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PNP for soft switch and reverse battery protection

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  PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-09 13:16 -0600
    Re: PNP for soft switch and reverse battery protection John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-09 11:34 -0800
      Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-09 16:47 -0600
        Re: PNP for soft switch and reverse battery protection John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-09 15:40 -0800
          Re: PNP for soft switch and reverse battery protection bitrex <bitrex@de.lete.earthlink.net> - 2017-02-10 10:47 -0500
            Re: PNP for soft switch and reverse battery protection John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-10 08:30 -0800
        Re: PNP for soft switch and reverse battery protection George Herold <gherold@teachspin.com> - 2017-02-10 07:25 -0800
          Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-10 11:37 -0600
            Re: PNP for soft switch and reverse battery protection Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-10 11:19 -0800
              Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 12:48 -0700
              Re: PNP for soft switch and reverse battery protection George Herold <gherold@teachspin.com> - 2017-02-10 12:24 -0800
            Re: PNP for soft switch and reverse battery protection George Herold <gherold@teachspin.com> - 2017-02-10 12:22 -0800
    Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-09 13:21 -0700
      Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-09 16:46 -0600
        Re: PNP for soft switch and reverse battery protection "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-09 17:01 -0600
          Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-09 18:59 -0700
            Re: PNP for soft switch and reverse battery protection "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-10 13:17 -0600
        Re: PNP for soft switch and reverse battery protection Winfield Hill <hill@rowland.harvard.edu> - 2017-02-10 14:29 -0800
          Re: PNP for soft switch and reverse battery protection Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-10 17:58 -0500
            Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 16:40 -0700
        Re: PNP for soft switch and reverse battery protection M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-10 18:23 -0500
    Re: PNP for soft switch and reverse battery protection Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-09 14:55 -0800
    Re: PNP for soft switch and reverse battery protection bill.sloman@ieee.org - 2017-02-09 17:31 -0800
    Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 08:50 -0700
      Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-10 11:18 -0600
        Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 12:41 -0700
          Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-10 16:28 -0600
            Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 16:44 -0700
              Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-10 20:49 -0600
                Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 20:10 -0700
                  Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-11 11:38 -0600
                    Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-11 11:07 -0700
                      Re: PNP for soft switch and reverse battery protection rickman <gnuarm@gmail.com> - 2017-02-11 18:46 -0500
                    Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-11 11:15 -0700
                      Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-11 18:31 -0600
                        Re: PNP for soft switch and reverse battery protection rickman <gnuarm@gmail.com> - 2017-02-11 19:50 -0500
                          Re: PNP for soft switch and reverse battery protection Clifford Heath <no.spam@please.net> - 2017-02-12 12:44 +1100
                            Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-11 23:26 -0600
                              Re: PNP for soft switch and reverse battery protection Clifford Heath <no.spam@please.net> - 2017-02-12 18:19 +1100
                              Re: PNP for soft switch and reverse battery protection Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-12 08:18 -0800
                              Re: PNP for soft switch and reverse battery protection rickman <gnuarm@gmail.com> - 2017-02-14 01:52 -0500
                        Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-11 18:04 -0700
                          Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-11 23:14 -0600
                            Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-12 08:18 -0700
                            Re: PNP for soft switch and reverse battery protection John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-12 08:29 -0800
      Re: PNP for soft switch and reverse battery protection whit3rd <whit3rd@gmail.com> - 2017-02-10 13:54 -0800
    Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 08:53 -0700
    Re: PNP for soft switch and reverse battery protection M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-10 18:08 -0500
      Re: PNP for soft switch and reverse battery protection Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-02-10 15:15 -0800
        Re: PNP for soft switch and reverse battery protection M Philbrook <jamie_ka1lpa@charter.net> - 2017-02-10 18:34 -0500
    Re: PNP for soft switch and reverse battery protection Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-11 12:47 -0700
    Re: PNP for soft switch and reverse battery protection Jasen Betts <jasen@xnet.co.nz> - 2017-02-14 06:13 +0000
      Re: PNP for soft switch and reverse battery protection whit3rd <whit3rd@gmail.com> - 2017-02-14 00:52 -0800
        Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-14 22:26 -0600
      Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-14 22:16 -0600
        Re: PNP for soft switch and reverse battery protection John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-14 21:42 -0800
          Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-15 00:21 -0600
            Re: PNP for soft switch and reverse battery protection Jasen Betts <jasen@xnet.co.nz> - 2017-02-15 11:44 +0000
              Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-15 08:15 -0600
                Re: PNP for soft switch and reverse battery protection makolber@yahoo.com - 2017-02-15 09:30 -0800
                  Re: PNP for soft switch and reverse battery protection Peabody <waybackNO584SPAM44@yahoo.com> - 2017-02-15 11:50 -0600
                    Re: PNP for soft switch and reverse battery protection makolber@yahoo.com - 2017-02-15 10:07 -0800
                    Re: PNP for soft switch and reverse battery protection "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-02-15 21:19 -0600
                  Re: PNP for soft switch and reverse battery protection George Herold <gherold@teachspin.com> - 2017-02-15 11:30 -0800
                    Re: PNP for soft switch and reverse battery protection makolber@yahoo.com - 2017-02-15 11:52 -0800
                      Re: PNP for soft switch and reverse battery protection George Herold <gherold@teachspin.com> - 2017-02-15 12:00 -0800
            Re: PNP for soft switch and reverse battery protection John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-15 10:41 -0800

