Constant current also can call steady flow, meaning close, need not add distinction commonly. Compare with the notional photograph of constant voltage, the concept of constant current is hard to understand a few, because cause of the constant voltage in daily life sees more, accumulator, dry cell is power source of dc constant voltage, and 220V alternating current, can consider as a kind of communication constant voltage power source, because their output voltage is basic and changeless, it is not to follow what output voltaic size and change considerably.

Above all illustrate: Constant voltaic value is moved to 1A, highest output voltage can amount to the power source of a constant current of 100V, when you open the mains switch of source of this constant current, can you see the volmeter of power source and ammeter show what is numeric? Can say for certain: Output voltage is 100V, output electric current is 0A. Somebody once asked so, are you the constant current source of 100V 1A? How is output 100V 1A? Here still should explain with Ohm's law, theoretic can be calculated so, the output voltage U=IR of power source, the U in type is output voltage, I is output electric current, r is laden resistor.

Divide 5 kinds of circumstances to explain below:

1. If power source is,carry for nothing, r can express with infinity, u=I*∞ , because power source can lose the electricity of 1A, if source current is 1A, so U=1A*∞=∞ , and power source voltage can output 100V only at most, sure power source can output his only 100V of the biggest voltage, because power source cannot output the voltage of infinity, consequently electric current can be very small only very little value, namely voltaic output is 0A, namely I=U/R=100V/∞=0A.

2. If Europe of laden resistor R=200, can output 100V only because of power source again so, because this electric current can be 0.5A only, namely I=U/R=100V/200R=0.5A origin: HTtp://tede.cn

3. If Europe of laden resistor R=100, because power source can output 100V, make electric current can achieve 1A, namely I=U/R=100V/100R=1A, right now as it happens of output electric current reachs the constant current value of power source.

4. If laden resistor continues to reduce, instead 50 Europe, if the basis is formulary I=U/R=100V/50R=2A. But the power source that the key here is us is a constant current value the power source that is 1A, because of this right now output electric current can be forced to restrict only in 1A cannot be 2A, consequently output voltage can be forced to fall only to 50V cannot be 100V. Here still should accord with Ohm's law, namely U=IR=1A*50R=50V

5. If laden resistor turns into 0 Europe (namely short circuit) , because export electricity,can be 1A only so, output voltage can be 0V only, namely U=I*R=1A*0R=0V

From above 5 example can see, if laden resistance is too great, make power source outputs electric current to cannot reach constant current value, so the voltage of outputs voltage to be able to rise power supply automatically the biggest output of constant current source, become only laden resistance is little to certain level, make power source outputs electric current to reach constant current value, power source just is in status of constant current job truly, as laden resistance reduce stage by stage, output voltage also drops by the rule, what export electricity in order to maintain is constant and changeless. This is the concept of constant current.
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