Searching \ for '[EE]: Low voltage boost regulator' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: techref.massmind.org/techref/power/regulators.htm?key=voltage
Search entire site for: 'Low voltage boost regulator'.

Exact match. Not showing close matches.
PICList Thread
'[EE]: Low voltage boost regulator'
2003\06\18@154616 by Olin Lathrop

face picon face
part 1 5212 bytes content-type:text/plain; (decoded 7bit)

I had a need to produce 10-15V at 20mA or so from a single AA battery, or
maybe two at most.  This is significant power for an AA cell, so
efficiency is important.  This means it would be desirable to have a FET
switching the inductor, but that is impossible to do efficiently on just
1V.  I also wanted a PIC in there to do a few smart things in dealing with
the battery and the load.

Of course a PIC won't run at 1V either, so the strategy was to have a dumb
circuit create 4-5V or so with minimal current draw, which provides just
enough power to do the smart things with the real (and much higher power)
load.

To this end, I came up with a circuit that uses only cheap off the shelf
parts, and can run a 12F629 on its internal oscillator from less than 1V.
The output voltage is high enough to allow switching the FET gate for the
high power boost regulator directly from a PIC pin.  The remaining smarts
related to the high power load are implemented in the PIC firmware, and
aren't relevant in this discussion.

I thought the dumb low voltage boost regulator might be useful in general,
so I put the schematic at http://www.embedinc.com/pic/lvboost.pdf.  I know
this looks like a lot of parts, but if you look carefully you will see
they are all of the cheap jellybean variety.  The most expensive component
is L1, which is available from Coilcraft (RFB0810-151) for $.64 in single
quantities.  The total parts cost is about $1.75 if buying hobby
quantities from Jameco, obviously less for real manufacturing volume.

I have also attached two plots that show the performance with 1Kohm and
470ohm loads as a function of input voltage.  A bare 12F629 running from
its internal 4MHz oscillator never presents less than a 1Kohm load worst
case over the full temperature and voltage range.  The typical at room
temperature is *much* higher.

The efficiency is about 2/3 over the desired range.  That's a bit low for
switching power supply standards, but not bad at all when you consider
that the input voltage is only a little more than the voltage drop of a
silicon junction.  Also, most of the battery power will go to the real
load, so the 50% extra required to run the PIC isn't all that significant.
This regulator is also well behaved in that the efficiency stays near its
maximum over wide input voltage and load ranges.  With no load, input
current is under 1.5mA at .85 to 1.0V input with over 4.5V output.

THEORY OF OPERATION

The rest of this message discusses how this circuit works with some
suggestions how to customize it for particular applications.

Q1, Q2, and Q6 form a low power free running oscillator.  Cap C3 charges
up thru R3 until Q2 turns on.  This turns on Q6, which turns on Q1, which
discharges C3 to start the cycle all over again.  C4 and R4 provide
positive feedback so that Q6 switches on and off a little more abruptly,
although that is a minor effect with these particular values.  Q3, Q7, and
Q4 amplify the pulse from Q6 and sharpen its edges.  C6 provides some more
positive feedback which sharpens the edges of the pulse a little more.  By
the time the pulse reaches Q4, it can sink substantial collector current
when the pulse is on.  This charges up L1 during the pulse, and causes the
energy in L1 to dump via D1 into C5 when the pulse ends and Q4 is abruptly
turned off.  R13, R14, and Q5 provide the output voltage regulation.  R13
and R14 are a voltage divider to turn on Q5 when the output reaches the
desired value.  When Q5 is on, further pulses are inhibited by holding C3
discharged.  The B-E voltage drop of Q5 is used as the reference voltage
to regulate the output.  This is not very accurate and dependent on
temperature, but good enough for this particular purpose.

The pulses are about 20uS long with these values.  When Q5 stays off, the
switching frequency is about 20KHz.  As the output voltage rises and
becomes regulated, the time between pulses is stretched.  With no load,
the switching frequency drops to a few Hertz.