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#447232

In article <20170209-224630.33.0@Peabody.ssl.astraweb.com>, 
waybackNO584SPAM44@yahoo.com says...
> 
> Jim Thompson says...
> 
>  >> The easiest alternative I can think of is to just
>  >> insert a diode between the base and resistor.  That
>  >> would prevent any reverse current flowing into the PNP
>  >> base up to the rating of the diode, which will be way
>  >> above 9V, while not really affecting how the transistor
>  >> functions.  In particular, it would have no effect on
>  >> the main E-C voltage drop in normal operation.
> 
>  > That won't keep the load from seeing a reverse voltage.
> 
>  > If you could find a small P-Channel device that would be
>  > your best bet.
> 
> I don't understand.  It seems to me the PNP C-E does exactly the
> same thing as a p-channel mosfet, which is to block current
> from flowing when the battery is connected backward.  So
> it's the same for the main load with either device.  It's
> just the pesky PNP base that I'n worried about.  The mosfet
> doesn't present that problem, but then it can't both switch
> and protect in a single device.

Ok, I miss understood the problem...

 First off, you still should use a PChannel for protection because
 of the body diode in the reverse state and haveing the gate pulled
 low will force it fully on in the correct state. Otherwise without
the gate pulled low, it'll pass voltage with one diode drop worth of 
loses

  Put another Pchannel after that one orientated the other way as the
circuit switch.
  
  The first one can be tied on at all times, the second you simply pull 
the gate to common when you want it.

  Basically you get a switch and protection that has very little drop.

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#447098

Den torsdag den 9. februar 2017 kl. 20.18.05 UTC+1 skrev Peabody:
> I'm working on a small circuit that will be powered by a 9V battery.  I would 
> like to combine the functions of a soft power switch and reverse battery 
> protection in a single device.  I think the answer may be to use a PNP 
> transistor on the high side, with a base resistor to ground - actually to 
> ground through a physical momentary switch, or indirectly to ground via an 
> NPN transistor controlled by a microcontroller output pin.  But for purposes 
> of this post, just think of a base resistor to ground.  I only need a few mA 
> of current, and the base resistor needed will be 100K.
> 
> My question concerns reverse polarity protection.  I believe I understand 
> correctly that current will not flow backwards from collector to emitter of 
> a PNP so long as the transistor's voltage rating is not exceeded.  So the 
> "main" power flow will be protected.
> 
> But the absolute maximum base-emitter reverse voltage for this transistor 
> (BC560C) is 5V. So if 9V were to be applied directly to the base, with the 
> emitter at ground, I think the transistor would be blown.  The question is 
> whether the 100K resistor limits current enough so that the transistor is not 
> damaged.  I just don't have any experience with this situation, and don't 
> knpw what actually works.  There is also a separate question as to whether 
> the limited reverse current flowing through the resistor would damage the 
> microcontroller (max 3.6V Vcc) since all of that current would actually flow 
> through it via its protection diodes.
> 
> I guess if it's clear that, at 9V, 100K is gonna keep anything from losing 
> its smoke, I would just go with that.  But I'm more than a little goosey 
> about that.  The easiest alternative I can think of is to just insert a diode 
> between the base and resistor.  That would prevent any reverse current 
> flowing into the PNP base up to the rating of the diode, which will be way 
> above 9V, while not really affecting how the transistor functions.  In 
> particular, it would have no effect on the main E-C voltage drop in normal 
> operation.
> 
> So what do you think?  Am I right at least about the theoretical risk?  If 
> so, does the 100K resistor cover me, or do I need the diode?  Or is there a 
> better way?  Well, I guess there's always a better way.  As I said, I want to 
> combine a soft switch with polarity protection.  A P-channel MOSFET can't do 
> both because the body diode has to be one way to function as a switch, and 
> the opposite way to function as polarity protection.  The PNP looks like the 
> right solution.
> 
> Thanks for any suggestions.

