Buck-boost converter  - Page 1
Forum section: electronics / projects

author: hussamaldean
author_rank: Unknown
timestamp: January 15, 2018, 08:34:47 pm
content: Dear all,I started to design buck-boost converter based on flyback buck-boost converter and I am using IRF510 N-channel MOSFET as switch with Arduino Uno. However, when I send PWM signal to the mosfet, the mosfet doesn't turn off and remains on all the time and it becomes so hot and the output voltage collapsed from 12V to something like 1V and all voltage are on the mosfetis there something wrong the design or the 5V can't control the MOSFET ?Note: I am planning to use MOSFET driver, which one do you recommend and with schematic if possibleRegards

author: Damianos
author_rank: Frequent Contributor
timestamp: January 15, 2018, 08:58:48 pm
content: Welcome!In the circuit, increase the value of the R204 and decrease the C127.Perhaps you forgot to show something?

author: Wimberleytech
author_rank: Super Contributor
timestamp: January 15, 2018, 10:46:44 pm
content: Quote from: Damianos on January 15, 2018, 08:58:48 pmI am shocked that you would recommend reducing C127. A more thorough analysis is in order.

author: hussamaldean
author_rank: Unknown
timestamp: January 16, 2018, 09:19:08 am
content: Hi,I attached my design with the postPWM signal from D5 with frequency of 64KHzis there something wrong ? or Arduino can't switch the mosfet fast enough ?

author: Zero999
author_rank: Super Contributor
timestamp: January 16, 2018, 11:49:41 am
content: Floating the load's voltage on top of the supply voltage seems like an odd decision.How much current do you require? The 1N4148 is only rated to 150mA.You may need a MOSFET driver, but if it's a low current, then use a smaller MOSFET, with less gate capacitance, such as the 2N7000.

author: hussamaldean
author_rank: Unknown
timestamp: January 16, 2018, 12:37:12 pm
content: Quote from: Hero999 on January 16, 2018, 11:49:41 amThank you for your replyIt turns out that what I used was zenor diode rather than actual diode which led to miss behaviour of the buck-boost system.I salvaged new SR5100 diode and see how things will go from here and keep you postedRegards

author: Damianos
author_rank: Frequent Contributor
timestamp: January 16, 2018, 04:28:23 pm
content: I agree with Hero999 above.In addition, are the commons of both circuits connected together? From your description, maybe the transistor is activated parasitically and remains uncontrolled.

author: hussamaldean
author_rank: Unknown
timestamp: January 16, 2018, 04:32:47 pm
content: updateI partially succeeded and managed to boost 5V to 8V when loaded without any problem but once the load is disconnected, the voltage shoots to high level like 72V due to uncontrolled environmentI'll see what will happen when I get my mosfet driver and the extra componentsI'll keep you all up to date

author: lem_ix
author_rank: Regular Contributor
timestamp: January 16, 2018, 04:56:52 pm
content: Definitely a driver, that mosfet can't be turned fully on by an arduino. Especially not at 64 Khz. I'd use a better mcu.

author: hussamaldean
author_rank: Unknown
timestamp: January 16, 2018, 07:21:56 pm
content: Quote from: lem_ix on January 16, 2018, 04:56:52 pmcould you suggest a good driver ?

author: Zero999
author_rank: Super Contributor
timestamp: January 16, 2018, 08:42:37 pm
content: Quote from: hussamaldean on January 16, 2018, 04:32:47 pmWell what do you expect? There's no feedback!What are your requirements? Input and output voltages? Current?If you only need to boost the voltage, then you don't need buck, just boost, which is much easier.If the output voltage can be below, as well as above the input voltage, then a buck-boost converter is needed.If the polarity of the output can be negative, then it's fairly simple.If the output voltage needs to be positive, then you need two transistors and two diodes, which is more complex.https://en.wikipedia.org/wiki/Boost_converterQuote from: hussamaldean on January 16, 2018, 07:21:56 pmI think that's the least of your problems, at the moment.

author: hussamaldean
author_rank: Unknown
timestamp: January 17, 2018, 03:58:34 am
content: Quote from: Hero999 on January 16, 2018, 08:42:37 pmthanks for these valuable informations and I will see them throughI'll keep you posted

author: hussamaldean
author_rank: Unknown
timestamp: January 17, 2018, 07:13:54 pm
content: Hi,I scraped the idea of buck-boost converter and I moving on with buck converter idea with LM2596 chip, PCF8591 ADC-DAC chip and arduino to control the voltage.I can tell I partially succeeded and managed to regulate the voltage manually. next step feedback system with constant current output.Note: it will be powered by 19V laptop power supply