Dear all
I want to design a power supply for a low power portable HF SSB rig with
maximum efficiency from a 12V battery
I will need +1.8V at around 200mA, +5V at low current, and +/-12V, with
the +12V at 1A unregulated. I thought of using a MAX1865 SMPS chip which
has multiple outputs with good efficiency. However I am conscious that
in a quiet analogue environment, the SMPS may be a problem with
switching noise. Is this a feasible idea? Should I use several separate
chips? What precautions should be taken? (I have read the Maxim app
notes on PCB layout and noise reduction, but I am not sure whether this
will be sufficient in this environment)

Thanks

Richard

However I am conscious that
in a quiet analogue environment, the SMPS may be a problem with
switching noise. Is this a feasible idea?

Richard-

This will probably be a good learning experience for you.

I purchased the Radio Shack switch-mode power supply, and was not surprised
when it caused severe interference with my receiver. Then I bought an MFJ 25
ampere supply that had a good reputation, but it also caused i some
interference.

When I bought a new Icom rig, it came with their switching supply. Although it
is the quietest of the three, there is also an increase in the noise floor when
it is in use.

To be fair, I must mention that I'm using a magnet-mount antenna on a nearby
clothes dryer. An outdoor antenna would certainly receive less radiation from
the power supply. At least you see how easy it is to pick up the switching
noise, and how hard it may be to eliminate it!

73, Fred, K4DII

However I am conscious that
in a quiet analogue environment, the SMPS may be a problem with
switching noise. Is this a feasible idea?

Richard-

This will probably be a good learning experience for you.

I purchased the Radio Shack switch-mode power supply, and was not surprised
when it caused severe interference with my receiver. Then I bought an MFJ 25
ampere supply that had a good reputation, but it also caused i some
interference.

When I bought a new Icom rig, it came with their switching supply. Although it
is the quietest of the three, there is also an increase in the noise floor when
it is in use.

To be fair, I must mention that I'm using a magnet-mount antenna on a nearby
clothes dryer. An outdoor antenna would certainly receive less radiation from
the power supply. At least you see how easy it is to pick up the switching
noise, and how hard it may be to eliminate it!

73, Fred, K4DII

Read Linear Tech www.linear.com 's Application Note 70 -- they have
conquered noise by using slew-control switching techniques. Instead of the
complete circuit used in the ARRL design you can jump off and use a slew
control chip. The prices of the Linear slew control chips are not bad,
probably $5 or $6 from Digikey. (and they can be purchased directly from
Linear in quantities less than 500.)

The other thing I have pondered is using a regular gate driver and a 2nd
order low pass filter to approximate a sine wave. You lose a lot of
efficiency going from a square wave to one which is rounded off, and a
filter has issues all its own issues, but I would think that "noise" or
"hash" would drop tremendously.

Jack

"Richard Hosking" wrote in message
...
Dear all
I want to design a power supply for a low power portable HF SSB rig with
maximum efficiency from a 12V battery
I will need +1.8V at around 200mA, +5V at low current, and +/-12V, with
the +12V at 1A unregulated. I thought of using a MAX1865 SMPS chip which
has multiple outputs with good efficiency. However I am conscious that
in a quiet analogue environment, the SMPS may be a problem with
switching noise. Is this a feasible idea? Should I use several separate
chips? What precautions should be taken? (I have read the Maxim app
notes on PCB layout and noise reduction, but I am not sure whether this
will be sufficient in this environment)

Thanks

Richard

Read Linear Tech www.linear.com 's Application Note 70 -- they have
conquered noise by using slew-control switching techniques. Instead of the
complete circuit used in the ARRL design you can jump off and use a slew
control chip. The prices of the Linear slew control chips are not bad,
probably $5 or $6 from Digikey. (and they can be purchased directly from
Linear in quantities less than 500.)

The other thing I have pondered is using a regular gate driver and a 2nd
order low pass filter to approximate a sine wave. You lose a lot of
efficiency going from a square wave to one which is rounded off, and a
filter has issues all its own issues, but I would think that "noise" or
"hash" would drop tremendously.

Jack

"Richard Hosking" wrote in message
...
Dear all
I want to design a power supply for a low power portable HF SSB rig with
maximum efficiency from a 12V battery
I will need +1.8V at around 200mA, +5V at low current, and +/-12V, with
the +12V at 1A unregulated. I thought of using a MAX1865 SMPS chip which
has multiple outputs with good efficiency. However I am conscious that
in a quiet analogue environment, the SMPS may be a problem with
switching noise. Is this a feasible idea? Should I use several separate
chips? What precautions should be taken? (I have read the Maxim app
notes on PCB layout and noise reduction, but I am not sure whether this
will be sufficient in this environment)

Thanks

Richard