3V to 12v Unreg DC-DC

Hi All,

I am looking for a way to boost 3v to 12V unregulated at about 500mA

I was thinking pf a NE555 time, switching transistor and inductor and diode

Any ideas would be appreciated.

JG

"Joe G (Home)" <joe.g@optusnet.com.au> wrote in message
news:439a8e7f$0$6195$afc38c87@news.optusnet.com.au ...

Hi All,

I am looking for a way to boost 3v to 12V unregulated at about 500mA

I was thinking pf a NE555 time, switching transistor and inductor and
diode

Any ideas would be appreciated.

JG
500mA, is a lot. You would be drawing over 4A, at the 3v rail. Driving a

transistor efficiently with only a 3v supply, from a NE555, will be hard,
and if not done efficiently, your consumption will shoot up...
If the 'about 500mA', is on the generous side, then look at the National
LM2623A. This will do about 400mA, and will be far more efficient than the
discrete solution. This will deliver 300mA, with something around 85%
efficiency, with the right inductor/capacitor/diode.

Best Wishes

On Sat, 10 Dec 2005 12:22:24 GMT, "Roger Hamlett"
<rogerspamignored@ttelmah.demon.co.uk> wrote:

"Joe G (Home)" <joe.g@optusnet.com.au> wrote in message
news:439a8e7f$0$6195$afc38c87@news.optusnet.com.au ...
Hi All,

I am looking for a way to boost 3v to 12V unregulated at about 500mA

I was thinking pf a NE555 time, switching transistor and inductor and
diode

Any ideas would be appreciated.

JG
500mA, is a lot. You would be drawing over 4A, at the 3v rail. Driving a
transistor efficiently with only a 3v supply, from a NE555, will be hard,
and if not done efficiently, your consumption will shoot up...
If the 'about 500mA', is on the generous side, then look at the National
LM2623A. This will do about 400mA, and will be far more efficient than the
discrete solution. This will deliver 300mA, with something around 85%
efficiency, with the right inductor/capacitor/diode.

Best Wishes

There are lots of MOSFET's that could do this. One example is the

Zetex ZXMN2A02N8: 40 milliohms at 2.5 volt gate drive with Id = 8.4
amps. STMicro also has some suitable parts that may be more readily
available in Europe and the UK, don't know about Oz.

"Don Foreman" <dforeman@NOSPAMgoldengate.net> wrote in message
news:ktpmp1dqvgm27fljomn5buau7cineodupp@4ax.com...

On Sat, 10 Dec 2005 12:22:24 GMT, "Roger Hamlett"
rogerspamignored@ttelmah.demon.co.uk> wrote:


"Joe G (Home)" <joe.g@optusnet.com.au> wrote in message
news:439a8e7f$0$6195$afc38c87@news.optusnet.com.au ...
Hi All,

I am looking for a way to boost 3v to 12V unregulated at about 500mA

I was thinking pf a NE555 time, switching transistor and inductor and
diode

Any ideas would be appreciated.

JG
500mA, is a lot. You would be drawing over 4A, at the 3v rail. Driving a
transistor efficiently with only a 3v supply, from a NE555, will be
hard,
and if not done efficiently, your consumption will shoot up...
If the 'about 500mA', is on the generous side, then look at the National
LM2623A. This will do about 400mA, and will be far more efficient than
the
discrete solution. This will deliver 300mA, with something around 85%
efficiency, with the right inductor/capacitor/diode.

Best Wishes

There are lots of MOSFET's that could do this. One example is the
Zetex ZXMN2A02N8: 40 milliohms at 2.5 volt gate drive with Id = 8.4
amps. STMicro also has some suitable parts that may be more readily
available in Europe and the UK, don't know about Oz.
Yes. However you have the problem of charging and discharging the gate

efficiently, and quickly. If the system is going to be a reasonable size,
the inductor/capacitor, needs to be a fairly low value. This implies a
fairly high switching frequency, and charging/discharging a gate
capacitance of perhaps 500 to 1000pF, at perhaps 500KHz, is not trivial.
The circuit complexity starts to 'creep up'. Given the cost of the 2623,
provided it'll do what is needed, it is going to be much the easiest
solution.

Best Wishes