Post by thread:Ringing Chokes and batteries

While rummaging the Archives i found the following discussion of powering a circuit from a single battery. However, the ascii diagram was munched. I tried to unscramble it, but i think i have it wrong. It is alleged to be a self-oscillating flyback converter. Does anyone recognize this and can you tell me where the load should be taken off, and how the transforemer goes? Thanks, Alice snipped segment follows: >From this explanation it seems like the circuit should work with a >higher voltage LED. Has anyone tried to power a blue LED from a single cell? snip%<----------------------------------------------------- {Quote hidden}>>> On 2/2/98 Pasi T Mustalahti wrote: >>> >>> -------8<-------- >>> > >>> > ------------------------------------- +U (0.6..1.55 V) >>> > | | >>> > R20K || < >>> > | || < >>> > ---------------> || < >>> > | > || < >>> > = 10nF /------> |--| >>> > | ----| BC337 | >>> > | \, | >>> > | | | >>> > -------------------------------------- >>> > > snip %< ---------------------------------------------------- {Quote hidden}>The circuit is best described as a self-oscillating flyback >converter. Each time the transistor turns on, it charges the >transformer with current until it saturates. When it saturates, the >voltage induced in the base winding decreases, causing the transistor >to turn off. The energy stored in the transformer is then dumped to >the load (LED in this case). > >For a given frequency of operation and transformer core, the circuit >will deliver approximately constant *power* to the load, regardless >of the load voltage. The power is distributed in pulses having the >energy that the transformer core can hold before it saturates. Since >it always charges until it saturates, the output power doesn't depend >on the input voltage, if (and this is a big "if"), the frequency >doesn't vary. > >If the DC supplied to the transistor base circuit is adequate, the >circuit will oscillate continuously at the highes practical frequency >(depends on the input voltage and the inductance of the winding). >More likely, Pasi's circuit is running in "relaxation mode". The base >current required by each cycle discharges the capacitor somewhat, to >less than Vbe so the transistor doesn't turn on right away after the >transformer voltage reaches zero (all energy having been delivered to >the LED). There is a delay during which the resistor has to charge up >the capacitor to start the transistor conducting again. So the >frequency probably decreases significantly with input voltage as the >current available thru the resistor decreases. Varying the resistor >should vary the frequency, and thus the brightness of the LED. A >diode in parallel with the transistor base (to keep it from going too >far negative) would supply current to the capacitor while the >transistor is off, and probably get the circuit to oscillate >continuously rather than in relaxation mode. However, the resulting >output power would likely be too high, and difficult to control. > >However, the experiment shows that it had satisfactory performance >over the life of the battery. The self-regulating properties of the >circuit are apparently working well enough. > snip%<---------------------------------------------------------------- ------------------------------------------------------ Wireless Link Corp. wllink.com web site spam_OUTbryanTakeThisOuTwllink.com email (408)739-5465 x103 ph (408)739-5483 fax

