Can someone help me with this one.
I have 35V and current from 1mA to 50mA.
Voltage signal is square with 2.5Khz and 35V and should stay the same.
How to manage to maintain signal and voltage to adjust current from 1 to 50mA?
How do you want to change current while maintaining voltage? Do you want a constant current load?
Please provide a circuit diagram.
I want to setup Current over a display connected on arduino. So when I setup 2mA I have all the time 2mA on output with 35V. When I setup 30mA I have all the time 30mA and 35V on output.
You can have 2mA but the voltage depends on the load. Why do you have a 2A power source for 50 mA output?
Where is that signal in your circuit diagram? Do you mean PWM?
In general you need a constant current source, as a low or high side driver, rated for 2W (35V*50mA). Do you want your load to float or connect to Gnd?
You can not control both the current and voltage into a load. You can only control current and specify a maximum/minimum source voltage, or control voltage and specify a maximum/minimum source current.
Also, since PWM is involved, are your current and voltage specs applied to the "on" portion of the PWM wave, or an averaged output?
1 Like
I don't want to control both, voltage will always be 35V. But I want to control current and that is what I will setup on display and it will limit the current. and that will be when load is conected and arduino is ON.
Ok I know voltage will change depends on load that is not a problem ususally falls from 35V to 30V. All what I need to do is to limit current on value which I will set.
I have 2A power set because I get it cheapper than others power supply. and also arduino and some relays will take all together about 500mA.
Can you please explain this? I don't understand what you mean.
"Where is that signal in your circuit diagram? Do you mean PWM?"
To avoid a huge time waste, please tell us the purpose of this circuit.
But you seem not to understand "constant current source" nor PWM. What's your skills at all?
Ok I googled PWM yes pulse with modulation source is 2 transistors like this but I have 35V here is 12V. Constant currenc source I need only to limit current to max what I setup no matter of load. So when I setup 15mA current can be whatever between 0 and 15mA. I dont need constant current source.
electrolysis with, Pulse with modulation where top duty is 85% and bottom duty is 15%
Do you know Ohm's Law? Current = Voltage/Resistance. If you want to increase current you can increase voltage or reduce resistance.
A constant current supply will adjust the voltage as necessary to get the desired current.
Sometimes we say "constant current" when we mean "controlled current" or variable constant current. High power LEDs run from constant current power supplies but a dimmable LED power supply is actually variable controlled current.
A regular power supply is "constant voltage". The voltage is always about the same and the current depends on the load.
If there is no connection to a constant current supply, the voltage goes-up to the maximum available as it "tries" to push current through an infinite resistance.
With a constant current (or controlled current) the current is approximately constant and the voltage depends on the load.
yes I understand that.
Point here is I have this already setup with CMOS and resistors which are controled with switch with 5 positions, which put differend resistors in paralel to another resistor to get desired current limit but i want it with arduino. All is clear how it will be, only the current part not. So I am looking for solution how to limit current in this electrolysis. Voltage as I said drops usually from 35V to 30V and varies between that and is not that important.
A PWM signal can be converted into a variable voltage, depending on the duty cycle. Then you add a constant current source controlled by that voltage. Here "constant" means that it's independent of the load.
Not to us, since you never posted a real schematic.
Current is dependent on both the voltage and load resistance. One cannot control current with a constant voltage without changing the load resistor.
Can you explain what your goal is?
OK, how can we limit current and leave for now voltage, with arduino I do now with resistors?
electrolysis
See #14 and #9.
Ok there are a number of circuits that will limit current to a load. here are two however I cannot attest to them being the "best"
In any case, without exception the current limiting circuits control the current by reducing the voltage.