Vehicular Lamp Circuit Bootstrap Charging for Low Input Voltage
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Solution Overview
Problem
Existing semiconductor light source lighting circuits for vehicular lamps face challenges in maintaining stable operation when input voltage decreases, particularly in maintaining the ON state of high-side n-type MOSFETs in voltage step-up mode due to reduced charge capacity of charge pumps.
Innovation Solution
The proposed semiconductor light source lighting circuit incorporates a voltage step-down unit, a voltage step-up unit, and a controller with a bootstrap unit, charge pump unit, and switch drive unit to manage the drive voltage across switching elements, ensuring the high-side n-type MOSFET remains on by charging a capacitor based on voltage changes and using a charge pump to maintain the ON state in voltage step-up mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charge pump is used to charge a bootstrap capacitor in voltage step-up mode, then the high-side n-type MOSFET can be turned on, but when input voltage is lowered, the charge capacity of the charge pump decreases, making it difficult to maintain the MOSFET in the ON state
Solution Approach 1:
The patent introduces a diode as an intermediary component to create an additional charging path for the bootstrap capacitor. When the switching element is in the ON state, the diode conducts and allows current to flow from the power supply terminal through the diode to charge the bootstrap capacitor, supplementing the charge pump's insufficient charging capability at low input voltages.
Solution Approach 2:
The patent pre-charges the bootstrap capacitor through the diode during the MOSFET ON state before the charge pump needs to operate. This preliminary charging action ensures that the bootstrap capacitor has sufficient voltage to maintain the MOSFET in the ON state even when the charge pump's charging capacity is reduced due to low input voltage.
2Loss of energy
If an n-type MOSFET is used as a high-side switching element to achieve lower on-resistance, then power loss is reduced, but a bootstrap circuit and charge pump are required, increasing device complexity
Solution Approach 1:
The diode serves multiple functions: it acts as a rectifier in the normal charge pump circuit, provides an additional charging path for the bootstrap capacitor, and enables the MOSFET to remain in the ON state during low input voltage conditions. This multi-functionality reduces the need for additional complex circuitry.
Solution Approach 2:
The patent merges the bootstrap capacitor charging function with the existing power supply terminal and diode, combining multiple functions into existing components rather than adding separate dedicated circuits. This integration reduces overall device complexity while maintaining the benefits of using an n-type MOSFET.
3Use of energy by moving object
If the input voltage is lowered, then power consumption is reduced, but the charge pump cannot adequately charge the bootstrap capacitor, causing the MOSFET to fail to remain in the ON state
Solution Approach 1:
The diode acts as a mediator that provides an alternative charging path for the bootstrap capacitor when the charge pump becomes insufficient at low input voltages. This intermediary component ensures continuous adequate charging of the bootstrap capacitor regardless of input voltage level, maintaining MOSFET ON state stability.
Solution Approach 2:
The patent changes the charging parameters of the bootstrap capacitor by introducing a second charging path through the diode. This allows the system to adapt to different input voltage conditions by switching between or combining charging paths, ensuring the bootstrap capacitor maintains sufficient voltage across a wide range of input voltages.
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
This configuration allows the lighting circuit to maintain stable drive voltage and emission characteristics even with lower input voltage, preventing the ON state failure of high-side n-type MOSFETs and ensuring consistent LED brightness.
Implementation Method 1
a bootstrap unit configured to charge a first capacitor based on a change in voltage at the other end of the first switching element in the voltage step-down mode
Implementation Method 2
a charge pump unit configured to repeat charging from a terminal to which the drive voltage is applied to a second capacitor and discharging from the second capacitor which is charged to the first capacitor in the voltage step-up mode
Data Source
AI summary
A semiconductor light source lighting circuit includes a voltage step-down unit configured to generate a drive voltage lower than an input voltage by turning on or off a first switching element in a voltage step-down mode, a voltage step-up unit configured to generate the drive voltage higher than the input voltage by turning on or off a second switching element in a voltage step-up mode, and a controller. The controller includes a charge pump unit configured to repeat charging from the drive voltage to a second capacitor and discharging from the charged second capacitor to the first capacitor in the voltage step-up mode, and a switch drive unit configured to apply a voltage higher than the voltage at the other end of the first switching element to the control terminal of the first switching element by using a voltage of the charged first capacitor.