Over-power compensation circuit for switched mode power supplies
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Solution Overview
Problem
Switched mode power supplies experience increased maximum power at high input voltages due to inherent propagation delays in current sense circuits, leading to higher current overshoot beyond desired thresholds, which is not effectively mitigated by existing feedback mechanisms.
Innovation Solution
The implementation of an over-power compensation circuit that includes a peak detector, sample-and-hold circuit, current offset generator, and reset circuit to dynamically adjust the current sense threshold, compensating for the overshoot by injecting an offset voltage to ensure timely shutdown of the power transistor, thereby regulating power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current sense circuit operates to prevent saturation of the primary winding, then transformer saturation is avoided, but propagation delays cause current overshoot above the desired threshold
Solution Approach 1:
The patent applies preliminary action by adjusting the current sense threshold in advance based on the rectified input voltage level. Before the propagation delay causes overshoot, the threshold is pre-adjusted to account for the expected delay, ensuring accurate current limiting despite the time lag in the control circuit.
Solution Approach 2:
The patent changes the parameter of the current sense threshold dynamically based on the rectified input voltage. The threshold is adjusted as a function of the input voltage level, allowing the system to compensate for propagation delays that vary with operating conditions, thereby maintaining measurement precision across different voltage levels.
2Power
If the slope of the current is proportional to the input voltage, then higher input voltage provides more power, but current overshoot is higher at high input voltage than at low input voltage for the same propagation delay
Solution Approach 1:
The patent dynamically changes the current sense threshold parameter based on the rectified input voltage level. By adjusting the threshold as a function of input voltage, the system compensates for the increased overshoot that occurs at higher voltages, maintaining accurate current measurement and control across the full operating voltage range.
3Power
If the maximum power at high input voltage is higher than at low input voltage, then power delivery is improved, but current overshoot causes inaccurate power regulation
Solution Approach 1:
The patent adjusts the current sense threshold parameter dynamically based on the rectified input voltage to maintain accurate power regulation. By changing the threshold in proportion to the input voltage level, the system compensates for overshoot effects and ensures precise power control across varying operating conditions.
Data Source
AI summary
An over-power compensation circuit for use in a switched mode power supply having a current sense circuit for sensing a current flowing through a power transistor of the switched mode power supply. The over-power compensation circuit includes a peak detector, a sample-and-hold circuit, a current offset generator, and an offset resistor. The peak detector has an input for receiving an input voltage derived from the input line, and an output. The sample-and-hold circuit has an input connected to the output of the peak detector, and an output. The current offset generator has an input connected to the output of the sample-and-hold circuit, and an output for providing an offset current. The offset resistor has a first terminal connected to the output of the current offset generator, and a second terminal adapted to be connected to a current conducting electrode of the power transistor.