luggsey Posted February 11, 2007 Posted February 11, 2007 A 5v6 zener Try and find a 2Amp one in a junkpile! Bet you can find a power transistor or some power diodes........ ----------------------------------------------------------------------------------------------------------------------------------- Life is like a box of chocolates, some bugger always gets the nice ones! My Amateur Radio Forum
Drew Posted February 11, 2007 Posted February 11, 2007 A string of diodes or one Zener are not a good answer (assuming they are connected in series with the supply.) Plot a graph of output voltage against output current (varying the load) and you would get the Andes rather than the nice flat line you want, risking damage to the connected load. Temperature stability would be a laugh too. A power transistor would not be useful without some kind of regulating circuitry - the thing I've suggested is not a power transistor, it's a voltage regulator. I'm not a bodger but I will revert to pedantic spod mode when I'm in the mood! Drew Hoggatt Managing Director Paxton Access Ltd Follow this link for important legal information
luggsey Posted February 11, 2007 Posted February 11, 2007 A string of diodes or one Zener are not a good answer (assuming they are connected in series with the supply.) Plot a graph of output voltage against output current (varying the load) and you would get the Andes rather than the nice flat line you want, risking damage to the connected load. Temperature stability would be a laugh too. A power transistor would not be useful without some kind of regulating circuitry - the thing I've suggested is not a power transistor, it's a voltage regulator. I'm not a bodger but I will revert to pedantic spod mode when I'm in the mood! Drew you know a lot more about this then I do but if you used a power transistor on a fixed load would the voltage not be stable..... ----------------------------------------------------------------------------------------------------------------------------------- Life is like a box of chocolates, some bugger always gets the nice ones! My Amateur Radio Forum
Drew Posted February 11, 2007 Posted February 11, 2007 I do but if you used a power transistor on a fixed load would the voltage not be stable..... You would need other components round a transistor to provide a stable supply. Have a look at this link as an example. The thing about a voltage regulator is that it is an integrated circuit providing really good performance very simply and cheaply. You would need a couple of dozen components to achieve the same stability, reliability and performance. Also, fixed loads are fairly rare. An electronic system that runs from 5V will not generally draw a constant current. The thing I like the most is that Lurch solved this hours ago. Sorry if I'm going on! Drew Hoggatt Managing Director Paxton Access Ltd Follow this link for important legal information
Guest Posted February 11, 2007 Posted February 11, 2007 Just been stripping another broken sat nav cradle down and found another LM2576, so I might even build myself a new regulator. Looking at the datasheet it only requires a few additional external components. The thing I like the most is that Lurch solved this hours ago. Sorry if I'm going on! You carry on, I'm just taking notes in the background. I only solved it in a temporary way. Still needs a bit of work somewhere to finish it off.
luggsey Posted February 11, 2007 Posted February 11, 2007 You would need other components round a transistor to provide a stable supply. Have a look at this link as an example. The thing about a voltage regulator is that it is an integrated circuit providing really good performance very simply and cheaply. You would need a couple of dozen components to achieve the same stability, reliability and performance.Also, fixed loads are fairly rare. An electronic system that runs from 5V will not generally draw a constant current. The thing I like the most is that Lurch solved this hours ago. Sorry if I'm going on! I was thinking of the unregulated wall transformers that "only" have a PT fitted after the transformer, loads fitted in my house on all sorts of gear with fixed loads and stable voltage, go on all u like Drew, I like to soak up knowledge wherever and whenever! ----------------------------------------------------------------------------------------------------------------------------------- Life is like a box of chocolates, some bugger always gets the nice ones! My Amateur Radio Forum
Drew Posted February 11, 2007 Posted February 11, 2007 Just been stripping another broken sat nav cradle down and found another LM2576, so I might even build myself a new regulator. Looking at the datasheet it only requires a few additional external components. National Semiconductor invented these and sell them with the "Simple Switcher" product name. They are a little more complicated to use than a linear regulator but are excellent at supplying high currents without getting hot, particularly with a big difference between output and input voltage. They can be fussy about circuit layout, though - a birds' nest won't do! Drew Hoggatt Managing Director Paxton Access Ltd Follow this link for important legal information
Guest Posted February 11, 2007 Posted February 11, 2007 They can be fussy about circuit layout, though - a birds' nest won't do! This project is going to take a little longer than first anticipated. Somewhere there is some lovely shiny sheets of veroboardy stuff, problem is, where............ I need to have a good clear out on the work bench, the dining table\kitchen worktop isn't the best place for doing this (so I've been told).
Guest Posted February 11, 2007 Posted February 11, 2007 This project is going to take a little longer than first anticipated. ... just go to THE shop and buy a necessary PSU and stop fiddling with it. Drew gave you a decent info but i i would suggest you to buy a PSU worth of
Drew Posted February 11, 2007 Posted February 11, 2007 i would suggest you to buy a PSU worth of Drew Hoggatt Managing Director Paxton Access Ltd Follow this link for important legal information
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