Current divider and Voltage divider

Thread Starter

Avijit Palit

Joined Jul 19, 2017
81
In variable bench power supply, how current adjust and voltage adjust works.
Is it somekind of current divider and voltage divider circuit implementation.
 

BobTPH

Joined Jun 5, 2013
8,813
A voltage divider is typically placed across the output, with one side being a pot for adjustability. The output of that is compared to a fixed reference to determine whether ro raise or lower the output to keep it at the set level.

For example, say a fixed reference of 2V is used, and we want 10V out. You would use a divider with a 4:1 ratio. The output of rhis divider is then 2V when the output is correct at 10V. If it was less than 2V, the power supply would increase the output until they match.

Current is measured by measuring the voltage across a small resistor in series with the output. Bench supplies typically have a cirrent limit function that will stop it from putting out more current than the setting, another pot, indicates.

Bob
 

MrChips

Joined Oct 2, 2009
30,720
In variable bench power supply, how current adjust and voltage adjust works.
Is it somekind of current divider and voltage divider circuit implementation.
In a DC power supply design, the voltage and current controls are not implemented with divider circuits in the traditional sense of voltage dividers.

Think of the VOLTAGE setting and the CURRENT setting as hard limits.
If the output voltage exceeds the set voltage, the voltage is limited using a voltage "fold-back" circuit that actively controls the output voltage.

Similarly, if the output current exceeds the set current, the current is limited using a similar active feed-back control circuit. In order to drop the current to the desired setting the output voltage must be reduced accordingly.

You cannot have both constant current and constant voltage at the same time. The power supply will hit one of the two limits, which ever comes first.
 

Thread Starter

Avijit Palit

Joined Jul 19, 2017
81
In a DC power supply design, the voltage and current controls are not implemented with divider circuits in the traditional sense of voltage dividers.

Think of the VOLTAGE setting the CURRENT setting as hard limits.
If the output voltage exceeds the set voltage, the voltage is limited using a voltage "fold-back" circuit that actively controls the output voltage.

Similarly, if the output current exceeds the set current, the current is limited using a similar active feed-back control circuit. In order to drop the current to the desired setting the output voltage must be reduced accordingly.

You cannot have both constant current and constant voltage at the same time. The power supply will hit one of the two limits, which ever comes first.
Then How this works?? download.jpg
 

dendad

Joined Feb 20, 2016
4,452
To control the output voltage, a sample of the voltage from the output via the voltage setting knob is compared to a fixed known reference voltage, and the comparing circuit generates an control voltage that is fed to the main voltage regulator to turn it on more or less to make the output voltage what is selected by the voltage setting knob.
To limit the current, a similar action takes place. When the current reaches the preset limit set by the current knob, this generates a signal that is used to modify the voltage setting and reduce the output voltage, over riding the voltage setting knob. The current limit setting will have no effect at all on the power supply UNTIL the preset current limit is reached. For a real explanation of actually how a power supply works you will have to read something like that PDFs above. There are a number of different ways to make a power supply so a specific answer is a bit hard.
 

Thread Starter

Avijit Palit

Joined Jul 19, 2017
81
To control the output voltage, a sample of the voltage from the output via the voltage setting knob is compared to a fixed known reference voltage, and the comparing circuit generates an control voltage that is fed to the main voltage regulator to turn it on more or less to make the output voltage what is selected by the voltage setting knob.
To limit the current, a similar action takes place. When the current reaches the preset limit set by the current knob, this generates a signal that is used to modify the voltage setting and reduce the output voltage, over riding the voltage setting knob. The current limit setting will have no effect at all on the power supply UNTIL the preset current limit is reached. For a real explanation of actually how a power supply works you will have to read something like that PDFs above. There are a number of different ways to make a power supply so a specific answer is a bit hard.
Plz give a schematics.
 
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