The input impedance and output impedance are used in many places and are very important. First of all, the input impedance and the output impedance are relative. We must first understand the meaning of the impedance. Impedance, in short, is an impediment, an equivalent resistance in a broad sense. Impedance is the resistance of the circuit or device to the current, and the output impedance is the impedance measured at the outlet. The smaller the impedance, the higher the ability to drive a larger load. Introducing the two words input impedance and output impedance, the biggest goal is to improve the efficiency in the design of the circuit, that is to achieve impedance matching to achieve the best results.
Output impedance The internal impedance of an equivalent voltage source (Thevenin equivalent circuit) or equivalent current source (Norton equivalent circuit) with independent power network output ports. Its value is equal to the input impedance seen from the output port when the independent power supply is set to zero.
The input impedance is the equivalent impedance of the input of a circuit. A voltage source U is added to the input terminal to measure the current I of the input terminal. The input impedance Rin is U/I. You can think of the input as a resistor. The resistance of this resistor is the input impedance.
With the two words input and output impedance, it is also convenient to design the two circuits separately. When the input impedance of circuit A is the same as the output impedance of circuit B (or within a certain range), the two circuits can be combined directly into a more complex circuit (or system) without any changes.
From the above can also be drawn: the input impedance and output impedance is actually the equivalent resistance, the same unit and resistance.
Difference between input impedance and output impedanceThe input impedance is the equivalent impedance of the input of a circuit. A voltage source U is added to the input terminal to measure the current I of the input terminal. The input impedance Rin is U/I. You can think of the input as a resistor. The resistance of this resistor is the input impedance.
In the case of the same input voltage, if the input impedance is low, large currents will flow, which will test the current output capability of the previous stage. If the input impedance is high, then only a small current is needed. This reduces the burden on the output power of the front stage. Therefore, try to increase the input impedance in the circuit design.
The input impedance is no different from an ordinary reactance element. It reflects the size of the current blocking effect. For a voltage-driven circuit, the greater the input impedance, the lighter the load on the voltage source, and thus the easier it is to drive without affecting the signal source. For a current-driven circuit, the smaller the input impedance is, the lower the input impedance is. The lighter the load on the current source. Therefore, we can think that if it is driven by a voltage source, the greater the input impedance, the better; if it is driven by a current source, the smaller the impedance, the better (Note: only suitable for low-frequency circuits, at high frequencies In the circuit, consider the impedance matching problem.) In addition, if you want to obtain the maximum output power, consider the impedance matching problem.
Voltage source driven circuit
The so-called voltage source driving can be understood as a constant voltage battery which has no internal resistance and is always full of energy as an energy source to supply power to the load.
A voltage source U, similar to the energy source, is added to both ends of the load, resulting in a current I, and then the impedance Rin of the load is U/I. The power consumption on the load P = UI = U / Rin, the formula shows that here Rin always play a role in reducing the current I, Rin larger, the smaller the energy consumed by the load; where the load impedance is the input of the load impedance.
Current source driven circuitContrary to the circuit driven by the voltage source, the current source drive can be understood as a constant current energy source I to supply the load.
Known from Ohm's law, the generated voltage is U=I*Rin, and the power consumed by the load is P=U*I=I*I*Rin. It can be known from the formula that the input impedance Rin of the load serves to increase the power. The circuit driven by the current source, the greater the resistance, the higher the voltage across the load, the greater the power consumed.
Output impedanceOutput impedance The internal impedance of an equivalent voltage source (Thevenin equivalent circuit) or equivalent current source (Norton equivalent circuit) with independent power network output ports. Its value is equal to the input impedance seen from the output port when the independent power supply is set to zero.
No matter the signal source or the amplifier or the power supply, there is a problem of output impedance. The output impedance is the internal resistance of a signal source. Originally, for an ideal voltage source (including power supplies), the internal resistance should be zero, or the impedance of an ideal current source should be infinite. The output impedance needs the most attention in the circuit design.
In reality, the voltage source can't do this, and an ideal voltage source is often connected in series with a resistor r to be equivalent to an actual voltage source. The resistor r in series with the ideal voltage source is the internal resistance of the source/amplifier output/supply. When this voltage source is supplying power to the load, current I flows from this load and a voltage drop of 1×r is generated across this resistor. This will cause the output voltage of the power supply to drop, thus limiting the maximum output power. Similarly, for an ideal current source, the output impedance should be infinite, but the actual circuit is impossible.
The output impedance refers to the equivalent impedance of the circuit when the circuit load is reversed from the circuit output port to the circuit. It is mainly for the energy source or the output circuit. It is the impedance measured at the output end of the energy source. Resistance.
Voltage source driven circuitWhen a voltage source is applied to a load, in addition to consuming energy at the load side, energy consumption is also generated by itself. This is because when the voltage source is outputting energy, there is an impedance that hinders the energy output, such as the internal resistance of the battery. For example, constant voltage source U, output impedance Rout, load terminal voltage Ur, load R, current I=U/(Rout+R), load terminal voltage Ur=I*R=U*R/(Rout+R) The power generated by the load is P=Ur*I=U2*R/(Rout+R)2. This formula shows that the smaller the output impedance, the greater the ability to drive the load.
Current source driven circuit
For a current source driven circuit, there is also an output impedance, and the output impedance is connected in parallel across the constant current source.
The current source outputs a constant current I, a part of In consumes the internal resistance Rout, and the remaining current Ir is consumed on the load R. It can be seen that the voltage on the load R is Ur=Ir*R, and the voltage across the internal resistance Rout is the same. That is, Ur=Ir*R=In*Rout, and because I=Ir+In deduces that Ur=I*Rout*R/(Rout+R), the load power:
P=Ur*Ir=Ur2/Rout=I2*Rout*R2/( Rout+R)2= I2*R2/( Rout+R2/Rout+2R)
It can be seen that when Rout=R, the external load P is the maximum. Therefore, for the constant current source load, in order to obtain the maximum power, it is necessary to match the resistance value of the load with the internal resistance of the current source, ie, to approach the same value as much as possible.
48V25Ah Lithium Ion Battery,48V25Ah Lifepo4 Battery,48V Lithium Battery For Electric Scooter,48V25Ah Lithium Battery Pack
Jiangsu Zhitai New Energy Technology Co.,Ltd , https://www.zhitainewenergy.com