You can see this working in both plots.  Initially the input current and
output voltage rise sharply as the input voltage is increased.  In this
region, the output voltage is below the desired threshold and pulse occur
at the maximum rate.  The time between pulses stretches out once the
output voltage becomes regulated.  At this point, the output voltage
flattens out and the input current starts to go down at the same time.
The peak of the input current curve therefore identifies the start of
output voltage regulation.

An important attribute of this circuit is that almost all active
components are off between pulses.  All current during that time flows
thru R3 and R13, which in this case are both 100Kohm resistors.

R13, R14, and Q5 are a very cheap but low quality regulation circuit.  The
output voltage could be made considerably stiffer and more accurate with a
more elaborate circuit using a real voltage reference.

The pulse duration can be changed by adjusting R4 and C4, and the free run
frequency is largely a function of R3 and C3.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.




part 2 8086 bytes content-type:image/gif; (decode)


part 3 8212 bytes content-type:image/gif; (decode)


part 4 2 bytes
-

2003\06\18@163509 by Tom Messenger

flavicon
face
At 03:38 PM 6/18/03 -0400, you wrote:
>I thought the dumb low voltage boost regulator might be useful in general,
>so I put the schematic at http://www.embedinc.com/pic/lvboost.pdf.

My guess is that in version 1.1, the anode of D1 connects to the collector
of Q4. But that's just a guess.

Tom M.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

2003\06\18@172930 by Olin Lathrop

face picon face
> My guess is that in version 1.1, the anode of D1 connects to the
> collector of Q4. But that's just a guess.

Oops, good guess.  I breadboarded it right but drew it wrong.  The
schematic at http://www.embedinc.com/pic/lvboost.pdf has been updated.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

2003\06\18@173855 by Spehro Pefhany

picon face
At 05:27 PM 6/18/2003 -0400, you wrote:
> > My guess is that in version 1.1, the anode of D1 connects to the
> > collector of Q4. But that's just a guess.
>
>Oops, good guess.  I breadboarded it right but drew it wrong.  The
>schematic at http://www.embedinc.com/pic/lvboost.pdf has been updated.

I've done that before. The brain sees (and wires) the right circuit even
if the eyes don't. ;-)

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.

2003\06\19@004915 by Bob Ammerman

picon face
You have another current loss when you are up to voltage...

When Q5 turns on (at reg) it will pull the lower end of R3 to ground. R3 is
now between +Vin and ground.

Bob Ammerman
RAm Systems

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

2003\06\19@013614 by Mike Singer

picon face
Olin Lathrop wrote:
> I had a need to produce 10-15V at 20mA or so from a
> single AA battery, or maybe two at most.  This is
> significant power for an AA cell, so efficiency is
> important.  This means it would be desirable to have
> a FET switching the inductor, but that is impossible
> to do efficiently on just 1V...

LEDs on your cap for hiking again?

Perhaps LM2623 would be better?

Mike.

AN-1250: Inductive Based Switching Regulator Circuits Provide High
Efficiency White LED Drives
AN-1258: LM2623 Boost Converter - A Simple Technology Twist Produces
the Industry's Most Versatile Supply
From
http://www1.national.com/ds.cgi/LM/LM2623.pdf

Ratio Adaptive Gated Oscillator Based, DC DC Boost
Converter-Low Vin, Low Ripple, General Purpose.
----------------------------------------------------------
The LM2623 is a high efficiency, general purpose, step-up
DC-DC switching regulator for battery-powered and low input
voltage systems. It accepts an input voltage between 0.8
and 14 volts and converts it into a regulated output voltage.
The LM2623 can be used to generate up to 14 volts using an
inductor and almost any positive voltage using a transformer.
It has an internal .17§Ù N-Channel MOSFET power switch.
Efficiencies up to 90% are achievable with the LM2623.
In order to adapt to a number of applications, the LM2623
allows the designer to vary the output voltage, the operating
frequency (300kHz to 2 MHz) and duty cycle (17% to 90%)
to optimize the part¡¯s performance. The selected values can
be fixed or can vary with battery voltage or input to output
voltage ratio. Using these techniques according to the design
guidelines may improve efficiency or reduce parts cost
or both. The LM2623 is a gated oscillator and uses a very
simple, on/off regulation mode to produce good efficiency
and stable operation over a wide operating range. It normally
regulates by skipping switching cycles when it reaches the
regulation limit (Pulse Frequency Modulation). In some applications,
with the proper selection of external feedback
components, it can also regulate cycle to cycle, similar to
Pulse Width Modulated parts. It does this by adjusting the off
time between switching cycles, while maintaining continuous
current through the coil. This cycle to cycle type of PFM
results in very low ripple on the output voltage and/or minimum
sized output capacitors, similar to PWM parts. This
mode also typically maximizes efficiency.
------------------------------

