Schematic analysis for an H-Bridge - Page 1
Forum section: electronics / projects

author: diablodude64
author_rank: Contributor
timestamp: December 19, 2024, 06:59:20 pm
content: Hey all,I am working on a motor controller for a power wheels project that will utilize a Teensy 3.2 microcontroller and full h-bridge design. The motors will be 775's in ran in parallel. I'd like to establish upfront that I am not an EE which will probably be obvious from my schematic. I am hoping to get some feedback as well as a few sets of eyes to tell me if there is anything glaringly wrong that I need to fix, as well as that I should or could do better prior to moving to the PCB layout.Thanks in advance!

author: Benta
author_rank: Super Contributor
timestamp: December 19, 2024, 07:20:06 pm
content: Schematic?

author: diablodude64
author_rank: Contributor
timestamp: December 19, 2024, 07:31:16 pm
content: I re-attached it. Not sure why it didn't come through the first time but let me know if you can see it now.

author: langwadt
author_rank: Super Contributor
timestamp: December 19, 2024, 07:55:21 pm
content: why the logic level converter? the gate driver will work with 3.3V. Why that particular gate driver rather than one of the numerous 8pin ones? you might want to consider a gate driver that prevents you from turning on both the high and low side at the same time

author: diablodude64
author_rank: Contributor
timestamp: December 19, 2024, 08:19:08 pm
content: I made an earlier version that utilized the 3.3v logic but after further research, it's my understanding that the drivers are optimized for 5v logic. With that in mind, I added the logic level converter. I plan to manage the high/low operation by building in a delay with the software. I will also utilize a contactor setup for the batteries that will be controlled by the Teensy (which is not shown on the schematic).

author: temperance
author_rank: Super Contributor
timestamp: December 19, 2024, 08:24:49 pm
content: -Why do you use low value gate source resistors? To power those you probably need those large capacitors on the floating supplies. I would increase those resistors and, lower the floating capacitors to something way smaller and add current limiting resistors in series with the bootstrap diodes (Something low value, based on required floating supply current which you can calculate from Qg the mosfet and the switching frequency.) as without them they are a noise source of the nasty kind.-You also need proper decoupling capacitors for those those bootstrapped power supplies before the diodes.-Resistors in series with the diodes towards the MOSFET gates might be required.Looking at the MOSFET data sheet, this one is rated for 195 A. If you are thinking about such currents or even 30 A, you will need a more advanced MOSFET driver with some descent protection features like short circuit protection, regenerative braking,... Allergo microsystems has those and for the price you will not be able to construct anything better. They work excellent if you are willing to spend a week on laying out the power stages until you think it can't be improved.

author: diablodude64
author_rank: Contributor
timestamp: December 19, 2024, 09:06:21 pm
content: Looking at the Allegro Microsystems A89506 driver and it appears that this would drastically reduce the components on the board as well as be (for my level of knowledge) much more straightforward to implement correctly. This being a DIY/learning as I go project, I appreciate the feedback and patience here. I think this might be a more appropriate direction to go.

author: Zero999
author_rank: Super Contributor
timestamp: December 19, 2024, 10:06:33 pm
content: Quote from: diablodude64 on December 19, 2024, 08:19:08 pmIt's specified to work down to VDD-VSSof 3V, which is plenty of leeway for 3.3V.What does R5 to R7 do apart from discharge the bootstrap capacitors? I'd get rid of them. The IR2110 is more than capable of turning the MOSFETs off, without any additional pull-down resistors.

