Current Context and Research Trends in Linear DC–DC Converters
Abstract
:1. Introduction
Evolution of Power Supply Design Technology
2. Switch Mode Power Supplies (SMPS)
2.1. Issues with SMPS
2.1.1. Inductors and Transformers
2.1.2. Capacitors
2.1.3. Switch Elements
3. Linear/Low-Dropout Regulators Operating Principle
4. Dominant Characteristics of LDOs
4.1. Higher Efficiency
4.2. Low Noise
4.3. Low Quiescent Current
4.4. Better Transient Performances
4.5. Small Package Size
5. Current LDO Application Trends and Their Market Share
6. LDO’s Recent Research Trends
6.1. Improving the Compactness
6.2. Reducing Noise Levels Further
6.3. Improving the Transient Performance
6.4. Improving the Efficiency
7. Current Context of Portable Power Supply Designs
- Variation of the current consumed by the subsystem.
- Fluctuation of the battery voltage in the portable device.
- Variations due to operating conditions of the device, such as temperature.
- Output rail voltage.
- Maximum load current.
- Output impedance of the power supply.
- Noise and ripple allowed.
- Input voltage range.
- Efficiency.
- Weight/volume of the power supply.
- Transient response capability and transient response.
- Radio frequency interference/electromagnetic interference (RFI/EMI).
- Reliability and the age of the power supply.
8. Future Prospects for LDO Regulators in Power Supplies
9. Supercapacitor-Assisted Low-Dropout Regulators (SCALDO) as a Solution to the Linear Regulator Efficiency Problem
9.1. Supercapacitors as Lossless Voltage Droppers
9.2. Concept of SCALDO
9.3. Advantages of Using SCALDO in Portable Devices
9.4. Limitations of SCALDO Technology
10. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
SMPS | Switch-mode power supplies |
SCC | Switched capacitor converters |
PMS | Power management system |
ESR | Equivalent series resistance |
LDO | Low-dropout regulator |
ETEE | End-to-end efficiency |
POL | Point of load |
SCALDO | Supercapacitor-assisted LDO |
EMI | Electromagnetic interference |
PSRR | Power supply rejection ratio |
SC | Supercapacitor |
Vref | Desired voltage in volts |
Vout | Output voltage in volts |
Iq | Current used by the control circuit in amps |
Vin | Input voltage in volts |
Vd | Dropout voltage in V |
PD | Power consumption across LDO in watt |
C | Capacitance in farads |
dv | Voltage change |
i(t) | Instantaneous current through the capacitor in amps |
tcharging | Charging time in seconds |
tdischarging | Discharging time in seconds |
IAVG | Average current drawn from the unregulated power supply in amps |
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Parameter | Linear Regulators and LDOs | SMPS | Charge Pumps |
---|---|---|---|
Design flexibility | Step down | Step up/Step down/Inversion | Step up/Step down/Inversion |
Circuit Diagram | LDO | Buck Converter | Switch capacitor voltage doubler |
Efficiency (typical) | Linear regulators: 50–60% LDOs up to 98% | Higher than 95% | 70–80% |
Complexity | Low | High | Low |
Size | small | Smaller than LDO | Smallest |
Total Cost | Low | High | Low |
Electromagnetic interference (EMI) | Low | High | Medium |
Noise | Low | High | Medium |
Input voltage range | Narrow | Wide | Narrow |
Thermal management | Moderate (mainly the series pass device) | Complex (multiple devices to deal with where the heat is dissipated) | Moderate (switches) |
Output current capability | Medium | High | Low |
Dropout Voltage (mV) | Input Voltage Range (V) | Output Voltage Range (V) | Current Rating (mA) | Maximum Efficiency (%) | Commercially Available LDOs |
---|---|---|---|---|---|
200 | 1.5–5.5 | −0.3 ± 0.3 | 200 | 96.36 | LDBL20 [13] |
65–125 | 0.8–5.5 | 0.8–3.6 | 1500 | 97.72 | LD59150 [14] |
80 | 1.5–5.5 | 0.8–3.3 | 100 | 98.55 | LD39015 [15] |
175 | 1.1–6.5 | 0.8–5.15 | 4000 | 97.31 | TPS7A54 [16] |
225 | 1.5–6 | 0.55–5.5 | 1000 | 96.25 | TLV752 [17] |
LDO Specific Property | Industrial Application | Commercially Available LDOs |
---|---|---|
Reduce noise and PSRR levels | High-speed communications applications, video processing applications, and high-accuracy measurement applications. | TPS717xx family [23] |
Compactness | Compact portable devices | TPS720 [24], TLV733P [25], ADP160 [26], ADP166 [26], ADM7160 [27] |
Lower quiescent current | Battery-powered applications | TPS7A19 [28], TPS7B69 [29], LT3009 [30], STLQ50 [31], LDK715 [32] |
Item | Loss | Reason | Remarks |
---|---|---|---|
1 | Static losses of the switches such as transistors and diodes |
| These show up a cumulative content known as “static losses” which increases with output voltage and the load current. |
2 | Dynamic losses in transistors and diodes increase with the switching frequency |
| The higher switching frequency of switch-mode power supplies increases the dynamic losses linearly with the frequency in general. |
3 | Secondary losses in inductors |
| Except for ohmic losses, others are frequency-dependent and have a nonlinear behaviour with frequency. |
4 | Secondary losses in capacitors |
| Smaller capacitors have high ESR and large capacitors have relatively lower ESR. |
5 | Power consumed by the controller circuit associated with the power stage |
| These losses depend on the control circuit section of the switch-mode power supply. |
6 | PCB track losses/interconnection losses in an IC version |
| The larger the current the higher these are. |
Parameter | Unit | Range |
---|---|---|
Rated voltage | V | 1.2–3.8 |
Capacitance | F | 1–3000 |
Specific energy density | Wh/kg. | 1–10 |
Specific power density | W/kg | <10,000 |
Cycle life | Cycle number | >50,000 |
Charge and discharge efficiency | % | 85–98 |
Fast charge duration | Seconds | 0.3–30 |
Fast discharge duration | Seconds | 0.3–30 |
Shelf life | Years | 20 |
Operating temperature | °C | −40 to 75 |
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Gunawardane, K.; Padmawansa, N.; Kularatna, N.; Subasinghage, K.; Lie, T.T. Current Context and Research Trends in Linear DC–DC Converters. Appl. Sci. 2022, 12, 4594. https://doi.org/10.3390/app12094594
Gunawardane K, Padmawansa N, Kularatna N, Subasinghage K, Lie TT. Current Context and Research Trends in Linear DC–DC Converters. Applied Sciences. 2022; 12(9):4594. https://doi.org/10.3390/app12094594
Chicago/Turabian StyleGunawardane, Kosala, Nisitha Padmawansa, Nihal Kularatna, Kasun Subasinghage, and Tek Tjing Lie. 2022. "Current Context and Research Trends in Linear DC–DC Converters" Applied Sciences 12, no. 9: 4594. https://doi.org/10.3390/app12094594