On Sun, 11 Jan 2004 14:05:21 GMT, (Mike W)
wrote:



The diode + relay circuit should be obvious to you, I use a 9v relay
coil with a 1N4001 in the activation side and a DPDT contact,in
parallel, to switch the power. For the power you are talking about a
14pin DIL relay should be adequate.

HTH, Mike W, G8NXD qthr

I'd like to call it "the PYE method" since it is generally applied in
those Westminster, Vanguard and Cambridge sets, while other
manufacturers only use a diode. I've copied it for the larger sets
which are often used in different places. The application of relay has
the advantage that nothing happens if you use the wrong polarity -
unless you have shortcircuit between two chassises, then you should
apply a two-pole relay.
Make sure that the relay stays operated under different operation,
check that the relay operates with 9V. Remember to put a diode or
other spark suppression across the coil, too.

73
LA8AK, http://home.online.no/~la8ak/c.htm
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In article ,
Dr. A.T. Squeegee wrote:

I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Power Schottky diodes are available that have a forward voltage
drop of 0.3 or less. More expensive, yes, but they really do work.

Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

When a power supply of the correct polarity is hooked up, the MOSFET's
intrinsic substrate diode is biased forward (conducting normally) and
the MOSFET is turned on "hard" (giving a low Rds, and thus a very low
forward voltage drop). If the supply is hooked up backwards, the
MOSFET is turned off (the gate is pulled down towards hard depletion)
and the substrate diode is reverse-biased, switching it off.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
Dr. A.T. Squeegee wrote:

I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Power Schottky diodes are available that have a forward voltage
drop of 0.3 or less. More expensive, yes, but they really do work.

Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

When a power supply of the correct polarity is hooked up, the MOSFET's
intrinsic substrate diode is biased forward (conducting normally) and
the MOSFET is turned on "hard" (giving a low Rds, and thus a very low
forward voltage drop). If the supply is hooked up backwards, the
MOSFET is turned off (the gate is pulled down towards hard depletion)
and the substrate diode is reverse-biased, switching it off.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Sun, 11 Jan 2004 21:17:43 -0000, (Dave Platt)
wrote:

Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

Nice one Dave

On Sun, 11 Jan 2004 21:17:43 -0000, (Dave Platt)
wrote:

Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

Nice one Dave

In article ,
Mike W wrote:

Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

Nice one Dave

Not my idea originally, by any means. If I recall correctly I first
saw it in Bob Pease's "Troubleshooting Analog Circuits" book - a
text I recommend to anyone who is fiddling around with analog
circuitry in any way.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
Mike W wrote:

Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

Nice one Dave

Not my idea originally, by any means. If I recall correctly I first
saw it in Bob Pease's "Troubleshooting Analog Circuits" book - a
text I recommend to anyone who is fiddling around with analog
circuitry in any way.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Jim
The rig will be powered from a 12V source eg battery/AC wallwart
/whatever. However, internally the rig needs various voltages, including
1.8V for logic and -12V. I want to ptotect against inadvertent
overvoltage or reverse voltage. I want it to be as efficient as
possible, so I dont want to use a linear regulator. SMPS seems the
obvious choice. I may well shield the PSU section, and isolate the
ground etc to reduce noise. I was seeking advice from the experts here
as to whether the idea is feasible and whether there is a redaymade
solution.

Richard

Jim Weir wrote:
I'm not understanding something here. You want to design a power supply that
protects against reverse voltage and overvoltage. OK. Is this power supply a
battery or are you actually building a power supply that runs from the wall
outlet?

The requirements are quite different, depending on what you are trying to
achieve.

Jim



Richard Hosking
shared these priceless pearls of wisdom:

-Dear all
-I want to design a power supply for a low power rig with protection for
-reverse and overvoltage.


Jim Weir, VP Eng. RST Eng. WX6RST
A&P, CFI, and other good alphabet soup

Jim
The rig will be powered from a 12V source eg battery/AC wallwart
/whatever. However, internally the rig needs various voltages, including
1.8V for logic and -12V. I want to ptotect against inadvertent
overvoltage or reverse voltage. I want it to be as efficient as
possible, so I dont want to use a linear regulator. SMPS seems the
obvious choice. I may well shield the PSU section, and isolate the
ground etc to reduce noise. I was seeking advice from the experts here
as to whether the idea is feasible and whether there is a redaymade
solution.

Richard

Jim Weir wrote:
I'm not understanding something here. You want to design a power supply that
protects against reverse voltage and overvoltage. OK. Is this power supply a
battery or are you actually building a power supply that runs from the wall
outlet?

The requirements are quite different, depending on what you are trying to
achieve.

Jim



Richard Hosking
shared these priceless pearls of wisdom:

-Dear all
-I want to design a power supply for a low power rig with protection for
-reverse and overvoltage.


Jim Weir, VP Eng. RST Eng. WX6RST
A&P, CFI, and other good alphabet soup

This sounds like a good solution

Thanks
Richard

Dave Platt wrote:
In article ,
Dr. A.T. Squeegee wrote:


I want to design a power supply for a low power rig with protection for
reverse and overvoltage. The requirement would be about 1A at 12-14V.
What is the best way of achieving this? I guess a diode would give
reverse voltage protection but the 0.6V drop is a problem.

Power Schottky diodes are available that have a forward voltage
drop of 0.3 or less. More expensive, yes, but they really do work.


Another trick I've seen is to use a hefty power MOSFET (one with a low
Rds[on]), with the source and drain leads reversed, in series with the
power. Depending on the voltages involved, you can either connect the
gate directly to the opposite side of the power supply, or (if the
supply voltage may exceed the Vgs limit) to a high-Z resistive divider.

When a power supply of the correct polarity is hooked up, the MOSFET's
intrinsic substrate diode is biased forward (conducting normally) and
the MOSFET is turned on "hard" (giving a low Rds, and thus a very low
forward voltage drop). If the supply is hooked up backwards, the
MOSFET is turned off (the gate is pulled down towards hard depletion)
and the substrate diode is reverse-biased, switching it off.