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'[EE]: Design challenge - switching regulator - upd'
2001\01\22@070443 by Russell McMahon

picon face
Progress to date and then a QUESTION below


Several people provided useful input which was mostly along lines of thought
I had considered.
Nobody missed the point which is much better than usual!

Peter's idea of a small startup smps to power the larger smps which won't
run on low voltage is potentially OK BUT still problematic as there is
sometimes NO low voltage supply at first and the small smps would have to
run on the full HV supply (0 - 130 volts) or shut down when it was no longer
needed. Not too hard to do but extra parts required.

I've tried Roman's idea of going back to a simple fixed cycle PWM modulator
with on/off control - I'd been "unkeen" to try this due to the potential for
disaster which modern dual loop current mode controllers help prevent.

I've resisted (so far) going all the way back to a single transistor self
oscillating ringing choke (I built my first one of these almost 30 years ago
! :-) ).
They have too much potential for problems especially with my vast input
voltage swing.(4 to 130 volts if possible - even lower would be nice).

I've modified the simple fixed cycle PWM to alter its mark-space as input
voltage increases. Improves ability to handle voltage range well.
Still just using a packet of hex Schmidt inverters. Not very pretty though
and passives are starting to proliferate.

The UCC3803 (grandson of UC3843) seems a near ideal solution EXCEPT for its
price of $US1.50 ish in 1000 volume.
This is a very nice IC with 4.1 volt startup (very precise :-) ), current
mode, much elimination of passives from original circuit, soft start,
current sense noise blanking etc and can be used for buck, boost,
buck/boost, flyback, forward, Sepik, .... (I'm talking myself into using
this IC at this rate ! )

I'm now looking at old and horrible smps controllers in the hopes that
something cheap and nasty will also be OK and give me the <= 5 volts startup
desired.
Some which are not meant to (eg ref voltage about 5 volts) MAY behave
properly in all cases but this is of course a risky path to take.
(Once running full operating voltage is immediately available).
Candidates include eg TL494 (US0.50/1000), UC3524 (cheap), even just maybe
LM723! (v cheap, v horrible)

BUT - I'm getting keener on the UCC3803 every time I rethink it :-)
Overkill, but ...

SO - QUESTION:

Can anyone suggest an IC I may not have thought of that will do most of the
job that the UCC3803 will do but at rather lower cost.
Many ICs with a more modern origin cost the same or more (eg various MAXIM
ICs).
Power out is very modest (600mA at 9v or so, 1,5A startup at somewhat lower
voltage) but recall the 4 volts or so desired start and run voltage and the
130 volts maximum input voltage.

I'll tidy up the hex inverter design to see how simple it can be made but
....
Maybe even dig out my vv old 1 transistor ringing choke designs?



regards


           Russell McMahon





     Russell McMahon
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{Original Message removed}

2001\01\22@074431 by Alan B. Pearce

face picon face
I come back to some bits you said before, but just let me reiterate my
understanding of what I think you have said so far.

1. The voltage source is a pedal alternator/generator, sort of thing that used
to be used for flying doctors service in the Aussie Outback. You aren't making
transceivers for New Guinea missionaries perhaps? Maybe a piece of exercise gear
for a gym.

2. The output from this is nominally about 10-12 volts at full load/optimum
pedal speed. The problem arises because the voltage can go to about 130V no
load/fast pedalling, but also the gear needs to operate at less than optimum
pedal speed.

3. You need a stable output of around 9 volt at about 600mA whatever the input.

It would seem to me that you should be limiting the maximum voltage to a "safe"
value that you can work with by sticking a hefty zener diode across the
generator output, say 25-30V, to act as a sink for excess energy. Some suitable
voltage above what you expect as an operating voltage once everything is up and
running, and with a current rating that would survive anything the generator can
provide. If a large zener as a single item is too expensive then something like
a 2N3055 with a suitable zener to base as a shunt regulator should work OK. I
also made the suggestion that when this operates an LED should light to let the
operator know they can ease off.

On the other hand, I guess if you are using it in a gym to stress test an
athlete you may need to operate in this area anyway, so it might not be as
applicable as I thought.

Just what sort of generator is it? If using a car alternator, the diodes in
these are usually rated at about 50V, and do not like running without a voltage
limiting load (read battery).

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2001\01\22@080139 by Michael Rigby-Jones

flavicon
face
> -----Original Message-----
> From: Alan B. Pearce [SMTP:spam_OUTA.B.PearceTakeThisOuTspamRL.AC.UK]
> Sent: Monday, January 22, 2001 12:44 PM
> To:   .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject:      Re: [EE]: Design challenge - switching regulator - update
>
>
> Just what sort of generator is it? If using a car alternator, the diodes
> in
> these are usually rated at about 50V, and do not like running without a
> voltage
> limiting load (read battery).
>
Most modern alternators will survive running disconnected, after all, they
are voltage regulated.  What they really don't like is being disconncted
while running, as can happen if you have a loose battery connection.  The
resulting "load dump" will blow lamps and can damage radios etc.  Most car
electronic systems are supposed to be designed to cope with this situation.

