Piezo Driver Board Issues - Page 1
Forum section: electronics / projects

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 02:19:11 pm
content: I'm trying to create a board that can drive a piezo actuator (https://www.ebay.com/itm/156164898495) at kHz frequencies while also being able to read in the voltage with an RX/TX switch.I attached an image.R13 in the schematic is DNP. We are using a 1k current limiting resistor in place of R9.I've been just testing the transmit side and there is an issue. For some reason it's shorting the negative supply when I put it at -12V. When I set it to -3V it seems fine. I can even put up the V+ higher. We were originally testing at V+/V- at 35V. The driver operational amplifier doesn't feel like it's getting hot. Then we set V+ = 12V and V- = 12V with 100mA limit. The V+ works perfectly, but the V- is current limiting on my supply. When I first powered on the board, it appeared to be working perfectly, but then I left it for the weekend and it started acting weird. This behavior is very intermittent.In the datasheet for the ADHV4702-1BCPZ-R7, they use protection diodes from the non-inverting terminals to the inverting terminal.I added these diodes and 10uF capacitors from V+ to ground and V- to ground and it didn't seem to fix the intermittent current limiting of my power supply. I wonder if I damaged the chip already? This is for a senior capstone project and we don't have much money, so we can't keep burning through these chips. We already burned through 1 during the assembly process. We are trying to measure the flow of water through a tube with piezo actuators.Here is our simulation:Any suggestions?

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 11, 2024, 03:32:49 pm
content: Post clear pictures of both sides of the actual PCB. Perhaps something is miswired. For example, if you mixed up the emitter and collector the Q2, mounted U4 wrong, bad soldering, etc...One other note. To receive on the same piezo element, you'll need some way of disabling the TX output (Make it Hi-Z) when trying to receive the echo. In lieu of that, a pair of paralleled back to back diodes in series with the TX output driver can also work (Echo would be less than 1.4Vp-p) as long as the TX output returns to 0V when idle.

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 03:36:33 pm
content: We currently don't have any of the circuitry for the receive side installed. I attached an image of the schematic for your edification. The layout is also attached.When I get back into the lab, I'll send a picture of the PCB.

author: xvr
author_rank: Frequent Contributor
timestamp: October 11, 2024, 03:41:43 pm
content: ADHV4702 has more pins that presented in your schema. Did you connect DGND and Radj pins? They should be connected.

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 05:32:26 pm
content: Yeah I split it into U4A and U4B in the Altium schematic. Those connections are right below in the picture I sent.

author: huababua
author_rank: Contributor
timestamp: October 11, 2024, 06:38:27 pm
content: I see tons off differences between the reference design and your implementation.This circuit can not work.Op amp needs to be at higher voltage than your power Transistors. Also what voltage are you targeting? Have you checked the max allowable voltages for this transistor ?

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 06:49:26 pm
content: But it works within the simulation. Those power BJTs are pretty high current and wattage.

author: huababua
author_rank: Contributor
timestamp: October 11, 2024, 06:59:46 pm
content: Okay then good luck 🤣

author: TimFox
author_rank: Super Contributor
timestamp: October 11, 2024, 07:13:23 pm
content: Max voltage, current, and power are separate specifications.A high value for max power and max current does not imply a high value for max voltage.

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 07:45:09 pm
content: The datasheets seem to hit all my requirements--unless I'm missing something:https://www.onsemi.com/pdf/datasheet/mjb41c-d.pdf

author: TimFox
author_rank: Super Contributor
timestamp: October 11, 2024, 07:46:33 pm
content: Yes, the data sheet shows 100 V, but you only stated power and current.

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 07:49:21 pm
content: We were driving at +/- 35V then it appeared to work. The next day it suddenly stopped working--curious if it wasn't working initially?I am current running it at V+ = 32V and V- = 5V and it doesn't appear to short. But when I changed the V- to -12V it appears to short.I appreciate the help. I'm definitely missing something or else it would be working.

