Choosing the right type of power supply is critical for any electronics project. The decision between using an isolated vs non-isolated power supply can impact performance, safety, and compliance with regulations. This guide will compare isolated and non-isolated power supplies to help you select the right option for your needs.
Key Differences Between Isolated and Non-Isolated Power Supplies
Isolation is one of the major differentiators between power supply types. Here are the key differences:
What is Isolation?
Isolation refers to the separation of the input and output sides of the power supply through a safety barrier. This barrier blocks electrical noise and prevents dangerous voltage levels on one side from reaching the other side.
Isolated Power Supplies have a transformer that provides isolation between the primary and secondary windings. This creates separate input and output sides.
Non-Isolated Power Supplies lack a transformer, so there is a conductive path between inputs and outputs. Noise and voltage spikes can pass directly through.
| Parameter | Isolated | Non-Isolated |
|---|---|---|
| Isolation Barrier | Yes, transformer-based | No |
| Noise Susceptibility | Lower, inputs isolated from outputs | Higher, no isolation |
| Safety | Safer, separation prevents shock risk | Less safe in many cases |
| Size/Weight | Larger and heavier due to transformer | Smaller size and lower weight |
| Efficiency | Usually 60-90% | Can exceed 90% in some models |
Grounding
Grounding is handled differently between isolated and non-isolated power supplies:
- Isolated - The ground wires on the input and output sides are fully isolated. They must be separately connected to system ground.
- Non-Isolated - Input and output ground wires are common and internally connected. Only one needs to connect to system ground.
Applications and Use Cases
Isolated power supplies are recommended for:
- Medical, industrial, and commercial devices where safety is critical
- Noise sensitive circuits
- Systems involving multiple power domains at different ground potentials
- Motor control, lighting, power distribution
Non-isolated supplies work well for:
- Lower power consumer electronics
- Devices with less stringent safety needs
- Low noise environments
Now that we've compared the key differences, let's take a deeper look at when to choose each type of power supply.
When to Choose an Isolated Power Supply
Safety Critical Applications
Isolation is vital for safety critical devices where human contact is a risk, like:
- Medical equipment - Defibrillators, ECG machines, surgical tools
- Industrial machinery - Motor drives, robotics equipment, programmable logic controllers (PLCs)
- Commercial products - Power tools, office equipment
The isolation barrier helps prevent dangerous shock hazards that could injure or kill users if faulty voltages were to pass to output side contact points. Standards like IEC 60601 require isolation for such applications.
Noise Sensitive Circuits
The input to output isolation of isolated power supplies also provides noise immunity benefits. The transformer blocking high frequency noise and surges from passing between input and output sides.
Devices with precision analog circuitry or complex digital electronics can be sensitive to electrical noise causing disruptions or errors. Examples include:
- Test and measurement equipment
- Automation systems
- Audio and video gear
- Recording studios
This makes isolated power critical for accuracy and performance.
Multiple Power Domains
Larger systems often have sub-circuits operating at different voltages with separate ground references. For example:
- Industrial motor drives - Multiple motors/controls at different ground potentials
- HVAC systems - Complex interconnections between components
- Automotive - Engine systems, transmission, infotainment can all have their own power
The isolation ensures errors or cross-talk does not occur between the domains while blocking noise from propagating.
Long Input-Output Wiring
For devices with long wire runs between the power supply and downstream electronics, isolation helps:
- Minimize interference over distances
- Improve safety for long output wires
- Limit ground loop currents
Examples include office equipment, machinery, instrumentation for remote monitoring.
Summary - When Isolated Supplies Are Advised
To recap, the key usages are:
- Safety critical applications
- Noise sensitive circuits
- Multi-power domain systems
- Long input-output wiring
In these cases, the benefits of the isolation barrier justify the larger size/cost of isolated power supplies.
Choosing a Non-Isolated Power Supply
While isolated power supplies have important advantages, non-isolated types have redeeming benefits that make them a better choice in many applications.
Cost and Size Constraints
A major driver toward using non-isolated power supplies is reducing cost and physical size.
Non-isolated supplies skip the bulky isolation transformer allowing for:
- Lower materials cost
- Smaller components
- Lighter weight
This makes them ideal for consumer electronics and compact devices where cost or small size are critical like:
- Mobile phones
- Laptops
- Small home appliances
- IoT and wearable devices
The following table compares some sample specifications.
| Supply | Isolated | Non-Isolated | % Reduction |
|---|---|---|---|
| Wattage | 100W | 100W | - |
| Size | 8" x 4" x 1.5" | 6" x 3" x 1.25" | 50% |
| Weight | 2 lbs | 1 lb | 50% |
| Cost | $50 | $25 | 50% |
By sacrificing isolation, the non-isolated supply has 50% better size, weight, and cost in this example.
High Efficiency Needs
Another benefit of non-isolated supplies is potentially higher energy efficiency, exceeding over 90% in some switch-mode models.
The isolation transformer in isolated supplies lowers efficiency ratings to 60-90% typically.
Higher efficiency helps reduce power usage and saves energy:
- Critical for battery-powered portable electronics to preserve runtime
- Saves electricity costs for appliances and smart home automation
- Greener for the environment to cut wasted power
This performance advantage makes non-isolated designs well-suited for energy efficient applications.
Low Noise Environments
If the electrical environment an electronic device operates in has minimal noise, the isolation may be an unnecessary feature.
Non-critical applications like home/office electronics can often tolerate more noise without performance issues. These lower noise environments make non-isolated supplies a good match including:
- Networking equipment - Modems, WiFi routers, switches
- Smart home devices - Lighting controls, thermostats
- Desktop computers and accessories
By tailoring the power supply to the noise expectations, non-isolated types can provide the most optimized solution.
Summary - When to Utilize Non-Isolated
To summarize, consider non-isolated power where:
- Cost, size, and weight must be minimized
- High efficiency operation is needed
- Operating noise conditions are favorable
Under these circumstances, non-isolated supplies can be the better choice for your application.
Key Considerations When Selecting a Power Supply
Beyond just the isolated vs non-isolated decision, several other factors matter when specifying a power supply. Keep these in mind for your project:
Power Output
Make sure to choose a power supply matched to your equipment's voltage and wattage needs. This includes:
- Output voltage(s) - 5V, 12V, 15V, 24V etc.
- Current/power rating - Amps, watts
- Dynamic loading - Peak power bursts
- Future expansion - Margin above present load
Undersizing can cause unstable operation or shutdowns. Oversizing adds cost for unused capacity.
Environmental Factors
Consider the operating ambient conditions as well:
- Temperature - Cooling method
- Humidity - Condensation protection
- Atmosphere - Dust/debris ingress
- Vibration - Shock mounting
- Altitude - De-rated power at higher elevations
Verify the supply is rated for your worst case deployments. Extreme situations may dictate enclosed power with fan cooling.
Safety and Compliance
Relevant safety, EMI, and compliance standards should also guide selection:
- Safety - UL, CSA, TUV marks
- Emissions - FCC, CE requirements
- Domain specific - Medical (60601), automotive, railway
Work with vendors to align with applicable regulations. Custom power solutions may be necessary for specialized applications.
Form Factor and Features
Finalize mechanical aspects like:
- Mounting - Desktop, DIN rail, rackmount
- Dimensions and I/O layout
- Controls - Voltage adjust, remote on/off
- Monitoring - Voltage readouts
- Redundancy - Dual inputs, parallel units
These design decisions finalize physical integration and capabilities.
Isolated vs. Non-Isolated Comparison Table
Here is a summary table contrasting key factors between
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