Bench Power Supply Simulator With CV and CC Modes

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.

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.

The current limit on the benchlive0.000 s 0.00x

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