Topology for stepping up wide range of input voltage? - Page 1
Forum section: electronics / projects

author: Artlav
author_rank: Frequent Contributor
timestamp: June 23, 2014, 07:40:42 pm
content: A battery generally discharges in a fairly flat fashion - if you have a 36V battery pack, it will stay close to 36V until drained.A supercapacitor, on the other hand, discharges linearly.To get 90% of the power out of it you should be able to draw it in a range from 30% of, to full rated voltage.So, for a 30V supercapacitor the converter needs to be able to accept voltages from 10V to 30V.Question is - what kind of a converter can handle stepping up 10-30 V input to, say, 36V at a few hundred W of power?A boost converter takes the range, but can't do much watts.I can't quite figure out anything else that would work.

author: rob77
author_rank: Super Contributor
timestamp: June 23, 2014, 08:23:58 pm
content: what you mean by boost converter can't do higher power ? of course there are practical limitations, but it's not an issue to design a high power boost converter.for example here is a design by LT ~ 380W even without heatsink.http://cds.linear.com/docs/en/design-note/dn453f.pdfbtw... what power levels are you talking about ?

author: poorchava
author_rank: Super Contributor
timestamp: June 23, 2014, 09:12:44 pm
content: The only problem with boost converter lies in high currents flowing through inductor, catch diode and switching transistor. Once that is solved and the power source has low enough impedance, then there is no problem.A problem with wide input voltage range may arise, because the duty cycle will change and the converter can go go between continuous conduction and discontinuous conduction modes. You need to read up a bit about those and then preferable design the converter in such a way that the mode is the same over whole operating range. At least that's what I'd do.Another thing is how much output ripple can the load tolerate?

author: penfold
author_rank: Frequent Contributor
timestamp: June 23, 2014, 09:20:55 pm
content: A boost converter itself isn't terribly well behaved at both high step-up ratios and high currents. They more often than not find themselves in an application involving only one OR the other, rarely both. If you do the calculations for current and voltage stresses in the components, you'll find out why, particularly if you then try and find a device that'll handle the voltages and currents and see how its parasitics play with your circuit.Just to point out, its not really the maximum step-up ratio (10:36) thats the issue, its the range of input voltage (10:30) that's the real killer.A common way of making a basic converter better suited to the step-up and current is to interleave a number of said basic converters as demonstrated in the linear app-note suggested by rob77.Some topologies such as the Cuk and SEPIC can handle the requirements a bit better, but they can be a bit of a pain when it comes to stability. And in particular the SEPIC can be a bit costly at higher current ratings because of the capacitor that'll have to be high value, reasonably high voltage, very low ESL and very low ESR...

author: David Hess
author_rank: Super Contributor
timestamp: June 26, 2014, 06:45:23 pm
content: They make special DC to DC converters which handle wider input ranges. 4:1 instead of 2:1 is typical.One of the design changes which helps is to do an impedance transformation by either using a tapped inductor or adding a transformer so the peak currents, peak voltages, and duty cycle variation can be moved to a more optimum range.

author: eneuro
author_rank: Super Contributor
timestamp: June 27, 2014, 05:10:12 pm
content: Quote from: rob77 on June 23, 2014, 08:23:58 pmIt looks very interesting while in one project I need to step up in custom controller alternator output voltage to higher voltage @ average power ratings about 250W and less.In schematics from this PDF there is 4x120uF electrolytic capacitors as marked in part of this circuit below or reverse?Did you tested how battery current is taken from battery using this 4phase boost converter-I mean, is it continous or pulsed if constant load eg. power heat resistor is connected ?One could expect nice continous current from this 4 phase boot converter, however these inductors have not too big inductance-at which frequency this thing can operate- 200kHz without external mosfet drivers?I've considered also using even 3 transformers 12VAC->120VAC 100W-150W each and make something like 3 phase AC output shifted 120 degrees in phase and drive AC motor directly, but if there is easy and quite efficient way to step up low voltage using this 4 phase boost converter maybe worth to play with it and see how it works

author: johansen
author_rank: Super Contributor
timestamp: June 27, 2014, 08:32:30 pm
content: I made a randomly interleaved 4 phase boost converter, using significantly cheaper parts than dedicated xx phase control chips.http://www.dutchforce.com/~eforum/index.php?s=3fc7eceba1fe8f54404c04587aa36795&showtopic=41477there are a few things that can be improved for this topology.1) use the on resistance of the fet to measure the current.2) mix the dc offset in separately rather than stacking current sense resistors.

author: Psi
author_rank: Super Contributor
timestamp: June 27, 2014, 09:14:08 pm
content: This thing can step up & down 6-24V DC input to steady 12V output @ 144W (though not at 6V, min 8V for full load)So its quite a good example of what your looking for, wide range, high current.http://store.mp3car.com/DSX12VD_140W_DC_DC_Regulator_p/pwr-025.htmIt's intended to power a computer from a car battery and not get interrupted by low volts under cranking.(that's why it works down do 6V) Pretty sure the 6V operation has a built in time limit though, probably due to inefficiency and heat. However you could design a similar system to operate continuously between 6-24V if you heatsinked the parts to handle that.It's got a ATmega which drives a switchmode IC so you could even clear/replace the AVR so you can code it yourself to do whatever.Im not sure how easy it would be to get the input range up to 30V with some margin. It might just need some higher voltage fets. I'm also not sure what the max output current is at 6V, but if you only need down to 10V then it can definitely do that at max 12A current which is plenty more than 100WAt the very least it might give some design ideas.I bought one of these so can provide high res photos if needed so you can see how it works and what the driver chip is.

author: eneuro
author_rank: Super Contributor
timestamp: June 27, 2014, 10:45:45 pm
content: Quote from: johansen on June 27, 2014, 08:32:30 pmThose dedicated LTC3862 phase controll chips are dificult to source when started to look around the web.Randomly interleaved 4 phase boost converter might have strange current draws wave shapes, isn't it ?Just wrote a few lines of code in C and simulated 3 phase sinus 250 W total power, current draws from battery/alternator at 13.5V (typical cyclic maximum voltage to do not overload charged battery).QuoteIn the case of 3 phase sinus waves, current drawn from battery will be around: 18.5 A and constant while transmited power using 3 wires is constant too, maximum current per sinus phase is 12.3A only so quite easy switching.Who knows what happends with current drawn from the battery in this 4 phase boost converter even in its oryginal (not randomly interleaved) design?