Boost converter for battery widget

[Richard H.]

To step-up a single-cell 1.5v battery to ~3.3v, is there a better option
than using a boost regulator like an LM2623?
(http://www.national.com/ds.cgi/LM/LM2623.pdf)

I'm trying to hack out power options for a simple battery-operated LED
gizmo, and it's turning out more complex than the gadget itself.

BTW, load is <1mA to ~100mA depending on LED duty cycle, with a lot of
"off" time. (The power needs to stay on, but the microcontroller will be
quiescent - I'm not sure that a simple transistor+inductor scheme will
give much battery life.)

Thanks!
Richard

 

[colin]

To step-up a single-cell 1.5v battery to ~3.3v, is there a better option
than using a boost regulator like an LM2623?
(http://www.national.com/ds.cgi/LM/LM2623.pdf)

I'm trying to hack out power options for a simple battery-operated LED
gizmo, and it's turning out more complex than the gadget itself.

BTW, load is <1mA to ~100mA depending on LED duty cycle, with a lot of
"off" time. (The power needs to stay on, but the microcontroller will be
quiescent - I'm not sure that a simple transistor+inductor scheme will
give much battery life.)

depends how well it is designed,
if it reduces the frequency of operation at idle it can
increase the efficiency becuase it lowers switching losses.
a hysteretic type would be ideal for this.
some others go into whats called burst mode.

you would need a very low power controller,
ive not had to look for such before.

maybe you could use the led pwm if its high enough frequency.

an alternative is the capacitor charge pump.
100ma is quite a bit, there are many wich are fairly low power,
not sure about 100ma.

depends what idle power consumption you can tolerate.
if its only a few microamps its difficult.

I used one of those micropwer op amps in a rf sniffer probe,
didnt have space for an on/off switch as well as a battery.
but got it down to 5 yrs life with no switch.

Colin =^.^=

 

[jack]

why not consider a super-capacitor and d.c-d.c converter -- the converter
can loaf along with a very low duty cycle

linear tech had a very low loss dc-dc converter application note which
appeared in EDN in the Spring.

 

[Richard H.]

why not consider a super-capacitor and d.c-d.c converter -- the converter
can loaf along with a very low duty cycle

linear tech had a very low loss dc-dc converter application note which
appeared in EDN in the Spring.

Yep, I'd planned to put an electrolytic near the load; it hadn't crossed
my mind to consider a super cap there. That could be a good match.
I'll look for the appnote.

Now, maybe a dumb question, but... DC-DC converter seems to be a generic
term in this area, with 'boost' and 'step-up' being more specific
synonyms (but I could be reading this all wrong). By DC-DC, do you mean
a linear regulator? Don't they generally have lower efficiency and
higher quiescent current? (This gadget won't have a power switch in
most cases, so the supply itself can't draw too much current when the
LEDs are idle.)

Cheers,
Richard

 

[Richard H.]

depends how well it is designed,
if it reduces the frequency of operation at idle it can
increase the efficiency becuase it lowers switching losses.
a hysteretic type would be ideal for this.
some others go into whats called burst mode.

you would need a very low power controller,
ive not had to look for such before.

maybe you could use the led pwm if its high enough frequency.

an alternative is the capacitor charge pump.
100ma is quite a bit, there are many wich are fairly low power,
not sure about 100ma.

depends what idle power consumption you can tolerate.
if its only a few microamps its difficult.

I used one of those micropwer op amps in a rf sniffer probe,
didnt have space for an on/off switch as well as a battery.
but got it down to 5 yrs life with no switch.

Colin =^.^=

Hmmm. The application here is something along the lines of Activate ->
blink LEDs for a while -> shutoff until re-activated. Activation is
likely to be manual (maybe a pushbutton or capacitive sensor) but maybe
also periodic timer (which could be another microcontroller in the power
module).

So, it's possible between cycles to fully quiesce the power regulator
for max battery life. I'm not sure an MCU will be required, but either
way perhaps triggering shutdown on the regulator or cutting off its
power completely with a MOSFET. (But then this calls for a separate
low-power stage to feed the control circuitry. Seems a lot for a
battery widget, but maybe not.)

 

[Chuck Harris]

Yep, I'd planned to put an electrolytic near the load; it hadn't crossed
my mind to consider a super cap there. That could be a good match. I'll
look for the appnote.

Now, maybe a dumb question, but... DC-DC converter seems to be a generic
term in this area, with 'boost' and 'step-up' being more specific
synonyms (but I could be reading this all wrong). By DC-DC, do you mean
a linear regulator?

Though technically a linear regulator is a DC-DC converter, so is a resistor.
The term is not usually used for such devices.

Usually a DC-DC converter implies a device that through some switching technique
increases, or decreases the supplied voltage to some other level.

Generally, it is not practical to raise the DC supply voltage without some kind
of switching, or AC creating device, be it a motor-generator, an inverter,
or some scheme of charging capacitors in parallel, and discharging them in series...

-Chuck

 

[colin]

To step-up a single-cell 1.5v battery to ~3.3v, is there a better option
than using a boost regulator like an LM2623?
(http://www.national.com/ds.cgi/LM/LM2623.pdf)

I'm trying to hack out power options for a simple battery-operated LED
gizmo, and it's turning out more complex than the gadget itself.

BTW, load is <1mA to ~100mA depending on LED duty cycle, with a lot of
"off" time. (The power needs to stay on, but the microcontroller will be
quiescent - I'm not sure that a simple transistor+inductor scheme will
give much battery life.)

just another thought, you could have the micro drive the LED via a mosfet
and inductor
therby doing the boost conversion from the batery voltage,
there wont be a need for a current limit resistor.

it then makes the micro supply a lot easier.

Colin =^.^=

 

[R&D]

Hi,
Look at the following link:
http://datasheets.maxim-ic.com/en/ds/MAX1759.pdf

I'm giong to use it for my supercapacitor powerd torch gadget .... if I can
get hold of it ...

Cheers
Dusan