Mike

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2001\01\22@192748 by Russell McMahon

picon face
>1. The voltage source is a pedal alternator/generator, sort of thing that
used
>to be used for flying doctors service in the Aussie Outback.

Yes.

>You aren't making
>transceivers for New Guinea missionaries perhaps? Maybe a piece of exercise
gear
>for a gym.

No.
Yes

>2. The output from this is nominally about 10-12 volts at full load/optimum
>pedal speed. The problem arises because the voltage can go to about 130V no
>load/fast pedalling, but also the gear needs to operate at less than
optimum
>pedal speed.
>3. You need a stable output of around 9 volt at about 600mA whatever the
input.


Yes more or less.
Yes.


>It would seem to me that you should be limiting the maximum voltage to a
"safe"
>value that you can work with by sticking a hefty zener diode across the
>generator output, say 25-30V, to act as a sink for excess energy.

No unfortunately.
The load needs to be set by the equipment with user feedback and adding
zener or other dissipation at this low a  level would add excessive
undesired loads in some modes.
In fact the absolute maximum "reasonable" voltage is probably 80 to 100
volts. Load is controllable via software (FET PWM)  and I intend to add load
under software control if voltage exceeeds some upper limit. The only people
liable to do this would be playing around for fun "how fast can I pedal this
thing on no load" and no useful features would be lost by presenting them
with a slowly increasing load above a certain speed.

>Just what sort of generator is it? If using a car alternator, the diodes in
>these are usually rated at about 50V, and do not like running without a
voltage
>limiting load (read battery).


Custom designed special - details not discloseable at this stage. I'kll tell
you all about it after the first 10,000 have been sold.

The change in the power supply is a late alteration occasioned by factors
outside my control.
Doing it is not TOO hard
Doing it ultra-cheaply is always a challenge.


regards



           Russell McMahon

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2001\01\22@192817 by Russell McMahon

picon face
>> Just what sort of generator is it? If using a car alternator, the diodes
>> in
>> these are usually rated at about 50V, and do not like running without a
>> voltage
>> limiting load (read battery).
>>
>Most modern alternators will survive running disconnected, after all, they
>are voltage regulated.  What they really don't like is being disconncted
>while running, as can happen if you have a loose battery connection.  The
>resulting "load dump" will blow lamps and can damage radios etc.  Most car
>electronic systems are supposed to be designed to cope with this situation.


The main limit is my electronics - PWM FET and filter capacitors.
These could be increased to survive ANY user action but there is no point in
doing so and there would be substantial extra cost in doing so.

RM

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2001\01\22@195320 by steve

flavicon
face
> The only people
> liable to do this would be playing around for fun "how fast can I pedal this
> thing on no load" and no useful features would be lost by presenting them
> with a slowly increasing load above a certain speed.

Being a cynical type of person and knowing that a generator is just
a few wires away from being a motor, I'd be tempted to teach them
a lesson. :-)

Steve.



======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: stevebspamKILLspamtla.co.nz      fax +64 9 820-1929
======================================================

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2001\01\23@052031 by Simon Nield

flavicon
face
you can't do anything cunning like changing the configuration of the windings on your generator can
you ?

i think they do the dual of this on the london tube: commutating the coils of the drive motors to
change the number of magnetic poles (probably in the stator, but i have no real clue)

i am guessing that switching the number of poles should be similar to changing taps on a
transformer: ie less/more volts and a corresponding more/less current... could be wrong, it's not my
field, just feels like that sort of thing.

an attempt at a google search without really knowing the right words for what i am after:
http://www.google.com/search?q=motor+drive+commutating+gear+ratio&hl=en&lr=&safe=off

one interesting looking result:
http://www.trainweb.org/railwaytechnical/tract-02.html

[ot][... on that second link they talk about IGBTs too. Long time since I have heard much about
them. no one on this list ever
seems to talk about them or suggest them... seemed to me that they were pretty cool devices from
what i can remember, but i don't deal with 'power' stuff
nowdays. any of you have any experience with these things ? are they fun ? are they handy ?]

Regards,
Simon

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2001\01\23@093119 by Russell McMahon

picon face
>you can't do anything cunning like changing the configuration of the
windings on your generator can
>you ?


No. 'fraid not.
For other reasons the alternator configuration is scrosanct. It has been
arrived at after quite some sweat and blood (mainly by others than me) and I
have to live with its constraints.

