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'[EE]: 2-tran boost circuit; 5v -> 13v'
2002\10\01@091456 by Roman Black

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Hi, in messing around I came up with a *really simple*
2-tran boost circuit that gives 13.3v regulated
output from a regulated 5v input.

It supplies up to 12mA @ 13.3v, but only starts up
reliably when output load is about 10k (about 1mA)
during startup. Only 2x NPN tran, 1N4148 and cheap
rf choke, 4 resistors, 2 caps, 13v zener.

It can be turned on/off at will by attaching one
tran base to a PIC output.

I think Myke was after something like this for a
cheap PIC programmer etc? If this spec is acceptable
i'll write it up or does it need more current etc??
-Roman

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2002\10\01@115701 by Mike Singer

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Roman Black wrote:
> Hi, in messing around I came up with a *really simple*
> 2-tran boost circuit that gives 13.3v regulated
> output from a regulated 5v input.
.
.
> I think Myke was after something like this for a
> cheap PIC programmer etc? If this spec is acceptable
> i'll write it up or does it need more current etc??
> -Roman

If Myke's programmer is fed with AC, why not use
voltage multiplier-rectifier and simplest regulator?

Mike.

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2002\10\01@125653 by Wagner Lipnharski

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Mike Singer wrote:
> Roman Black wrote:
>> Hi, in messing around I came up with a *really simple*
>> 2-tran boost circuit that gives 13.3v regulated
>> output from a regulated 5v input.
> .
> .
>> I think Myke was after something like this for a
>> cheap PIC programmer etc? If this spec is acceptable
>> i'll write it up or does it need more current etc??
>> -Roman
>
>  If Myke's programmer is fed with AC, why not use
> voltage multiplier-rectifier and simplest regulator?
>
>  Mike.

There are plenty of DC Adapters entitled as 12Vdc@xxmA that in real supply
15Vdc up to @100mA, this somehow helps a lot, isn't it?  Nothing that a
7812 with one or two diodes in series at the ground lead to output you 12.6
or 13.2V, and another 7805 for the 5V.  Simple, neat, low cost and easy,
what is a difficult thing to get, right?  "Simple" and "Easy" are not
synonyms, and they are not found together very often.

/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
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Orlando FLorida - USA - http://www.ustr.net
/_/_/_/ Atmel AVR Consultant /_/_/_/

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2002\10\01@135520 by Dave Tweed

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Roman Black <spam_OUTfastvidTakeThisOuTspamEZY.NET.AU> wrote:
> Hi, in messing around I came up with a *really simple* 2-tran boost
> circuit that gives 13.3v regulated output from a regulated 5v input.
>
> It supplies up to 12mA @ 13.3v, but only starts up reliably when output
> load is about 10k (about 1mA) during startup. Only 2x NPN tran, 1N4148
> and cheap rf choke, 4 resistors, 2 caps, 13v zener.
>
> It can be turned on/off at will by attaching one tran base to a PIC output.
>
> I think Myke was after something like this for a cheap PIC programmer
> etc? If this spec is acceptable i'll write it up or does it need more
> current etc??

Yes, please do. I'd like to see how it compares with one that I came up
with a few days ago. I need a regulator that can take a battery voltage of
3-4 volts and provide 5V at up to 100 mA max with good efficiency. I came
up with a circuit with 5 res, 2 cap, zener, choke, 1 NPN and 1 PNP.


                                      diode
   3-4 V o----+------------CCCCC---+---AK----+---+----o 5V @ 100 mA
              |            68 uH   |         |   |+
              R                    +------+  R  --- 100uF
         1000 R                    |  .001|  R  ---
              R      PNP           |     --- R   |
              |             100    C     --- |   V
              +--+---E C---RRRRR--B  NPN  |  |  Gnd
              |  |    B            E      +--+
       LM336  Z ---   |            |      |  |
        -2.5  Z ---   |            V      |  R
              Z  |.047|    2200   Gnd     |  R
              |  V    +---RRRRR-----------+  R
              V Gnd                          |
             Gnd                             V
                                            Gnd

Actually, the two resistors providing the voltage divider for the feedback
are a 25K pot on my breadboard. I'm not sure what it's actually set to. And
the "zener" is actually an LM336, because I have a few on hand. The circuit
starts up just fine under load, at least under modest loads of 15 and 30 mA.

