Power supply suggestions for my Behringer TD-3 Daughter Board Project? - Page 1
Forum section: electronics / general

author: JenniferG
author_rank: Frequent Contributor
timestamp: November 19, 2022, 02:16:31 pm
content: Hey everyone,I am working on a Behringer TD-3 Daughter Board to host an arduino, reed relays, DIY vactrols and a breadboard style perforated area. The board is for hosting all the mods one might make to this bass line synthesizer, including ability to add dozens of extra mods controlled via arduino with 3 push button rotary encoders, a shift button.. which in turn turn on and off relays and send PWM writes to the LED's in the DIY vactrols.Here is a link to project on Modwiggler:https://www.modwiggler.com/forum/viewtopic.php?t=267971The full length 11.59" wide board conveniently sits inside the case mounted to the TD-3 PC with standoffs.I am pretty much done with the PCB design, except for the power section. I just don't know what I should go with and how I should design the PCB. I need to regulate from the 9V input from the wall wart jack/switch on the TD-3 -- I'll connect a ground and power wire to each of those and run to the daughter board.The current draw of my PCB will only be on average probably less than 200ma as little as 60ma. But I want the ability to say handle up to 500ma (in case there are more current hungry custom mods one might add in the breadboard area).Should I go with a buck converter or stick to linear regulator since all these mods inside done on the breadboard area are audio signals.I have 4 ground planes -- one on each layer of this 4 layer board. I know the 7805 heat sink area is ground if I recall. I could lay it flat on an exposed pad area with lots of vias running through all 4 layers of the board. So all 4 layers of the ground plane, all that copper would act as a heat sink no?Should I go with an AMS1117? Thing is it doens't have much of a heat sink and the heat sink area is output voltage not ground.How would you power this given the specifications? i.e. handle up to 500ma current reliably and not too noisy.When I am done with this project I am making it opensource.. the C++ arduino code, kicad files, gerbers, and printable labels / drill template.Here's an image of the top layer, the red traces. The power will be to the right and it first runs along the 5V breadboard row, then to the relays and finally to the Arduino Mini Mega 5V pin.

author: JenniferG
author_rank: Frequent Contributor
timestamp: November 19, 2022, 02:26:48 pm
content: I should add that the TD-3 case is not vented.

author: Faringdon
author_rank: Super Contributor
timestamp: November 19, 2022, 02:46:15 pm
content: So its 9V to 5V at 0.5A max.Just use a little Buck module, eg by Recom, TDK, Murata, etc.What about this one...https://uk.farnell.com/multicomp-pro/mp-k7805t-500r3-100/dc-dc-converter-5v-0-5a/dp/393515095p

author: JenniferG
author_rank: Frequent Contributor
timestamp: November 19, 2022, 02:49:55 pm
content: Quote from: Faringdon on November 19, 2022, 02:46:15 pmDo you think the noise from the inductor / the switching, will get into the audio lines of the TD-3? I am keeping the Arduino circuitry isolated form the TD-3 though.. i.e. it's only controlling reed relays and brightness of LEDS in DIY vactrols. I just need the 5V to power the arduino and relays along with the OLED display. I have 4 ground planes, one on each layer.

author: JenniferG
author_rank: Frequent Contributor
timestamp: November 19, 2022, 02:51:15 pm
content: Quote from: Faringdon on November 19, 2022, 02:46:15 pmDoes it need an inductor as well or is that inside the package?EDIT: Lookuing at the data sheet sorry for the question.

author: Faringdon
author_rank: Super Contributor
timestamp: November 19, 2022, 02:52:21 pm
content: It'll be ok as long as you dont run sensitive signal tracks directly under the dcdc module.If you read the datasheet it may ask you to add some input and output capacitors.I think the power inductor is inside that module.......there are some modules where you have to add the power inductor, but not many.You may be asked to add some filter inductor , but the datasheet will tell of this.

