QSPICE is a free circuit simulation tool from Qorvo that helps engineers test designs fast. If you want to know how to create a choke in QSPICE, you are in the right place. A choke is an inductor that blocks high-frequency noise while letting DC or low-frequency signals pass. It is common in power supplies, filters, and noise suppression circuits. In the first paragraph, we will cover the basics of how to create a choke in QSPICE using simple components.

Engineers and students use QSPICE to model real-world parts like chokes. This guide shows easy steps for beginners and pros alike.
What Is a Choke and Why Model It in QSPICE?
A choke is a coil of wire that stores energy in a magnetic field. It acts as a filter in electronic circuits. There are two main types:
- Single-winding choke: Used in DC power lines to smooth current.
- Common mode choke: Has two windings to block noise that flows in the same direction on both lines.
Modeling a choke helps you see how it works before building the circuit. QSPICE supports inductor modeling in SPICE styles, including coupled ones for better accuracy.
Common mode choke in QSPICE is popular for EMC designs. You can add effects like winding resistance or leakage.
Basic Way: Creating a Simple Single-Winding Choke
The easiest way to start how to create a choke in QSPICE is with a basic inductor.

- Open QSPICE and start a new schematic.
- Press ‘L’ or go to the component menu and pick Inductor.
- Place it in your circuit.
- Right-click the inductor and set its value, like 10mH for 10 millihenry.
- Add series resistance if needed: Right-click > enter Rser=0.5 for 0.5 ohms winding resistance.
This models a simple choke for power supply ripple reduction.
For better results, add parallel resistance (Rpar) for core losses.
Tip: Use realistic values from datasheets. Many chokes range from 1µH to 100mH.
Advanced: Modeling a Common Mode Choke in QSPICE
A common mode choke in QSPICE needs two coupled inductors. This is key for noise filters.
QSPICE uses the standard SPICE coupling statement, just like LTspice.
Step-by-Step Guide to Coupled Inductors
Follow these steps to build a coupled inductor SPICE model:
- Place two inductors (L1 and L2) in your schematic.
- Connect them as 1:1 windings: One for each line (like live and neutral).
- Set both to the common mode inductance value, e.g., L1 = 10mH, L2 = 10mH.
- Add a SPICE directive for coupling: Click the .op button or press ‘T’ for text.
- Type: K1 L1 L2 0.95
- K1 is the name.
- L1 and L2 are your inductor names.
- 0.95 is the coupling factor (close to 1 for good chokes, like 0.9 to 0.99).
The coupling factor controls leakage. Lower K means more leakage, which lets some differential signal pass.
Adding Real Effects
Make your model better:
- Winding resistance: Add Rser=0.1 to each inductor for DC resistance.
- Leakage inductance: Use K < 1 (e.g., 0.95).
- Parasitic capacitance: Add small capacitors across windings if needed for high-frequency simulation.
Here is a sample netlist snippet:
text
L1 in1 out1 10mH Rser=0.1
L2 in2 out2 10mH Rser=0.1
K1 L1 L2 0.95
This creates a realistic common mode choke in QSPICE.
Using the Built-in Transformer Component
QSPICE has a Transformer symbol for ideal cases.
- Go to Symbols & IP > Behavioral > Analog > Transformer.
- Place it and set TURNS=1 1 for 1:1 (common mode).
- It assumes perfect coupling (K=1).
This is quick for ideal simulations but lacks leakage. Use coupled inductors for real chokes.
QSPICE simulation tutorial tip: Always ground both sides properly for AC analysis.
Best Practices for QSPICE Choke Modeling
- Start with datasheet values for inductance and current rating.
- Run .tran for time-domain and .ac for frequency response.
- Check impedance plot to match real choke behavior.
- For power electronics simulation, add saturation if needed (advanced behavioral sources).
Coupled inductor SPICE model helps in filter design SPICE.
Bold related terms like SPICE transformer simulation show how chokes relate to transformers.
Common Mistakes to Avoid
- Forgetting the K statement: Inductors stay independent.
- Using K=1 without leakage: Too ideal for common mode.
- Ignoring resistance: Overestimates Q factor.
Examples in Action
Imagine a power supply filter:
- Add your choke before a capacitor.
- Simulate noise injection.
- See how common mode noise drops.
Students can use this for homework on noise suppression in circuits.
Hobbyists try it for DIY audio filters.
Frequently Asked Questions
What is the difference between a simple inductor and a choke in QSPICE?
A simple inductor blocks AC while passing DC. A choke is designed for noise suppression, often modeled as a single inductor for basic use or coupled inductors for common mode types1.
How do I add coupling for a common mode choke in QSPICE?
Place two inductors, set equal values (e.g., 10mH each). Add a SPICE directive: K1 L1 L2 0.99. Use a coupling factor close to 1 (like 0.95-0.99) for realistic leakage.
Can I use the built-in transformer symbol for chokes in QSPICE?
Yes, for ideal 1:1 common mode chokes. Find it under Symbols & IP > Behavioral > Analog > Transformer. Set turns ratio to 1:1, but it assumes perfect coupling (no leakage).
Why add series resistance when modeling a choke?
Real chokes have winding resistance (DCR). Right-click the inductor, add Rser (e.g., 0.1 ohm). This models DC losses and makes simulations more accurate.
Conclusion
You now know how to create a choke in QSPICE from simple inductors to advanced common mode models. Start with basic L, then add coupling for real results2. This skill helps in power electronics simulation and EMC design. Practice with different values to see effects.
What kind of choke are you modeling in your next project? Share in comments!
References
- “How can I model this common mode choke in LTspice?” – Stack Exchange. Detailed coupled inductor examples with K statements (applies directly to QSPICE). https://electronics.stackexchange.com/questions/330500/how-can-i-model-this-common-mode-choke-in-circuit-in-ltspice ↩︎
- “QSPICE: The Transformer (Part 15)” – Power Electronics News. Explains built-in transformer for ideal coupling. https://www.powerelectronicsnews.com/qspice-the-transformer-part-15/ ↩︎























