Multiphase choppers, also known as multilevel choppers or multistage choppers, are power electronic devices used in high power circuits. They are designed to convert a fixed DC voltage into a variable DC voltage with high efficiency and precise control.

Explanation:

1. **What are Multiphase Choppers?**
- Multiphase choppers consist of multiple power electronic switches connected in series to create a higher voltage rating and power handling capacity.
- These switches are typically semiconductor devices like power transistors or insulated gate bipolar transistors (IGBTs).
- The switches are controlled using pulse width modulation (PWM) techniques to achieve the desired output voltage.

2. **Low Power Circuits**
- Low power circuits generally refer to circuits with power ratings below a few kilowatts.
- In such circuits, single-phase choppers or basic choppers are commonly used.
- Basic choppers are simple and cost-effective, suitable for low power applications like battery charging, motor speed control, etc.
- Multiphase choppers are not typically used in low power circuits because they add complexity and cost without significant benefits.

3. **High Power Circuits**
- High power circuits refer to circuits with power ratings in the range of several kilowatts to megawatts.
- In these high power applications, multiphase choppers offer several advantages over single-phase choppers.
- By distributing the load across multiple phases, multiphase choppers can handle higher power levels without excessive current or voltage stress on individual switches.
- This leads to improved efficiency, reduced losses, and increased reliability.
- Multiphase choppers are commonly used in high power applications like electric vehicle motor drives, renewable energy systems, industrial motor drives, etc.

4. **Medium Power Circuits**
- Medium power circuits generally refer to circuits with power ratings between low power and high power ranges.
- In medium power applications, the choice between single-phase and multiphase choppers depends on the specific requirements and cost considerations.
- If the power level is closer to low power, single-phase choppers may still be sufficient.
- However, if the power level is closer to high power, or if there is a need for better performance and reliability, multiphase choppers may be preferred.

In conclusion, multiphase choppers are primarily used in high power circuits where their advantages in terms of power handling capacity, efficiency, and reliability outweigh the added complexity and cost. They are not commonly used in low power circuits, while their usage in medium power circuits depends on the specific requirements and cost considerations.