Purpose of MCU in laboratory PSU- Gophert. (controling tl494)  - Page 1
Forum section: electronics / projects

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 06, 2021, 07:51:54 pm
content: Hi,i would like to ask what mcu actually doing? (in PSU like gophert)tl494 has current and voltage control. Does mcu only sets reference values at DAC outputs for tl494? Its not necessary to have mcu then? It also probably control user interface...thanks

author: strawberry
author_rank: Super Contributor
timestamp: December 06, 2021, 08:27:35 pm
content: general purpose MCU is unreliable as main controller and short circuit protection ... in PSU (hard to predict all software bugs and easy to blow transistors in process)in this case you can use MCU to set reference and user interfacededicated PSU MCU have dedicated built in hardware (MCU with built in 494 like circuit but with ADC inputs and fancy control registers)most of those cheap powersupply have weird circuits. for example CC done via shutdown pin and second comparator disabled

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 07, 2021, 06:59:47 am
content: Can you recommend me a decent example of PSU please? thanks

author: strawberry
author_rank: Super Contributor
timestamp: December 07, 2021, 07:40:44 am
content: https://www.infineon.com/dgdl/Infineon-AN-EVAL-2HS01G-300W-1-AN-v01_00-EN.pdf

author: MacIntoshCZ
author_rank: Regular Contributor
timestamp: December 07, 2021, 08:31:20 am
content: thanks, LLC topology is not much suitable for variable output voltage. Or am i wrong?I would like to see decent example of switching laboratory powersuply. Do you think LLC+buck boost converter is good combo for lab. psu?

author: profdc9
author_rank: Frequent Contributor
timestamp: December 07, 2021, 11:08:55 am
content: I designed a TL494 controlled by a MCU. The TL494 does the short circuit protection and voltage regulation, and the MCU sets the voltage and current limits.https://github.com/profdc9/FlexibleCharger/tree/main/LiFePO4smartchargerThe schematic ishttps://github.com/profdc9/FlexibleCharger/blob/main/LiFePO4smartcharger/LiFEPO4smartcharger.pdfNotice the high side current sensing at Q3 which pulls the duty cycle to zero when a short circuit is detected.

author: rpiloverbd
author_rank: Regular Contributor
timestamp: December 07, 2021, 04:35:31 pm
content: Yeah you can use TL494 alone without any MCU, as you can see in the below figure, its a modified sine wave circuit using TL494 and they haven't used any MCU.Source ->https://www.theengineeringprojects.com/2017/06/introduction-to-tl494.htmlBut thing is if you want to make your project more flexible and user controllable then you need to use MCU.In PSUs, its used for creating user-provided thresholds, for controlling siplays i.e. LCDs or 7-segments etc.So, I would say MCU is a necessity when it comes to PSU or any embedded product.

author: penfold
author_rank: Frequent Contributor
timestamp: December 07, 2021, 04:50:42 pm
content: Quote from: MacIntoshCZ on December 07, 2021, 08:31:20 amIn general, I think you're correct there. LLCs do tend to suffer from a slightly narrow range of control and at least the control dynamics change rather a lot if you push them to the limits. There are things that are possible with mixing PWM and frequency control to extend their control range... but its a bodge really. LLCs make for a better front end, as you can keep the losses relatively low and they are less sensitive to transformer parasitics and afterall, in a lab supply you can suffer a slightly lower efficiency by using a second converter, especially if it keeps the output well controlled.There are of course plenty of MCUs that make themselves well suited to direct PSU control, and you can do things to prevent un-determined startup conditions and faults from locking the PWM high etc (like using a watchdog to inhibit the gate drivers), but, yeah, I burned through a lot of FETs when debugging a control loop! Best to just use a DAC to set the reference to an analogue controller.