12VDC to 18.5VDC
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From: mrdarrett on 8 Aug 2006 22:56 pschoen(a)etiinc.com wrote: > mrdarrett(a)gmail.com wrote: > > mrdarrett(a)gmail.com wrote: > > > I have an old laptop (366MHz) which takes in 18.5V @ 3A by external > > > (switching?) power supply. (It didn't have a battery with it when I > > > bought it - got it 2 years ago for about $200.) > > > > > > I recently built an external battery pack, powered by 16 Energizer 1.2V > > > 2500mAh NiMH AA cells, to power my laptop in lieu of the external power > > > supply, and it does work. So far I have been able to run the laptop > > > for about an hour and a half, and still going strong. (Decided to stop > > > stress-testing at 1:15am, since I had work the next morning.) A far > > > cry from paying $150 for a "new" laptop battery, when the laptop only > > > cost me $200. Although, my 16 NiMH AA battery pack screams "GEEK!" at > > > anyone who glances at it... ;-) > > > > > > For my next project, a DC-DC converter. > > > > > > So... I'd like to convert 12VDC from a jump-start car battery to > > > 18.5VDC, at 3A. > > > > > > After reading a recent thread about avoiding Maxim like the plague, I > > > went over to TI's website, entered my parameters (Input V: 12VDC; > > > output V: 18.5 VDC; current: 3A.) > > > > > > I found this from the search result: > > > > > > http://focus.ti.com/lit/ds/symlink/tps5430.pdf > > > > > > but I was a bit confused why this would have been suggested, since it > > > seems to be a step-DOWN regulator. > > > > > > Any suggestions...? > > > > > > Thanks, > > > > > > Michael > > > > > > Eh, no response from sci.electronics.basics; belatedly cross-posting to > > SED. Better than multiposting... ;-) > > > > Michael > > You could use an isolated 12 V to 6 V DC-DC converter and add the > output to your 12 volts from the battery. You could probably run it > with a full square wave without regulation to simplify feedback. Just a > high frequency transformer driven by something like a UC3526 and a > couple MOSFETs, and a simple rectifier and filter on the isolated > output in series with the battery voltage to get what you need. You > could use the PWM to make it regulated if you want. > > Paul Say... how would I get the 6V DC isolated? I was thinking of using a transformer driven by a PWM circuit I built awhile back and just happen to have in a box, but where could I get a 12VDC(a)1.5A (primary) to 6VDC(a)3A (secondary) transformer? Jameco doesn't seem to carry such a beast... Michael
From: Tam/WB2TT on 9 Aug 2006 00:09 <mrdarrett(a)gmail.com> wrote in message news:1155092195.721314.127360(a)n13g2000cwa.googlegroups.com... > > pschoen(a)etiinc.com wrote: >> mrdarrett(a)gmail.com wrote: >> > mrdarrett(a)gmail.com wrote: >> > > I have an old laptop (366MHz) which takes in 18.5V @ 3A by external >> > > (switching?) power supply. (It didn't have a battery with it when I >> > > bought it - got it 2 years ago for about $200.) >> > > >> > > I recently built an external battery pack, powered by 16 Energizer >> > > 1.2V >> > > 2500mAh NiMH AA cells, to power my laptop in lieu of the external >> > > power >> > > supply, and it does work. So far I have been able to run the laptop >> > > for about an hour and a half, and still going strong. (Decided to >> > > stop >> > > stress-testing at 1:15am, since I had work the next morning.) A far >> > > cry from paying $150 for a "new" laptop battery, when the laptop only >> > > cost me $200. Although, my 16 NiMH AA battery pack screams "GEEK!" >> > > at >> > > anyone who glances at it... ;-) >> > > >> > > For my next project, a DC-DC converter. >> > > >> > > So... I'd like to convert 12VDC from a jump-start car battery to >> > > 18.5VDC, at 3A. >> > > >> > > After reading a recent thread about avoiding Maxim like the plague, I >> > > went over to TI's website, entered my parameters (Input V: 12VDC; >> > > output V: 18.5 VDC; current: 3A.) >> > > >> > > I found this from the search result: >> > > >> > > http://focus.ti.com/lit/ds/symlink/tps5430.pdf >> > > >> > > but I was a bit confused why this would have been suggested, since it >> > > seems to be a step-DOWN regulator. >> > > >> > > Any suggestions...? >> > > >> > > Thanks, >> > > >> > > Michael >> > >> > >> > Eh, no response from sci.electronics.basics; belatedly cross-posting to >> > SED. Better than multiposting... ;-) >> > >> > Michael >> >> You could use an isolated 12 V to 6 V DC-DC converter and add the >> output to your 12 volts from the battery. You could probably run it >> with a full square wave without regulation to simplify feedback. Just a >> high frequency transformer driven by something like a UC3526 and a >> couple MOSFETs, and a simple rectifier and filter on the isolated >> output in series with the battery voltage to get what you need. You >> could use the PWM to make it regulated if you want. >> >> Paul > > > Say... how would I get the 6V DC isolated? I was thinking of using a > transformer driven by a PWM circuit I built awhile back and just happen > to have in a box, but where could I get a 12VDC(a)1.5A (primary) to > 6VDC(a)3A (secondary) transformer? Jameco doesn't seem to carry such a > beast... > > Michael > The thing that TI came up with is a buck regulator. You want a boost, or a buck/boost. The boost regulator looks almost the same, but the inductor is connected in a different way. The same IC may work, but you would be better off with one that shows the boost use on the data sheet. You might try the TI configurator again, or look at National or Linear. If you Google on buck boost regulator, you will get gobs of hits. Tam