use two pfets back to back

or maybe a diode and a voltage regulator with enable

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#447124

On Friday, February 10, 2017 at 6:18:05 AM UTC+11, Peabody wrote:
> I'm working on a small circuit that will be powered by a 9V battery.  I would 
> like to combine the functions of a soft power switch and reverse battery 
> protection in a single device.  I think the answer may be to use a PNP 
> transistor on the high side, with a base resistor to ground - actually to 
> ground through a physical momentary switch, or indirectly to ground via an 
> NPN transistor controlled by a microcontroller output pin.  But for purposes 
> of this post, just think of a base resistor to ground.  I only need a few mA 
> of current, and the base resistor needed will be 100K.
> 
> My question concerns reverse polarity protection.  I believe I understand 
> correctly that current will not flow backwards from collector to emitter of 
> a PNP so long as the transistor's voltage rating is not exceeded.  So the 
> "main" power flow will be protected.
> 
> But the absolute maximum base-emitter reverse voltage for this transistor 
> (BC560C) is 5V. So if 9V were to be applied directly to the base, with the 
> emitter at ground, I think the transistor would be blown.  The question is 
> whether the 100K resistor limits current enough so that the transistor is not 
> damaged. 

The resistor will prevent gross damage, but it is known that even a small reverse current through the base emitter junction of a bipolar transistor progressively degrades the junction and the forward current gain of the transistor. The damage can be annealed out, and there was a Hewlett-Packard function generator where one of the routine service procedures involved the service engineer stubbing out his cigarette on a particular output transistor to do just that.

The story dates back to the days when most people smoked ...

> I just don't have any experience with this situation, and don't 
> knpw what actually works.  There is also a separate question as to whether 
> the limited reverse current flowing through the resistor would damage the 
> microcontroller (max 3.6V Vcc) since all of that current would actually flow 
> through it via its protection diodes.

The protection diodes will be fine. The microcontroller might not be. The protection diodes inject charge carriers into the substrate of the device, and they can do unexpected things. The microcontroller can't be relied to perform as specified when the protection diodes are conducting.

-- 
Bill Sloman, Sydney

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#447157

On Thu, 09 Feb 2017 13:16:44 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> wrote:

>I'm working on a small circuit that will be powered by a 9V battery.  I would 
>like to combine the functions of a soft power switch and reverse battery 
>protection in a single device.  I think the answer may be to use a PNP 
>transistor on the high side, with a base resistor to ground - actually to 
>ground through a physical momentary switch, or indirectly to ground via an 
>NPN transistor controlled by a microcontroller output pin.  But for purposes 
>of this post, just think of a base resistor to ground.  I only need a few mA 
>of current, and the base resistor needed will be 100K.
>
>My question concerns reverse polarity protection.  I believe I understand 
>correctly that current will not flow backwards from collector to emitter of 
>a PNP so long as the transistor's voltage rating is not exceeded.  So the 
>"main" power flow will be protected.
>
>But the absolute maximum base-emitter reverse voltage for this transistor 
>(BC560C) is 5V. So if 9V were to be applied directly to the base, with the 
>emitter at ground, I think the transistor would be blown.  The question is 
>whether the 100K resistor limits current enough so that the transistor is not 
>damaged.  I just don't have any experience with this situation, and don't 
>knpw what actually works.  There is also a separate question as to whether 
>the limited reverse current flowing through the resistor would damage the 
>microcontroller (max 3.6V Vcc) since all of that current would actually flow 
>through it via its protection diodes.
>
>I guess if it's clear that, at 9V, 100K is gonna keep anything from losing 
>its smoke, I would just go with that.  But I'm more than a little goosey 
>about that.  The easiest alternative I can think of is to just insert a diode 
>between the base and resistor.  That would prevent any reverse current 
>flowing into the PNP base up to the rating of the diode, which will be way 
>above 9V, while not really affecting how the transistor functions.  In 
>particular, it would have no effect on the main E-C voltage drop in normal 
>operation.
>
>So what do you think?  Am I right at least about the theoretical risk?  If 
>so, does the 100K resistor cover me, or do I need the diode?  Or is there a 
>better way?  Well, I guess there's always a better way.  As I said, I want to 
>combine a soft switch with polarity protection.  A P-channel MOSFET can't do 
>both because the body diode has to be one way to function as a switch, and 
>the opposite way to function as polarity protection.  The PNP looks like the 
>right solution.
>
>Thanks for any suggestions.

