A power supply is a device that supplies electric power to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy (mechanical, chemical, solar) to electrical energy. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source.
Every power supply must obtain the energy it supplies to its load, as well as any energy it consumes while performing that task, from an energy source. Depending on its design, a power supply may obtain energy from:
- Electrical energy transmission systems. Common examples of this include power supplies that convert AC line voltage to DC voltage.
- Energy storage devices such as batteries and fuel cells.
- Electromechanical systems such as generators and alternators.
- Solar power.
A power supply may be implemented as a discrete, stand-alone device or as an integral device that is hardwired to its load. Examples of the latter case include the low voltage DC power supplies that are part of desktop computers and consumer electronics devices.
Commonly specified power supply attributes include:
June 12, 2012
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More Power! ... QRO Power Supplies
Armed with some basic principles and the right components, you can design just the right solution for your needs!
Overview
One of the things we usually take for granted is the good ol' DC power supply for the projects on our bench. The near-ubiquitous "12-volt" supply will power most of our circuits and we usually don't even give this important function a second thought. But what happens when you need a good deal of current, beyond what you can get from that handy-dandy AC adapter borrowed from laptop use? Or suppose you are unwittingly powering a receiver with one of those new-fangled switching power adapters and you are getting some unusual hash in the spectrum that cannot be explained?
So in this week's session we'll be delving into the wide-ranging world of electrical power conversion, and exploring the various types of supplies out there and what the preferred use is for them. And in our usual tradition, we have a hands-on, DIY project that illustrates many of the principles of the discussion, and it's something that you can easily build with confidence of it doing the job for your specific needs.
73, George N2APB & Joe N2CX
Audio Recording ... (Listen to the MP3 podcast)
Discussion Notes:
<20:24:35> "Ray K2ULR": Clack and Clack.... still on the
air!!!
<20:24:55> "Ray K2ULR": Click & Clack... the Tappet brothers. :)
<20:26:44> "Armand WA1UQO": Sorry to say they retired this week. All shows from
now on will be from their archives .
<20:28:09> "Pete - WB2QLL": New shows 'til they retire in September.
<20:28:52> "Armand WA1UQO": Great ! Thanks :)
<21:02:32> "Rick K3IND": So those lumps on the power supply cables are toroids
to grab that noise?
<21:08:37> "George - N2APB": Cypress PSoC links ...
<21:08:40> "George - N2APB": • Training for PSoC and PSoC Creator (including an
introduction to PSoC 3 and PSoC 5) can be found here:
http://www.cypress.com/?rID=40547
and here
http://www.cypress.com/?id=2232&rtID=134
• PSoC Insider - a blog with complete projects, videos, and more is here:
http://www.cypress.com/?id=3503
• A description of the new features in Creator 2.0 can be found at this URL:http://www.cypress.com/?id=2232&rID=38406
• The book ""My First Five PSoC 3 Designs", available in printed form or PDF, is
here:http://www.cypress.com/?rID=43123
• The Cypress Developer Community, featuring Forums, Videos, Blogs, and Training
is here:
http://www.cypress.com/?id=2203
• Need Creator on CD? See
http://www.cypress.com/?rID=53608
<21:09:25> "Frank N3PUU": marlin p jones usually has some surplus xformers
mpja.com
<21:17:22> "Frank N3PUU": its a shame you guys werent around when I was trying
to build up a 100A supply.. made lots of smoke :) good presentation, thanks!
<21:17:56> "Mike - WA8BXN": forgive me, i have had to be in and out a bit
tonight, has the "This weeks project = 13.6 v supply" been discussed yet?
<21:18:49> "Ray K2ULR": I think it's a switcher.
<21:18:59> "Pete - WB2QLL": super capacitor
<21:19:26> "Ray K2ULR": http://www.gammaresearch.net/hps-1a.html
<21:20:54> "Sid KC2EE": Gammaresearch.net HPS-1A supply
<21:22:21> "WA0ITP Terry": Thank You
<21:29:16> "Rick K3IND": 73
SESSION NOTES ["Under Construction" up to showtime]
Wikipedia ...
Linear, Programmable Power Supplies, from Hameg Adjustable, Linear, 15A (MFJ) Classic ham use 20a liner PS (Clegg)
Open Chassis Linear (Sola) 13.6V fixed, 2A Switching PS (MFJ)
Linear versus switching supplies
You all know how a typical linear power supply operates: A heavy transformer takes the line voltage and converts it into something slightly above the desired final voltage. Some diodes rectify it, a big filter capacitor smoothes out the DC, and a series pass transistor burns up the excess voltage, so you get the desired output. A simple control circuit drives the pass transistor to hold the output voltage constant. The circuit is simple and uses few parts, but several of these parts are big, heavy, and expensive. And the efficiency is usually only around 50%, often even lower. That produces a lot of heat, which must be removed by big heat sinks and fans.The switching approach is totally different: The line voltage is directly rectified and filtered, resulting in about 300 or 150V DC (300 is more commonly used). This feeds a power oscillator which produces output at about 20 to 500 kHz. This relatively high frequency allows the use of a small, lightweight and low cost transformer to reduce the voltage. The output is then rectified and filtered. And now comes the most interesting feature: Instead of just burning up the excess energy, in the switching power supply the control circuit steers the power oscillator in such a way that it delivers just the amount of energy needed. So, very little energy is wasted, resulting in high efficiency (75 to 90%), almost no heating, and a much reduced electricity bill!
[For a more in-depth discussion on Linear-vs-Switching Power supplies, see ... http://power-topics.blogspot.com/2007/08/linear-vs-switch-mode-power-supplies.html]
And now, our presentation! ...
