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OT: Question about LM334 and 1N457

 

The LM334 datasheet specifies the use of a diode to cancel the temperature coefficient of the LM334, saying:

"The recommended diode for use in this circuit is the 1N457 because its tempco is centered at 11 times the tempco of the LM134, allowing R2 = 10 R1."

All well and good, but the 1N457 datasheet doesn't specify the TC, and anyway the 1N457 is getting rather hard to find.

Can anyone recommend a suitable substitute? Ideally in a surface mount package.

Thanks
David Partridge
 

David,

Mouser has buckets of 1N457's at $0.14 each.

Leon Robinson ?? K5JLR

Political Correctness is a Political Disease.


--- On Sat, 7/14/12, David C. Partridge wrote:

From: David C. Partridge
Subject: [TekScopes] OT: Question about LM334 and 1N457
To: TekScopes@..., hp_agilent_equipment@...
Date: Saturday, July 14, 2012, 1:18 PM

?

The LM334 datasheet specifies the use of a diode to cancel the temperature coefficient of the LM334, saying:

"The recommended diode for use in this circuit is the 1N457 because its tempco is centered at 11 times the tempco of the LM134, allowing R2 = 10 R1."

All well and good, but the 1N457 datasheet doesn't specify the TC, and anyway the 1N457 is getting rather hard to find.

Can anyone recommend a suitable substitute? Ideally in a surface mount package.

Thanks
David Partridge
 

Perhaps better for David, Farnell have them as well.? Since they are made by Fairchild, they should be using the correct ex-National process.



I don't know a surface mount equivalent.


On Sat, Jul 14, 2012 at 12:47 PM, Leon Robinson <leon-robinson@...> wrote:


David,

Mouser has buckets of 1N457's at $0.14 each.

Leon Robinson ?? K5JLR

Political Correctness is a Political Disease.

--- On Sat, 7/14/12, David C. Partridge <david.partridge@...> wrote:

From: David C. Partridge <david.partridge@...>
Subject: [TekScopes] OT: Question about LM334 and 1N457
To: TekScopes@..., hp_agilent_equipment@...
Date: Saturday, July 14, 2012, 1:18 PM


?

The LM334 datasheet specifies the use of a diode to cancel the temperature coefficient of the LM334, saying:

"The recommended diode for use in this circuit is the 1N457 because its tempco is centered at 11 times the tempco of the LM134, allowing R2 = 10 R1."

All well and good, but the 1N457 datasheet doesn't specify the TC, and anyway the 1N457 is getting rather hard to find.

Can anyone recommend a suitable substitute? Ideally in a surface mount package.

Thanks
David Partridge
 

Every time I read the LM334 data sheet, I wonder the same thing. The
1N457 is not particularly fast or low leakage so I do not know what
distinguishes it for this application other than the data sheet
recommendation and comment about temperature coefficient which is not
all that helpful in finding a replacement without testing.

The LM334 data sheet and application notes have enough information to
calculate the required temperature coefficient. I would just build a
circuit and fixture to test a variety of diodes including common
transistor junctions.

The temperature coefficient of the current source for the 7081 AC
Buffer should not affect the output anyway. If it does, then
something else is wrong.

On Sat, 14 Jul 2012 19:18:04 +0100, "David C. Partridge"
<david.partridge@...> wrote:

The LM334 datasheet specifies the use of a diode to cancel the temperature coefficient of the LM334, saying:

"The recommended diode for use in this circuit is the 1N457 because its tempco is centered at 11 times the tempco of the LM134, allowing R2 = 10 R1."

All well and good, but the 1N457 datasheet doesn't specify the TC, and anyway the 1N457 is getting rather hard to find.

Can anyone recommend a suitable substitute? Ideally in a surface mount package.

Thanks
David Partridge
 

David,

In theory that may be so, but try telling *all* my 7071 and 7081 meters that this is the case - the AC buffer amplifier drifts for a lengthy period after power on. Before the latest change (C714 replacement) this has typically been over 24 hours before it stabilised. I'm still waiting to see how much better this might be after replacing C714. First signs are encouraging, but I've been misled before.

Regards,
David Partridge

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of David
Sent: 14 July 2012 21:05
To: TekScopes@...
Subject: Re: [TekScopes] OT: Question about LM334 and 1N457

Every time I read the LM334 data sheet, I wonder the same thing. The
1N457 is not particularly fast or low leakage so I do not know what distinguishes it for this application other than the data sheet recommendation and comment about temperature coefficient which is not all that helpful in finding a replacement without testing.

The LM334 data sheet and application notes have enough information to calculate the required temperature coefficient. I would just build a circuit and fixture to test a variety of diodes including common transistor junctions.

The temperature coefficient of the current source for the 7081 AC Buffer should not affect the output anyway. If it does, then something else is wrong.

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