SLUUCI9A January   2022  – December 2022 UCC28781

 

  1.   Abstract
  2.   Trademarks
  3. 1 Introduction
  4. 2 General Texas Instruments High Voltage Evaluation (TI HV EVM) User Safety Guidelines
  5. 3 Description of EVM
  6. 4 Electrical Performance Specifications of EVM
  7. 5 Schematic Diagram of EVM
  8. 6 Operating the EVM from a DC or an AC Source
    1. 6.1 Typical Applications
    2. 6.2 Using the EVM with a DC Voltage Source
    3. 6.3 Using the EVM with an AC Voltage Source
  9. 7 Test Set-ups
    1. 7.1 Test Set-up Requirements
      1. 7.1.1 Test Set-up Requirements for DC Input
      2. 7.1.2 Test Set-up Requirements for AC Input
    2. 7.2 Test Set-up Diagrams
    3. 7.3 Terminals and Test Points
  10. 8 Performance Data and Typical Characteristic Curves
    1. 8.1 Table of Efficiency Measurements with DC Input
    2. 8.2 Table of Efficiency Measurements with AC Input
    3. 8.3 Efficiency Graphs with DC Input Voltage (Typical Results)
    4. 8.4 Switching Frequencies in Various Operating Modes
    5. 8.5 Key Switching Waveforms and Operating Mode Load Current
    6. 8.6 Thermal Images at Full Load (15 V, 4.0 A) with DC and AC Inputs
  11. 9 Transformer Details
  12. 10EVM Assembly and Layout
  13. 11List of Materials
  14. 12Revision History

6.2 Using the EVM with a DC Voltage Source

When the DC input is used, the AC section of the EVM should remain completely unused, without any connections to terminal blocks J1 and J2. Also, the XCD Jumper should be installed in the "XCD Disabled" position at J5 before DC power is applied.

The UCC28781EVM-053 may be powered directly from an isolated high-voltage DC source ranging from 500 V down to < 50 V. In general, input voltage must be > 100 V to start and may be reduced to < 50 V after start-up. Output current should be limited to 2 A or less when starting with input voltage < 250 V.

Set DC source current limit to 1 A. Full-rated output power (60 W) may be obtained for input voltages in the [250-V to 500-V] range. Output power rating is reduced (30 W) for input voltages in the [50-V to 250-V] range due to the high rms level of primary current at low input voltages.

The isolated DC source should be connected to the EVM at J3 (DC INPUT terminal block) using a low-impedance cable such as suitably-insulated 18AWG twisted-pair wire less than 1 meter in length. The EVM has very little on-board bulk-voltage by-pass capacitance at the DC input, so an additional high-voltage capacitor may be added externally to J3 to augment the DC bulk voltage for certain performance tests.

At light loads, the DC input current consists of pulses at the burst mode frequency, which digital multimeters (DMMs) cannot properly average and measure. For accurate input current measurements at light loads, a high-voltage 2-μF film capacitor should be applied across the DC input terminal block. Also, a 10-W, 100-Ω resistor should be inserted in series with the DC input as shown in Figure 7-1 to form an R-C filter which smooths the pulsing input currents.

The output of the EVM (15 V) is taken from terminal block J4 which should be connected to a passive resistor load or to an active electronic load. An active load usually affords great flexibility in loading methods and perturbations.