SLAA898 September   2022 TAS3251 , TPA3255

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Power Amplifiers
    2. 1.2 Discrete Power Amplifier Implementation
    3. 1.3 Class-D Amplifier Implementation
    4. 1.4 Advantage of a Class-D Implementation
  4. 2Background
    1. 2.1 Why Use Constant Voltage Audio Systems
    2. 2.2 Basic Principle of Constant Voltage Systems
    3. 2.3 Power Loss in Transformer
    4. 2.4 Auto-Transformer
  5. 3System Test (Based on TPA3255)
    1. 3.1 Transformer Characteristics
      1. 3.1.1 Turns Ratio and Resistance Match
      2. 3.1.2 DCR of the Transformer
    2. 3.2 System Build-Up
    3. 3.3 System Test
  6. 4Efficiency Analysis and Optimization
    1. 4.1 Efficiency of Three Parts
      1. 4.1.1 Efficiency for TPA3255
      2. 4.1.2 Efficiency for Step-Up Transformer
      3. 4.1.3 Efficiency for Step-Down Transformer 330-040
    2. 4.2 Improvements on System Efficiency
      1. 4.2.1 Improve Resistance Matching
      2. 4.2.2 Apply a Transformer With Less Power Loss
  7. 5Considerations on Building a Constant Voltage System
    1. 5.1 Transformer Saturation
    2. 5.2 Low DCR
    3. 5.3 Resistance Matching

4.2.2 Apply a Transformer With Less Power Loss

Another efficiency limitation is the low efficiency of the transformer. This can be improved by applying a new step-up transformer from EDCOR® (EA300, see Figure 3-2, Table 3-2, and Table 3-5) to replace the 18737.

GUID-896319F7-CB0A-4CF8-B370-70C9F4384CB9-low.pngFigure 4-4 Efficiency Characterization for the EDCOR® Step-Up Transformer (EA300)

Configure EA300 as 4 Ω in the primary side, and 70 V in secondary side (a 16-Ω resistor load can make a 4-Ω equivalent load for the amplifier according to Table 3-2). See the characterization result from Figure 4-4. The efficiency of the EA300 can be 0.94.

Continue to use the EA300 with ten 10 W-configured 330-040s and 4-Ω resistors (N is set as 10 to simplify the system; actually more step-down transformers and resistors can be used in parallel), and test the performance and efficiency of the system. Since the resistance ratio of EA300 is much larger (from 1/12.5 to 1/4.16), the equivalent resistance of the amplifier is about 12 Ω, thus ηamp can be as high as 0.9. So in theory, the system efficiency is:

Equation 27. η=ηampηupηdown=0.9×0.94×0.84=0.71

The measured efficiency was 0.67, which is close to the calculated value of 0.71. Figure 4-5 shows the THD+N performance using the EA300. The performance is better than the previous transformer.

GUID-F5A56021-6F88-49C5-88D6-4EA21D9CC865-low.pngFigure 4-5 THD+N Versus Frequency Results Based on TPA3255 With One EA300 and 10 330-040s (4 Ω as Primary Side and 70 V as Secondary Side)