>[ot][... on that second link they talk about IGBTs too. Long time since I
have heard much about
>them. no one on this list ever
>seems to talk about them or suggest them... seemed to me that they were
pretty cool devices from
>what i can remember, but i don't deal with 'power' stuff
>nowdays. any of you have any experience with these things ? are they fun ?
are they handy ?]


Depends greatly on your application.
IGBT's have an increasing place in power electronics as they get faster and
generally more capable.
An IGBT is essentially a FET front end on a bipolar transistor. While a FET
has a constant on resistance an IGBT has a constantish voltage drop.
At lower currents and voltages FETs generally end up with a better voltage
drop/speed/power/cost mix.
For voltages over a few hundred volts and not-too-fast switching (tens of
kiloHertz) IGBTs are pretty convincing.
My client has a DC motor PWM controlled treadmill operated offline at about
2 kW and this operates with a single IGBT power switch.

regards,



               Russell McMahon

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2001\01\23@175750 by Peter L. Peres

picon face
TL494 starts at abt. 7V if I am not wrong. This is just barely legal for
end-of-life of zinc-carbon 6F22 (9V) batteries. It also has some of the
most temperamental opamps I've ever seen. Not that I am not using it.

Peter

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2001\01\25@140645 by Peter L. Peres

picon face
I just had a luminous idea: what if you use a upconverting autotransformer
and a relay to switch it off when the voltage increases enough ? You need
only 3:1 or so and it can be a cheapo audio transformer (about $1.50 in
qty.). A small relay or a VDR can separate the transformer when it is no
longer needed (at higher voltage).

After all, there is a minimum speed you need to take into account, as the
alternator will drop towards zero (and ugly pulsed waveforms due to
core saturation) as it slows down.

Peter

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2001\01\27@072550 by Russell McMahon

picon face
> I just had a luminous idea: what if you use a upconverting autotransformer
> and a relay to switch it off when the voltage increases enough ? You need
> only 3:1 or so and it can be a cheapo audio transformer (about $1.50 in
> qty.). A small relay or a VDR can separate the transformer when it is no
> longer needed (at higher voltage).
>
> After all, there is a minimum speed you need to take into account, as the
> alternator will drop towards zero (and ugly pulsed waveforms due to
> core saturation) as it slows down.


I assume that you mean that I use the alternator AC to feed the
auto-transformer?
If so its not really likely to be viable as the frequency increases with
voltage and the range is about as extreme as the voltage range :-)
Also the higher voltages need to be stepped down once they get much over
target voltage.

I have "discovered" the very old truly horrible but incredibly cheap
MC34063A. I think Noah used these in the ark to eke out every bit of energy
from the storage batteries for below decks lighting. Not current mode but
does have a current trip but it appears to ONLY be a high side current trip
which is no good when my high side exceeds the chip Vcc max but I can add a
1 transistor current detector to drive it and ..... .

It's major advantages are cheap, runs on a few volts minimum, cheap, uses
few external components (coz it doesn't do much :-) ), cheap and it's also
cheap.

That and the UCC3803 seem the two leading challengers,.

The MC34063A (and a range of higher current brethren) look rather useful for
REALLY cheap and (really) nasty designs where every dollar counts. despite
its age its available in DIP and SO packages.

Another interesting smps IC is the MC33364 which is cheapish and excellent
for low cost offline supplies with very low standby power levels.
It uses a mode I hadn't met before which they refer to as "critical
conduction" mode. It provides "just in time" switching of the inductor as
energy is "drained" - the penalty is variable frequency operation which can
be an advantage from an EMI point of view.
Not suited to my current project but worth looking at generally

Some interesting material and excellent app notes at

   http://www.onsemi.com

The suspicious close resemblance to Motorola is not coincidental :-)

.
   Russell

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2001\01\28@135151 by Peter L. Peres

picon face
>Another interesting smps IC is the MC33364 which is cheapish and
>excellent

You mean, they put the infamous Schmitt Trigger switching regulator in a
chip ;) I have to see this.

Peter

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2001\01\28@192140 by Russell McMahon

picon face
> >Another interesting smps IC is the MC33364 which is cheapish and
> >excellent
>
> You mean, they put the infamous Schmitt Trigger switching regulator in a
> chip ;) I have to see this.

Fraid not.
Much more sophisticated.
It has all the features of a modern current controlled SMPS with soft start,
over voltage shut down etc  PLUS they have a pin where you feed in up to 700
volts directly to power the startup circuit and it turns this off once it
gets going. They have onchip thermal protection so that it will hiccup
thermally in startup mode if needs be.  Only real problem for me is the
minimum start voltage which is a bit high.

RM

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