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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I have one of those Maxwell boost caps, as stated in previous threads...
I need a boost converter to make the voltage actually useful for real world devices, and well, I'm having a hard time finding designs to work with 2.5 volts, down to 1 volt...
TI has a chip, but it's currently discontinued.
Is there any other way of effectively getting the voltage up to something around 12-9 volts?
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I've got a small PNP 200 mA one...
As far as I know, a regular joule thief wouldn't work; I'm trying to power motors and stuff along those lines, so it would need to be a rather high powered version or something, and plus the efficiency...
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Is it allowable to have an auxiliary supply voltage, such as a 9-volt battery or a few lithium coin cells? Removing the "bootstrap" requirement makes the converter problem easier. (I like your joule thief reference. JT's need a higher voltage to start than to run.)
Example: one recent board design here has a low-dropout-voltage linear regulator (1.5 V to 1.2 V at about 20 amperes). The series pass element is a discrete N-channel MOSFET (FDD8586). The controller/gate driver is a teeny-weeny MAX8564 chip, with auxiliary supply voltage (+ 8 volts was handy). Maybe you can find a boost converter controller along those lines.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
m4ge123 wrote ... Don't BJTs have a voltage drop of about 1-2V when turned on?
That could be normal for IGBTs and Darlingtons and operation at relatively high currents. The traditional rule-of-thumb value for Vce_sat is 0.2 volts.
BJTs can be fabricated with much smaller saturation values. IIRC, the details include a less unsymmetric doping of the collector and emitter. A web search just turned up the NSS12601CF8-D from On Semiconductor: The datasheet claims equivalent On resistance of 30 milliohms, which is consistent with 2 A at 60 mV in the (semi-logarithmic) chart above.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
If I go to digikey and I search for all step up switching voltage regulators with input voltage ranges down to 1 volt or lower I see a lot of devices, not so many through hole though ... only one has a high output voltage capability : TL499ACP-ND
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Is there any problem with using the standard "joule thief" circuit? It starts oscillating with some 0.6 volts. When the BJT turns on through positive feedback, it drops just a fraction of a volt.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
BJT's would waste way too much energy in their voltage drop, be them germanium or siliocon... a germanium transistor based joule theif would make a good auxiliary supply I suppose, but for high power boost for this voltage you want to use some super-low Rds-on mosfets, like those from motherboard power converters or better. Some dedicated control IC would help a lot too.
Too much hassle in my opinion though, apart from buying some more caps and greatly simplifying everything.
What is your intended final application anyway/how much power do you actually need?
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Designing a 1 volt boost converter
