Source: https://mokxi.com/parts/psu Updated: 2026-11-10 Part # Bench power supply 0 to 30 V with a current limit, and CV and CC lamps that say which of the two it is holding. See every part - 2 pins - 3 settings - In 10 projects - In 8 lessons Drawn live by the editor's own code, at the size you see it. At a glance ## The Bench power supply in brief What it is, and every setting the properties panel gives it. A bench power supply has two control loops on one output, one holding the voltage you set and one holding the current you allowed, and its CV and CC lamps say which is winning. Mokxi’s part goes from 0 to 30 volts with a 0 to 3 amp limit, 5 V and half an amp by default, adjustable while the circuit runs. In constant voltage it is a stiff source behind 10 milliohms; past the limit it holds the current and the terminal voltage becomes whatever the load makes of it, so 12 volts into 10 ohms with a 1 amp limit reads 10.0 V, 1.00 A and CC. A 10 microfarad output capacitor means a short empties it before the supply lands in constant current. V- is an ordinary node, so tie it to the circuit’s ground yourself. The common mistakes are reading the knob instead of the display, and leaving the limit at maximum. For simply powering an Arduino or ESP32, the vcc rail symbol is the lighter choice. There is no ripple, no thermal fold-back and no latching overcurrent trip. Family Timers and analog Pins 2 voltage 5 0 to 30 V, 5 V by default. What the voltage knob is set to, which is what the terminals hold while the supply is in constant voltage and not otherwise. limit 0.5 0 to 3 A, 0.5 A by default. The most current the supply will deliver. output true the output button, on by default. Off, the terminals are a bleeder resistor and nothing else, which is not the same as the supply being set to zero. Pins ## 2 pins Named as the editor names them, so a wire lands where you expect it. Pin What it does V+ The positive terminal. V- The return. It is an ordinary node, not an earth: tie it to the circuit's ground yourself. How to use it ## How to use a bench power supply Wire V+ to the top of the circuit and V- to its ground, then set the current limit before you press Run: the most the circuit should draw, not the maximum. The project here sets 12 V and a 1 A limit into ten ohms. Ohm’s law wants 1.2 A, so the supply holds 1.00 A, the CC lamp lights and the output sits at 10 V. Turn the limit up past 1.2 A while it runs and the lamp flips to CV at 12 V. The output button takes the terminals off the circuit, which is not the same as setting the voltage to zero. The load is a 10 W resistor because ten watts is what it has to carry. Part pin Board pin V+ 10 ohm load resistor V- Ground rail To power a board, the vcc rail symbol is the lighter part; the bench supply is for the circuit you are not yet sure about. Click to open it in the editor This is the simulator itself, running here. Click anything to open it in the editor. Open this project in the editor Read the full tutorial How it is modeled ## What is true about the Bench power supply, here In its help article’s own words: what the simulation gets right, and where it stops. ### Modeled Constant voltage is a stiff source behind 10 milliohms; constant current is the same two elements with the resistor turned up to a megohm. A current source with a resistor across it is a voltage source behind that resistor (Norton and Thevenin are the same two numbers written differently), so the mode changes by restamping two values and the matrix stays linear. The part picks the mode from the terminal voltage after each solve, the way the op-amp's rail clamp does: in constant voltage it is delivering (voltage − v) / 0.01, and when that is more than the limit the voltage loop has lost; in constant current the terminal voltage is whatever the load makes of the limit, and when that reaches the setting the load is light enough again. The two tests are not each other's negation, so a load sitting exactly on the knee stays in whichever mode it arrived in instead of chattering between them. Twelve volts set, a 1 A limit and ten ohms across the terminals reads 10.0 V, 1.00 A, CC, because twelve volts across ten ohms would be 1.2 A and it is not allowed. A short reads the limit current and almost no volts. An LED straight across it with no series resistor reads the limit and the LED's own forward drop, which is the other thing a bench supply is for. There is a 10 µF output capacitor across the terminals, because a real supply has one and because it is what stops the crossover being instantaneous: short the output of a supply sitting in CV and the voltage does not jump to zero, the capacitor empties into the short first and the supply arrives in CC a moment later. The supply is an analog source, so the nets it feeds are solved in the matrix. That is the difference between this part and the vcc symbol, which is a digital rail and the lighter thing for powering a board. ### Not modeled No ripple, no noise and no line regulation, because there is nothing upstream of it. No transient response beyond the output capacitor: the control loop itself is instantaneous, so a load step has no overshoot and no recovery time. Nothing gets hot, so there is no thermal fold-back, no over-temperature shutdown and no fan; the supply will sit in constant current for ever. The limit is a limit and not a trip, so it does not latch off the way a lab supply in OCP mode would. The readout is the solver's own answer, with no meter accuracy specification, no calibration and no more resolution than the digits on the face. There is no earth terminal, no remote sense, and no series or parallel tracking with a second supply. The output is not floating: V- is a node like any other. From Bench power supply, in full. Projects ## See the Bench power supply in a project 10 built-in projects use it. Each opens in the editor, already wired. Lessons ## Where it turns up in a lesson 8 lessons place it in their own circuits. ### Learn articles 8 lessons - Series vs Parallel Circuits, Seen With LEDs - Circuit Lab Practice Test: 30 Questions and Answers - How to Use a Multimeter: Practice on a Virtual One - Circuit Lab Division B: Middle School Starter Guide - SkillsUSA Electronics Technology Practice Circuits - TSA Electrical Applications: Practice Circuits - Arduino ACS712 Current Sensor: Wiring and Code - Arduino 0-25 V Voltage Sensor: Wiring and Code Boards ## The boards it is shown on Each of these 2 boards has a built-in project with the Bench power supply in it. - Arduino Uno R3 - Arduino Mega 2560 More parts ## The rest of the bench Every one of these is drawn and simulated the same way. Full-size breadboard A real 0.1 inch grid with the rails and the center channel, 63 columns wide. Jumper wires Drag from any pin or hole to any other. Corners snap, and you can drag them. Power A supply rail at the voltage you choose. Ground The other end of every circuit. LED Lights when current flows. Five colors, and the brightness is what your eye would see. Filament lamp A tungsten bulb in a holder: an inrush when it is switched on cold, tens of milliseconds to warm up, and dim on half its voltage. Resistor Any value you like, with the color bands drawn to match. ESP32-C3-DevKitM-1 A RISC-V board that runs your firmware at 160 MHz on the real memory map. Pushbutton A 12 mm tactile switch. Hold it while the simulation runs. Raspberry Pi Pico The RP2040 board on our own Cortex-M0+ core. Pick a program and press Run. Raspberry Pi Pico W Raspberry Pi Pico W (RP2040). The same board and the same pinout as a Pico, with the CYW43439 on it. The WiFi is simulated (no radio; real internet through the Cloud panel’s switch), and the on-board LED, which hangs off that chip rather than off GP25, is driven through the same path. Everything else is the Pico. Raspberry Pi 4 Model B Raspberry Pi 4 Model B: the 40-pin header, driven by main.py with RPi.GPIO or gpiozero. See every part ## Wire up the Bench power supply Open the editor and push it into the breadboard. It is free, and it runs on your own machine. Start building free Open the editor