Power Supply Voltage

Definition of Power Supply Voltage

The power supply voltage is the voltage supplying a circuit with power. It is created by the power supplier. The power supplier can be either a public grid or a voltage source such as a battery or a switching power supply. In a serial circuit with multiple consumers in a circuit, the input voltage is evenly distributed to each consumer by their individual resistances. The cables that connect the individual consumers with the voltage source also have a resistance which causes a voltage drop. Due to the voltage drop in the cable, the input voltage for each individual consumer is lower than the power supply voltage which is delivered by the voltage source.

The power supply voltage that is supplied by a voltage source may not be fitting for the application. If instead of an alternating current a dc voltage is required, the power supply voltage is fluctuating, too high or too low. A voltage regulator may be used to convert the original power supply voltage into the power supply voltage required by the application. Voltage regulators for power supply voltage are available in a number of different variations. Depending on the design they offer a fixed or an adjustable voltage.

DC/DC-Converters supply the required Power Supply Voltage

If the power supply voltage is either too high or too low a DC/DC converter can be used to convert the input voltage into an output voltage required by the consumer.

What is VCC?

In electric documents such as product data sheets and wiring diagrams abbreviations are used for the power supply voltage. A capital V is commonly used for voltage. Indexes are used for distinction. Some examples are: B, C, D, E and the double indexes BB, CC, DD and EE. The use of such indexes has been established in the common language used in electrical engineering. The indexes are derived from the English terms of the connections on a transistor. On a bipolar transistor B equals base, E equals emitter and c equals collector. Additionally the abbreviations g (gate), s (source) and d (drain) are used for field effect transistors. Nowadays the indexes are no longer used simply for labelling the connections of transistors. Double indexes are commonly used to label the power supply voltage against the ground.

VCC is generally understood as positive power supply voltage. Extensive discussions in expert forums recommend an exact determination of the meaning of the term by means of technical documents such as product data sheets, manuals and technical documents provided by the manufacturer to avoid misunderstandings, malfunctions or damage.

What is VDD?

VDD is a common index for a positive power supply voltage. The index d is derived from the connection d for drain in FET-technology. A diligent check of available documents is required to avoid misunderstandings, malfunctions or damage.

What does negative voltage mean?

The negative voltage can be explained by the voltage potential. If the voltage is negative, the voltage potential is below the ground (GND). Negative voltage can be created by using a transformer with an additional coil or a charge pump. The charge pump is made out of a capacitor and a switch. The advantage of a transformer is the galvanic insulation. Charge pumps have an advantage in lower cost but can only supply a limited output power.

There are applications that require a negative voltage. One of these applications is measuring of signals up to 0 V. To select the source for negative voltage low noise, operation free of failure and power demand have to be taken into account.

Down converters, up converters and inverting converters (Buck-Boost Converter) are additional circuits in power electricity to create a negative voltage. They combine inductivity, the charger of capacitor and switch. If a galvanic insulation, is required a flyback converter may be used.