YZ Linear Regulated Power Supply Project

Introduction

The YZ Linear Regulated Power Supply is an easy to assemble, all-in-one power supply solution for audio amplifiers such as the Audinst HUD-MX1.  The design borrows heavily from various other LRPS designs such as the σ25 from AMB but is meant to provide a slightly more integrated solution along with moderately better performance.

The YZ LRPS utilizes a TO-220 form factor positive fixed linear regulator such as the LM340 or LM7815 series and takes an input voltage of up to 35Vpeak from a wall transformer based on the regulator used. (Note that for a negative output you’d have to switch the + and – output of the bridge rectifier chip)  The fuse, switch wirepads, and all of the linear power supply circuitry is integrated on one board – it is meant to be used inside of a HAMMOND project enclosure and all it needs is reduced VAC from a wall transformer of your choice to function.  DO NOT connect this directly to the 115VAC from your wall outlet, as you will simply fry pretty much everything on the board with the high voltage!  Alternatively you could use it with an unregulated DC power supply and omit CSH and the bridge rectifier.

Theory of Operation
A reduced VAC (say 16VAC) comes in from your wall transformer to the board.  CSH shunts away high frequency line noise and transients.  Five fairly large input filter capacitors are used along with the bridge rectifier to provide an excellent filtering stage.  At this point you essentially have a fairly good unregulated DC signal.  A bleeder resistor (R2) is implemented in order to provide a discharge path for the capacitors when the power supply is turned off for safety purposes.

CBY bypasses the input to the voltage regulator IC and helps reduce input ripple.  A 1N4002 diode is implemented as a protection diode for the regulator IC.  Electrolytic, tantalum, and ceramic capacitors (C5, C6, C7) are paralleled at the output of the regulator in order to provide excellent transient performance and extremely low impedance over the entire high frequency range.  This was an idea I got from Application Report SLTA055 by TI.

Input/output voltages and your on/off switch are hooked up by terminal blocks which accept between 26-16AWG.  I find that these work fairly well and provide an easy means of wiring stuff to the PCB.  I considered using Molex connectors as well but I honestly don’t think they are particularly useful here.  Since this power supply can technically handle 1A of max current I’d recommend using at least 22AWG thick wire throughout the build – I’ve used fairly thick traces to account for this on the PCB as well.  A fairly large ground plane is implemented in order to reduce noise and minimize stray inductance among other benefits.

Schematic and Board Layout  (Board layout is 1:1 scale so you can print it out if you want to get an idea of the dimensions)

Parts List

Note that I’m building a 15V power supply specifically for the Audinst HUD-MX1, but only slightly tweaks need to be made if you want different output voltages for other applications.  Many of these parts are incredibly common and you can probably get cheap alternatives for almost everything from a vendor such as Tayda Electronics.  You can do quite lot with the board and I encourage you to come up with your own customizations and part selections – this parts list is more or less here just to get your started.

