数控恒流源设计外文翻译[精品].doc

附录 1、CURRENT SOURCE A current source is an electrical or electronic device that delivers or absorbs electric current. the resistance of current source much larger than the load impedance，the fluctuation of load impedance will not change the value of current .Connect resistance in current source circuit is pointless because it will not change load current and load voltage too. In the schematic diagram such resistance should be reduced. it is meaningful when load resistance parallel connection to current source. Current source share current with resistance. Because of resistance and several reasons， an Ideal current source does not exist in real world，but This model is Very valuable to circuit analysis. Actually if current change obvious when voltage change in a current source we are consider it as an ideal current source.Figure 1 shows a schematic for an ideal current source driving a resistor load. Figure 1 1、Ideal current sources In circuit theory, an ideal current source is a circuit element where the current through it is independent of the voltage across it. It is a mathematical model, which real devices can only approach in performance. If the current through an ideal current source can be specified independently of any other variable in a circuit, it is called an independent current source. Conversely, if the current through an ideal current source is determined by some other voltage or current in a circuit, it is called a dependent or controlled current source. Symbols for these sources are shown in Figure 2. Figure 2 An independent current source with zero current is identical to an ideal open circuit. For this reason, the internal resistance of an ideal current source is infinite. The voltage across an ideal current source is completely determined by the circuit it is connected to. When connected to a short circuit, there is zero voltage and thus zero power delivered. When connected to a load resistance, the voltage across the source approaches infi