Meter protecting diodes

[Jim Hawkins]

I need to protect a 100 microamp moving-coil meter with a pair of
back-to-back diodes.
Can someone recommend suitable types ?
I have various 1N400x types but I presume these would not be suitable.

Jim Hawkins

 

[Pieter]

On Fri, 25 Jan 2008 12:37:12 -0000, "Jim Hawkins"
<jimhawkins@manx.net> wrote:

I need to protect a 100 microamp moving-coil meter with a pair of
back-to-back diodes.
Can someone recommend suitable types ?
I have various 1N400x types but I presume these would not be suitable.

Jim Hawkins

What is the voltage at 100 microamp? Or the resistance?

A 1N400x is a bit slow. But may be enough.

I would suggest using diodes that are fast enough like the good old
1N41418 or maybe some shottkys or zeners. Depends on the voltage. And
on the maximum current that can flow through the diodes.

P.

 

[Bill S.]

In article <13pjm2u7p43r685@news.supernews.com>, jimhawkins@manx.net
says...

I need to protect a 100 microamp moving-coil meter with a pair of
back-to-back diodes.
Can someone recommend suitable types ?
I have various 1N400x types but I presume these would not be suitable.

Most meters in this range drop a couple hundred millivolts at
full scale. Rectifier diodes will probably be too leaky, try
something in a small signal diode. I used to like the FDH300's
but they were discontinued. You might get away with 1N4148's,
check for nonlinearity approaching full scale. There used to
be a device formulated just for this application, but the
bottom pretty much fell out of the analog meter market with
the advent of low power CMOS A/D converters.

 

[Jim Hawkins]

"Bill S." <NoSpam@OnMe.com> wrote in message
news:MPG.2203da262a544bb9989690@news-server.woh.rr.com...

In article <13pjm2u7p43r685@news.supernews.com>, jimhawkins@manx.net
says...
I need to protect a 100 microamp moving-coil meter with a pair of
back-to-back diodes.
Can someone recommend suitable types ?
I have various 1N400x types but I presume these would not be suitable.

Most meters in this range drop a couple hundred millivolts at
full scale. Rectifier diodes will probably be too leaky, try
something in a small signal diode. I used to like the FDH300's
but they were discontinued. You might get away with 1N4148's,
check for nonlinearity approaching full scale. There used to
be a device formulated just for this application, but the
bottom pretty much fell out of the analog meter market with
the advent of low power CMOS A/D converters.

Thanks for that Bill. I found that Fairchild-Direct still have a couple of
thousand
FDH300s in stock so I've ordered some.

Jim Hawkins

 

[John Robertson]

Jim Hawkins wrote:

I need to protect a 100 microamp moving-coil meter with a pair of
back-to-back diodes.
Can someone recommend suitable types ?
I have various 1N400x types but I presume these would not be suitable.

Jim Hawkins

You could add an MOV in parallel to further protect the meter movement.
Simply choose an MOV that clamps higher than the maximum voltage you
plan on reading, yet low enough that the needle won't wrap around a peg
before the protection kicks in..

An MOV as a backup to the diodes would be belt & suspenders...

John :-#)#

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