NimH AAA to 5V, suggestions?
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From: dagmargoodboat on 4 Aug 2010 23:36 On Aug 3, 9:55 am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Tue, 3 Aug 2010 05:56:40 -0700 (PDT)) it happened Jan > Panteltje <pantel...(a)gmail.com> wrote in > <081bd806-cb72-4733-b3ae-2ffde3fa0...(a)w30g2000yqw.googlegroups.com>: > > > > >On Aug 3, 7:32 am, "Tim Williams" <tmoran...(a)charter.net> wrote: > >> The trick is to put a regulator around it. The worst thing about a fix= > >ed bias circuit is it cooks the transistor if your load opens up! > > >> This works, if a bit cheezy:http://myweb.msoe.edu/williamstm/Images/Block= > >ing%20Oscillator%20Suppl... > > >> Once the output voltage comes up, all sorts of regulation schemes can be = > >applied using slightly more voltage-hungry approaches (TLV431, etc.). Yo= > >u could even use a small one to provide bias for a FET circuit, which could= > > keep working to arbitrarily low voltages (not that you can get any current= > > out of aAAAat 0.2V). > > >> Tim > > >Tim, great, nice regulator. > >Did not see your reply in my newsreader, so I did see Grant reply, > >looked it up with google. > > PS > I build your circuit, and it works perfectly, even with almost empty NiMHs. > Will make a little PCB for it, and use that, it seems more efficient then my version. > No need to order some chip :-) > Here is the setup, I use the box to switch between full and almost empty NiMH batteries. > ftp://panteltje.com/pub/1.2_to_5V_converter_test_img_2249.jpg > This is the collector waveform: > ftp://panteltje.com/pub/1.2_to_5V_converter_Vce_img_2250.jpg > The 7805 on the LED PCB is disconnected, I go in after that. > Project page: > http://panteltje.com/panteltje/pic/sign_pic/index.html > > Thanks :-) The switching transistor isn't saturating very well--that's costing you a few % in efficiency. FMMT617 is quite good. What kind are you using? If the output's 5.5V, then that collector waveform must be about 1.2V/ division. What's the deal, is the output set low, or are those metric volts? -- Cheers, James Arthur
From: Tim Williams on 5 Aug 2010 05:45 "Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:i3c59s$2r4$1(a)news.albasani.net... > On a sunny day (Wed, 04 Aug 2010 16:31:50 GMT) it happened Jan Panteltje > <pNaonStpealmtje(a)yahoo.com> wrote in <i3c4lv$1uh$1(a)news.albasani.net>: > >>This is that coil in detail, I added a 5 turns secondary for feedback >>:-) > Forgot lthe link: > ftp://panteltje.com/pub/1.2_to_5V_converter_coil_detail_img_2256.jpg That's like the constant current buck switcher I made, http://myweb.msoe.edu/williamstm/Images/CC_Buck1.jpg but I only needed two turns. BJTs sure have high transconductance. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jan Panteltje on 5 Aug 2010 07:17 On a sunny day (Wed, 4 Aug 2010 20:36:09 -0700 (PDT)) it happened dagmargoodboat(a)yahoo.com wrote in <703ed962-238a-4025-a4b7-bebc334b49cc(a)14g2000yqa.googlegroups.com>: >> PS >> I build your circuit, and it works perfectly, even with almost empty NiMH= >s. >> Will make a little PCB for it, and use that, it seems more efficient then= > my version. >> No need to order some chip :-) >> Here is the setup, I use the box to switch between full and almost empty = >NiMH batteries. >> �ftp://panteltje.com/pub/1.2_to_5V_converter_test_img_2249.jpg >> This is the collector waveform: >> �ftp://panteltje.com/pub/1.2_to_5V_converter_Vce_img_2250.jpg >> The 7805 on the LED PCB is disconnected, I go in after that. >> Project page: >> �http://panteltje.com/panteltje/pic/sign_pic/index.html >> >> Thanks :-) > >The switching transistor isn't saturating very well--that's costing >you a few % in efficiency. FMMT617 is quite good. What kind are you >using? Just a BC547. >If the output's 5.5V, then that collector waveform must be about 1.2V/ >division. What's the deal, is the output set low, or are those metric >volts? I think in that version it was 4.85 V output. See my other post for the improved version, different coil.
From: Jan Panteltje on 6 Aug 2010 10:53 On Aug 5, 11:45 am, "Tim Williams" <tmoran...(a)charter.net> wrote: > "Jan Panteltje" <pNaonStpealm...(a)yahoo.com> wrote in message > > news:i3c59s$2r4$1(a)news.albasani.net... > > > On a sunny day (Wed, 04 Aug 2010 16:31:50 GMT) it happened Jan Panteltje > > <pNaonStpealm...(a)yahoo.com> wrote in <i3c4lv$1u...(a)news.albasani.net>: > > >>This is that coil in detail, I added a 5 turns secondary for feedback > >>:-) > > Forgot lthe link: > >ftp://panteltje.com/pub/1.2_to_5V_converter_coil_detail_img_2256.jpg > > That's like the constant current buck switcher I made,http://myweb.msoe.edu/williamstm/Images/CC_Buck1.jpg > but I only needed two turns. BJTs sure have high transconductance. > > Tim Yes, I just monitored Vce on the scope and kept adding turns until I no longer did see any improvement. Also tried a synchronous detector with a BJT, but the Schottky was better and simpler. Even tried it as a switch 'upside down'. About 70% efficiency is OK at 1.2 V I think. What I am thinking about now is a simple low battery detector to switch it off when battery voltage drops below say 1.05 V. At .95 V the circuit no longer hacks it, and the output drops to 3V, and The PIC stops working correctly. It is easy to detect with a BJT using the 0.7 V Vbe as reference, , but it needs some flip-flop action too. To protect the expensive rechargeables.
From: Tim Williams on 6 Aug 2010 11:12
"Jan Panteltje" <panteltje(a)gmail.com> wrote in message news:b7a1c629-c960-47d1-9204-ac2584b6371d(a)m1g2000yqo.googlegroups.com... > What I am thinking about now is a simple low battery detector to > switch it off when battery voltage drops below say 1.05 V. > At .95 V the circuit no longer hacks it, and the output drops to 3V, > and The PIC stops working correctly. > It is easy to detect with a BJT using the 0.7 V Vbe as reference, , > but it needs some flip-flop action too. > To protect the expensive rechargeables. I've observed hysteretic operation in these before. Obviously they turn on at 0.7-0.8V, but they turn off slightly below due to bias generated by base rectification. You could tweak the turn-on voltage with a high-ohm divider (not exactly open circuit, but arbitrarily low leakage anyway), and turn-off voltage by boosting base current. You can generate more base current by rectifying the flyback, which is negative going at the base: http://webpages.charter.net/dawill/tmoranwms/Circuits_2010/RegBO.png Worst case of this circuit is an E-B diode, which clamps base at -0.7V, forcing maximum base current back into the circuit, making it run at full throttle. An optoisolator, of course, is an excellent controlled current source. This goes for Vebo(max) breakdown, too, which is why it's a good idea to clamp the flyback voltage on these things (maybe instead of RCD snub, a diode + TVS), and to use a series base diode, to prevent runaway action. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |