DC-DC｜Application
Failure to Start of a Power Supply Using a Linear Regulator Case 5: Startup Failure on One Side of a Positive-Negative Power Supply
2024.04.24
Points of this article
・In a positive-negative power supply that uses positive and negative linear regulators, if the supply voltage rise speeds are different for the positive and for the negative linear regulators, a reverse voltage occurs for the device with the slower rise, and startup problems occur.
・Countermeasures include shutting off paths that link the two outputs, adding a diode to reduce the reverse voltage, and using a linear regulator IC having an overcurrent protection circuit with a drooping characteristic. In all cases, testing in actual equipment is mandatory.
Case 5: Startup Failure on One Side of a Positive-Negative Power Supply
In a positive-negative power supply like that of Fig. 1, there are many cases in which the speed of voltage rise is different for positive and negative supplies. In such cases, if there are loads between the positive and negative sides such as RL3, or unintended current paths formed by multiple circuits, the power supply that has risen earlier absorbs current output from the other power supply through RL3 (broken-line path), so that a reverse voltage appears at the output of the positive voltage regulator (in the case of Fig.1). As a result, the same startup problems as in “Case 2: Startup Problems Caused by Constant-Current Loads” occur.
Fig. 1. Current paths when the negative power supply starts first in a positive-negative power supply circuit
When problems occur in startup due to such causes, the following countermeasures are conceivable.
- ・Shut off the RL3 path.
- ・In order to reduce the reverse voltage and alleviate the failure of the output voltage to rise, connect a Schottky barrier diode with a low VF between the output and ground (D1, D2 in Fig. 2). ※When using this countermeasure, a product must be selected that can supply a larger current value than the reverse current value. Due to variance, however, there is no 100% guarantee of normal startup.
- ・A linear regulator IC is used that has an overcurrent protection circuit with a drooping characteristic. ※In this case, if a current flows in the electrostatic damage protection diode between the IC output pin and ground, or in parasitic diodes, degradation or destruction may occur. To prevent this, a Schottky barrier diode is inserted between the output pin and ground (D1, D2 in Fig. 2).
Fig. 2. Countermeasure example when problems occur in startup of a positive-negative power supply circuit
DC-DC
Basic
- Operation During Shutdown of a Boost DC-DC Converter
- Linear Regulator Basics
-
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
- Seven Representative Power Supply Circuits: From Low-noise to Boost Specs
- Concluding Remarks
- What is a DC/DC Converter?
Design
- Overview of Selection of Inductors and Capacitors for DC-DC Converters
-
Overview of DC-DC Converter PCB Layout
- Ringing at switching nodes
- Placement of input capacitors and output diodes
- Placement of Thermal Vias
- Placement of Inductors
- Placement of Output Capacitors
- Feedback Path Wiring
- Ground
- Resistance and Inductance of Copper Foil
- Noise countermeasures: corner wiring, conducted noise, radiated noise
- Noise countermeasures: snubber, bootstrap resistor, gate resistor
- Summary
-
PCB Layout of a Step-Up DC-DC Converter – Introduction
- The Importance of PCB Layout Design
- Current Paths in Step-up DC-DC Converters
- PCB Layout Procedure
- Placement of Input Capacitors
- Placement of Output Capacitors and Freewheel Diodes
- Inductor Placement
- Placement of Thermal Vias
- Feedback Path Wiring
- Ground
- Layout for Synchronous Rectification Designs
- Resistance and Inductance of Copper Foil
- Relationship Between Corner Wiring and Noise
- Summary
Evaluation
- Overview of Characteristics and Evaluation Method of Switching Regulators
- How to Read Power Supply IC Datasheets: Cover, Block Diagram, Absolute Maximum Ratings and Recommended Operating Conditions
- Evaluating a Switching Regulator: Output Voltage
-
Introduction
- Definitions and Heat Generation
- Losses in Synchronous Rectifying Step-Down Converters
- Conduction Losses in Synchronous Rectifying Step-Down Converters
- Switching Losses in Synchronous Rectifying Step-Down Converters
- Dead Time Losses in Synchronous Rectifying Step-Down Converters
- Controller IC Power Consumption Losses in a Synchronous Rectifying Step-Down Converter
- Gate Charge Losses in a Synchronous Rectifying Step-Down Converter
- Conduction Losses due to the Inductor DCR
- Example of Power Loss Calculation for a Power Supply IC
- Simplified Method of Loss Calculation
- Heat Calculation for Package Selection: Example 1
- Heat Calculation for Package Selection: Example 2
- Loss Factors
- Matters to Consider When Studying Miniaturization by Raising the Switching Frequency
- Important Matters when Studying High Input Voltage Applications
- Important Matters when Studying Large Output Currents Applications: Part 1
- Important Matters when Studying Large Output Currents Applications: Part 2
- Summary
Application
-
Important Points in the Design of a Power Supply Using a Linear Regulator
- Typical Application Circuit Examples of Linear Regulator ICs
- Input/output capacitor design and ripple prevention for linear regulator ICs
- How to determine efficiency and Thermal design for linear regulator ICs
- Protection of Linear Regulator IC Terminals
- Soft Starting of a Linear Regulator IC
- Overcurrent Protection（OCP） and Thermal Shutdown（TSD） of Linear Regulator IC
-
Important Points in the Design of a Power Supply Using a Floating Type Linear Regulator
- Example of Power Supply Circuit Based on a Floating Type Linear Regulator IC
- Input/output capacitor design and ripple prevention for linear regulator ICs
- How to determine efficiency and Thermal design for Floating Type Linear Regulator ICs
- Terminal protection for linear regulator ICs
- Startup characteristics for linear regulator ICs
- Failure to Start of a Power Supply Using a Linear Regulator, Case 1: Damage to the IC and Peripheral Components Due to Hand-Soldering
- About Parallel Connections of LDO Linear Regulators
-
Introduction
- Power Supply Sequence Specification ①: Power Supply Sequence Specifications and Control Block Diagrams
- Power Supply Sequence Specification①: Sequence Operation at Power Turn-on
- Power Supply Sequence Specification①: Sequence Operation at Power Shutoff
- Power Supply Sequence Specification①： Example of Actual Circuit and Component Value Calculations
- Power Supply Sequence Specification①: Example of Actual Operations
- Power Supply Sequence Specification②:Power Supply Sequence Specifications and Control Block Diagrams
- Power Supply Sequence Specification②:Sequence Operation at Power Turn-on
- Power Supply Sequence Specification②: Sequence Operation at Power Shutoff
- Power Supply Sequence Specification②: Example of Actual Circuit and Component Value Calculations
- Power Supply Sequence Specification②: Example of Actual Operations
- Circuits to Implement Power Supply Sequences Using General-Purpose Power Supply ICs ーSummaryー
- Easy Stabilization/Optimization Methods for Linear Regulators – Introduction
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