From: Paul E. Schoen on 9 Aug 2006 00:11 <mrdarrett(a)gmail.com> wrote in message news:1155092195.721314.127360(a)n13g2000cwa.googlegroups.com... > > pschoen(a)etiinc.com wrote: >> mrdarrett(a)gmail.com wrote: >> > mrdarrett(a)gmail.com wrote: >> > > I have an old laptop (366MHz) which takes in 18.5V @ 3A by external >> > > (switching?) power supply. (It didn't have a battery with it when I >> > > bought it - got it 2 years ago for about $200.) >> > > >> > > I recently built an external battery pack, powered by 16 Energizer >> > > 1.2V >> > > 2500mAh NiMH AA cells, to power my laptop in lieu of the external >> > > power >> > > supply, and it does work. So far I have been able to run the laptop >> > > for about an hour and a half, and still going strong. (Decided to >> > > stop >> > > stress-testing at 1:15am, since I had work the next morning.) A far >> > > cry from paying $150 for a "new" laptop battery, when the laptop >> > > only >> > > cost me $200. Although, my 16 NiMH AA battery pack screams "GEEK!" >> > > at >> > > anyone who glances at it... ;-) >> > > >> > > For my next project, a DC-DC converter. >> > > >> > > So... I'd like to convert 12VDC from a jump-start car battery to >> > > 18.5VDC, at 3A. >> > > >> > > After reading a recent thread about avoiding Maxim like the plague, >> > > I >> > > went over to TI's website, entered my parameters (Input V: 12VDC; >> > > output V: 18.5 VDC; current: 3A.) >> > > >> > > I found this from the search result: >> > > >> > > http://focus.ti.com/lit/ds/symlink/tps5430.pdf >> > > >> > > but I was a bit confused why this would have been suggested, since >> > > it >> > > seems to be a step-DOWN regulator. >> > > >> > > Any suggestions...? >> > > >> > > Thanks, >> > > >> > > Michael >> > >> > >> > Eh, no response from sci.electronics.basics; belatedly cross-posting >> > to >> > SED. Better than multiposting... ;-) >> > >> > Michael >> >> You could use an isolated 12 V to 6 V DC-DC converter and add the >> output to your 12 volts from the battery. You could probably run it >> with a full square wave without regulation to simplify feedback. Just a >> high frequency transformer driven by something like a UC3526 and a >> couple MOSFETs, and a simple rectifier and filter on the isolated >> output in series with the battery voltage to get what you need. You >> could use the PWM to make it regulated if you want. >> >> Paul > > > Say... how would I get the 6V DC isolated? I was thinking of using a > transformer driven by a PWM circuit I built awhile back and just happen > to have in a box, but where could I get a 12VDC(a)1.5A (primary) to > 6VDC(a)3A (secondary) transformer? Jameco doesn't seem to carry such a > beast... > > Michael > You will probably need to "roll your own", but it should really be nothing much more than a small toroid about 1" diameter, wound with a couple dozen turns of wire, if you use about 50 kHz PWM. #22 to #26 AWG wire should be OK for 3 amps or so. Otherwise, you could probably use parts of an old computer power supply. Of course, you can just buy a DC-DC converter, but 18 watts will probably cost at least $50. Paul
From: mrdarrett on 9 Aug 2006 01:01 Paul E. Schoen wrote: .... > > Say... how would I get the 6V DC isolated? I was thinking of using a > > transformer driven by a PWM circuit I built awhile back and just happen > > to have in a box, but where could I get a 12VDC(a)1.5A (primary) to > > 6VDC(a)3A (secondary) transformer? Jameco doesn't seem to carry such a > > beast... > > > > Michael > > > > You will probably need to "roll your own", but it should really be nothing > much more than a small toroid about 1" diameter, wound with a couple dozen > turns of wire, if you use about 50 kHz PWM. #22 to #26 AWG wire should be > OK for 3 amps or so. Otherwise, you could probably use parts of an old > computer power supply. Of course, you can just buy a DC-DC converter, but > 18 watts will probably cost at least $50. > > Paul Oh, thanks! Good idea... roll my own... what kind of torus... powdered ferrite? Where could I get more detailed information on the gauge of wire, versus current... I'd like to build in a safety factor, so, if I want 3A I'd like it to be able to handle 4A without getting too hot. Thanks again, Michael
From: mrdarrett on 9 Aug 2006 01:16 Paul E. Schoen wrote: .... > You will probably need to "roll your own", but it should really be nothing > much more than a small toroid about 1" diameter, wound with a couple dozen > turns of wire, if you use about 50 kHz PWM. #22 to #26 AWG wire should be > OK for 3 amps or so. Otherwise, you could probably use parts of an old > computer power supply. Of course, you can just buy a DC-DC converter, but > 18 watts will probably cost at least $50. > > Paul My PWM controller is basically this: Probably a silly question to ask, but just making sure: should I make C1 equal to 200 (or the more commonly available 220) pF to get 50 kHz? Any special type of cap, or would a simple ceramic do? Thanks, Michael
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