Buck/Boost converter for DC motor - Page 1
Forum section: electronics / projects

author: illusive
author_rank: Regular Contributor
timestamp: July 10, 2017, 07:17:59 pm
content: Hi everyone!I got myself a 775 DC motor (12-36V, 0.14-0.2A no load current) for various projects. The load current seems to be in the 1-2A range. I want to built a PWM driver for it that will be powered from a 19V 4.17A laptop PSU. The basic plan is to use a boost converter IC to step-up the voltage to or near 36V and then using a microcontroller or a simple 555 timer to generate PWM signal switching a mosfet thus controlling the motor speed.The first problem i face is choosing the boost converter IC. MC34063 crossed my mind but is seems a bit dated and inefficient because of its low switching frequency therefore a big inductor is needed, also it will need an external transistor. LM2577 is a bit more beefy but it also has low switching frequency. Then i come acrossAX5201ESA, a 500Khz switcher capable of 3A but i have no experience with it and i don't know if that small package can handle that motor.What do you think, any suggestions for something more practical? Better boost IC? Thanks!

author: illusive
author_rank: Regular Contributor
timestamp: August 23, 2017, 05:13:20 am
content: Ok, thanks for the advice. Coming back to this project i've changed the setup a bit. i got a 24V 6.25A DC power supply. Now i just need to manually adjust the voltage from about 5V (the lower limit is not critical) to the 24V by stepping it down with a buck convertor for better efficiency, thus adjusting the RPM. In a nutshell i need a buck convertor with input voltage of 24V or more and output current of about 5A and to have adjustable output voltage. The no load current of the motor is 330mA at 24V but loading it the current may reach several amps.I have looked around and narrowed down several ICs but i need advice on are they going to do job, are they suitable for this application and which one fits the bill.Links with datasheets:LM3489LM3485LM5085MC33167TPS54531

author: ajb
author_rank: Super Contributor
timestamp: August 23, 2017, 06:08:10 am
content: There's no benefit to using a buck converter here. Just PWM the motor.

author: Someone
author_rank: Super Contributor
timestamp: August 23, 2017, 06:51:24 am
content: Quote from: ajb on August 23, 2017, 06:08:10 amDC motor = one enormous inductorIt needs controlling, but once you incorporate the motor as an electrical element you can design some much better (and simpler) drive systems.

author: illusive
author_rank: Regular Contributor
timestamp: August 23, 2017, 10:24:28 am
content: I did a quick research and i found out that with a PWM control i will loose more torque, thats why i decided to go with buck convertor.

author: David Hess
author_rank: Super Contributor
timestamp: August 23, 2017, 02:08:56 pm
content: Quote from: illusive on July 10, 2017, 07:17:59 pmLow frequency just means larger values of inductance and capacitance so larger inductors and capacitors are needed. Efficiency is actually higher because switching losses are lower because there is less switching. Designers use higher frequencies so smaller inductors and capacitors can be used for higher power density.An alternative to a boost converter is a simple inverter where the output voltage will track the input voltage.