A crude solution...

<http://www.analog-innovations.com/SED/Peabody_Switch.png>

Runs the PNP inverted, so low Beta, burns extra bias current to make
up for the low Beta, but collector junction is exposed to 9V instead
of emitter junction.

		
                                        ...Jim Thompson
-- 
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

     Thinking outside the box... producing elegant solutions.

[toc] | [prev] | [next] | [standalone]

#447178

Jim Thompson says...

 > A crude solution...

 > <http://www.analog-innovations.com/SED/Peabody_Switch.png>

 > Runs the PNP inverted, so low Beta, burns extra bias
 > current to make up for the low Beta, but collector
 > junction is exposed to 9V instead of emitter junction.

Thanks very much.  And I saw your followup about the diode
not being needed.

But I don't understand R2.  Shouldn't it be tied to the
collector?  It seems that with your placement the transistor
would be always-on.  Or if it's off, then when the load side
voltage drops below 8.4V, it would begin to oscillate.

After posting yesterday, I got out my breadboard and some
2N3906's, and got some surprising results which I need to
investigate further.  Basically, with the battery connected
backward so that C is positive and E is negative, I get some
current flowing from C through to E, pretty much regardless
of what the base is doing - even if it's open.  I didn't
think that was supposed to happen.  And that's on two
different transistors, so not just a bad part.

Well, I've always just used transistors in the normal
orientation, and with the power supply connected properly,
but have never looked at what happens when you hook them up
backwards.  So I have some experimenting to do - including
on your inverted orientation of the PNP.

Thanks again.

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#447195

On Fri, 10 Feb 2017 11:18:43 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> wrote:

>Jim Thompson says...
>
> > A crude solution...
>
> > <http://www.analog-innovations.com/SED/Peabody_Switch.png>
>
> > Runs the PNP inverted, so low Beta, burns extra bias
> > current to make up for the low Beta, but collector
> > junction is exposed to 9V instead of emitter junction.
>
>Thanks very much.  And I saw your followup about the diode
>not being needed.
>
>But I don't understand R2.  Shouldn't it be tied to the
>collector?  It seems that with your placement the transistor
>would be always-on.  Or if it's off, then when the load side
>voltage drops below 8.4V, it would begin to oscillate.
>
>After posting yesterday, I got out my breadboard and some
>2N3906's, and got some surprising results which I need to
>investigate further.  Basically, with the battery connected
>backward so that C is positive and E is negative, I get some
>current flowing from C through to E, pretty much regardless
>of what the base is doing - even if it's open.  I didn't
>think that was supposed to happen.  And that's on two
>different transistors, so not just a bad part.
>
>Well, I've always just used transistors in the normal
>orientation, and with the power supply connected properly,
>but have never looked at what happens when you hook them up
>backwards.  So I have some experimenting to do - including
>on your inverted orientation of the PNP.
>
>Thanks again.

R2 causes the emitter-base junction voltage to be too small in the
reversed input voltage mode to leak and pass large currents.
		
                                        ...Jim Thompson
-- 
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

     Thinking outside the box... producing elegant solutions.

[toc] | [prev] | [next] | [standalone]

#447217

Jim Thompson says...

 > R2 causes the emitter-base junction voltage to be too
 > small in the reversed input voltage mode to leak and
 > pass large currents.

Ok, I breadboarded the PNP circuit in both the normal
orientation of the transistor and with the transistor placed
backward.  Since the base is the middle pin, I just turned
the transistor around 180 degrees.

The two circuits are shown here:

https://s28.postimg.org/8tdthq4il/Peabody_breadboard.jpg

In the normal orientation, the 2N3906 functioned normally.
Opening the base via J1 turned off the transistor
completely, at least to the limit of my meters, at any
V+ up to 12V.

In the reverse orientation, at low V+ levels, it also
functioned normally, but with  a bit less output current.
This presumably results from the lower beta.

However, as I ramped up the V+ power supply, C-E current
began to flow regardless of what was happening at the base -
even if the base was completely open.  Using the best meter
I have for measuring very low currents, which is my old
analog meter on the 50 uA scale, I found that the needle
just began to move when V+ reached 8.03V, and current
continued to increase as I increased V+ further, reaching 75
uA with V+ at about 11.9V.

This current was minimized with the pullup resistor (your
R2, my R1) connected to the collector.  "Off" current
increased if I connected it to the emitter where you had it.

