Switching Power Supply Controller Startup Circuit
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Solution Overview
Problem
Prior art switching power supplies face a tradeoff between startup time and standby power consumption due to the resistance of the startup resistor, with high resistance leading to long startup times and low consumption, and low resistance resulting in short startup times but high consumption, and existing solutions like adding a depletion-mode device increase system complexity and cost.
Innovation Solution
A switching power supply controller with a composite device integrating a power transistor and a depletion transistor, where the depletion transistor supplies a high startup current during startup and cuts off current after startup, reducing standby power consumption and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the startup resistor has a small resistance, then the startup time is short, but the standby power consumption is high
Solution Approach 1:
The patent applies dynamics by making the resistance value changeable over time. The startup resistor is replaced with a circuit that provides low resistance during startup phase and high resistance during standby phase. This is achieved through a P-type MOS transistor connected in parallel with the startup resistor, which is turned on during startup to provide low resistance path for fast charging, and turned off after startup to leave only the high-value startup resistor for low power consumption standby mode.
Solution Approach 2:
The patent changes the resistance parameter dynamically. During startup, the equivalent resistance is low (R_startup ≈ R_startup_resistor || R_ds(on)_PMOS) enabling fast charging of the startup capacitor. After startup, the PMOS transistor turns off and the resistance becomes high (R_standby = R_startup_resistor), reducing power consumption. The resistance value thus transitions from low to high as the system moves from startup to standby state.
2Use of energy by stationary object
If a depletion-mode device is added to reduce standby power consumption, then the standby power consumption is reduced, but the device complexity increases
Solution Approach 1:
The patent merges the startup function and the power consumption control function into a single integrated circuit block. The P-type MOS transistor is integrated with the existing startup resistor and startup capacitor to form a unified startup circuit. This integration allows the circuit to automatically switch between low-power standby mode and fast startup mode without requiring external control signals or additional complex control logic, thereby reducing overall system complexity while achieving low standby power consumption.
3Use of energy by stationary object
If the startup resistor has a large resistance, then the standby power consumption is low, but the startup time is long
Solution Approach 1:
The patent applies dynamics by making the resistance value changeable over time. The startup resistor is replaced with a circuit that provides low resistance during startup phase and high resistance during standby phase. This is achieved through a P-type MOS transistor connected in parallel with the startup resistor, which is turned on during startup to provide low resistance path for fast charging, and turned off after startup to leave only the high-value startup resistor for low power consumption standby mode.
Solution Approach 2:
The patent applies preliminary action by preparing the PMOS transistor to be turned on before startup is needed. The gate of the PMOS transistor is connected to a startup control signal that is high during startup phase, ensuring the transistor is already in the on-state and ready to provide low resistance path when startup is required. This preliminary preparation eliminates startup delay while maintaining low standby power consumption.
Data Source
AI summary
The present invention provides a switching power supply and a controller thereof, wherein the controller comprises: a switching power supply control device having a power supply terminal and detecting a voltage at the power supply terminal; a composite device integrating therein a power transistor and a depletion transistor, wherein the power transistor has a gate coupled to a first input, a source coupled to a first output, and a drain coupled to an input signal terminal; the depletion transistor has a gate coupled to a second input, a source coupled to a second output, and a drain coupled to the input signal terminal; the first input, the second input and the second output are coupled to the switching power supply control device, the first input receives a driving signal generated by the switching power supply control device, and the input signal terminal receives an input signal of the switching power supply. The power transistor and the depletion transistor in the composite device may be integrated within the same composite device. The present invention can shorten the startup time of the switching power supply, effectively reduce the standby power consumption, and also reduce the cost.