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'Recommended Brounout Protection Circuit doesnt wor'
1996\07\27@194837 by NEIL GANDLER

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I have tried the recommended brownount protection circuit p. 2-415 in
the PIC microcontroller databook.
I used a 2N3906 for the pnp transistor and a 3.9v zener diode for
a cutoff at 4.6v. I tried it without the PIC and monitored the output
voltage. There was no switch in logic state on the output when I dropped the
supply voltage, only a linear drop. I even tried other pnp transistors
and even npn transistors and switching connections of the emmitter and
collector. No luck. Does anyone know of a SIMPLE circuit that will
do the same thing or indicate what I may be doing wrong?

               Neil Gandler

1996\07\28@001222 by Paul Mathews

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NEIL GANDLER wrote:
>
>  I have tried the recommended brownount protection circuit p. 2-415 in
> the PIC microcontroller databook.
> I used a 2N3906 for the pnp transistor and a 3.9v zener diode for
> a cutoff at 4.6v. I tried it without the PIC and monitored the output
> voltage. There was no switch in logic state on the output when I dropped the
> supply voltage, only a linear drop. I even tried other pnp transistors
> and even npn transistors and switching connections of the emmitter and
> collector. No luck. Does anyone know of a SIMPLE circuit that will
> do the same thing or indicate what I may be doing wrong?
>
>                 Neil Gandler


The combination of a high gain transistor with the typical 3.9V Zener
doesn't yield a crisp transfer function with this simple circuit with
no hysteresis.  Zeners have worse and worse 'knees' as you get down in
the lower Voltages.  Reduce the resistance of the collector load
resistor (40K in their diagram) and your circuit will behave a little
better.  At 40K, only 100uA collector current will raise it to 4V!  Beta
of a 2N3906 could be 200 or more, so a small Zener leakage is all it
takes.

Of course, you're wasting current in the collector load resistor, so
what else can be done?  Some possibilities:

1. Use several forward biased switching diodes in series instead of the
zener.
2. Use a couple of red LEDs in series instead of the Zener.  LEDs have
very sharp knees, and you get a power indicator in the bargain.
3. Use a reset IC with Schmitt input such as MAX809 or MC33164 instead.
--

Paul Mathews, consulting engineer
AEngineering Co.
spam_OUToptoengTakeThisOuTspamwhidbey.com
non-contact sensing and optoelectronics specialists

1996\07\28@181819 by Karel Hladky

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In article <.....01I7KUQI131I8XKP1BKILLspamspam@spam@ubvms.cc.buffalo.edu>, NEIL GANDLER
<V064MB9KspamKILLspamUBVMS.CC.BUFFALO.EDU> writes
>
>I used a 2N3906 for the pnp transistor and a 3.9v zener diode for
>a cutoff at 4.6v. I tried it without the PIC and monitored the output
>voltage. There was no switch in logic state on the output when I dropped the
>supply voltage, only a linear drop. I even tried other pnp transistors
>and even npn transistors and switching connections of the emmitter and
>collector. No luck. Does anyone know of a SIMPLE circuit that will
>do the same thing or indicate what I may be doing wrong?

Not very good, is it ? If you can afford a bit more than the cost of a
transistor and a zener try a dedicated IC such as Maxim MAX700. Well
worth it if dodgy PSUs are likely. Power-on reset and brownout
protection is something Microchip ought to sort out properly on the
chip.

Karel
--
++++++++.....khladkyKILLspamspam.....khdesign.demon.co.uk++Manchester M14 6BF England++++++++

1996\07\28@200808 by gary skinner

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At 07:39 PM 7/27/96 -0500, Neil Gandler wrote:
> I have tried the recommended brownount protection circuit p. 2-415 in
>the PIC microcontroller databook.
--- snip ---

I have used and highly recommend the 3 pin voltage detectors from Seiko
S-805 and S-807 series.  You can get open drain, or CMOS output.
TO-92, SOT23 or SOT89 packages
Available in voltage ranges from 1.0 to 7.7 volts.
I generally pay about $.30 to .35 in thousands.

Can't get much simpler than this.

They also have some really low quiescent current regulators.

And they now have both regualtor and detector in 1 package.

Hope this helps.
Gary Skinner,  Electronic Solutions Inc
Design of custom control circuits
Denver CO  303-469-9322

1996\07\29@005051 by Neil Gandler

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On Sun, 28 Jul 1996, gary skinner wrote:

> At 07:39 PM 7/27/96 -0500, Neil Gandler wrote:
> > I have tried the recommended brownount protection circuit p. 2-415 in
> >the PIC microcontroller databook.
> --- snip ---
>
> I have used and highly recommend the 3 pin voltage detectors from Seiko
> S-805 and S-807 series.  You can get open drain, or CMOS output.
> TO-92, SOT23 or SOT89 packages
> Available in voltage ranges from 1.0 to 7.7 volts.
> I generally pay about $.30 to .35 in thousands.
>

Do you have a tel# for Seiko. Are they available in small quantities?
Sounds what I'm looking for. The To-92 package is perfect.

               Neil

1996\07\29@042936 by Ray Gardiner

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>On Sun, 28 Jul 1996, gary skinner wrote:
>
>> At 07:39 PM 7/27/96 -0500, Neil Gandler wrote:
>> > I have tried the recommended brownount protection circuit p. 2-415 in
>> >the PIC microcontroller databook.
>> --- snip ---
>>
>> I have used and highly recommend the 3 pin voltage detectors from Seiko
>> S-805 and S-807 series.  You can get open drain, or CMOS output.
>> TO-92, SOT23 or SOT89 packages
>> Available in voltage ranges from 1.0 to 7.7 volts.
>> I generally pay about $.30 to .35 in thousands.
>>
>
>Do you have a tel# for Seiko. Are they available in small quantities?
>Sounds what I'm looking for. The To-92 package is perfect.
>

You might also consider the mitsubishi 51943A series, The one we use
for 5v PIC applications is 51943A this is available in TO-92 package
approx $0.40. Trips at approx 4.25v with  50 mv hysteresis.

The 51943B is an open collector version of the same thing.

1996\07\29@124558 by David Schmidt

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Also check out the Panasonic MN1381 series power supervisors.  You can
get them from Digi-key, about $0.74 in 100 qty.

At 12:50 AM 7/29/96 -0400, you wrote:
{Quote hidden}


'Recommended Brounout Protection Circuit doesnt wor'
1996\08\11@033952 by gary skinner
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At 12:50 AM 7/29/96 -0400, you wrote:

>Do you have a tel# for Seiko. Are they available in small quantities?
>Sounds what I'm looking for. The To-92 package is perfect.

US  310-517-7771
Japan  043-211-1213
Germany  001-49-6102-297-0

sorry to be so slow getting back to you.
Gary Skinner,  Electronic Solutions Inc
Design of custom control circuits
Denver CO  303-469-9322

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