Totem-Pole PFC Coil Current Detection Using Sense Resistors
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Solution Overview
Problem
Existing power converting devices with totem pole type power factor improving circuits face complexity and increased costs due to the need for current detection and conversion, which complicates control and increases expenses with the use of current transformers.
Innovation Solution
A power converting device configuration that includes a totem pole type power factor improving circuit with a current detection circuit using resistances to generate a signal indicating the current flowing through a coil, allowing the control circuit to control pulse widths for efficient sinusoidal current conversion without the need for expensive current transformers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current transformer is used to detect AC current, then current detection accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the current detection function from the complex current transformer and isolates it into a simple resistance-based voltage detection circuit. By detecting voltage across a series resistance instead of directly measuring current with a transformer, the system achieves adequate detection accuracy without the complexity of current transformers, insulation requirements, and signal conversion circuits.
Solution Approach 2:
The patent replaces the expensive current transformer with a simple, low-cost resistance element that serves the detection function. This resistance-based approach uses inexpensive components that can be easily replaced or adjusted, eliminating the need for costly transformer hardware and associated insulation and signal conditioning circuits.
2Measurement precision
If a current transformer is used to detect AC current, then current detection is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces the expensive current transformer with a simple, low-cost resistance element that serves the detection function. This resistance-based approach uses inexpensive components that can be easily replaced or adjusted, eliminating the need for costly transformer hardware and associated insulation and signal conditioning circuits.
Solution Approach 2:
The patent substitutes the mechanical/electromagnetic current transformer system with an electrical voltage detection system. Instead of using electromagnetic induction to detect current, the system uses Ohm's law (V=IR) to detect current through voltage measurement across a known resistance, simplifying the manufacturing process and reducing costs.
3Ease of operation
If current detection result is converted to signal with reference to GND, then control IC compatibility is improved, but circuit complexity increases
Solution Approach 1:
The patent establishes an equipotential reference system where the detection circuit and control IC share a common ground reference. By designing the resistance-based detection circuit to output voltages referenced to the same GND as the control IC, the system achieves direct compatibility without requiring insulation transformers or complex signal level conversion circuits.
Data Source
AI summary
A power converting device includes a totem pole type power factor improving circuit and a control circuit. The totem pole type power factor improving circuit includes a coil connected to a first terminal of an AC power supply, a first half-wave switch in which a source terminal is connected to the coil via a first current detector, a second half-wave switch in which a drain terminal is connected to the coil via a second current detector, a first diode in which a cathode is connected to a drain terminal of the first half-wave switch and an anode is connected to a second terminal of the AC power supply, a second diode in which an anode is connected to a source terminal of the second half-wave switch and a cathode is connected to the second terminal of the AC power supply, and a smoothing capacitor connected between the cathode of the first diode and the anode of the second diode. The control circuit controls the pulse width to turn on or off the first half-wave switch and the second half-wave switch based on a total value of a result of detecting the DC voltage of the first current detector and a result of detecting the DC voltage of the second current detector.