It has been suggested that this article or section be merged with Current source. (Discuss)

A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force. A primary voltage source can supply (or absorb) energy to a circuit while a secondary voltage source dissipates energy from a circuit. An example of a primary source is a common battery while an example of a secondary source is a voltage regulator. In electric circuit theory, a voltage source is the dual of a current source. Wikipedia does not have an article with this exact name. ... It has been suggested that this article or section be merged with Voltage source. ... Electromotive force (emf) is the amount of energy gained per unit charge that passes through a device in the opposite direction to the electric field existing across that device. ... Four double-A (AA) rechargeable cells A Duracell AA alkaline cell In science and technology, a galvanic cell is an electrochemical cell that stores chemical energy and makes it available in an electrical form, and a battery is a string of two or more cells in series. ... A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. ... In electronics, the word dual refers to two devices or circuits that have mathematical descriptions that are identical except that voltages in one correspond to currents in the other, and vice versa. ... It has been suggested that this article or section be merged with Voltage source. ...

An ideal voltage source, V, driving a resistor, R, and creating a current I

Image File history File links Ohms_law_voltage_source. ... Image File history File links Ohms_law_voltage_source. ...

Ideal voltage sources

In circuit theory, an ideal voltage source is a circuit element where the voltage across it is independent of the current through it. It only exists in mathematical models of circuits. If the voltage across an ideal voltage source can be specified independently of any other variable in a circuit, it is called an independent voltage source. Conversely, if the voltage across an ideal voltage source is determined by some other voltage or current in a circuit, it is called a dependent or controlled voltage source.

An independent voltage source with zero voltage is identical to an ideal short circuit. For this reason, the internal resistance of an ideal voltage source is zero. The current through an ideal voltage source is completely determined by the external circuit. When connected to an open circuit, there is zero current and thus zero power. When connected to a load resistance, the current through the source approaches infinity as the load resistance approaches 0 (a short circuit). Thus, an ideal voltage source can supply unlimited power forever and so represents an unlimited source of energy. Connecting an ideal short circuit to an ideal non-zero voltage source is not valid in circuit analysis as the circuit equation is invalid, e.g., 5 = 0. For alternate meanings see Short circuit (disambiguation) A short circuit (sometimes known as simply a short) is a fault whereby electricity moves through a circuit in an unintended path, usually due to a connection forming where none was expected. ... The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, induction and capacitance. ... Open circuit can mean:- In electronics, where there is nothing connected to a load and no current can flow. ... The input impedance or load impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to it. ...

No real voltage source is ideal (no unlimited energy sources exist) and all have a non-zero internal resistance (none can supply unlimited current). However, the internal resistance of a physical voltage source is effectively modeled in circuit analysis by combining a non-zero resistance in series with an ideal voltage source.

Physical voltage sources

Mains electricity

This is probably the most familiar form of AC voltage source known. Generally its output impedance is very low (much less than one ohm).

Cell

The simplest form of practical DC voltage source is the common cell, which is available in numerous voltages and current ratings. More than one cell can be combined in series or parallel or series-parallel to achieve greater voltage/current ratings. Such combinations are known as batteries. Four double-A batteries In science and technology, a battery is a device that stores energy and makes it available in an electrical form. ... Four double-A (AA) rechargeable cells A Duracell AA alkaline cell In science and technology, a galvanic cell is an electrochemical cell that stores chemical energy and makes it available in an electrical form, and a battery is a string of two or more cells in series. ...

Sources using active electronic devices

Many techniques for producing sources of emf in electronic devices/circuits exist. Most of the circuits in their basic form involve placing a resistor in series with the load and then dumping the remaining power which means that the incoming power is as high at no load as at full load. This issue can be mostly resolved by adding an emitter follower to the output. It should be pointed out however that all the sources listed using active devices do not necessarily dissipate less power than their passive brothers under normal load and that all forms of linear regulation waste power. Switching regulators can be used to increase the efficiency of the conversion, but have their own disadvantages, such as noise and cost. In electronics, a common collector circuit, also known as an emitter follower circuit, refers to one type of circuit arrangement in which a bipolar transistor drives a load circuit such as a resistor or the next stage in an electronic amplifier. ... A switched-mode power supply, or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator - an internal control circuit that switches the load current rapidly on and off in order to stabilise the output voltage. ...

LED Voltage source

An LED in series with a resistor can be used to make voltage source with an output voltage of about 1.5 V depending on the current passing through the LED. The load and line regulation is reasonably good and this circuit is akin to the zener diode stabilizer. If even smaller regulated voltages are required, a common silicon diode can be substituted for the LED. In this case voltages of around 0.6 V are produced providing reasonable load and line regulation but poor temperature stability (−2 mV/°C) External links LEd Category: TeX ... The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). ...

