Design review: M103v1 bench power supply - Page 1
Forum section: electronics / projects

author: technix
author_rank: Super Contributor
timestamp: March 26, 2016, 05:09:24 pm
content: Please review... Thanks in advance.Specifications:* Input: 24V AC (at PCB input point)* Main Output: 0-20V, 0-10A, power limited by software (50W,) input LM2596 (about 90W) and input fuse (about 60W at 2A), front panel banana jacks, relay switched, double fused* Secondary output: 5.3V, 2A maximum, USB Type A, with programming resistors for iPhone and iPad, double polyfused* Topology: main output: non-isolated switch-mode & linear combo; secondary output: non-isolated switch mode only* Thermals: active-cooled heat sink with PWM-controlled fans, automatic thermal shutdown, no thermal fuses* Control interface: iPhone app (over Bluetooth Low Energy,) keypad & LCD* Firmware: DreamOS/embedded based, over-the-air updates (firmware updates are released together with the associated iPhone app updates, installed over Bluetooth link)* Supports both local and remote sensing, terminals internally relay switchedAnalog section:Digital section:Interface board (separate PCB)I try to keep the cost down, and my main heatsink have a 7-component limit. The most expensive components on this board are LM35DT, INA126 and ATmega328P.

author: 3141592
author_rank: Regular Contributor
timestamp: March 27, 2016, 08:11:38 am
content: Couldn't you use a bimetal switch instead of the LM35 circuit for thermal shutdown? Also the TO92 variants of the LM35 are a lot cheaper, if you could accept using epoxy to couple the sensor to the heatsink, it would be a bit cheaper.

author: mij59
author_rank: Frequent Contributor
timestamp: March 27, 2016, 09:04:56 am
content: Some things I noticed.Specs 0-1.0 A I think.There is no real need for a pre-regulator.When K2 is off there is not feedback, Vout will be maximal.C11 4700 uF slightly high, how about 47 uF.No frequency compensation for the current and voltage control loop, circuit will not be stable.C8, C9 very high value, will slow down the control loop of the LM2596.Feedback circuit for the LM2596 can be simplified.What's F3 for ?When there is no feedback from the remote terminal Vout will be maximal.

author: technix
author_rank: Super Contributor
timestamp: March 27, 2016, 09:52:29 am
content: Quote from: mij59 on March 27, 2016, 09:04:56 amThat K2 switches from local to remote sensing... F3 is a polyfuse protecting the remote sensing line.

author: mij59
author_rank: Frequent Contributor
timestamp: March 27, 2016, 09:55:50 am
content: Quote from: technix on March 27, 2016, 09:52:29 amK1 switches to remote sensing, F3 protects a 56k resistor.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 27, 2016, 11:35:26 am
content: The LM2596 will not deliver much more than 3 A, but I will not comment much on the SMPS part here anyway, as there is a separate parallel thread.The output stage will not work this way - maybe with Q2 as a PNP, but this is tricky - the usual way would be a Darlington configuration. The output stage should also have protection against to negative voltage a the base (diode to output) and than a current limiting for the 2N7002, to limit the current flow out of a possible large output capacitor.With the output disconnected, the otuput capacitor will charge up all the way - so a massive spike when enabling the output this way.The linear part still lacks the compensation - the main difficulty on a linear supply, especially with remote sensing.

author: prasimix
author_rank: Unknown
timestamp: March 28, 2016, 10:35:39 am
content: Maybe you'll be surprised how Atmega328 class of MCU that is frequently mentioned in may DIY power supplies is inadequate to accomplish decent functionality. You can always dosomethingthat is more thennothing, but at the end if you are really going to spent hundreds of hours to make a functional device then is highly possible to feel sorry in one moment why more capable MCU (with more SRAM and processing power) is not selected from the start.If you are going to add remote control, why not use from the start MCU or module that comes with Wifi or Bluetooth?

author: technix
author_rank: Super Contributor
timestamp: March 28, 2016, 10:56:30 am
content: Quote from: prasimix on March 28, 2016, 10:35:39 amThen I run into a price and/or package and/or RF design brick wall. I have a limited budget, cannot solder BGA or QFN reliably, and may run into trouble with RF designs on my own PCB. All my PCB stay below 500MHz, most of the time.

author: prasimix
author_rank: Unknown
timestamp: March 28, 2016, 11:40:46 am
content: I was thinking about ready to use solution such asESP8266modules. If you need more GPIO lines then cheap I/O expander or shift registers should do the job.

author: timb
author_rank: Super Contributor
timestamp: March 28, 2016, 01:01:34 pm
content: Quote from: AcHmed99 on March 28, 2016, 11:43:29 amAnother good example would be the PSoC by Cypress. And unlike most uCs with a few fixed analog functions, it has a real, fully configurable analog section. You get op-amps, DACs, PWMs, comparators, high and low resolution ADCs, muxes, etc.They've even got a version with built-in BTLE! If you don't want to solder the QFN package and do the simple RF design required, then you could just buy one of the $10 dev modules. Essentially it's just the MCU soldered on a DIP breakout board (with an ISP header and the relevant RF stuff for the BTLE model).There's even a macro for supply tracking and margining that uses digital logic and analog blocks almost exclusively, so it's fast (no CPU overhead).

author: technix
author_rank: Super Contributor
timestamp: March 29, 2016, 11:00:12 am
content: Quote from: timb on March 28, 2016, 01:01:34 pm30V tolerant?

author: timb
author_rank: Super Contributor
timestamp: March 29, 2016, 12:54:52 pm
content: Quote from: technix on March 29, 2016, 11:00:12 amNo, but no uC is. (Though the PSoC does have a group of pins they call SIO. They are tolerant to inputs well above the supply levels; digital only though.)At any rate, you would level shift the 30V analog signals down to 5V with a resistor divider. You'd have to do that with pretty much any discrete ADC/comparator/whatever solution anyway.

author: technix
author_rank: Super Contributor
timestamp: March 29, 2016, 03:26:47 pm
content: Quote from: timb on March 29, 2016, 12:54:52 pmThen, 1) what series are you talking about, 2) how much would it cost, 3) where to find the tools and 4) how much would those tools cost? I am budget restricted.