Dave wrote:> > Thanks to everyone that responded. To summarize: > > - Yup, I need 24VAC. That's what is present on the incoming power > supplies I need to interface with. > - TI did buy power trends, and the software that TI puts up for power > supply design is nice. Going with a high switching frequency makes > the inductor smaller, but also puts many more parts on the board. > Price-wise, it's actually better to go with the national 2576 switcher > because it can actually support > 48VDC (which is a bonus for me). > - I checked on the LT parts also, but again, National's solution had > fewer parts. Cost-wise, it works better. > - I still need to check through for those other higher frequency parts > that aren't supported in WebBench. > > You guys rock. I have the utmost respect for hardware folks.There are two things I don't understand. If you checked out the Power Trends stuff, how is that not the simplest solution? They are modules that need no external components, AFAIK. They are not chip level devices that need coils and caps. The other is how are the higher freq parts more complicated? Are you talking about the compensation components? Counting components may have a value, but resistors and small caps don't cost much at all. A reel of 5000 resistors costs maybe $15. Caps are the same until you get above 0.1 uF or so. The input and output caps need to be larger and start costing some money (still under a buck), but the higher freqs allow these to be smaller and cheaper. Normally the chip is the most expensive part regardless. Am I missing something? Are the slow, older converters just a lot cheaper than the new high freq parts? -- Rick "rickman" Collins rick.collins@XYarius.com Ignore the reply address. To email me use the above address with the XY removed. Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design URL http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX
24VAC Power Supply options
Started by ●February 20, 2004
Reply by ●February 21, 20042004-02-21
Reply by ●February 21, 20042004-02-21
rickman <spamgoeshere4@yahoo.com> wrote in message news:<40370DC6.97A73EE3@yahoo.com>...> Dave wrote: > > > > Thanks to everyone that responded. To summarize: > > > > - Yup, I need 24VAC. That's what is present on the incoming power > > supplies I need to interface with. > > - TI did buy power trends, and the software that TI puts up for power > > supply design is nice. Going with a high switching frequency makes > > the inductor smaller, but also puts many more parts on the board. > > Price-wise, it's actually better to go with the national 2576 switcher > > because it can actually support > 48VDC (which is a bonus for me). > > - I checked on the LT parts also, but again, National's solution had > > fewer parts. Cost-wise, it works better. > > - I still need to check through for those other higher frequency parts > > that aren't supported in WebBench. > > > > You guys rock. I have the utmost respect for hardware folks. > > There are two things I don't understand. If you checked out the Power > Trends stuff, how is that not the simplest solution? They are modules > that need no external components, AFAIK. They are not chip level > devices that need coils and caps.Sorry - The power trends modules are also completely expensive (~30-60 bucks.) The entire board costs about 60 bucks before this part. A non-starter...> > The other is how are the higher freq parts more complicated? Are you > talking about the compensation components? Counting components may have > a value, but resistors and small caps don't cost much at all. A reel of > 5000 resistors costs maybe $15. Caps are the same until you get above > 0.1 uF or so. The input and output caps need to be larger and start > costing some money (still under a buck), but the higher freqs allow > these to be smaller and cheaper. Normally the chip is the most > expensive part regardless. > > Am I missing something? Are the slow, older converters just a lot > cheaper than the new high freq parts?The National semi - low freq parts solution (~150kHz) was something like 4-5 components on the order of about 5 bucks total. Picking the same input/output parameters from the TI site put together about 25 components (my "complexity" argument.) I didn't even bother pricing them out. I can handle the big inductor on the low freq part. It just looked weird on the board. Simple/cheap/but big. The board's all through hole anyhow (old equipment) so no biggie. For other product, I'll probably use the TI solution (but will also look into National because someone mentioned some higher frequency parts that WebBench didn't know about.) These other products will need the smaller footprints because of more dimensional constraints. I guess there is also the EMI problem you can create for yourself using the low frequency parts. Something else for me to think about. Thanks again. -- Dave
Reply by ●February 21, 20042004-02-21