Zener voltage source

Constant voltage source using zener diode.

This circuit can be used to provide a source of lower voltage (or EMF) when only a higher voltage is available. Its output impedance is generally much lower than that of the potential divider because of the wasted current passing through the zener diode. The image shows a constant voltage source (CVS) using a zener diode (DZ). This circuit acts as a voltage regulator in that it maintains a constant voltage across the load (R₂) irrespective of its value or variation in V_S. This circuit is usually used when the load current is very small (or R₂ is large) and does not vary. This CVS appears in constant current source circuits. Once the load current (I_R2) is known, resistor R₁ can be calculated as, Image File history File links A simple zener voltage regulator. ... Zener diode schematic symbol A Zener diode is a type of diode that permits current to flow in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger (not equal to, but larger) than the rated breakdown voltage known as Zener knee... In electronics, a linear regulator is a voltage regulator based on a transistor operating in its linear region. That transistor acts like a variable resistor. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... In electricity, current refers to electric current, which is the flow of electric charge. ... Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ...

where, V_Z is the zener voltage and I_Z is the zener current. This circuit wastes power by dissipating V_Z·I_Z watts; to achieve good regulation, I_z must be large relative to I_load. This CVS is used in non-critical applications where some variation in the output voltage is acceptable. A large filter capacitor placed in parallel with DZ (or R₂) can reduce output ripple. When R₂ is replaced with the base-emitter circuit of a transistor, the circuit acts as a voltage source (regulator) for the emitter resistor and as a current source for the collector resistor. See linear regulator and current source for applications of this voltage source. Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top right; through-hole electrolytic at bottom right. ... In electronics, a linear regulator is a voltage regulator based on a transistor operating in its linear region. That transistor acts like a variable resistor. ... It has been suggested that this article or section be merged with Voltage source. ...

V_BE multiplier voltage source

A V_BE multiplier constant voltage source.

A V_BE multiplier voltage source is shown in the image on the left. It works by virtue of the fact that as long as the transistor Q has a high enough current gain (h_FE), the base current is negligible, and the output voltage depends only on the transistor's V_BE and the ratio of the resistors R1 and R2. Analysis of the circuit is as follows: Image File history File links A VBE multiplier constant voltage source. ... Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier. ... Although related to the more mathematical concepts of infinitesimal , the idea of something being negligible is particularly useful in practical disciplines like physics, chemistry, mechanical and electronic engineering, computer programming and in everyday decision-making. ... Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ...

Since base current of the transistor is negligible, therefore I_R1 = I_R2 = I_BB and so, Although related to the more mathematical concepts of infinitesimal , the idea of something being negligible is particularly useful in practical disciplines like physics, chemistry, mechanical and electronic engineering, computer programming and in everyday decision-making. ...

But, ,

So,

and,

From the above equation, it follows that the output voltage of this circuit depends only on V_BE and the ratio of R1 and R2. The circuit is known as a "V_BE multiplier", since the above equation shows that the V_BE is multiplied by (1 + R1/R2). This circuit has a much better performance than the zener voltage source, and provides a constant output voltage that is set by the ratio of R1 and R2, if V_BE is constant. Also, R1 (or R2) can be made variable to compensate for V_BE variations due to device tolerance. A V_BE multiplier is also known as a rubber diode or a rubber zener. [1]

Uses of V_BE multiplier

Because it does not require a ground connection (that is, it is a floating circuit) and gives a predictable and easily adjustable voltage drop, this circuit is frequently used in biasing the class-AB output stages of power amplifiers. R1 (or R2) is varied till the required voltage is achieved. Sometimes R1 and R2 are replaced by a potentiometer for easy adjustment. Since V_BE decreases with increasing temperature (thereby reducing the V_BE multiplier's output voltage) this circuit also acts to compensate for temperature induced changes of V_BE in the output devices. This tends to counteract the effect of reduction in V_BE of the output devices and helps prevent thermal runaway of the output stage. This is called bias temperature compensation in the electronics industry at large, but a "bias servo" in the field of audio amplifiers. There are several meanings of float: an air-filled vessel that floats on water, such as some types of lifeboats buoyancy float (project management) floating currency floating exchange rate floating point, a datatype in computer science free float of company stock insurance (investable policyholder funds) root beer float: ice cream... It has been suggested that Rf power amplifier be merged into this article or section. ... It has been suggested that Linear taper be merged into this article or section. ... In chemical engineering, thermal runaway is a process by which an exothermic reaction goes out of control, often resulting in explosion. ... The term servo can refer to: Servomechanism - usually just shortened to servo, is a device used to effect mechanical motion for a specified distance. ...

