Switching Power Supply High-Side FET Control Circuit
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Solution Overview
Problem
Existing switching power supply apparatuses face challenges in efficiently controlling two switching devices in accordance with variations in input voltage while maintaining cost-effectiveness, particularly when a PFC converter or DC-DC converter is used, as the ON period of the high-side FET is fixed, making it difficult to adjust the high-side FET's operation in response to input voltage changes.
Innovation Solution
A switching power supply apparatus with a transformer, a low-side switching device, a resonant capacitor, and a high-side switching device, where a first control circuit controls the low-side switching device and a second control circuit, including capacitors and charging/discharging circuits, adjusts the high-side switching device's operation based on the voltage generated in the drive winding, allowing for zero-voltage switching and complementary switching to prevent arm short circuits and optimize efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a time constant circuit is used to control the high-side FET, then the circuit structure is simple, but the ON period of the high-side FET is fixed and cannot be adjusted according to input voltage variations
Solution Approach 1:
The control circuit uses the voltage generated in the drive winding itself to control the high-side FET switching. The capacitor charges and discharges based on the drive winding voltage, creating a self-regulating system that adjusts the high-side FET ON period according to input voltage variations without requiring external control signals or complex control circuits.
Solution Approach 2:
The circuit changes the operating parameters by using a capacitor whose charge/discharge state varies with the drive winding voltage. As the input voltage changes, the drive winding voltage changes, which directly affects the capacitor voltage and thus the high-side FET gate voltage, dynamically adjusting the switching timing to maintain optimal operation across different input conditions.
2Reliability
If a driver IC is used to control the high-side FET in accordance with low-side FET operations, then efficient FET control is achieved, but cost increases
Solution Approach 1:
The system achieves coordinated control of both FETs by using the drive winding voltage to simultaneously control the high-side FET while the low-side FET is controlled by its own control circuit. The capacitor couples the drive winding voltage to the high-side FET gate, creating complementary switching without requiring a driver IC or complex control logic, thereby reducing cost while maintaining control reliability.
Solution Approach 2:
The capacitor acts as an intermediary element that transfers the drive winding voltage signal to control the high-side FET. This simple passive component enables the high-side FET to switch in complement to the low-side FET without requiring active control devices like driver ICs, achieving reliable coordinated control through a cost-effective intermediary mechanism.
3Adaptability or versatility
If the high-side FET ON period is fixed, then the control circuit is simple, but it is difficult to improve power factor when PFC converter is used
Solution Approach 1:
The control circuit automatically adapts to input voltage variations by using the drive winding voltage to control the high-side FET switching timing. When input voltage changes, the drive winding voltage changes proportionally, which directly adjusts the capacitor charge/discharge timing and thus the high-side FET ON period, enabling the circuit to maintain optimal power factor correction performance across different input conditions without requiring complex voltage sensing or adjustment circuits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enables efficient control of both switching devices with a dead time between operations, allowing the high-side switching device's ON period to adjust with input voltage variations, achieving low-noise, high-efficiency operation and improved power factor while reducing component count and costs.
Implementation Method 1
a transformer including a primary winding, a secondary winding, and a drive winding magnetically coupled to one another
Implementation Method 2
A resonant capacitor, a resonant inductor, and a high-side switching device connected across the primary winding so as to define a closed loop
Data Source
AI summary
In a switching power supply apparatus, a low-side switching device is connected in series with a primary winding. A high-side switching device and the primary winding define a closed loop. A voltage induced in a high-side drive winding is applied to the high-side switching device to turn on the high-side switching device. A transistor, which is turned on/off in accordance with the voltage across a capacitor charged by the voltage induced in the high-side drive winding, is connected to the gate terminal of the high-side switching device. When the capacitor is charged and the transistor is turned on, the high-side switching device is turned off. The capacitor is discharged by the voltage induced in the high-side drive winding, during the ON period of the low-side switching device.