Part Qty Mouser Part ## Description
AC Adapters 120VAC to 16VAC 1.0A 1 553-WAU16-1000 Wall transformer from TRIAD Magnetics that dumbs the AC line voltage down to 16VAC; excellent build quality but rather large
ACIN/DCOUT/SW – Fixed Terminal Blocks 2P LS5.08mm 90DEG 3 651-1729128 Hardy little terminal blocks from Phoenix Contact that I use for hooking up wires to the PCB – you could alternatively solder everything directly to the PCB but then if anything goes wrong have fun with that…
DCOUT – DC Power Connector 2.1mm Pwr Plug Red Tip Blk Handle 1 502-762 Very high quality 2.1mm ID / 5.5mm OD DC power connector from Switchcraft – very expensive but I still like it a lot
I’m not sure why DC power connectors cost so much off of Mouser but they are good quality connectors
*DCOUT (Alt) – DC Power Plug 2.1mm x 5.5mm x 9.5mm 1 N/A Cheapo part from Tayda Electronics
Rubber Grommets (optional) 2 534-740, 534-731 Just little grommets you fill holes in your enclosure with to pass wires through; choose your own from the Mouser mounting hardware section
F1 Fuseholder for 5x20mm fuses 1 576-65600001009 Just the fuseholder for a standard 5x20mm fuse – you could short this and not use a fuse at all but I wouldn’t recommend this – I’ve already blown one myself while testing this thing
F1 Fuseholder Cover (optional) 1 576-66000001009 This is a little cover for the fuse holder if you feel like being neat – not at all necessary
F1 5x20mm 1A Fast-Acting Fuse 1 576-0217001.MXP This guy will blow immediately if more than 1A of current passes through it, which is probably what we want since most of the parts in this list can only take that much current
SW – any panel mount switch from Mouser or Radio Shack 1 Find your own Mouser carries a huge selection of switches; Radio Shack has a good selection as well and you can choose one that you think looks cool  (make sure your switch can handle line voltages)
Since the board is fairly small you should have quite a lot of space inside your enclosure to work with so switch dimensions shouldn’t be an issue for the most part
CSH/CBY/C8 – Multilayer Ceramic Capacitors (MLCC) – Leaded 0.22uF 50volts 10% X7R 5mm LS (Vishay) 3 594-K224K20X7RF53H5 These little ceramic capacitors are used for high frequency bypassing throughout the circuit
B1 – Bridge Rectifier 1 Amp 400 Volt DO-41 (Diodes Inc.) 1 621-DF04M DO-41/DB form factor bridge rectifier
*B1 (Alt) – DB104G Single Phase 1A 400V Glass Passivated Bridge Rectifiers (Taiwan Semi) 1 N/A Cheaper alternate part available from thaishopetc
RB – Metal Film Resistors – Through Hole 1/4watt 10Kohms 1%  (Vishay) 1 71-CMF5510K000FKEK Bleeder resistor that provides a discharge path for the input filter capacitors when the circuit is turned off – this part is included for safety purposes
C1-5 – Aluminum Electrolytic Capacitors – Leaded 35V 1000uF 20% 12.5×20 mm 5 140-REA102M1VBK1320P Input filter capacitors; general purpose part from Lelon
12.5mm diameter / 20mm length / 5mm lead spacing
D1 – 1N4002 Diode Rectifiers Vr/100V Io/1A Glass Passivated (Vishay) 1 625-1N4002GP-E3/54 Standard 1N4002 diode – serves as a protection diode for the VREG
VREG – 15V Standard Fixed Linear Regulator (National Semi) 1 926-LM340T-15/NOPB You can use more or less any TO-220 fixed output voltage regulator in this spot – the Audinst HUD-MX1 needs 15V in so I recommend the 15V edition of the LM340 from National Semi
TO-220 VREG Heatsink (required) 1 Find your own Try to find something that doesn’t stick out to the sides or front of the VREG too much or you’ll end up running into C6 or CBY
I have a bunch from thaishopetc that work quite well and are very cheap
C6 – Aluminum Electrolytic Capacitors – Leaded 25VDC 150uF 6.3×11.2mm LS 5.0mm (Panasonic) 1 667-EEU-FR1E151B Aluminum electrolytic output capacitor
C7 – Tantalum Capacitors – Solid Leaded 25V 10uF 10% (AVX) 1 581-TAP106K025SCS Tantalum output capacitor
RLED – Metal Film Resistors – Through Hole 1/4watt 680ohms 2%  (Vishay) 1 71-RL07S-G-680 Resistor to set LED operating current which will depend on your desired output voltage and LED – you can easily calculate this with one of the many LED resistor calculators available online [http://ledz.com/?p=zz.led.resistor.calculator]
For my 15V power supply and the LED in this parts list this yields about 17mA of current through the LED which I find is decently bright.
LED – Standard LED – Through Hole Blue Round LED 1 941-C503BBCSCV0Z0461 LED from Cree that has a 3.2V typical forward voltage and a desired operating current of around 20mAYou can be lazy and just drill a hole through the enclosure for the light to shine through or you can use an actual LED panel mount (Mouser #749-CR-174)
Project Enclosure (HAMMOND) 1 546-1591XXSSBK The specific project enclosure that this PCB is designed to fit in – measures 4.3L x 3.2W x 1.6H
You only use two #4 screws to mount one side of the PCB down onto the enclosure
If you want to use another enclosure you can always drill mounting holes of your own into the PCB or just use some sort of adhesive on the backside
*Project Enclosure (Alt)(HAMMOND) 1 546-1591XXTSBK A possible alternate enclosure if the recommended one is out of stock – measures 4.8L x 3.2W x 2.2H
You’ll need to re-drill two holes to mount the PCB inside this one
PCB Screws for Project Enclosures 1 546-1593ATS50 #4 self-tapping screws that HAMMOND makes for screwing down PCBs in its enclosures; you could simply go to a local hardware store and buy a couple as well since these are standard screws anyway

