DC Motor Controller - Page 1
Forum section: electronics / projects

author: MAntunes
author_rank: Regular Contributor
timestamp: November 12, 2017, 12:33:24 am
content: Hi guys, my name is Miguel and I'm a senior EE student from Portugal, majoring in Automation and Robotics. My favourite favourite topics were electronics, mechatronics and sensors. My Master Thesis project is about sensors and energy harvesting so I thought about doing my first real personal project about mechatronics.I want this project this project to help me learn about real world electronics, PID controllers in the real world, PCB design, SMD soldering and many other things.I want this controller to have:Dual H-Bridge, for controlling two DC motors simultaneously. My objective is to use it in a differential robot, another future project idea.Quadrature encoder inputs, for speed and position control.Communication with the outside: with a computer, a Raspberry PI, another micro-controller, etc.Current sensing, for binary control and limiting the current.You could also suggest some features that you consider interesting.The micro-controller I'm going to use is going to be a dsPIC33FJ128MC802. They allow 16 bit PWM and have two quadrature encoder interfaces and I have a few lying around.For the operating range I though about 24V max supply and 10A max current, seems doable.This is just an introductory post and I will post some updates as I'm advancing in this project.

author: MAntunes
author_rank: Regular Contributor
timestamp: November 12, 2017, 10:59:17 pm
content: So, for this project I'm going to use KiCAD for the circuit and PCB design.Today was the day of choosing MOSFETs for the H-Bridge. The H-Bridge will be discrete so I can probe around and also because of cost, I think I can keep the cost down a bit by designing a discrete circuit.I've decided to go with an all N-Channel MOSFET Bridge, and yes, I know that that I'll need to use some kind of circuit for driving the high-side MOSFETs. The MIC5014 form Micrel (now part of Microchip) seems like a good option and I can get free samples as a student.Choosing the MOSFETs: I went to Mouser and filtered all SMD MOSFETs for max Vds higher than 40V and max Id higher than 15A and RdsOn lower than 20mOhm. There here approximately 1800 parts to choose from. Then, I ordered them by price and here are some choices (https://goo.gl/UWJuFK):621-DMN4026SK3-13 - 40V, 28A, 20mOhm, 9.6nC, 0.395€/unit726-IPD50N04S4L-08 - 40V, 50A, 6.2mOhm, 30nC, 0.505€/unit863-NTD5865NLT4G - 60V, 40A, 13mOhm, 29nC, 0.44€/unitAmong many more, but I would like to stay below the 0.5€/unit. Which would you choose, between these or others?And about the catch diodes, can they be regular diodes, schottky or other?

author: H.O
author_rank: Frequent Contributor
timestamp: November 13, 2017, 05:37:05 pm
content: I might be reading the datasheet wrong but that driver IC doesn't look that great if you're going for the "standard" switching frequency around 20kHz. The IC can only source 50mA meaning the attached MOSFET will take a long time to turn on (obviously depending on gate capacitance). The highside turn -n time is in the hundreds of microseconds range according to the graph on page 4.You'd need four of them at $2.27 (Digikey) each and you'd need to implement cross conduction protection outside of the IC or you will most likely blow the bridge while developing the code... (Yes, I know you said you'd get them for free but still...)I suggest you look for a combined high/low side driver or a half bridge driver instead. Some implements logic preventing you from turning on both switches at the same time, some have internal deadtime generators (which you don't really need since the PCPWM module in the PIC can handle that). Take a look at the IR2183 as a starting point, two of those are cheaper than four MIC5014 and I believe a much better option for your application.

author: MAntunes
author_rank: Regular Contributor
timestamp: November 13, 2017, 09:40:20 pm
content: Quote from: H.O on November 13, 2017, 05:37:05 pmYou are absolutely right. I've read read the datasheet again and I saw that the MIC5014 is no good. The Half-Brigde drivers seem like a much better option. I went to Microchip's website and found the MCP14700. They can source/sink arround 2A and acording to the datasheet.And about the MOSFETs do you or anyone have any sugestions?

author: langwadt
author_rank: Super Contributor
timestamp: November 13, 2017, 10:00:35 pm
content: Quote from: MAntunes on November 13, 2017, 09:40:20 pmhttp://www.st.com/en/evaluation-tools/eval-vnh5019-p1.htmla single ic and protected against most abuse

author: MAntunes
author_rank: Regular Contributor
timestamp: November 14, 2017, 12:09:32 am
content: Quote from: langwadt on November 13, 2017, 10:00:35 pmAs this is kind of an "educational" project I really want to design a discrete circuit. It's a choice I've made.