Im planning to use a step up buck converter but i want to have a variable current where the ammount of current is limited to the amount of current needed like a pc power supply

 

Have you chosen a circuit as a starting point?

 

For a regulated voltage type of power supply the delivered current will depend on the load, up to the current capability limit of the power supply. That is how it works for an adjustable regulated voltage power supply.
For a non-regulated adjustable voltage supply it works in a similar manner except that the effective internal resistance of the supply tends to reduce the output voltage in proportion to the current drawn by the load.
Generally the process for selecting a power supply starts with determining the voltage and current it will be required to supply, as well as tghe external source of power.

 

Im planning to use a step up buck converter but i want to have a variable current where the ammount of current is limited to the amount of current needed like a pc power supply

A buck converter is a step down converter and a boost converter is a step up converter. Hold that thought.

The following from the Wiki:

A buck converter or step-down converter is a DC-to-DC converter which steps down voltage (while stepping up current) from its input (supply) to its output ...

A boost converter (step-up converter) is a DC-to-DC power converter that steps up voltage (while stepping down current) from its input (supply) to its output (load). It is a class of switched-mode power supply (SMPS) containing at least two semiconductors (a diode and a transistor) and at least one energy storage element: a capacitor, inductor, or the two in combination. To reduce voltage ripple, filters made of capacitors (sometimes in combination with inductors) are normally added to such a converter's output (load-side filter) and input (supply-side filter).

Note what happens with the current in a buck or boost converter. There is no free ride so to speak.

In either case the load will only draw the current it requires as long as the source can supply it. Just as an example I have a LM2596 DC-DC Buck Converter laying here.

• The input voltage: DC 3 -40 V (Input voltage must be 1.5 V higher than the output voltage, no boost.)
• The output voltage: DC 1.5 - 35 V adjustable.
• The output current: It is recommended to use under 2A, maximum 3A(Additional heatsink is required).

If I apply a load of 1.0 Amp the load will draw 1.0 Amp If I apply a 0.5 amp load the same even though the converter can supply 2.0 amps. So as long as your load does not draw current exceeding the supply capability things are fine. Also the terminology.

Ron

 

Im planning to use a step up buck converter

No you're not.
Buck converters step DOWN.
If you want to step UP, you need a boost converter.

 

I was hoping to see what the TS was thinking about where it comes to "step up buck".