Converting electrical power to a more convenient form
· AC line voltage to DC to power rigs
· AC line voltage to operate your computer
· Convert battery power to AC
· Battery power from solar cell to steady 12V DC
· Battery Power to 5V to charge cell phone or USB device
Types of supplies
· Step down supply
◦ Transformer to drop 120V AC to about 12V AC
◦ Rectifier and filter to get DC from AC
◦ Usually a regulator to get constant output voltage
▪ Linear regulator
▪ Switching regulator
· Step up supply
◦ Transformer to increase 120V AC to several hundred V DC
◦ Rectifier and filter to get DC from AC
◦ With tube rigs also step down winding for filaments
▪ Often no voltage regulator
· DC to DC converter
◦ Oscillator to generate sine wave AC or square wave
◦ Transformer to step up or down voltage
◦ Rectifier and filter to convert AC back to DC
◦ May or may not have regulator
· DC inverter
◦ Oscillator to generate sine wave AC or square wave
◦ Transformer to convert to 120V AC
Power supply circuitry
· Linear regulator power supplies
◦ Simple circuitry
◦ Need heavy iron transformer
◦ Large filter capacitor
◦ Output has low noise and ripple
◦ Loses power in pass transistor
· Switching power supplies
◦ Often rectify and filter at AC line voltage
▪ Generate square wave AC at KHz to MHz
· Transformer for line isolation
· Much smaller, lighter than 60 Hz
▪ Rectify and filter DC out of xfmr
· Filtering much easier at higher freq.
▪ Sense output level and send sample back to regulator
· Regulator works at rectified line voltage
· Regulates by PWM on HF square wave
▪ More complex circuitry
· But IC's can make simple
◦ On-line design tools
· Needs special transformers and chokes
◦ Smaller and less expensive than 60 Hz
· May generate kHz or MHz noise
◦ Both conducted on DC output and radiated
Power supply physical format
· Familiar large metal chassis
· Wall warts
· Small pc cards
Linear Power Supply vs. Switching Power Supply vs. Unregulated Power Supply
|
Switching Regulated Power Supplies |
Linear Regulated Power Supplies |
Unregulated Power Supplies |
|
| Circuit Design | complex | moderately complex |
simple |
|
Part
Count |
high | medium | low |
|
Load
Regulation |
0.05% to 0.5% | .005% to 0.2% | +10%
(1/2 load to No Load (NL)) -10% (1/2 load to Full Load (FL)) |
| Line Regulation | 0.05% to 0.2% | 0.005% to 0.05% |
directly proportional to AC input change |
| Ripple (RMS) | 10 mv to 25 mv | 0.25 mv to 1.5 mv | 0.5 v to 5 v |
|
Transient Recovery |
300
microseconds (1/2L to FL) |
50-100 microseconds (NL to FL) |
N/A |
| Efficiency | 70-85% | 40-60% | 90-95% |
| Hold-up Time | 15-30 milliseconds | 1-2 milliseconds | |
| EMI | high | very low | very low |
| Leakage | high | low | very low |
|
Size (power density) |
small size (high power density) |
large size (low power density) |
medium size (medium power density) |
|
Weight (Power to Weight Ratio) |
light (high) |
heaviest (low) |
heavy (low) |
| Power Factor | 0.6
- 0.7 without PFC
>0.95 with PFC |
0.6 - 0.7 | 0.6 - 0.7 |
| Cooling | convection or fan | convection or fan | convection |
| Isolation | yes | yes | yes |
|
Input
Voltage Range |
90 -
132 VAC (without PFC) and/or 180 - 264 VAC (without PFC) ----------------- 90 - 264 VAC (with PFC) |
105
- 125 VAC and/or 210 - 250 VAC |
0 -
125 VAC 0 - 250 VAC Output directly proportional to input |
| Values in chart above are for comparison purposes only. | |||
THIS WEEK'S PROJECT:
13.6V, 5A Linear Power Supply
IN-PROGRESS PROJECT:
Remote Controlled Antenna Switch ... (Continued from previous week's session)
REFERENCES
1. SGS Thomson Power Supply Design Basics ... Do a Google search for "Power Supply Design Basics"
2. On-line linear reg design ... <http://www.changpuak.ch/electronics/power_supply_design.php>
3. TI WEBENCH power supply designer ... <http://www.ti.com/ww/en/analog/webench/power.shtml>
4. Linear Technology LTPower CAD software ... <http://www.linear.com/designtools/software/#LTPower>
5. Comprehensive listing of switchmode power supply design ... <http://www.smps.us/smpsdesign.html>
6. Linear vs. Switching Power Supplies ... http://power-topics.blogspot.com/2007/08/linear-vs-switch-mode-power-supplies.html
7, 13.8V 20A linear power supply ... http://ludens.cl/Electron/Ps20/Ps20.html
8. 0-28V, 6A linear power supply using the LM317 ... http://electronics-diy.com/power-supply-lm317-2n3055-0-28v-6-8a.php
9. 10A power supply using the LM317 ... http://www.phoenixcomputerlabs.com/All-About-Mixers/LM317.html
10. Reverse engineering iPhone chargers ... Here's a couple of really neat blog posts, tearing down an Apple iPhone charger as well as a non-Apple iPhone charger. Both of them are tiny; the Apple charger is beautifully engineered, while the non-Apple one is slightly terrifying. 73, Josh AJ9BM
-
http://www.arcfn.com/2012/05/apple-iphone-charger-teardown-quality.html
-
http://www.arcfn.com/2012/03/inside-cheap-phone-charger-and-why-you.html
11. Adafruit ... Josh AJ9BM says: "I learned about these from the Adafruit blog, which is a pretty good source of interesting electronics (and other DIY) articles: http://www.adafruit.com/blog/."
12.