# current source or current sink?

1. ## consatnt current source and sink

Hi all

I have to use a constant current,but I'm not sure current source or sink is suitable, what should I take care.
Or which one I can use, and why?

Thanks a lot

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chmr

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2. ## simple current sink

hope some expert explan the difference among current source or sink and voltage source or sink

3. ## constant current source sink

Current Sourcing it means the driver directly injects the current to the load. Current Singking merely passes the current to the load or from the load (open collector circuitryies).

Most of the time, a device can sink more current than source the current. It is due to the fact that sourcing current is from inside the chip itself or core itself.

I am open to comments if there is something wrong on my explaination.

4. ## Re: current source or current sink?

The source or the sink is the direction of current flow. In digital logic you source because the +5v is creating current in one direction while the sink of 0v is creating current in the opposite direction. The current of the source in digital logic should be close to zero but for some reason it's a little higher. The idea of source and sink can then be applied to transistors. You can use a constant current source or sink to change the value of the current in a main branch. You can add current to the main branch or you can subtract current from a main branch by adding a transistor that is biased to source a more positive voltage that adds current. Or a sink to ground which subtracts current.

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5. ## current source or current sink?

is there anything called voltage source or sink

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6. ## Re: current source or current sink?

Not really .... there is no such thing as voltage source or sink, ...... but you have

(a) power/Supply/Vdd : thats supplies the required voltage or charge flow to the circuit.

(b) Ground : sort of sink that collects the charge flow.

regards
Ramgopal

7. ## Re: current source or current sink?

When speaking about current Sink or Source, this isn't just a specific voltage level with resporc to another. There is a big thing you leed to know about power supplies and regulators, and IC output pins.

If you take one of the simple power source, a battery. If the battery is 9V, and you put a load across the two poles, then the current flow through the load. The current will go in one direction. One pole could be refferenced as GND, the other as Vcc. However, if you take two batteries, one is the above 9V battery, the other is a 12V battery. You connect the negative poles togetter, let it be the GND refference. Then, if you connect a load between the two positive poles (one pin on 9V battery + pole, the other pin on the 12V battery + pole), then, currect will flow, but will go in the *other* direction, in the 9V battery, than in the first case.

When the 9V battery provide current, which goes out of 9V (using conventional current), the battery is said to *source* current. When the battery is absorbing current, it is said to *sink* current. Source and Sink really only does tell in which direction the conventional current flow.

Now, batteries are ideal power supply. This kind of power supply isn't usually found in electrical circuits. Many power regulators, converters, ... can only flow current in one direction. So, for example, a 7805 5V regulator can only *provide* current. It can only *source* current. If you replace the 9V battery in the above example, with this kind of regulator, no current will flow. Since no current flow through the load, by ohm's law, the voltage at the regulator output will be 12V (in the above example). Note that the regulator doesn't provide 12V, it come from the other voltage source. Such a case can cause problems in circuits, like blowing the regulator or other components.

So, you'll ofted see device specs about current *Sink* and *Source*. If the device tell that it can source (or *drive*) a specific current amount, but nothing is said about sink current, chances are that this device can only source current. It also often occur that a device pin can sink and source different current ammount. For example, open-drain or open-collector outputs, by design, can only sink current. A simple device that can sink and source current, for example, is an operational amplifier.

So, that's pretty much all about *sink* and *source* current specs.

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8. ## current source or current sink?

In a word, Source and Sink really only does tell in which direction the conventional current flow.
I really appreciate your help.

9. ## Re: current source or current sink?

Think it as this way

Current source : provides constant source of positive charge carriers
Current Sink : absorbs the a constant flow of positve charge carriers

10. ## Re: current source or current sink?

Shortly:
Current Source gives a current from up to the down (Vcc to gnd), and sink takes current from up to the down.

11. ## Re: current source or current sink?

Current sinks and sources are only matter of direction of the current otherwise they are the same, and no voltage sinks only sources.

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12. ## Re: current source or current sink?

if u need to save power use current sink if u are using any microcontroller there may be limits on the currents

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