Alice; You were right, your ascii is pretty hard to read. Just my two cents, with a saturating core converter, the current spike at the very end of the core charge is quite high. When the core saturates, inductance drops and the primary acts like a near short. I suggest making or having made a custom transformer, as opposed to using a junk drawer one. Production repeatablility will depend very heavily on the reporducibility of the transformer. You can experiment with the transformer by adding a low value sense resistor (and an IA to get clear voltages) in the primary circuit, and then compare time and current. As an inductor, the current will be a straight linear ramp, until saturation begins. The abruptness of this roll off depends on core material. There are materials with sharp BH loop curves that maximize this sharpness and minimize the high current pulse at the end. Also, with a flyback, the goal is to store energy. Many flybacks have a gap cut into the core. That increases the core inductance and thus the storage capacity (think I got that the right way around). Make sure you have a diode in the secondary or you don't have a valid circuit. If the secondary is in phase, you have a forward converter. If it is reversed, you have a flyback converter. The easy way to keep it straight, with a flyback current flows in the primary and secondary at different times, never the same time. A forward converter results in current flow simultaneously. Just an idea, you might try a PIC trick. If you can control the pulse width, you could let the PIC drive the transistor. Essentially, drive the transformer in an open loop mode. You would have to take production variation and temperature effects into account, as there is no primary loop current feedback. If you leave the pulse on for too long, POOF, it is over. There is a trick you can do to limit the current, by adding a resistor in the ground connection, which drives an NPN base emitter. Set the resistor value to 0.65V/Imax. Then connect the collecor to the base of the drive transistor. (assuming you switched to an NPN power trans for this trick). Make sure there is some resistance between the PIC and base, and voila, you have built in current limit. Then size the drive transistor to survive an infinite current limit. G'luck. Chris Eddy Pioneer Microsystems, Inc. Alice Campbell wrote: {Quote hidden}> While rummaging the Archives i found the following discussion of > powering a circuit from a single battery. However, the ascii diagram > was munched. I tried to unscramble it, but i think i have it wrong. > It is alleged to be a self-oscillating flyback converter. Does > anyone recognize this and can you tell me where the load should be > taken off, and how the transforemer goes? > > Thanks, > Alice > > snipped segment follows: > > >From this explanation it seems like the circuit should work with a > >higher > voltage LED. Has anyone tried to power a blue LED from a single cell? > > snip%<----------------------------------------------------- > >>> On 2/2/98 Pasi T Mustalahti wrote: > >>> > >>> -------8<-------- > >>> > > >>> > ------------------------------------- +U (0.6..1.55 V) > >>> > | | > >>> > R20K || < > >>> > | || < > >>> > ---------------> || < > >>> > | > || < > >>> > = 10nF /------> |--| > >>> > | ----| BC337 | > >>> > | \, | > >>> > | | | > >>> > -------------------------------------- > >>> > > > > snip %< ---------------------------------------------------- > >The circuit is best described as a self-oscillating flyback > >converter. Each time the transistor turns on, it charges the > >transformer with current until it saturates. When it saturates, the > >voltage induced in the base winding decreases, causing the transistor > >to turn off. The energy stored in the transformer is then dumped to > >the load (LED in this case). > > > >For a given frequency of operation and transformer core, the circuit > >will deliver approximately constant *power* to the load, regardless > >of the load voltage. The power is distributed in pulses having the > >energy that the transformer core can hold before it saturates. Since > >it always charges until it saturates, the output power doesn't depend > >on the input voltage, if (and this is a big "if"), the frequency > >doesn't vary. > > > >If the DC supplied to the transistor base circuit is adequate, the > >circuit will oscillate continuously at the highes practical frequency > >(depends on the input voltage and the inductance of the winding). > >More likely, Pasi's circuit is running in "relaxation mode". The base > >current required by each cycle discharges the capacitor somewhat, to > >less than Vbe so the transistor doesn't turn on right away after the > >transformer voltage reaches zero (all energy having been delivered to > >the LED). There is a delay during which the resistor has to charge up > >the capacitor to start the transistor conducting again. So the > >frequency probably decreases significantly with input voltage as the > >current available thru the resistor decreases. Varying the resistor > >should vary the frequency, and thus the brightness of the LED. A > >diode in parallel with the transistor base (to keep it from going too > >far negative) would supply current to the capacitor while the > >transistor is off, and probably get the circuit to oscillate > >continuously rather than in relaxation mode. However, the resulting > >output power would likely be too high, and difficult to control. > > > >However, the experiment shows that it had satisfactory performance > >over the life of the battery. The self-regulating properties of the > >circuit are apparently working well enough. > > > snip%<---------------------------------------------------------------- > ------------------------------------------------------ Wireless Link > Corp. wllink.com web site .....bryanKILLspam@spam@wllink.com email (408)739-5465 x103 ph > (408)739-5483 fax

part 0 1666 bytes content-type:application/octet-stream; name="EOLE6O0.MSG"Attached is one of the original messages containing the circuit to which you ref er, with the correct ASCII art. (If you are using a fixed point font, of course...) Dan On Mon, 8 Nov 1999 00:08:00 PST, Alice Campbell wrote: {Quote hidden}>While rummaging the Archives i found the following discussion of >powering a circuit from a single battery. However, the ascii diagram >was munched. I tried to unscramble it, but i think i have it wrong. > >>From this explanation it seems like the circuit should work with a >>higher >voltage LED. Has anyone tried to power a blue LED from a single cell? > >snip%<----------------------------------------------------- >>>> On 2/2/98 Pasi T Mustalahti wrote: >>>> >>>> -------8<-------- >>>> > >>>> > ------------------------------------- +U (0.6..1.55 V) >>>> > | | >>>> > R20K || < >>>> > | || < >>>> > ---------------> || < >>>> > | > || < >>>> > = 10nF /------> |--| >>>> > | ----| BC337 | >>>> > | \, | >>>> > | | | >>>> > -------------------------------------- >>>> > >> Content-Type: application/octet-stream; name="EOLE6O0.MSG" Attachment converted: wonderland:EOLE6O0.MSG (????/----) (0000F3CD)