Constant On-Time Switching Regulator Fixed-Frequency Control
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Solution Overview
Problem
Prior art constant on-time switching regulators fail to operate in fixed-frequency due to inaccuracies in on-time calculation caused by non-ideal conditions such as turn-ON resistances of power switches, leading to incorrect duty ratios and failure in achieving fixed-frequency operation.
Innovation Solution
A constant on-time switching regulator with an on-time calculation circuit that includes a driver gate, low pass filter, and on-time generator, where the driver gate operates between reference voltages and ground, and the low pass filter generates a second reference voltage with a duty ratio matching the power switch gate signal, allowing comparison with a ramp signal to determine the correct on-time, using a current source to charge a capacitor and compare voltages to calculate the on-time accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a prior art Ton calculation circuit is used to calculate on-time based on input and output voltages, then the circuit can operate in fixed-frequency, but the on-time calculation is inaccurate due to non-ideal conditions such as turn-ON resistances of power switches
Solution Approach 1:
The patent replaces the complex voltage-based on-time calculation circuit with a simplified current-based timing circuit. Instead of calculating on-time from voltage ratios affected by non-ideal conditions, the invention uses a current source to charge a capacitor and compares the resulting voltage with a reference voltage, eliminating the need for complex voltage measurement and calculation circuits while achieving accurate fixed-frequency operation
Solution Approach 2:
The patent changes the fundamental parameter used for on-time calculation from voltage-based ratios to current-based charging. By using a current source to charge a capacitor and timing based on the voltage rise rate, the system achieves accuracy independent of power switch turn-ON resistances and other non-ideal conditions that affect voltage-based calculations
2Ease of operation
If the starting point of on-time depends on feedback voltage comparison timing, then the circuit is simple to operate, but the switching regulator does not operate in fixed-frequency
Solution Approach 1:
The patent implements preliminary action by pre-calculating the required on-time duration before the switching cycle begins. The control circuit determines the exact on-time value based on the desired fixed-frequency operation and duty ratio, then uses this predetermined value to control the power switch, ensuring both operational simplicity and frequency stability
3Device complexity
If the duty ratio is calculated based on ideal voltage ratio assuming Vin*D=Vout, then the calculation is simple, but the duty ratio is incorrect due to turn-ON resistances of power switches
Solution Approach 1:
The patent replaces the inaccurate voltage-ratio-based duty ratio calculation with a current-based timing method. By using a current source to charge a capacitor and comparing the voltage rise with a reference, the system determines duty ratio through time-based measurement rather than voltage ratio calculation, eliminating errors from power switch turn-ON resistances while keeping the circuit relatively simple
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
The solution enables the constant on-time switching regulator to operate in fixed-frequency by accurately calculating the on-time, correcting the duty ratio and ensuring stable operation, overcoming the limitations of prior art by accounting for real-world conditions.
Implementation Method 1
a low pass filter receiving the driver gate output signal from the driver gate and generating a second reference voltage
Implementation Method 2
an on-time generator comparing the second reference voltage from the low pass filter with a ramp signal to determine the on-time of the power switch
Implementation Method 3
using a current source to charge a capacitor and compare voltages to calculate the on-time accurately
Data Source
AI summary
The present invention discloses a constant on-time switching regulator, a control method therefor, and an on-time calculation circuit for calculating an on-time period of a constant on-time switching regulator. The on-time calculation circuit calculates on-time according to practical conditions. It includes: a driver gate receiving a gate signal of a power switch in a switching regulator, the driver gate operating between high and low levels of a first reference voltage and ground; a low pass filter receiving an output from the driver gate and generating a second reference voltage, a ratio between the second reference voltage and the first reference voltage being substantially the same as a duty ratio of the gate signal; and an on-time generator comparing the second reference voltage with a ramp signal to determine an on-time of the power switch.