SBOA510 March   2021 OPA455 , OPA462

 

  1.   Trademarks
  2. 1Introduction
  3. 2Three Op Amp OPA462 HV Solution
  4. 3Lower Voltage, Lower Cost Three Op Amp Solution
  5. 4OPA462 300 Vpp Output Solution With Discrete Transistor Supply-Rail Drivers
  6. 5Lessons Learned from the Practical Implementation of the HV Op Amp Solutions
  7.   A Appendix
    1.     A.1 Overview
    2.     A.2 Summary of Results
    3.     A.3 Test Setup and Equipment
    4.     A.4 Printed Circuit Boards
    5.     A.5 Power Supply, Source Measurement Unit (SMU)
    6.     A.6 Arbitrary Waveform Generator (AWG)
    7.     A.7 Oscilloscope
    8.     A.8 Circuit 1: OPA462 Three op amp Solution
      1.      A.8.1 Schematic
      2.      A.8.2 Conventions
      3.      A.8.3 Results
    9.     A.9 Circuit 2: Lower Voltage, Lower Cost Three Op Amp Solution
      1.      A.9.1 Schematic
      2.      A.9.2 Conventions
      3.      A.9.3 Results
    10.     A.10 Circuit 3: OPA462 300 Vpp Output Solution With Discrete Transistor Supply-Rail Drivers
      1.      A.10.1 Schematic
      2.      A.10.2 Conventions
      3.      A.10.3 Results

1 Introduction

In the distant past, first vacuum tubes and then in the not so distant past, discrete high-voltage (HV) bipolar and MOS semiconductors were applied in countless HV amplifier designs. They proved capable of satisfying linear HV amplifier needs for many years. In time the precision and ease of use provided by operational amplifier (op amp) solutions made them a desired option to replace some of the more conventional HV transistor solutions. The very first op amps used vacuum tubes, but had limited applications. Most practical discrete and monolithic op amps in the early decades were designed for ±15 V (30 V) or less, and the availability of higher voltage options was limited. But yielding to the proverb “Necessity is the mother of invention”, op amp designers moved the state of the art forward and worked to develop ever higher voltage op amps.

Burr-Brown introduced the 3580 series of hybrid op amps during the 1970s and 1980s that were capable of being used with power-supply voltages up to ±150 V (300 V). These early HV solid-state op amps used hybrid construction made up of discrete HV transistor and passive component “chips” mounted on a ceramic substrate. They were wire bonded between the chip pads and substrate metallization, and had laser-trimmable thick film resistors. Their maximum output current capabilities were in the 50- to 60-mA range, sufficient for many applications. Many of their electrical parameters were highly precise, but their power dissipation and cost tended to be high, limiting where they could be practically applied. Their packaging in large, 8-pin TO-3 packages often required an external heat sink to dissipate heat. Based on the hybrid high-voltage op amp successes, work moved onward in the development of increasingly higher voltage, smaller monolithic (IC) op amps that could operate with supplies much greater than the common industry standard ±15 V.

Through the 1980s monolithic op amp supplies moved upwards to ±30 V (60 V) for HV op amps, and by the mid 1990s the OPA445 was introduced, which could be powered by ±45 V (90 V). This was followed in the early 2000s by the OPA454, capable of operating with supplies of ±50 V (100 V). More recently the OPA462 was introduced from TI, which operates with supplies up to ±90 V (180 V).

For many HV applications these op amps are well suited, yet the need for even higher voltage op amps continues. Much of this is driven by HV piezoelectric transducer and actuator applications.

Op amp supply voltages climbed as new HV semiconductor processes, designs and package types became more available that could sustain the higher voltage levels. During that time new applications have come on the scene that require increasingly higher voltages, beyond what individual HV op amps are able to handle on their own.

This application report presents three novel HV op amps circuits using multiple op amps or transistors to extend the useable HV range out even further. The OPA462 ±90 V (180 V) HV op amp is used in all three circuits, but the techniques should be applicable to other HV op amps as well. Some minor circuit adjustments will likely be required for other HV op amps because their electrical specifications can be different from the OPA462. These circuit techniques being presented should be useable with lower voltage ±15 V op amps too. Doing so allows their precise electrical performances to be exploited in applications where somewhat higher supply and output voltages are required.