Notice that I believe in putting my money where it counts so I don’t go around suggesting overkill parts for your build – my Lelon input filter capacitors  and AVX tantalum cap really won’t perform any worse in this circuit than Nichicon and Kemet caps.  Things like heatshrink, wire, and solder I expect you to find by yourself or just have laying around. For solder I usually use Cardas quad (can be found on eBay) or 62/36/2 from RadioShack.  Heatshrink and wire I usually just buy in bulk off of eBay or Tayda Electronics.

Assembly
All parts on this board are through-hole and fairly well spaced so that even those new to soldering can assemble this project with relative ease.  The design still manages to remain reasonably compact with overall board dimensions of 2.5″L x 2.0625″W.  You’ll end up with quite a bit of free space inside the HAMMOND enclosure to work with.

The parts in my recommended parts list are for a 15V power supply for the Audinst HUD-MX1 audio amplifier – if you need a different output voltage you can use your own parts as necessary.  You can pretty much build a power supply for any fixed TO-220 linear regulator that you can find on the market – just make sure you are familiar with the design and know what you are doing before you go around using random parts of your own.  I won’t take any responsibility for things getting blown up – I just provide the board and what you put on it is your own problem.

Images of fabricated PCB and project assembly pictures to come…eventually…
I intend to provide the board via eBay at a sub $10 price to those who may want it.  I think it’ll make a good project for beginner hobbyists or those who need a simple but good LRPS.  I realize that there are a lot of other LRPS designs out there already but I think this one has its merits or I wouldn’t have bothered putting it up.  In fact I’ll list a few alternatives right here for you to check out and compare for yourself:
AnalogMetric LV30 LRPS
AnalogMetric SR50 Variable Shunt Regulator
NightFire Kit #1772
AMB σ25 Regulated Power Supply
AMB σ11 Regulated Power Supply

Safety Note:  Be careful when working with live circuits as they can kill you!  The discharge from the four filter caps is most definitely lethal, though implementation of the bleeder resistor does allow things to decay to safe levels fairly quickly.  Always ask someone more experienced to help you if you are unsure about something.

Prototype
Has similar parts and topology to the full version that I plan on making so I’ve been testing it out.  So far it seems to be working great without any issues.  The green PCB you see in the picture is the Nightfire Electronics Kit #1772 with mostly parts from the parts list above. (I didn’t use anything included in their kit, though they actually include some pretty decent stuff)  The separate board with the fuse and terminal blocks is a simple one layer PCB that I etched in my basement.  The circuit board in this project is more or less a combination of the two boards in the picture with some more bells and whistles.

I tested this power supply vs the stock Audinst HUD-MX1 power supply by loading them to 200mA of output current and AC coupling the output to my true RMS benchtop DMM by means of a 0.47uF WIMA MKS cap and a 100K resistor.  This way I could use the smallest 200mVAC range on my DMM to get an idea of the ripple voltages.  I’ll try to follow up with better measurements sometime if I can get my hands on a decent oscilloscope.
The stock Audinst HUD-MX1 switching power supply measured ~1mVrms which is not bad at all for a switching unit. (was getting some variation in the measurements)  The switching frequency appears to be around 680KHz or so which is well above the audio range.  My prototype LRPS measured 0.04mVrms (consistently) which is very good.  The Audinst stock unit is actually not too bad as far as swtiching power supplies go, but for a bit of your time and money you can do quite a bit better and learn something in the process by building yourself a nice little LRPS like the one pictured above.

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