eaecbfae083e46a)<br> <br> then ask again appropriately thanks.