author: mariush
author_rank: Super Contributor
timestamp: November 19, 2022, 02:53:53 pm
content: I'm not a fan of 1117 regulators as they're picky about output capacitance and esr (some need ESR of output capacitors between 0.1 ohm and 1 ohm, others are designed to work even with ceramic capacitors on output)I'd suggest LM1085 / LM1084 / LD1085 (1085/1084 is made by many like 1117 series) or something that's available in DPAK/DDPAK / TO-263 as you can have that big pad to solder it to and dissipate some heat into the pcb, but note that some regulators' tab is Vout, on others it's ground, so before you connect that pad to ground on the bottom using vias, make sure regulator's tab is ground.If this will be in a case, or at least partially, the power consumption is low enough that you could use pcb mounted transformers and then you'd get the "cleanest" voltage.You rectify the AC to DC using a small bridge rectifier, smooth it out with a capacitor, then use a linear regulator to produce 5v or whatever you need.For example, here's a low profile 2 x 115v AC -> 2 x 9v (10VA) transformer :https://www.tme.eu/en/details/bvui3920076/pcb-transformers/hahn/bv-ui-392-0076/You can use it with both 115v AC or 230v AC depending how you connect the primary windings. Same for secondary .. parallel them for 9v 10VA or leave them separate for +/- 9v 5VA or in series for 18v ACYou'll just have to put some insulator under the pcb where the transformer pins are, and where the AC connector is.

author: JenniferG
author_rank: Frequent Contributor
timestamp: November 19, 2022, 03:06:10 pm
content: Quote from: mariush on November 19, 2022, 02:53:53 pmThanks I'll look into those voltage regulators. My project is a modification of the Behringer TD-3 bass line synthesizer (303 like). The TD-3 power switch and power jack are supplied by 9V wall wart. Since my daughter board PCB is inside this TD-3, I need to use the existing power switch and 9V jack. So I am going to Y off the wall wart, regulating 9V down to 5V.i've made a couple of my own linear power supplies in the past .. was fun

author: themadhippy
author_rank: Super Contributor
timestamp: November 19, 2022, 03:14:06 pm
content: If you go down the linear path and worried about noise maybe a LM317 as there supposedly quieter than the fixed versions,only requires 2 extra resistors ( 270 and 820 ohm gets pretty dam close to 5v) over the fixed version.

author: jonpaul
author_rank: Super Contributor
timestamp: November 19, 2022, 06:11:05 pm
content: avoid any SMPS reg in such a design.You would need a transformer with shield for isolation and post regulators.We did this in 1980s..1990s, for many 1000s of 16 bit stereo DSP devlopemnt boards.Design was 5V>>push pull inverter>>+/- 18VDC>>Linear regs>>+/- 15, +/-5Load on 5V PC ISA bus was ~ 1A.Jon

author: Faringdon
author_rank: Super Contributor
timestamp: November 19, 2022, 11:13:20 pm
content: Here is a good way to do it with a linear regulator....just use a couple_or_6_0r_7 of PNP TO92 transistors in parallel, with an opamp to control it all.Save messing around with heatsinks.(Considering 9v to 5v at 0.5A)LTspice and jpeg as attached

author: JenniferG
author_rank: Frequent Contributor
timestamp: November 21, 2022, 09:02:05 am
content: Thanks for all the help.I think I will just use a 7805 but horizontal. I have to figure out how to make a large square copper pad for the 7805 to lay on; with vias all over that rectangle which go through the 4 layers of the board, connecting all 4 ground plane layers together. Shouldn't all 4 layers of copper of the pcb then act has a huge heat sink?EDIT: Using KiCad.

author: Faringdon
author_rank: Super Contributor
timestamp: November 23, 2022, 05:29:35 pm
content: ...well, not huge, its only thin 0.035mm copper film if its 1 oz....but yes it does help you carry the heat to the bottom layer, where you can thermal pad it to a real heatsink i suppose.Or you could just use a DPAK 7805.....or the next size up from that....D2PAK.You can also screw a to220 heatsink to an 7805, and bend the whole thing over and screw it into the PCB