# Current source and figure

So, is Q1 in cutoff, the triode region, or the saturation region? This is called current division. However, when the current source reaches its compliance voltage, it abruptly stops Current source and figure a current source.

But the basic circuit is a good place to start, because the two-transistor current mirror remains the conceptual core of the higher-performance topologies. Source symbols An ideal current source generates a current that is independent of the voltage changes across it.

This will ensure that the current travels from source to load. Active current sources without negative feedback[ edit ] In these circuits the output current is not monitored and controlled by means of negative feedback. Adjusting and Steering This handy current-source circuit becomes even better when you realize how flexible it is.

The internal resistance of an ideal current source is infinite. For example, no physical current source can operate when applied to an open circuit.

The load resistor re-attaches between the two open points of the equivalent circuit. This can be calculated using current division.

The transistor, Q1, adjusts the output collector current so as to keep the voltage drop across the constant emitter resistor, R2, almost equal to the relatively constant voltage drop across the Zener diode, DZ1. Nowadays, though, manufacturers use on-chip resistors that have been trimmed in order to achieve adequate precision.

October Learn how and when to remove this template message They are implemented as a voltage follower with series negative feedback driven by a constant input voltage source i.

Since the internal resistance of the current source is infinite, any changes in resistance value of the load have no effect on changing the steady current value.

It is given by the ratio of the voltage drop across the resistor the difference between the exciting voltage and the voltage across the load to its resistance. An independent current source with zero current is identical to an ideal open circuit. These circuits behave as dynamic resistors changing their present resistance to compensate current variations.

The external load of this current source is connected somewhere in the path of the current supplying the current sensing resistor but out of the feedback loop. This is why we construct the ideal current source to have infinite internal resistance.

This predetermined current needs to be stable and independent of the voltage across the current-source component.

The external floating load of this current source is connected to the collector so that almost the same current flows through it and the emitter resistor they can be thought of as connected in series. The op-amp voltage-to-current converter in Figure 3, a transimpedance amplifier and an op-amp inverting amplifier are typical implementations of this idea.

Single cell Figure 2: A Zener diodewhen reverse biased as shown in the circuit has Current source and figure constant voltage drop across it irrespective of the current flowing through it.

The total current through the short between the load connection points is the sum of these two currents: This means that the bias current is always exactly equal to the reference current.

The input voltage source and the resistor R constitute an imperfect current source passing current, IR through the load Fig. Transistors functioning as linear amplifiers need to be biased such that they are operating in a desirable portion of their transfer characteristic.

To calculate the Norton resistance RNortonwe do the exact same thing as we did for calculating Thevenin resistance RThevenin: When connected to a load resistancethe voltage across the source approaches infinity as the load resistance approaches infinity an open circuit.

Remember that a current source is a component whose job is to provide a constant amount of current, outputting as much or as little voltage necessary to maintain that constant current. The floating load is a serious disadvantage of this circuit solution.

We can customize this reference current by choosing an appropriate value for RSET. This figure of 14 amps becomes the Norton source current INorton in our equivalent circuit: Again, apologies for the confusion.

As with the Thevenin equivalent circuit, the only useful information from this analysis is the voltage and current values for R2; the rest of the information is irrelevant to the original circuit.•Norton’s Theorem is a way to reduce a network to an equivalent circuit composed of a single current source, parallel resistance, and parallel load.

•Steps to follow for Norton’s Theorem: •(1) Find the Norton source current by removing the load resistor from the original circuit and calculating current through a short (wire) jumping. A current source that depends on a current input is generally referred too as a Current Controlled Current Source or CCCS.

Generally, an ideal current dependent source, either voltage or current controlled is designated by a diamond-shaped symbol where an arrow indicates the direction of the current, i as shown.

Given a current source as the input, the input section of the current mirror looks like a virtual short circuit and reflects (swaps the direction of flow) this current to produce a current sink (the current exiting the mirror); as a result, we obtain a current sink (figure.

Example: Determine the power supplied by each of the sources, independent and dependent, in this circuit: Solution: We’ll begin by choosing the bottom node to be the reference node.

Next we’ll label the other nodes and some element voltages: Notice that the 8 Ω resistor, the 10 Ω resistor and the two independent current sources are all.

Constant-current sources figure prominently in circuit-analysis exercises and network theorems, then they seem to more or less disappear unless you’re an IC designer.

Though rarely encountered in typical PCB design, current sources are ubiquitous in the world of analog ICs. The two resistors R1 and R2 in Figure are connected in series to a voltage source∆V.

By current conservation, the same current I is flowing through each resistor. Figure (a) Resistors in series.

Current source and figure
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