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 07:51:36 pm
content: I'm slightly concerned we might've shorted the V+ and V- at some point during testing. The leads were physically close to each other on the board.It just doesn't make sense to me that it works at V+ at 32V and V- at -5V without current limiting... but switching to 32V and -12V causes current limiting. The output of the push pull stage is only like 9V which is also strange when at the 32V and -5V V+/V-.I thought decreasing R9 might be necessary at some point to allow more current into the bases of the push pull stage.

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 11, 2024, 08:05:38 pm
content: Do you have a thermal camera? If so, increase the V- supply until it starts to limit at 100mA. See what starts to get hot.Obviously running it with asymmetrical supply voltages will effect the output waveform, but what does the real world output waveform look like when you're running it with V+ at 32V and V- at -5V?Also what is the current draw on both V+ and V- when you're running it with V+ at 32V and V- at -5V?

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 08:15:33 pm
content: This is the output being fed into a piezo. Putting it above ~12V it starts current limiting.So like +35V and -12V aroundAlso scoped the output of the signal with the function generator disabled. This is just with the supply on like 60Hz noise.

author: inse
author_rank: Super Contributor
timestamp: October 11, 2024, 08:27:55 pm
content: I only know a little about piezo driving, but to achieve reasonable levels of output power you need to drive them at high voltage like several hundreds of volts.To maximize efficiency they are placed in a resonant circuit.You are driving it like an audio speaker - is the limited power ok for you?What are you trying to achieve anyway - something like a sonar system?

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 08:32:44 pm
content: Quote from: inse on October 11, 2024, 08:27:55 pmWe are planning on driving it at a lower voltage -- the operational amplifier for the push pull can only do +/-100V max. I was just hoping the push pull stage would allow us to get more current because the op amp maxes out at 25mA-50mA. By buffering it with the BJTs I was hoping to get like a lot more current.We are trying to make an ultrasonic flowmeter for our senior capstone.

author: inse
author_rank: Super Contributor
timestamp: October 11, 2024, 08:39:56 pm
content: Senior capstone- what’s that, Google didn’t make me smarter.Flowmeter - is that a good project to start from scratch?

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 08:41:43 pm
content: Senior capstone is like an undergraduate final project. It's a class we have to take where we make a project.We have like a small budget to develop everything ~$700

author: inse
author_rank: Super Contributor
timestamp: October 11, 2024, 08:43:46 pm
content: Ahh, you need help with your homework 🤣

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 08:47:02 pm
content: This is a completely custom project. Every team does a completely different project. We don't really have anyone to asks questions to with this type of expertise haha.

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 09:22:10 pm
content: We just assembled a third board and it works perfectly. IDK why the old board wasn't working hmmm

author: TimFox
author_rank: Super Contributor
timestamp: October 11, 2024, 09:28:29 pm
content: My last piezo project was with a commercial micro manipulator that could achieve maybe 1 mm extension at high force in one direction at +1000 V bias.To move In two directions required fighting it with a Belleville washer spring.This reduces the maximum motion due to the mechanical compliance of the long piezo stack (something like 50 mm, iirc).I designed the driver but I don’t remember the circuit. Maybe it used an Apex hybrid? They have expensive devices up to 2500 V.

author: helloThere
author_rank: Contributor
timestamp: October 11, 2024, 09:37:31 pm
content: Quote from: TimFox on October 11, 2024, 09:28:29 pmThat sounds extremely interesting, I'd be curious how you did it. Any resources? This is an extremely simple approach just because our budget was so small

author: moffy
author_rank: Super Contributor
timestamp: October 11, 2024, 09:48:18 pm
content: Try a small feedback capacitor across R7(first dwg) of the order of 10pF see if that stabilises the oscillations.Edit: Two drawings

author: TimFox
author_rank: Super Contributor
timestamp: October 11, 2024, 09:48:24 pm
content: I’m retired now, and don’t have the records available.The commercial manipulator was from a German company, whose name escapes me. Their app notes discussed external springs. Google finds several: maybe it was “PI”?That was a stack of piezo elements, and achieved high force at low extension.With so many elements wired in parallel, the capacitance was huge, maybe 1 uF.They also make “bimorphic” activators, using long strips bonded together so that the assembly bends as one extends and the other shrinks. This gives much more motion at much less force.I’m now sure that the amplifier was a 1200 V or so unit from Apex Microtechnology (q.v.).

