# What is supply voltage

## Electrical voltage U

• The electrical voltage is the pressure or the force on free electrons.
• The electrical voltage is the cause of the electrical current.
• The electrical voltage (pressure) is created by the difference in charge between two points or poles.

The electrical voltage at voltage sources or power generators:

Voltage sources always have two poles with different charges. On the one hand, there is the positive pole with a shortage of electrons. On the other hand, the negative pole is with an excess of electrons. The electrical voltage U indicates how much energy is necessary to achieve this difference in the number of electrons. If there is a connection between the poles, a discharge occurs. An electric current flows during this process.

The electrical voltage in electronic circuits:

The concept of voltage is used in various forms in a circuit. In the case of voltage generators (voltage source or mains voltage) in the form of a generator or power supply unit that supplies the voltage Utotal or UBat provide. This voltage is also called the source voltage Uq or primal tension. This voltage is distributed to the consumers in the circuit (series connection). The partial voltages are referred to as voltage drop, but they have nothing to do with garbage or dirt. This means the drop (reduction) of the source voltage at the consumer.

Voltage sources always have two poles with different charges. On the one hand, there is the positive pole with a shortage of electrons. On the other hand, the negative pole is with an excess of electrons. The electrical voltage U indicates how much energy is necessary to achieve this difference in the number of electrons. If there is a connection between the poles, a discharge occurs. An electric current flows during this process.

### Unit of measurement

...
1,000,000 V = 1 MV (megavolt)
100,000 V = 100 kV (kilovolts)
10,000 V = 10 kV (kilovolts)
1,000 V = 1 kV (kilovolts)
100 V (volts)
10 V (volts)
1 V (volt)
0.1 V = 100 mV (millivolts)
0.01 V = 10 mV (millivolts)
0.001 V = 1 mV (millivolt)
0.0001 V = 100 µV (microvolt)
...

The legal basic unit of electrical voltage is 1 volt (V). Normally, the voltage values ​​in electronics are between a few millivolts and several hundred volts. In high-voltage technology, kilovolt (kV) and megavolt (MV) are used.

### Formula symbol

The symbol for electrical voltage is the capital "U". In the English-language literature, the symbol "V" is used for the electrical voltage. Voltage designations such as V are often found in circuit technologyOUT (Output voltage), VBAT (Battery voltage) and others. Both the symbol and the unit are both V.
Deviating from this, there are different spellings in upper and lower case with additional symbols that have a specific meaning. While the capital "U" is generally used as a symbol for DC voltage variables, the small "u" ​​is often used as a symbol for AC voltage variables. A number or letters as an index identify a certain voltage in a circuit.

U: electrical voltage
u: instantaneous value of an alternating voltage
û: peak value of an alternating voltage
V.CC : Operating voltage of a circuit
UTOTAL : Total voltage of a circuit
UR1 : Voltage across resistor R1
...

How the German symbol U came about is unknown. There are, however, many different explanations for this. One explanation says that the German symbol U is derived from the Latin "urgere" (urge, drive, press).

### Types of tension

The abbreviations "AC" and "DC" are often used in connection with the unit V (volt).

• The abbreviation "AC" stands for "alternating current" (English) and means "alternating current" in German.
• The abbreviation "DC" stands for "direct current" (English) and means "direct current" in German.

Why do you mark a voltage with a current? Alternating voltage always indicates that we are dealing with alternating current. Furthermore, current always occurs together with voltage. If there is electricity flowing somewhere, then there is also a voltage.

### Potential and voltage direction

The potential phi of a point is equal to the voltage of this point in relation to the reference point 0 V. The reference point is also referred to as ground. The specification or measurement of a potential always refers to the reference point.
When measuring a positive value, the potential is more positive than the reference point. The sign is plus. When measuring a negative value, the potential is more negative than the reference point. The sign is minus.
The tension has a specific direction of action. In a circuit, this direction is indicated by an arrow. Basically, the voltage arrow points from plus to minus or from a higher voltage value (potential) to a lower voltage value (potential).
In a circuit, the voltage arrow of a voltage source is directed from the plus to the minus pole. The voltage arrow of a voltage drop (partial voltage) at a consumer (e.g. resistor) points in the direction of the technical current direction, because the current always flows from the higher potential to the lower potential.

### Measure the electrical voltage

• The measurement is usually made with a digital multimeter (multimeter).
• The voltmeter is always connected in parallel to the voltage source or to the component.
• In contrast to current, the voltmeter can be connected and disconnected during operation.
• Voltage measurement
• Voltage tester

### Voltage generation

Generation byComponentVoltage range
Pressure or bendingPiezo effect, crystal processingin the mV range
frictionHard rubber dayup to kV
MoveGenerator, dynamoup to 500 V
warmingThermocouplein the mV range
Chemical conversionBattery, accumulatorup to 24 V.
Magnetic fieldsHall generatorin the mV range
lightPhoto element, solar cellmV to V

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