Dave wrote:> > The National semi - low freq parts solution (~150kHz) was something > like 4-5 components on the order of about 5 bucks total. Picking the > same input/output parameters from the TI site put together about 25 > components (my "complexity" argument.) I didn't even bother pricing > them out.Can you give me the part no. I thought that there were simple higher Vin regulators that would do what you want with the standard arrangement of components. 25 sounds very excessive unless this is a controller and you need external FETs and diodes, etc.> I can handle the big inductor on the low freq part. It just looked > weird on the board. Simple/cheap/but big. The board's all through > hole anyhow (old equipment) so no biggie. > > For other product, I'll probably use the TI solution (but will also > look into National because someone mentioned some higher frequency > parts that WebBench didn't know about.) These other products will > need the smaller footprints because of more dimensional constraints. > > I guess there is also the EMI problem you can create for yourself > using the low frequency parts. Something else for me to think about.I am not a power supply engineer, but I have had to do a couple for myself. I don't really know much about EMI, but I would expect the higher freqs and smaller inductor would generate less EMI. But then again, the higher freq will be harder to deal with. So it may be a trade off. -- Rick "rickman" Collins rick.collins@XYarius.com Ignore the reply address. To email me use the above address with the XY removed. Arius - A Signal Processing Solutions Company Specializing in DSP and FPGA design URL http://www.arius.com 4 King Ave 301-682-7772 Voice Frederick, MD 21701-3110 301-682-7666 FAX
Reply by ●February 21, 20042004-02-21
rickman <spamgoeshere4@yahoo.com> wrote in message news:<4037B6A7.49E5719D@yahoo.com>...> Dave wrote: > > > > The National semi - low freq parts solution (~150kHz) was something > > like 4-5 components on the order of about 5 bucks total. Picking the > > same input/output parameters from the TI site put together about 25 > > components (my "complexity" argument.) I didn't even bother pricing > > them out. > > Can you give me the part no. I thought that there were simple higher > Vin regulators that would do what you want with the standard arrangement > of components. 25 sounds very excessive unless this is a controller and > you need external FETs and diodes, etc. >I didn't save the design. I just downloaded the TI tool, input my parameters, and out popped a schematic and BOM. It did have external fets, diodes, etc. I'd do it again and report the part to you, but it's on my machine @ work.> > > I can handle the big inductor on the low freq part. It just looked > > weird on the board. Simple/cheap/but big. The board's all through > > hole anyhow (old equipment) so no biggie. > > > > For other product, I'll probably use the TI solution (but will also > > look into National because someone mentioned some higher frequency > > parts that WebBench didn't know about.) These other products will > > need the smaller footprints because of more dimensional constraints. > > > > I guess there is also the EMI problem you can create for yourself > > using the low frequency parts. Something else for me to think about. > > I am not a power supply engineer, but I have had to do a couple for > myself. I don't really know much about EMI, but I would expect the > higher freqs and smaller inductor would generate less EMI. But then > again, the higher freq will be harder to deal with. So it may be a > trade off. >Dunno. Guess I'll find out during UL and FCC testing. Gulp. -- Dave
Reply by ●February 22, 20042004-02-22
"rickman" <spamgoeshere4@yahoo.com> schrieb im Newsbeitrag news:40363D54.894EFA3F@yahoo.com...> Felix Bonjour wrote: > > > > "Dave" <daveoman@aol.com> wrote in message > > news:26a6bac8.0402192010.18abcdcd@posting.google.com... > > > Hi all. > > > > > > I'm looking to replace a 24VAC power supply. Currently, the board > > > takes 24VAC with a center tap. Piece of cake taking the + and - > > > sides, rectifying them, sending them to 7812s, 7805s and 7912s, and > > > away we go. I need to convert to one that does not use a center tap. > > > I've eliminated the negative rail needs of the board, so now just need > > > +12/+5 VDC outputs. The current requirements are ~ 1.5A on the 12V > > > line and 500mA on the +5. > > > > > > I've used the national semi webbench stuff and it puts a nice little > > > switching supply together for me. The problem is, it sticks a big ol' > > > inductor on there. This thing is a beast (like 1.5" by 0.75" by > > > 0.75"). I can find a horizontal mount one, but it takes up a ton of > > > board real estate. > > > > > > The linear regulator design gets to the Vin limits of a typical 7812. > > > Max input voltage is 35VDC, and the full wave rectified voltage is > > > about 36VDC (the actual transformer voltage varies between 19 and > > > 28VAC.) Needless to say, that regulator gets too darn hot and > > > eventually blows. > > > > > > I'm just a lowly firmware guy, so any hardware types have any answers > > > to a smaller component version of that power supply? I'd really like > > > something that didn't take up so much room and have such a high > > > profile. > > > > look at power trends. They have pincompatible switcher replacement forthe> > old 78xx and 79xx linear regulators. > > That's the name, Power Trends. Aren't they the company that TI bought? > > -- > > Rick "rickman" CollinsYes TI was hungry, PowerTrends was one of thouse that got eaten...... On the TI homepage I din't found those nice things again.