Load regulation seems really solid, but I'm not happy with the efficiency.
The problem is the base drive of the switching transistor, which needs to
be high enough for the peak coil current, but doesn't contribute to the
output current at all. This is probably an application that really needs a
FET instead of a BJT.

I think I'm better off with a MAX1678, which achieves >80% at 1mA load
current at 5V (!). I've ordered some samples.

Anyway, Vpp supply would be a good application for this type of circuit.
Let's see yours, then we can tweak from there.

-- Dave Tweed

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2002\10\01@151653 by David Minkler

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Hi Roman,

I'd certainly be interested.  I have a 3 transistor voltage inverter
(+5V to -15V) which I was considering posting (not nearly as elegant as
your 2 transistor circuits but quite stable).  As you know, we
frequently get requests on list for such circuits for LCD contrast and
other (low current) purposes.  Perhaps we can adapt your 2 xstr boost
circuit to voltage invert.

Best regards,

Dave Minkler

Roman Black wrote:
{Quote hidden}

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2002\10\01@154937 by Wagner Lipnharski

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David Minkler wrote:
> Hi Roman,
>
> I'd certainly be interested.  I have a 3 transistor voltage inverter
> (+5V to -15V) which I was considering posting (not nearly as elegant
> as your 2 transistor circuits but quite stable).  As you know, we
> frequently get requests on list for such circuits for LCD contrast and
> other (low current) purposes.  Perhaps we can adapt your 2 xstr boost
> circuit to voltage invert.
>
> Best regards,
>
> Dave Minkler


For most low current negative bias, including extended temperature LCD
units, we've being using this without any problem;


 any clock signal
   above 1kHz
       o
       |
      _|_
      \ /  Any inverter
       V
       o
       |
      _|_ 1nF
      ---
       |
       o----|<|----o----> -3V
       |           |
      _|_         _|_-
      \ /         === 1uF
      _V_          |
       |           |
      _|_         _|_
      GND         GND

       1N4148 x 2

/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
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/_/_/_/ Atmel AVR Consultant /_/_/_/

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2002\10\01@193726 by David Minkler

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Wagner,

Yes, we use this in some of our circuits as well.  I was hoping to work
out a simple circuit which would operate 'stand alone' to fill the
occasional on list request for a regulated voltage inverter, as Roman
has done (in the Buck case) with his Black converter.  I suspect a minor
topology change from Roman's 2 xstr boost converter will fit the bill
however, I would need to see it to know.  Of course, if one is already
operating his (Roman's) Buck converter, the VM/charge pump you have
suggested will work just fine fed from the switch node (if regulation
doesn't become an issue).

Best regards,
Dave

Wagner Lipnharski wrote:
{Quote hidden}

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2002\10\01@201918 by Mike Singer

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I was slightly wrong since Myke Predko mentioned
"AA" battery to drive a PICmicro MCU from and to create
Vpp voltage in a programmer circuit." (09.23.02)

Anyway, Vpp consumes no current, just  voltage  and
7805 when fed from 15Vdc at 100mA would dissipate 1W.
Not very efficient idea.
And I suspect those adapters, entitled as 12Vdc@xxmA,
would not produce 15v under max load.

Mike.

Wagner Lipnharski wrote:
{Quote hidden}

supply
> 15Vdc up to @100mA, this somehow helps a lot, isn't it?  Nothing that
a
> 7812 with one or two diodes in series at the ground lead to output you
12.6
> or 13.2V, and another 7805 for the 5V.  Simple, neat, low cost and
easy,
> what is a difficult thing to get, right?  "Simple" and "Easy" are not
> synonyms, and they are not found together very often.

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2002\10\01@202338 by Roman Black

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Dave Tweed wrote:
>
> Roman Black <.....fastvidKILLspamspam@spam@EZY.NET.AU> wrote:
> > Hi, in messing around I came up with a *really simple* 2-tran boost
> > circuit that gives 13.3v regulated output from a regulated 5v input.