Other types of practical (real world) voltage sources

There are other naturally occurring voltage sources in the world. One example is the voltage produced by the contact of two dissimilar metals.

Potential Divider

This is the simplest way of producing a source of lower EMF from a source of higher EMF, and is the basic operating mechanism of the 'potentiometer' (a measuring device for accurately measuring potential differences). However to gain a low output impedance the parallel combination of the two resistors must be low. This means that to achieve a stable output voltage over a variety of loads the power wasted in the potential divider must be significantly greater than the power delivered to the load. Also the potential divider can only produce a stable output voltage if it has a stable input voltage. Sometimes the potential divider is used as a simple, cheap method of providing a source of voltage where the output impedance is not too important (such as voltage references for high input impedance op-amps). It has been suggested that Linear taper be merged into this article or section. ... An operational amplifier or op-amp is an electronic circuit module (normally built as an integrated circuit, but occasionally with discrete transistors or vacuum tubes) which has a non-inverting input (+), an inverting input (-) and one output. ...

Capacitor

A capacitor (especially a large one) can be considered a voltage source and in many ways resembles a cell. High energy density supercapacitors have been developed to act as high energy voltage sources for power backup and other applications sometimes replacing conventional batteries or cells, and share properties with both. Various types of capacitors A capacitor (occasionally referred to using the older term condenser) is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. ...

Comparison between voltage and current sources

Most sources of electrical energy (the mains, a battery, ...) are best modelled as voltage sources. An ideal voltage source provides no energy when it is loaded by an open circuit (i.e. an infinite impedance), but approaches infinite energy and current when the load resistance approaches zero (a short circuit). Such a theoretical device would have a zero ohm output impedance in series with the source. A real-world voltage source has a very low, but non-zero output impedance: often much less than 1 ohm. Conversely, a current source provides a constant current, as long as the load connected to the source terminals has sufficiently low impedance. An ideal current source would provide no energy to a short circuit and approach infinite energy and voltage as the load resistance approaches infinity (an open circuit). An ideal current source has an infinite output impedance in parallel with the source. A real-world current source has a very high, but finite output impedance. In the case of transistor current sources, impedances of a few megohms (at low frequencies) are typical. An ideal current source cannot be connected to an ideal open circuit. Nor an ideal voltage source to an ideal short circuit, since this would be equivalent to declaring that "5 is equal to 0". Since no ideal sources of either variety exist (all real-world examples have finite and non-zero source impedance), any current source can be considered as a voltage source with the same source impedance and vice versa. Voltage sources and current sources are sometimes said to be duals of each other and any non ideal source can be converted from one to the other by applying Norton's or Thevenin's theorems. Mains may mean or refer to, or be a subject of: Mains electricity Electricity transmission Public utility, about mains services, including electricity, natural gas, water, and sewage disposal Mains (Scotland), about the central steading of a townland BMX racing See also: Main Mane Category: ... Four double-A (AA) rechargeable cells A Duracell AA alkaline cell In science and technology, a galvanic cell is an electrochemical cell that stores chemical energy and makes it available in an electrical form, and a battery is a string of two or more cells in series. ... Open circuit can mean:- In electronics, where there is nothing connected to a load and no current can flow. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ... The input impedance or load impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to it. ... For alternate meanings see Short circuit (disambiguation) A short circuit (sometimes known as simply a short) is a fault whereby electricity moves through a circuit in an unintended path, usually due to a connection forming where none was expected. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ... The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, induction and capacitance. ... The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, induction and capacitance. ... The input impedance or load impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to it. ... Open circuit can mean:- In electronics, where there is nothing connected to a load and no current can flow. ... Infinity is a word carrying a number of different meanings in mathematics, philosophy, theology and everyday life. ... The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, induction and capacitance. ... The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, induction and capacitance. ... The ohm is the SI derived unit of electrical resistance (derived from the ampere and the watt). ... The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, induction and capacitance. ... In electronics, the word dual refers to two devices or circuits that have mathematical descriptions that are identical except that voltages in one correspond to currents in the other, and vice versa. ... Nortons theorem for electrical networks states that any collection of voltage sources and resistors with two terminals is electrically equivalent to an ideal current source, I, in parallel with a single resistor, R. For single-frequency AC systems the theorem can also be applied to general impedances, not just... Thevenins theorem for electrical networks states that any combination of voltage sources and resistors with two terminals is electrically equivalent to a single voltage source V and a single series resistor R. For single frequency AC systems the theorem can also be applied to general impedances, not just resistors. ...

Voltage Source		Current Source		Controlled Voltage Source		Controlled Current Source		Battery of cells

Source symbols