Low-Power COT Timing Circuit Using RC Extraction
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Solution Overview
Problem
Existing COT timing circuits face high static power consumption and audible noise due to their dependence on duty ratio, which affects the working frequency and power efficiency.
Innovation Solution
A low-power-consumption COT timing circuit design using an RC circuit with current injection to maintain first-order correlation between timing length and duty ratio, decoupling working frequency from duty ratio and reducing static power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a common adaptive COT module circuit is used to maintain constant working frequency, then the working frequency remains constant, but the EA static power consumption becomes relatively high
Solution Approach 1:
The patent extracts the timing function from the high-power EA circuit and implements it using a passive RC circuit with current injection. The RC circuit performs the timing function without requiring continuous EA operation, thereby eliminating EA static power consumption while maintaining constant working frequency through the relationship tON=K1*R*C+K2*VIN where working frequency fSW=1/tON
2Device complexity
If the working frequency of COT modulation BUCK is inversely proportional to duty ratio, then the timing circuit is simple, but the working frequency changes greatly with duty ratio causing audible noise
Solution Approach 1:
The patent introduces a dynamic current injection mechanism that adapts the charging current to the duty ratio. The injection current is proportional to the duty ratio, which compensates for the duty ratio variation and maintains a substantially constant working frequency. This dynamic adjustment eliminates audible noise while keeping the circuit structure simple
3Use of energy by stationary object
If an RC circuit is used for timing to eliminate static power consumption, then static power consumption is eliminated, but maintaining first-order correlation between timing length and duty ratio requires complex current injection control
Solution Approach 1:
The patent uses the duty ratio signal itself as an intermediary to control the current injection magnitude. By making the injection current proportional to the duty ratio, the circuit automatically adjusts the RC charging rate to maintain first-order correlation between timing length and duty ratio. This approach simplifies control logic while achieving the desired timing characteristic
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 effectively eliminates static power consumption and reduces audible noise by maintaining independence between working frequency and duty ratio, enhancing power efficiency and circuit simplicity.
Implementation Method 1
a Resistor-Capacitor (RC) circuit is adopted for timing, to eliminate static power consumption of a timer
Implementation Method 2
the RC circuits of other stages compensate a capacitor charging and discharging circuit of the RC circuit of the first stage to keep first-order correlation between a capacitor charging current and VIN
Data Source
AI summary
Provided is a low-power-consumption Constant-On-Time (COT) timing circuit design method and a timing circuit. A Resistor-Capacitor (RC) circuit is adopted for timing, to eliminate static power consumption of a timer. A specific structure includes a fourth P-channel Metal Oxide Semiconductor (MOS) transistor M4 of which a source is connected to an input voltage VIN, a gate is connected to a COT control terminal TON_CONTROL and a drain is connected with one end of a fourth resistor R4. The other end of the fourth resistor R4 is connected with one end of a fourth capacitor C4. The other end of the fourth capacitor C4 is grounded. A negative input of a comparator VCMP is connected with a reference voltage, and a positive input is connected between the fourth capacitor C4 and the fourth resistor R4.