> Yes, please do. I'd like to see how it compares with one that I came up
> with a few days ago. I need a regulator that can take a battery voltage of
> 3-4 volts and provide 5V at up to 100 mA max with good efficiency.



Hi Dave, i'll post my circuit here but it really
is not very suitable for your PIC supply use?


                 470uH              1N4148
+5v ------*-----*---L---*---------*---->|----------*---*-- 13.3v
(reg)     |     |       |         |                |   |   12mA
in       |     |       |         |                |   |   max.
         |     R1      |         |                |   |   out
         | 10k |       C         |                |   |
         |     *-----B   NPN     | 15k            |   |
         |     |       E BC337   R4           13v |   |
         |     |       |         |          zener |   |
    22uF |     |       |         |          400mW -   | 4.7uF
    16v  C     '-------|---------|----,           ^   C 16v
         |             |         |    |           |   |
         |             |         |    C           |   |
         |             *----R3---*--B   NPN       |   |
         |             |    1k   |    E BC337     |   |
         |             |         |    |           |   |
         |        6.8  R2        C    |           |   |
         |        ohm  |         |    |           |   |
         |             |     1nF |    |           |   |
         |             |         |    |           |   |
Gnd ------*-------------*---------*----*-----------*---*-- Gnd

My circuit is a *constant power* system that dumps
a set amount of energy into the 13v zener. It's only
good for tiny output current, but pretty much any
output voltage by just changing the zener.

It has two good features; R1 can be connected to a
PIC pin, and turns the thing on/off when it is needed.
Also oscillation (turn off) occurs when the coil
current reaches a set level, giving very reliable
operation and known max coil current, and hence input
power. When running it always draws 5v @ 46mA,
output is 13.3v up to 12mA. It doesn't start well on
full load or with a large output cap.

It DOES work perfectly for generating a 13v programming
supply from a normal 5v source. :o)
-Roman

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2002\10\01@210834 by Roman Black

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Dave Tweed wrote:

{Quote hidden}

I'm not sure I fully understand your boost circuit.
What causes turnoff?? I can see that WHEN the output
has reached spec at 5v it might oscillate around that
point, but when it starts (and output is about 3v)
won't the transistors just turn on and stay on, burning
out the coil??

What efficiency did you get? I think 2-tran circuits
sometimes work better when one tran turns the other
OFF, so you get a distinct "multivibrator" type effect
with fast on/off transitions, timed delays by adding a
cap, and tanking to dump energy forward and back.

Your losses via the PNP are only a couple of mA, so
where are the main losses? Is it switching slowly or
maybe the sat losses in the diode and NPN??
-Roman

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2002\10\01@225920 by Russell McMahon

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> I'm not sure I fully understand your boost circuit.
> What causes turnoff??

I puzzled over that for a while too :-)

I THINK the output transistor  goes into Beta drive limiting as inductor
current increases which reduces the rate of increase of current in the coil
which leads to regenerative action as the field begins to collapse. The 1 NF
feedback capacitor then increases the feedback voltage and you get positive
feed-back turnoff. The risk seems to be that if you stabilised it linearly
it MIGHT sit there and not switch. (As was claimed for a certain other 3
transistor circuit in the past :-) ).


       Russell McMahon


________________

{Quote hidden}

efficiency.
> > The problem is the base drive of the switching transistor,
>

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2002\10\02@010732 by Wagner Lipnharski

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Sometimes I understand the effort for the search the best possible solution
using the simple components. But also, sometimes I suggest to move and use
actual available technology, something that, by the way, is just here based
on our own requirements and demands for a better and easier solution.

The MC34063 is a switching regulator, one of the best price/performance I
ever used. By less than 75 cents a piece, it is very difficult not to think
about to use it. It is almost the cost of coulpe of zener diodes. Output
switching current in excess of 1.5A, working from 3 to 40V, with a
regulation around 2% (better than most 7805 around). Step up, Step down.
What else do you need?

