米6体育平台手机版

SLAA898 September 2022 TAS3251 , TPA3255

3.2 System Build-Up

To use a 70-V constant voltage system to deliver power to different smaller speakers, the voltage must be converted to 70.7 V_RMS first through one step-up transformer, and then down to the proper voltage by the Peavey step-down transformers (see Figure 3-5; suppose N speakers are used, so N step-down transformers). The TPA3255 (along with a LC filter) is used as the amplifier (51 V, BTL mode, same condition in all of the following experiments). A Peavey step-up transformer (abbreviated as 18737) and a step-down transformer (abbreviated as 330-040) were used. In the first experiment, the configuration for the 18737 is 1,2 as primary and A,B as secondary, while the configuration for the 330-040 can vary between 10 W, 5 W, 2.5 W, 1.25 W, and 0.62 W in the primary side (secondary is fixed with a 4 Ω load).

Figure 3-5 Full System for Constant Voltage System Based on TPA3255

Equation 11.

\frac{R_{L}}{R} = (\frac{U_{L}}{U})^{2}

Equation 12.

U' = U

Equation 13.

P_{0} = \frac{{U_{0}}^{2}}{R_{0}}

Equation 14.

\frac{R'}{R_{0}} = (\frac{U'}{U_{0}})^{2} = \frac{U^{2}}{P_{0} R_{0}}

Equation 15.

R = \frac{R'}{N}

Equation 16.

R_{L} = R \frac{{U_{L}}^{2}}{U^{2}} = \frac{R'}{N} \frac{{U_{L}}^{2}}{U^{2}} = \frac{1}{N} \frac{{U_{L}}^{2}}{U^{2}} \frac{U'^{2}}{{U_{0}}^{2}} R_{0}

To best match the resistance, R_L should be more than 4 Ω. If the 18737 configuration is fixed as 20 V to 70 V and 330-040 is fixed as 10 W, 4 Ω:

Equation 17.

N \leq \frac{{U_{L}}^{2}}{U^{2}} \frac{U'^{2}}{{U_{0}}^{2}} \frac{R_{0}}{R_{L}} = \frac{1}{12.496225} \times 124.97 \times \frac{4 Ω}{4 Ω} \approx 10

Note that R_L is not always 4 Ω; it gets higher if using a lower power level for the 330-040. So N = 10, and ten 4-Ω resistors are used to simulate 4-Ω speakers.