Key Engineering Takeaways
- •A bench power supply provides adjustable, regulated DC voltage (0-30V) and current (0-5A/10A) with real-time digital readouts.
- •In Constant Voltage (CV) mode, the supply keeps voltage fixed while the circuit draws whatever current it requires.
- •In Constant Current (CC) mode, the supply caps the maximum current, automatically dropping voltage if a short occurs to protect silicon chips.
- •Always short the output terminals with voltage set low to preset your maximum safe current limit before connecting a new prototype board.
- •Linear power supplies provide ultra-low electrical ripple for sensitive analog sensors; switching supplies are lighter and more energy efficient.
Prerequisites
- • Ohm's Law and Electrical Power (P = V · I)
Required Hardware / Tools
- • Adjustable DC Bench Power Supply (0-30V, 5A)
- • Banana-to-Alligator Lead Cables
- • Digital Multimeter
- • Test Load / Breadboard
Anatomy of a Variable DC Bench Power Supply
A **DC Bench Power Supply** replaces stacks of disposable batteries on your workbench, providing stable, dial-adjustable DC power for microcontrollers, motor drivers, and sensor prototypes.
### Front Panel Controls:
- **Voltage Knobs (Coarse & Fine)**: Adjusts output potential from 0.00V to 30.00V.
- **Current Knobs (Coarse & Fine)**: Sets the maximum current threshold (0.00A to 5.00A or 10.00A).
- **Output Terminals**:
- **Red (+)**: Positive DC voltage.
- **Black (-)**: Negative DC return.
- **Green (GND / Earth)**: Chassis safety earth ground connected to the wall mains ground plug.
Constant Voltage (CV) vs Constant Current (CC) Mode
Every bench power supply operates in one of two automatic states depending on the load:
### 1. Constant Voltage (CV Mode - Green LED):
The supply maintains the exact voltage you dialed (e.g. +5.00V). As the load resistance changes, current fluctuates naturally according to Ohm's Law (I = V/R), as long as current remains below your preset limit.
### 2. Constant Current (CC Mode - Red LED):
If the load attempts to draw MORE current than your preset limit (for example, if you have a short circuit on your board), the power supply instantly clamps current at your limit and **drops the output voltage toward 0V**.
How to Set Current Limits as an Electronic Fuse
The single most valuable feature of a bench power supply is its ability to act as an **indestructible electronic fuse** that prevents the dreaded "magic smoke" on new circuit prototypes:
### The Safe Current-Limit Calibration Procedure:
1. Turn Voltage knob to a low level (~2V).
2. Turn Current knob all the way down counter-clockwise to 0A.
3. Connect the **Red (+) and Black (-) banana leads directly together** (a deliberate dead short).
4. Slowly turn the Current knob clockwise until the digital ammeter reads your target safety limit (e.g., 100mA for an ESP32 board, or 500mA for a sensor circuit).
5. Disconnect the shorted leads.
6. Dial the voltage to your required operational level (e.g., +5.00V or +12.00V).
If your newly soldered board has an unintended short, the supply will immediately enter **CC mode** and limit current to 100mA, keeping your microcontrollers and ICs 100% safe!
Bench Golden RuleAlways set a tight current limit (100mA - 200mA) before powering on a freshly assembled board for the very first time.
Linear vs Switching Bench Power Supplies
### Linear Power Supplies:
- **Pros**: Ultra-clean DC output with microvolt-level ripple and zero high-frequency switching noise. Ideal for sensitive analog audio, RF wireless transceivers, and precision ADCs.
- **Cons**: Bulky, heavy copper transformers; dissipates excess voltage as heat.
### Switching Mode Power Supplies (SMPS):
- **Pros**: Highly efficient (85-95%), compact, and lightweight.
- **Cons**: Generates high-frequency switching ripple (20kHz - 200kHz) that can couple into high-resolution analog sensor signals.
Frequently Asked Questions
Should I connect the green Earth Ground terminal to the black negative terminal?
In most robotics DC prototyping, leave the black terminal floating (unconnected to green earth). This creates a "floating ground" that prevents ground loops between your bench supply, oscilloscope, and computer USB ground.
Can I charge a LiPo or 18650 battery using a bench power supply?
Yes! A bench power supply set to CC/CV profile is the standard method for charging lithium cells: set voltage to cell cutoff (4.20V) and current to 0.5C (e.g. 1.0A for a 2000mAh battery). The supply charges in CC mode until voltage hits 4.20V, then smoothly transitions to CV mode as current tapers to zero.
Tags:#Power Supply#Lab Equipment#Bench Skills#Constant Current#Voltage Regulation#Current Limiting