{"id":171,"date":"2018-09-18T17:01:02","date_gmt":"2018-09-18T17:01:02","guid":{"rendered":"http:\/\/blogs.plymouth.ac.uk\/embedded-systems\/?page_id=171"},"modified":"2018-09-18T17:03:32","modified_gmt":"2018-09-18T17:03:32","slug":"constant-voltage-source-glossary-item","status":"publish","type":"page","link":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/glossary-2\/constant-voltage-source-glossary-item\/","title":{"rendered":"Constant Voltage Source (Glossary Item)"},"content":{"rendered":"

A theoretical concept used for modeling real electronic circuits. The voltage across a constant voltage source (CVS) is fixed, irrespective of how much current I is drawn from it. It is the perfect power supply. It makes no sense to short-circuit a CVS as this would create a paradox.<\/p>\n

\"\"<\/p>\n

Real voltage sources are modeled in conjunction with other components. For example, in the figure below we model a real voltage source with a resistor and a CVS:<\/p>\n

\"\"<\/p>\n

R is known as \u201cinternal resistance\u201d – this might represent the resistance of internal wiring of a power supply or chemistry of a battery. You cannot access or change this as it\u2019s a physical characteristic of the power source.<\/i><\/p>\n

Vout<\/sub> is the actual voltage presented to other parts of the circuit. We want this to be as close to V as possible.<\/p>\n

When a current I flows, an internal voltage is dropped across R. Therefore:<\/p>\n

\"V_{out}=V-V_{int}\"<\/p>\n

or<\/p>\n

\"V_{out}=V-I \cdot R\"<\/p>\n

As the current \"I\" increases, so \"V_{out}\" further reduces. Therefore, circuit and power supply designers try to make R as small as possible.<\/p>\n

In the limit:<\/p>\n