author: temperance
author_rank: Super Contributor
timestamp: December 19, 2024, 10:07:57 pm
content: Those are straight forward to implement but there are some components missing in the data sheet to make it work properly. Directly on the output of each driver you need a diode connected in reverse between the output and the reference for that output. For the high side drivers this would be from the drive output GHB to and SB for example. Without those, you risk driving the gate drive beyond the maximum rating while the MOSFET reverse diode is being driven into conduction during dead time.The diodes together with the gate drive resistors protect the outputs from going to far below GND. (See date sheet: absolute maximum ratings table, motor outputs. -2...52 V)(The same construction would also be required for the IR2110)

author: Benta
author_rank: Super Contributor
timestamp: December 19, 2024, 10:10:02 pm
content: Oh, no.https://www.eevblog.com/forum/chat/please-rate-my-designschematic-ltrantgt/

author: diablodude64
author_rank: Contributor
timestamp: December 19, 2024, 10:24:41 pm
content: I'm going to spend some time cleaning up the schematic. It's funny you should mention the blocks... I have seen it both ways and prior to the pdf posted, I have always created them in the traditional left to right fashion. Maybe the forum should have a sub-forum distinguishing the noobs from the purists? Either way, I appreciate the constructive feedback.

author: temperance
author_rank: Super Contributor
timestamp: December 19, 2024, 10:46:44 pm
content: Quote from: Benta on December 19, 2024, 10:10:02 pmSomething like this?1. The motor current sensing is decoupled from bridge. It is a better approach towards readability to keep those components together.2. The power supply isn't very clear. Also, it is a better approach to create the 12 V supply and from this intermediate voltage you create a 5 V rail.3. Some GND symbols are pointing upwards.4. J5 can be connected directly to the CAN transceiver.5. The motor connectors can be placed where they connect to the bridges.6. I don't see any fuses.7. Switching regulators require 100 nF ceramic X7R or X5R capacitors on the input. If you go for surface mount types you will need at leas 0805 or larger because the capacitance drops with applied bias voltage.8. The pedal inputs require some TVS diodes and series resistors to protect the Teensy inputs.9. The arrows for supply rails should point upwards for positive supplies and downwards for negative supplies.10. Consider drawing the schematic for the full bridge such that the schematic makes it clear where currents are supposed to flow. (Something like a star GND for example instead of net labels.)Some people in here are allergic for schematics divided into blocks which don't add any useful information.

author: diablodude64
author_rank: Contributor
timestamp: December 19, 2024, 11:06:17 pm
content: Thanks temperance, this is the kind of info that is super helpful to me. I will implement these changes as well.

author: Benta
author_rank: Super Contributor
timestamp: December 19, 2024, 11:11:28 pm
content: Quote from: diablodude64 on December 19, 2024, 10:24:41 pmAlready there:1: Beginners2: Projects

author: diablodude64
author_rank: Contributor
timestamp: December 19, 2024, 11:27:56 pm
content: Maybe sub of a sub... perhaps boredom?

author: diablodude64
author_rank: Contributor
timestamp: February 07, 2025, 08:41:07 pm
content: Hey everyone,I'm back with an updated schematic that is utilizing an Allegro A89506 gate driver. Being a noob, there are likely things that don't make sense or that are wrong. Just want to say thank you for the constructive feedback prior to this post and I welcome more.Would you all mind taking this apart, including schematic layout tips so in the future I can do a better job?p.s. Temperance, I am working through your list and plan to implement fuses as well as the TVS diodes.Thank you!

author: langwadt
author_rank: Super Contributor
timestamp: February 08, 2025, 02:27:50 pm
content: the current sense is definitely wrong

author: diablodude64
author_rank: Contributor
timestamp: February 08, 2025, 05:38:54 pm
content: Can you elaborate? That was one section I was not all that confident on so if you could give me some pointers they'd be much appreciated.Here is a link to the data sheet for the gate driver.https://www.allegromicro.com/-/media/files/datasheets/a89506-datasheet.pdf?sc_lang=en

author: diablodude64
author_rank: Contributor
timestamp: February 08, 2025, 06:07:06 pm
content: Okay, so I think I might have figured it out.LowSourceB ---- LowSourceA|| -------SENSE PINRsense||GNDDoes that make more sense?If I assume stall current between the 775 motors is 100A, that means these current sense resistors need to handle at least 40 watts ideally slightly more so would it be better to utilize a shunt rather than current sense resistors here?