I see circuits like these in VCRs a lot... not really anywhere else, for
some reason. Not the greatest efficiency, but the parts are a lot cheaper
than a whole UC3842 or TL494 deal. Maybe not worthwhile against TOPswitches
and such these days.

Efficiency as shown is around 67%. Runs at ~200kHz full power, much slower
at lighter loadings (it fires a full cycle, then stays off for a while)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Self oscillating and fairly simple, yes.
when you start adding power factor correction or special control functions
like soft start, a smps chip makes more sense. The trend in some new power
supplies is to actually use a microprocessor for control.
Microchip for one has been pushing their 32bit DSC chip for this:
http://www.microchip.com/stellent/id...ote= cn531747

Happy New Year all
Oppie (aka bob Oppenheimer)


"Tim Williams" wrote in message
...
I see circuits like these in VCRs a lot... not really anywhere else, for
some reason. Not the greatest efficiency, but the parts are a lot cheaper
than a whole UC3842 or TL494 deal. Maybe not worthwhile against
TOPswitches and such these days.

Efficiency as shown is around 67%. Runs at ~200kHz full power, much
slower at lighter loadings (it fires a full cycle, then stays off for a
while)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Oppie wrote:
Self oscillating and fairly simple, yes.
when you start adding power factor correction or special control
functions like soft start, a smps chip makes more sense. The trend in
some new power supplies is to actually use a microprocessor for control.
Microchip for one has been pushing their 32bit DSC chip for this:
http://www.microchip.com/stellent/id...ote= cn531747


Happy New Year all
Oppie (aka bob Oppenheimer)


"Tim Williams" wrote in message
...
I see circuits like these in VCRs a lot... not really anywhere else,
for some reason. Not the greatest efficiency, but the parts are a lot
cheaper than a whole UC3842 or TL494 deal. Maybe not worthwhile
against TOPswitches and such these days.

Efficiency as shown is around 67%. Runs at ~200kHz full power, much
slower at lighter loadings (it fires a full cycle, then stays off for
a while)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


32 bits for such _simple_ work?? Like using a sledge hammer to kill
an ant.

On Fri, 01 Jan 2010 19:34:04 -0800, the renowned Robert Baer
wrote:

Oppie wrote:
Self oscillating and fairly simple, yes.
when you start adding power factor correction or special control
functions like soft start, a smps chip makes more sense. The trend in
some new power supplies is to actually use a microprocessor for control.
Microchip for one has been pushing their 32bit DSC chip for this:
http://www.microchip.com/stellent/id...ote= cn531747


Happy New Year all
Oppie (aka bob Oppenheimer)


"Tim Williams" wrote in message
...
I see circuits like these in VCRs a lot... not really anywhere else,
for some reason. Not the greatest efficiency, but the parts are a lot
cheaper than a whole UC3842 or TL494 deal. Maybe not worthwhile
against TOPswitches and such these days.

Efficiency as shown is around 67%. Runs at ~200kHz full power, much
slower at lighter loadings (it fires a full cycle, then stays off for
a while)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


32 bits for such _simple_ work?? Like using a sledge hammer to kill
an ant.

It's actually a 16-bit microcontroller with some rudimentary
fixed-point DSP functionality barnacled onto it.


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

On Fri, 1 Jan 2010 11:56:28 -0600, "Tim Williams"
wrote:

I see circuits like these in VCRs a lot... not really anywhere else, for
some reason. Not the greatest efficiency, but the parts are a lot cheaper
than a whole UC3842 or TL494 deal. Maybe not worthwhile against TOPswitches
and such these days.

Efficiency as shown is around 67%. Runs at ~200kHz full power, much slower
at lighter loadings (it fires a full cycle, then stays off for a while)

Tim

Here's my +12 to -12 converter. The IC is just a schmitt-trigger gate
driver.

ftp://jjlarkin.lmi.net/Inverter.jpg

At powerup it self-oscillates at a calculated duty cycle, 75% maybe,
until the -12 comes up, turns on the common-base transistor, and backs
down the duty cycle.

John

"Tim Williams" wrote in message
...
I see circuits like these in VCRs a lot... not really anywhere else, for
some reason. Not the greatest efficiency, but the parts are a lot cheaper
than a whole UC3842 or TL494 deal. Maybe not worthwhile against
TOPswitches and such these days.

Most of the discrete PSUs I've encountered in field service have been much
more complex, and a right PITA to fault find compared to IC designs (apart
from TDA4600 types which should be classified as a notifiable disease!),
probably they have to comply with requirements for safety shutdown circuits
which are usually included on-chip.

"Spehro Pefhany" wrote in message
...
32 bits for such _simple_ work?? Like using a sledge hammer to kill
an ant.

It's actually a 16-bit microcontroller with some rudimentary
fixed-point DSP functionality barnacled onto it.


Best regards,
Spehro Pefhany

My bad. thanks for the correction.
I've seen several reference designs now for power supplies, inverters and
motor drives that are using low pin count 16 bit DSPics for the control
elements.
My biggest problem with this is running a debugger. Not only does the system
have to be isolated (affecting the impedance of the power source) but what
happens when you hit a breakpoint and emulation stops. I keep asking the
emulator manufacturers to make available a hardware flag for emulation
stopped so power can be safely controlled. No takers yet.
Oppie

On Sat, 2 Jan 2010 14:02:28 -0500, "Oppie" wrote:



"Spehro Pefhany" wrote in message
.. .
32 bits for such _simple_ work?? Like using a sledge hammer to kill
an ant.

It's actually a 16-bit microcontroller with some rudimentary
fixed-point DSP functionality barnacled onto it.


Best regards,
Spehro Pefhany

My bad. thanks for the correction.
I've seen several reference designs now for power supplies, inverters and
motor drives that are using low pin count 16 bit DSPics for the control
elements.
My biggest problem with this is running a debugger. Not only does the system
have to be isolated (affecting the impedance of the power source) but what
happens when you hit a breakpoint and emulation stops. I keep asking the
emulator manufacturers to make available a hardware flag for emulation
stopped so power can be safely controlled. No takers yet.
Oppie

Optically coupled JTAG?

John

On Sat, 2 Jan 2010 14:02:28 -0500, the renowned "Oppie"
wrote:


My biggest problem with this is running a debugger. Not only does the system
have to be isolated (affecting the impedance of the power source) but what
happens when you hit a breakpoint and emulation stops. I keep asking the
emulator manufacturers to make available a hardware flag for emulation
stopped so power can be safely controlled. No takers yet.
Oppie

That would be very convenient-- just hook it to the fault input on the
drivers.

It's not that hard to debug in chunks, implement monitors, use burn &
crash, etc., but it would be nice to be able to avoid that.


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