author: TimFox
author_rank: Super Contributor
timestamp: October 12, 2024, 10:36:55 pm
content: I remembered the vendor for the piezo manipulator for my project 30 years ago:It was Physik Instrumentehttps://www.pi-usa.us/en/for the US office.

author: mawyatt
author_rank: Super Contributor
timestamp: October 13, 2024, 12:28:46 am
content: We've developed custom controllers for Physic Instrumente Piezo Actuators some time ago. These were for nanometer level camera/subject positioning for making ultra high resolution (Giga-Pixel) chips images we designed.Some may find this link useful.https://www.photomacrography.net/forum/viewtopic.php?f=25&t=40510Be sure to study the details in this link, and the nanometer measurement technique (will discuss how this was accomplished if interested, very clever method), also if interested follow the related threads for piezo actuator driver(s) which started out as Open Loop Control. We can't remember much about this, so please study in detail the link and associated links over at Photomacrography mentioned above, will try an answer details if we can remember (been a long time).BTW piezo stages are highly capacitive and make a normal op-amp type low output impedance amp go unstable. To remedy this a compensation scheme needs to be in place, and/or a different type output stage (current mode).Best,

author: inse
author_rank: Super Contributor
timestamp: October 13, 2024, 05:59:36 am
content: Until a couple of years I was supporting the development of electronic drivers for piezo Diesel injectors.The driving method for actuators is probably very different to the sonar application the op is looking for.However I wonder he is about to use a single element for send and receive.The short google search showed up diagrams of flow meters consisting of separate channels.But I have no clue about that kind of application.All the best for your homework/project, I hope the eevblog will be cited as resource 😁

author: helloThere
author_rank: Contributor
timestamp: October 13, 2024, 01:11:51 pm
content: Quote from: mawyatt on October 13, 2024, 12:28:46 amInteresting, I was thinking about trying and making it current mode. I wanted to use a low number of components due to the budget/everything having to be hand assembled. I'm assuming there's a good chance we'll have a lot of ripple on the output due to driving a capacitive load. When designing the system, I didn't know what piezo element we were going to use, so just designed it very generally. The current piezos are pretty low capacitance.

author: mawyatt
author_rank: Super Contributor
timestamp: October 13, 2024, 01:16:37 pm
content: Quote from: inse on October 13, 2024, 05:59:36 amInteresting, we completed a project for a customer last year developing Injector Drivers & Testers, these were for the Inductive Drive for Marine use but also worked with Automotive types including GDI. Plans were to continue with Piezo Driver design which required a completely different approach, however clients funds couldn't support the continued development, so project has been put on hold.Best,

author: mawyatt
author_rank: Super Contributor
timestamp: October 13, 2024, 01:20:56 pm
content: Quote from: helloThere on October 13, 2024, 01:11:51 pmMight be a good idea to spend some time modeling the Piezo Device. Once you have a decent model representing the Piezo Device you can then begin the stability analysis and design of the amplifier.Good luck on your project.Best

author: helloThere
author_rank: Contributor
timestamp: October 13, 2024, 02:28:14 pm
content: Quote from: mawyatt on October 13, 2024, 01:20:56 pmThe project is still very much a WIP. I'm doing the electronics but we have a few physics majors on the team. I just don't know the equation relating the displacement for each piezo to the necessary transmission through the volume. TLDR it needs to be able to properly drive a few different piezos if necessary as we test them. We're basically doing TOF measurements with flowing water and seeing how it changes. We're also planning on doing a doppler effect measurement. The physics of calculating the speed from the transmission is very much not my ballpark. We're attempting to do everything with a scope first then doing everything with a more embedded approach. The ADC speed is a lot higher than we expected, so our embedded guy is trying to work that out.