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamKILLspammitvma.mit.edu with SET PICList DIGEST in the body

2003\06\19@034802 by Alan B. Pearce

face picon face
>I had a need to produce 10-15V at 20mA or so from a single AA battery, or
>maybe two at most.  This is significant power for an AA cell, so
>efficiency is important.  This means it would be desirable to have a FET
>switching the inductor, but that is impossible to do efficiently on just
>1V.  I also wanted a PIC in there to do a few smart things in dealing with
>the battery and the load.

Have you looked at the TrenchFET's from Vishay Siliconix? The particular one
I am looking at is the Si5447DC, which is a P channel one, but they also
come as N channel. These are 1.8V rated, and looking at the transfer curve
will be well able to self oscillate a coil with a feedback winding at 1.5V.
The knee of the transfer curve is about 1.1V. Output characteristics show a
drain current of about 1.5A at Vds of 0.5V with Vgs = 1.5V, before it starts
to go round the corner towards zero current.

At this rate it probably would not work to the 0.9V you show on your
circuit, but may be an alternative worth looking at. The device comes in an
"8 pin" 1208 package which seems to be getting popular these days.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam.....mitvma.mit.edu with SET PICList DIGEST in the body

2003\06\19@084547 by Olin Lathrop

face picon face
> You have another current loss when you are up to voltage...
>
> When Q5 turns on (at reg) it will pull the lower end of R3 to ground.
> R3 is now between +Vin and ground.

Right.  As I said, "All current during that time flows thru R3 and R13,
..."


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email EraseMElistservspam_OUTspamTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

2003\06\19@085107 by Olin Lathrop

face picon face
> Have you looked at the TrenchFET's from Vishay Siliconix? The
> particular one I am looking at is the Si5447DC, which is a P channel
> one, but they also come as N channel. These are 1.8V rated, and looking
> at the transfer curve will be well able to self oscillate a coil with a
> feedback winding at 1.5V. The knee of the transfer curve is about 1.1V.
> Output characteristics show a drain current of about 1.5A at Vds of
> 0.5V with Vgs = 1.5V, before it starts to go round the corner towards
> zero current.
>
> At this rate it probably would not work to the 0.9V you show on your
> circuit, but may be an alternative worth looking at. The device comes
> in an "8 pin" 1208 package which seems to be getting popular these days.

I was not aware of these devices, but I was hoping to run this from a
single NiMH cell down to empty.  That's about 800mV, so I didn't quite
achieve that, but the closer the better.  The real power will be switched
by a FET driven from the 5V created by this low voltage booster.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

2003\06\19@090814 by Bob Ammerman

picon face
Oops, sorry!

----- Original Message -----
From: "Olin Lathrop" <@spam@olin_piclistKILLspamspamEMBEDINC.COM>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Thursday, June 19, 2003 8:32 AM
Subject: Re: [EE]: Low voltage boost regulator


{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spamBeGonelistservspamBeGonespammitvma.mit.edu with SET PICList DIGEST in the body

2003\06\21@123300 by Dave Dilatush

picon face
Olin wrote...

>I thought the dumb low voltage boost regulator might be useful in general,
>so I put the schematic at http://www.embedinc.com/pic/lvboost.pdf.

Nice circuit: a "vampire" converter that can suck all the blood
out of a single-cell battery while producing a regulated 5V
output, using nothing but cheap jelly-bean components.

This has beaucoup uses.  Thanks for posting it.

DD

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

More... (looser matching)
- Last day of these posts
- In 2003 , 2004 only
- Today
- New search...