HV Buffer Amp for AWG - Page 1
Forum section: electronics / testgear

author: mawyatt
author_rank: Super Contributor
timestamp: August 09, 2021, 06:40:17 pm
content: We are working on a project that requires high voltage waveforms of various types, some are custom waveforms. The available AWG we have, and the usual ones available at reasonable cost can't produce higher voltages. So we set out to develop our own, like we've done with other types of test equipment.The package concept is based upon the low cost JunTek DPA-2698 & DPA -1698 style, these are nice low cost amps that are small, 12V powered and convenient to use. We used the readily available eBay 100m by 70mm by 35mm extruded case, end plates were replaced with custom 3D printed versions.The electrical design uses 2 of the TI OPA462 HV Op-Amps setup for an overall gain of 10X. We also have a design based upon the APEX PA443, and another for lower voltage, higher current use based upon the LM3866, we haven't assembled these just yet tho.12 Volt Input boost converted with a MAX1771 converter up to +-85VDC, so the output is capable of providing greater than +-80V peak signals. Low level bandwidth is >500KHz and slew rate limited to ~100KHz.Works OK for our needs so farAnyway, here's what it looks like.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: August 09, 2021, 06:43:51 pm
content: With Case. Added output spectrum at 1KHz and +34dBV (142VPP).Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: August 09, 2021, 09:13:10 pm
content: It looks so much nicer than any of my Arb interfaces. I'm surprised that we don't see more amplifiers like this. Maybe they are just too specialized. I've heard of people using audio amps in some cases.For low frequency, high voltage, high impedance, I've got a box with a couple of small signal transformers inside. The outputs can run through a bridge or two sets of back to back diodes.I've also wanted to use my Arb and RF generators for digital work and have made various buffers using LVDS and what not.Many years ago I designed a small DC coupled buffer/amp using discrete transistors for low frequency use. Picture showing a recent test with the amp on the left.Here it's being used to drive some speakers that were made into a poor mans vibration table.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 09, 2021, 11:01:07 pm
content: I've shown this simple box in a few videos to demonstrate DMM's AC+DC modes. It's nothing more than a simple line transformer and some diodes. Back to back diodes are there to compensate for the loss in the bridge. So it's basically full wave rectified or not rectified. It will provide 400 VACrms with a 10Vp-p 50 ohm input.

author: mawyatt
author_rank: Super Contributor
timestamp: August 10, 2021, 12:54:51 am
content: Our requirements are for DC coupling, so transformers are not an option. We also have some designs finished and the PCBs fabbed for up to 350VPP which was required initially to supply over 300VPP waveforms for our project, later we discovered we needed ~160VPP and this is why we built the OPA462 version first. The 350VPP version can also supply a 120VRMS mains waveform which may prove useful in studying the effects of 120VAC line waveforms on certain things. Here's some of these designs.Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: August 10, 2021, 01:08:19 am
content: How much power can you get out of it at for mains work?

author: mawyatt
author_rank: Super Contributor
timestamp: August 10, 2021, 02:17:50 am
content: Not that much, limited by how much current a APEX PA443 can deliver and still remain within the SOA, and within thermal limits. Our intended use does not require much current. Of course one could design a higher power/current version if the need justified, you would want a larger case & fan tho.Best,

author: joeqsmith
author_rank: Super Contributor
timestamp: August 10, 2021, 01:47:26 pm
content: For higher power, DC coupled applications, I have used Techron.https://aetechron.com/index.shtml

author: mawyatt
author_rank: Super Contributor
timestamp: November 16, 2022, 03:04:53 pm
content: Per request here's the PA443 Based HV Buffer information, note the PCB is incorrect as the PA443 A & B In/Out pinouts were hosed up. To use, carefully study the actual APEX PA443 data sheet package pinouts and the attached schematic and alter PCB layout which has the errors, please make corrections to the PCB layout before fabrication. Vaguely recall that some of the A and B amps input/outputs were swapped. Note the Gerber shown is a txt file, needs to be changed to a zip file after downloading, also the BOM is a txt file and should be changed to a CSV per EasyEDA format.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: July 02, 2023, 04:47:59 pm
content: This is an update for another thread, but thought it better to update here. We added a surface heatsink to the PA443 package. Using the PA443 with various waveforms, note the VPP values at 270VPP.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: February 28, 2025, 02:31:47 am
content: Finally got around to creating a case for the HV Amp (PCB) based upon the Apex PA443. 3D printed a header for the PA443 Heat Sink and added a small 12V Fan (PCB was laid out for fan). Also 3D printed the main case, end plates and covers as shown.Best

author: mawyatt
author_rank: Super Contributor
timestamp: March 27, 2025, 05:49:30 pm
content: We have some potential work coming up to excite a Piezo Electric Cell that will require ~450VP unipolar signal with various waveforms at low frequencies.After thinking about the complexity of designing a custom solution to drive the HV Load we thought about using our custom 10X HV AWG Buffer Amp based upon the Apex PA443, but this has an output limit of +-200V. So we thought about using a differential approach where each HV Amp would be driven by the same AWG source signal except one side inverted and the result for the load which is floating would be connected across each amps output lead, so an "H" Bridge type.However the load requires a somewhat unipolar signal so using a diode clamping approach to create a unipolar from a bipolar waveform could be employed.This still left us short of the goal of a ~450VP unipolar arbitrary waveform peak since our AWG (SDS2042X) has a maximum 20VPP unloaded output, and the HV Amp gain is 10X. So we used a Dual 2X Junket Buffer Amp which can supply 40VPP to drive our 10X Gain HV Amp to achieve a ~450VP unipolar output. Since the requirements are for low frequency use, we only need to worry about the Diode Clamp Low Frequency Response which is dictated by the coupling capacitor. For the initial test we used a 1uF Mylar film but later found a couple 22uF 400V Electrolytics, so put two in series to be safe!!Anyway, this seems to work well for our needs, so we'll forgo the custom design of another HV AWG amp!!Best