VIN
o--o---RLIM--o-------L100uH------o---|>|--o----o--->
    |        |                   |        |    |
    |        |        .-------.  |        |   _|_
    |        |        |       |  |        R   ---
    |        o--R180--8       1--'        |    |
    |        |        |    FB 5----1.25V--o    |
    |        '--------7       |           |    |
    '-----------------6       3--.        |    |
                      |       |  |        R    |
                      '-2---4-' _|_       |    |
                        |   |   --- 1nF   |    |
                       _|_ _|_  _|_      _|_  _|_

http://www.st.com/stonline/books/pdf/docs/5257.pdf

Wagner Lipnharski - email:  wagnerspamKILLspamustr.net
UST Research Inc. - Development Director
http://www.ustr.net - Orlando Florida 32837
Licensed Consultant Atmel AVR _/_/_/_/_/_/


Roman Black wrote:
{Quote hidden}

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2002\10\02@095646 by Jim

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  "Beta drive limiting"

???

How does the 'forward current transfer ratio' become
limited in a common emitter circuit?

   "The current gain in the common-emitter circuit
    is called BETA (b). Beta is the relationship of
    collector current (output current) to base
    current (input current)."

From:
http://www.tpub.com/neets/book7/25f.htm

Do you perhaps mean the transistor is 'deep into
saturation' - excess base current injected beyond
that needed to obtain the desired collector
current where the ratio of base/collector
current results in a lower *apparent* beta?


RF Jim



{Original Message removed}

2002\10\02@110738 by Scott Touchton

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In an ideal transistor it doesn't.  In the real world, Beta decreases as Ic
increases.  I believe it has to do with recombination in the base.

You can observe this on a curve tracer.
{Original Message removed}

2002\10\02@140349 by Mike Singer

picon face
Wagner Lipnharski wrote:
> Sometimes I understand the effort for the search the best possible
solution
> using the simple components. But also, sometimes I suggest to move and
use
> actual available technology, something that, by the way, is just here
based
> on our own requirements and demands for a better and easier solution.
>
> The MC34063 is a switching regulator, one of the best
price/performance I
> ever used. By less than 75 cents a piece, it is very difficult not to
think
> about to use it. It is almost the cost of coulpe of zener diodes.
Output
> switching current in excess of 1.5A, working from 3 to 40V, with a
> regulation around 2% (better than most 7805 around). Step up, Step
down.
> What else do you need?


This thread is a child of the thread “Re: [PIC]:  2-tran SMPS 5v reg now 90% efficicient!” initiated
by Myke Predko:
> ...I'd love to have something cheap that would allow
> me to drive a PICmicro MCU from a "AA" battery or to
>create Vpp voltage in a programmer circuit...

I suggested on 09.24.02:

> From http://www.national.com/ds/LM/LM2703.pdf :
> The LM2703 is a micropower step-up DC/DC
> (Li-Ion 12V Application - attached .gif)
> - 2.2V to 7V input range
> - 0.01µA shutdown current

I think MC34063 is not acceptable here, since it eats 4mA
(Vpp current is much less, LM2703 consumes <0.3 mA)

And MC34063, working from 3V, wouldn’t work from 3V batteries, LM2703 (2.2V) would.

Mike.

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2002\10\02@181944 by Dave Tweed

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Roman Black <@spam@fastvidKILLspamspamEZY.NET.AU> wrote:
{Quote hidden}

Well, the intent was to establish a fixed on-time based on the R-C time
constant of the left-hand capacitor and the 100-ohm resistor discharging
through the base of the NPN transistor. While it is true that the
transistors can be forced on or forced off by setting the feedback pot too
low or to high, at normal settings this does not occur.

When the transistors are on, the base current to the NPN is dropping while
its collector current is rising. At some point, the NPN comes out of
saturation and its collector voltage starts to rise. Once this happens,
positive feedback through the right-hand capacitor makes the turn-off very
fast.

I'm finding that the on-time is very stable over a wide range of load
currents and oscillation frequencies.

> What efficiency did you get?

With no load (i.e., just the feedback divider, ~0.3 mA), the circuit draws
about 4 mA. With moderate loads (10-30 mA), I'm getting about 55-60%
efficiency, which seems low. I'm using a cheap choke that has about 3 ohms
resistance, and the peak coil current is 200 mA. I figure that accounts for
at least half of my losses.

Maybe overall efficiency can be improved by shooting for a narrower
operating range and optimizing the coil size and operating frequency for
each application. I'll keep playing with it.

-- Dave Tweed

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