Active Clamp Flyback Driver Supply Replenishment for Voltage Drop
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Solution Overview
Problem
Conventional ACF circuits face a voltage drop problem in the power supply of the driver due to continuous capacitor charge consumption, which is not fully resolved by increasing capacitance or reducing static power consumption.
Innovation Solution
Incorporating a replenishment power transistor in the conversion circuit, coupled to the active clamp flyback circuit and drive circuit, which conducts when a voltage threshold is exceeded, allowing power replenishment to the drive circuit through the active clamp flyback circuit, thereby maintaining stable voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the low-side power transistor QL is in cutoff state for too long time, then the voltage of VB drops and the driver enters under-voltage state, but increasing the capacitance of the bootstrap capacitor or reducing static power consumption can only slow down the voltage drop and cannot completely resolve the problem
Solution Approach 1:
The patent applies preliminary action by proactively replenishing the bootstrap capacitor voltage before it drops to dangerous levels. The detection circuit continuously monitors the voltage of the bootstrap capacitor, and when it detects that the voltage is lower than a threshold voltage, it activates the third power transistor to recharge the bootstrap capacitor through the second power transistor, preventing the driver from entering an under-voltage state before it happens.
Solution Approach 2:
The patent implements feedback by using a detection circuit to continuously monitor the voltage of the bootstrap capacitor and compare it with a threshold voltage. Based on the detection result, the control circuit adjusts the conduction state of the third power transistor to maintain the bootstrap capacitor voltage within the required range, creating a closed-loop control system that automatically responds to voltage changes.
2Reliability
If the capacitance of the bootstrap capacitor is increased, then the voltage drop is slowed down, but the voltage drop problem cannot be completely resolved
Solution Approach 1:
The patent applies self-service by enabling the power supply circuit to automatically recharge the bootstrap capacitor when needed, without requiring external intervention or manual adjustment. The detection circuit monitors the bootstrap capacitor voltage and triggers the recharge process through the control circuit and third power transistor, making the system self-regulating and eliminating the need for oversized capacitors to compensate for voltage drop.
3Reliability
If the static power consumption of the driver is reduced, then the voltage drop is slowed down, but the voltage drop problem cannot be completely resolved
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the conduction state of the third power transistor based on the detected bootstrap capacitor voltage. When the voltage is sufficient, the third power transistor remains off, minimizing power consumption. When the voltage drops below the threshold, the third power transistor turns on to recharge the capacitor, then turns off again, creating an adaptive power management strategy that balances voltage stability with energy efficiency.
Data Source
AI summary
A conversion circuit and an adapter that resolve a voltage drop problem of a power supply of a driver in an ACF circuit. The conversion circuit includes an active clamp flyback circuit, a drive circuit, and a replenishment power transistor. The active clamp flyback circuit is configured to perform power conversion. The drive circuit is configured to output a drive signal and a reference voltage. The drive signal is used to drive the active clamp flyback circuit. A first terminal of the replenishment power transistor is coupled to an input terminal of the active clamp flyback circuit, a second terminal of the replenishment power transistor is coupled to a power supply terminal of the drive circuit, and a gate of the replenishment power transistor is configured to receive the reference voltage.