kushal nandanwar
Full Member level 3
I am looking for Variable power supply with output range 0 VDC to 24VDC with constant 250mA current. Input Voltage 25VDC
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A common solution to such a requirement is the LM317 variable regulator.
It has built in over-current and over-temperature limiting so it's very rugged.
It's minimum output voltage is 1.2V but that's usually sufficient for most applications.
If the slider of your 10k pot has NO LOAD CURRENT and the 25V supply does not change then the slider will produce 0V to 20.66V. If there is any load current then the voltage will drop because your simple circuit has no voltage regulation.
A voltage regulator circuit usually has an opamp, a voltage reference and some transistors. Look at Voltage Regulator Circuit in Google.
A simple way to achieve voltages below 1.25v with a LM317 is to provide a small negative bias.
This bias requires to supply a few milliamps (for the adjustment current), so it is not very complex circuit.
That is a very nice voltage regulator. But we do not know if the OP wants the current regulated at 250mA or limited at 250mA.
The input voltage has nothing to do with the OUTPUT current. Do you want the output current always to be REGULATED at 250mA or do you want the output current to be LIMITED to no more than 250mA??
Hi,
I´d go for a SEPIC controller.
You may use a pot in the feedback path to adjust output voltage and a resistor to pull up the feedback voltage to the desired level. Better way is to use an OPAMP for (feedback) voltage regualtion.
For a simple fixed current limitation you could use a shunt with about 2.2 Ohm and a BJT with B and E across the shunt. With a load of abut 250mA the bjt switches ON.
(if you use the current limit with the shunt, then the voltage feedback should be connected after the shunt.9
Klaus