DC-DC|Basic
Supplement-Protective Function: Output Pre-bias Protection
2019.10.23
Points of this article
・Protection is provided for a pre-bias state in which a voltage already appears at the output upon startup of a synchronous rectifying step-down switching regulator.
・A function is provided to prevent the possibility of breakdown of the low-side switch due to drawing of an excessive current when the switch is turned on while in a pre-bias state.
This article is a supplement to ” Protective and Sequencing Functions” in ” Switching Regulator Basics”. In recent years, an increasing number of DC-DC converters have been provided with this protection function.
Output Pre-bias Protection
The voltage Vout when a DC-DC is started is assumed to be essentially 0 volts. However, due to the circuit configuration, restarting after a short time interval, and other factors, a voltage Vout may exist prior to startup, that is, the voltage may not be zero. In many cases, charge remains on the Cout connected to Vout, or on a Cin of the load (the IC being fed) or the like; or, it may be due to a leakage current via another route, or to a bias from a pull-up resistor or the like.
In a state with this pre-bias, when the low-side switch (MOSFET) of a synchronous rectifying step-down converter is turned on, an excessive current is drawn, and breakdown of the MOSFET is possible. In order to prevent such an occurrence, the pre-bias production function executes control so as not to turn on the low-side switch until the output voltage exceeds the pre-bias voltage.
【Download Documents】Switching Regulator Basics
The basics of step-down switching regulators, including their operation and functions, are explained. Comparison with linear regulators, synchronous rectification and diode rectification, control method, auxiliary functions, etc. are also explained.
List of articles related to the「Supplement-Protective Function: Output Pre-bias Protection」
- Switching Regulator Basics
- Types of Switching Regulators
- Advantages vs Disadvantages in Comparison with Linear Regulator
- Supplement-Current Paths during Synchronous Rectifying Step-Down Converter Operation
- Operating Principles of Buck Switching Regulator
- Differences between Synchronous and Nonsynchronous Rectifying DC-DC Conversion
- Control Methods (Voltage Mode, Current Mode, Hysteresis Control)
- Efficiency Improvements at Light Load for the Synchronous Rectifying Type
- Protective and Sequencing Functions
- Considerations on Switching Frequencies
- Behavior when Vin Falls Below Vout
Download Technical Documents
Basic of Linear Regulators and Switching Regulators
Basic studies for linear regulators and switching regulators as a DC-DC converter.
DC-DC
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Basic
- Linear Regulator Basics
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Switching Regulator Basics
- Types of Switching Regulators
- Advantages vs Disadvantages in Comparison with Linear Regulator
- Supplement-Current Paths during Synchronous Rectifying Step-Down Converter Operation
- Operating Principles of Buck Switching Regulator
- Differences between Synchronous and Nonsynchronous Rectifying DC-DC Conversion
- Control Methods (Voltage Mode, Current Mode, Hysteresis Control)
- Efficiency Improvements at Light Load for the Synchronous Rectifying Type
- Protective and Sequencing Functions
- Considerations on Switching Frequencies
- Behavior when Vin Falls Below Vout
- Supplement-Protective Function: Output Pre-bias Protection
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Concluding Remarks
- Design
- Evaluation
- Application
- Product Information
- FAQ