SLOA284A january   2020  – may 2023 AFE5832 , AFE5832LP , ISO7741 , ISOW7841 , LM25037 , LM25180 , LM5180 , LM5181 , LM5181-Q1 , TX7316 , TX7332

 

  1.   1
  2.   Designing Bipolar High Voltage SEPIC Supply for Ultrasound Smart Probe
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Key Design Challenges
    2. 1.2 Potential Topologies for Generating High Voltage Supply
  5. 2Design of high voltage circuit using SEPIC topology
    1. 2.1 TI HV Supply Architecture Using SEPIC Topology
  6. 3Test Results
    1. 3.1 Efficiency and Load Regulation
    2. 3.2 Output Ripple Measurement
    3. 3.3 Load Transient Test
    4. 3.4 Noise Measurement
    5. 3.5 Thermal Performance
  7. 4Possible Variants of the Design
    1. 4.1 Option 1: Programmable Output Voltage
    2. 4.2 Option 2: Support Input From 1S Li-Ion Battery
    3. 4.3 Option 3: Output Voltage Up to ±100 V
  8. 5Layout Guidelines
  9. 6Clock Synchronization
  10. 7Summary
  11. 8References
  12. 9Revision History

1.2 Potential Topologies for Generating High Voltage Supply

Considering the voltage requirements (up to 80 V, and 100 V in some cases) ,low power levels (approximately 2 W per rail) and small size of the solution, the most optimum power supply topologies are Boost/Cuk, Flyback and SEPIC. Since negative rail is required Flyback and SEPIC are better choices, due to ease of implementation. A brief description and comparison of both topologies is provided below.

SEPIC: SEPIC is a flexible topology that can function as step-up and step-down voltage regulator, it features minimal active components, a simple controller, and clamped switching waveforms to minimize switching noise

Flyback: Flyback converter is the most commonly used SMPS circuit for low output power applications where the output voltage must be isolated from the input main supply. The flyback topology is essentially the buck-boost topology that is isolated by using a transformer as the storage inductor.

In Table 1-2, a comparison between Flyback and SEPIC converter is shown:

Table 1-2 Pros and Cons of Flyback and SEPIC Topology
ProsCons
Flyback
  • High step-up ratio
  • Lower diode stress
  • Lower magnetic components count
  • Low efficiency at light loads
  • Custom transformer (height increases)
  • Snubber required
  • Higher surge current
  • Higher FET stress
SEPIC
  • Off-the-shelf inductors (height decreases)
  • High efficiency at light loads
  • Reduced switching losses (no leakage inductance of transformer)
  • Lower FET stress
  • Smaller step-up ratio
  • Higher diode stress
  • Higher magnetic components count

Considering the challenges discussed in Section 1.1, Flyback topology is also suitable to generate bipolar high voltage supply. Nevertheless, the height of the Flyback transformer cannot accomplish an upper limit in the order of 5 mm (unless costly custom planar transformer is used in the design). This is the reason for selecting the SEPIC topology with off-the-shelf uncoupled inductors in this design.