SMPS Soft-Start Circuit Sampling Output Voltage
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Solution Overview
Problem
Existing switched mode power supply (SMPS) systems face challenges in achieving fast start-up times due to high in-rush currents, which can lead to battery voltage drops and erratic operations, especially in multi-mode cellular phone transmitters where traditional soft-start methods result in prolonged start times and additional charging currents.
Innovation Solution
A control circuit and method that samples the output voltage at an appropriate time slot to enable soft-starting of the internal soft-start reference voltage from the sampled output voltage, allowing it to pre-charge or continue charging the output voltage close to the input voltage level, eliminating the need for external reference capacitors and enabling fast transient response without requiring specific control loop arrangements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional soft-start methodology is used to limit in-rush current, then battery voltage stability is improved, but start-up time becomes too long for multi-mode cellular phone transmitters
Solution Approach 1:
The patent applies preliminary action by pre-charging the output capacitor through the body-diode of the power switch before the main power conversion begins. This initial charging action occurs naturally when the output voltage is below the input voltage, reducing the subsequent charging current requirements and enabling faster start-up without compromising battery voltage stability.
Solution Approach 2:
The patent implements dynamics by using a dynamic soft-start reference voltage that adapts based on the relationship between output and input voltages. When output voltage exceeds input voltage (as in boost mode), the soft-start reference is adjusted to account for the pre-charged state, preventing excessive charging currents while maintaining fast start-up performance across different operating modes.
2Loss of energy
If output voltage is pre-charged to reduce in-rush current, then charging current is reduced, but output voltage may be discharged when control circuitry tries to make converter output voltage follow from 0V starting internal reference voltage
Solution Approach 1:
The patent applies feedback by continuously monitoring the output voltage and adjusting the soft-start reference voltage accordingly. When the output voltage is pre-charged above the input voltage level, the feedback mechanism detects this condition and modifies the reference voltage trajectory to prevent the control circuitry from discharging the output capacitor, thereby maintaining output voltage stability throughout the start-up process.
3Productivity
If power switches are arranged to allow output voltage pre-charging, then wake-up phase is optimized, but start time is still too long when soft-start methodology is accomplished in traditional way
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the soft-start reference voltage parameters based on the operating mode and voltage relationships. Instead of using a fixed soft-start profile, the reference voltage parameters are modified to account for pre-charged output conditions, enabling the system to achieve both fast wake-up and efficient power transfer by adapting the charging profile to actual operating conditions.
Data Source
AI summary
There is provided a control circuit including a sampling controller configured to sample an output voltage of a power converter at an appropriate time slot by opening a control loop. A soft-start circuit configured to enable soft-starting of an internal soft-start reference voltage to start from the sampled output voltage and to control the internal soft-start reference voltage to a predetermined target value in order to pre-charge the output voltage close to an input voltage level, or to continue charging the output voltage to a predetermined output voltage value.