Application Note 35: Step-Down Switching Regulators
A guide to designing efficient step-down (buck) switching regulators using the LT1074 IC, featuring dual-output, negative-output, and current-boosted circuit configurations.
Overview
This application note provides a technical overview of step-down (buck) switching regulator design. It details the theory of buck converters, comparing their efficiency performance against standard linear regulators like the LM317 and LT1086. The document focuses on practical implementations using the LT1074 IC, including a standard 5V/1A regulator, a dual-output (+15V and -5V) configuration using coupled inductors, and two methods for generating negative outputs, including the 'Nelson’s Circuit.' Additionally, it covers current-boosted designs for higher output currents and the implementation of linear post-regulation for applications requiring low noise and fast transient response.
Use Cases
- High-efficiency DC-DC conversion from high input voltages
- Generating positive and negative supply rails from a single positive input
- Thermal management by replacing linear regulators with switching alternatives
- Power supply design requiring low output noise and fast transient response
Topics
Referenced Parts
PE-51509
Pulse Engineering, Inc.
L1 = PULSE ENGINEERING, INC. #PE-51509
PE-65050
Pulse Engineering, Inc.
PULSE ENGINEERING, INC. #PE-65050
PR-65282
Pulse Engineering, Inc.
L1 = PULSE ENGINEERING, INC. #PR-65282
1N5831
Motorola
D2 = 1N5831
| MBR745 | Motorola | MBR745 |
| MUR120 | Motorola | MUR120 |
| PE-51516 | Pulse Engineering, Inc. | L1: PULSE ENGINEERING, INC. #PE-51516 |
| PE-92103 | Pulse Engineering, Inc. | L1 = PULSE ENGINEERING, INC. #PE-92103 |
| PE-92116 | Pulse Engineering, Inc. | L1: PULSE ENGINEERING, INC. #PE-92116 |
| 1N4148 | Generic | 1N4148 |
| 2N3904 | Generic | Q1 2N3904 |
| LT1004 | Linear Technology | LT1004 reference |
| LT1006 | Linear Technology | A1 LT1006 |
| LT1017 | Linear Technology | 1/2 LT1017 |
| LT1074 | Linear Technology | practical circuit using the LT1074 IC regulator |
| LT1084-5 | Linear Technology | LT1084-5 |
| LT1085 | Linear Technology | LT1085 operates in normal fashion |
| LT1086 | Linear Technology | LT1086 linear regulators |
| 1N748 | Motorola | 1N748 |
| MUR110 | Motorola | D1 = MUR110 |
| 74C04 | National Semiconductor | 74C04 paralleled inverters |
| LM317 | National Semiconductor | Efficiency for the LM317 and LT1086 linear regulators suffers |
| PE-51509 | Pulse Engineering, Inc. | L1 = PULSE ENGINEERING, INC. #PE-51509 |
| PE-65050 | Pulse Engineering, Inc. | PULSE ENGINEERING, INC. #PE-65050 |
| PR-65282 | Pulse Engineering, Inc. | L1 = PULSE ENGINEERING, INC. #PR-65282 |
| 1N5831 | Motorola | D2 = 1N5831 |