So this is either a characteristic of the 2N3906, or perhaps
I have two of them that just happened to fail in the same
way, or there's something about the resistor values I used
that's causing this result.

But if none of those apply, and notwithstanding what Spice
may have to say, it's possible that this is a characteristic
of all PNP transistors, or possibly all bipolars.  And if
that's the case, then what I wanted to do, which is use one
device for both switching and polarity protection, will work
fine at, say, 5V or less, but not if you're using a 9V
battery.

I guess the good news is that for 3.3V or 5V, this actually
works, and you don't even have to turn the transistor around
because the reverse voltage is less than the Vebo maximum.
You can switch the power on and off with the PNP, and you
get free polarity protection to boot.  But it appears this
doesn't work at higher voltages - unless of course I screwed
something up that can be corrected.

If anyone wants to try confirming my test, I would be
interested in the results.  Meanwhile, unless there's a fix
I haven't thought of, it looks like the backwards P-channel
MOSFET will be needed for polarity protection for the 9V battery.

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#447237

On Fri, 10 Feb 2017 16:28:22 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> wrote:

>
>Jim Thompson says...
>
> > R2 causes the emitter-base junction voltage to be too
> > small in the reversed input voltage mode to leak and
> > pass large currents.
>
>Ok, I breadboarded the PNP circuit in both the normal
>orientation of the transistor and with the transistor placed
>backward.  Since the base is the middle pin, I just turned
>the transistor around 180 degrees.
>
>The two circuits are shown here:
>
>https://s28.postimg.org/8tdthq4il/Peabody_breadboard.jpg
>
>In the normal orientation, the 2N3906 functioned normally.
>Opening the base via J1 turned off the transistor
>completely, at least to the limit of my meters, at any
>V+ up to 12V.
>
>In the reverse orientation, at low V+ levels, it also
>functioned normally, but with  a bit less output current.
>This presumably results from the lower beta.
>
>However, as I ramped up the V+ power supply, C-E current
>began to flow regardless of what was happening at the base -
>even if the base was completely open.  Using the best meter
>I have for measuring very low currents, which is my old
>analog meter on the 50 uA scale, I found that the needle
>just began to move when V+ reached 8.03V, and current
>continued to increase as I increased V+ further, reaching 75
>uA with V+ at about 11.9V.
>
>This current was minimized with the pullup resistor (your
>R2, my R1) connected to the collector.  "Off" current
>increased if I connected it to the emitter where you had it.
>
>So this is either a characteristic of the 2N3906, or perhaps
>I have two of them that just happened to fail in the same
>way, or there's something about the resistor values I used
>that's causing this result.
>
>But if none of those apply, and notwithstanding what Spice
>may have to say, it's possible that this is a characteristic
>of all PNP transistors, or possibly all bipolars.  And if
>that's the case, then what I wanted to do, which is use one
>device for both switching and polarity protection, will work
>fine at, say, 5V or less, but not if you're using a 9V
>battery.
>
>I guess the good news is that for 3.3V or 5V, this actually
>works, and you don't even have to turn the transistor around
>because the reverse voltage is less than the Vebo maximum.
>You can switch the power on and off with the PNP, and you
>get free polarity protection to boot.  But it appears this
>doesn't work at higher voltages - unless of course I screwed
>something up that can be corrected.
>
>If anyone wants to try confirming my test, I would be
>interested in the results.  Meanwhile, unless there's a fix
>I haven't thought of, it looks like the backwards P-channel
>MOSFET will be needed for polarity protection for the 9V battery.

You have R1 the wrong way around in the emitter-toward-load mode.  And
it should be about the same value as the bias resistor.

And lose the diode.
		
                                        ...Jim Thompson
-- 
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

     Thinking outside the box... producing elegant solutions.

[toc] | [prev] | [next] | [standalone]

#447262

Jim Thompson says...

 > You have R1 the wrong way around in the
 > emitter-toward-load mode.  And it should be about the
 > same value as the bias resistor.

 > And lose the diode.

With the transistor in the backwards orientation, and V+ at
12V:

I made all three resistors 47K, and removed the diode.

I still get C-E current with the base open.  If I move R1 to
the emitter side, it INCREASES the OFF current from 75 uA to
200 uA.  So that makes things worse.  

I tested three NPN transistors the same way - connecting C
or E to 12V through a 47K resistor with the other
connected to ground, but with the base open, and got similar
results.  If I connect C and E in normal polarity, no
current flows (because there is no base current), but when I
reverse the polarity of the C and E connections, I get
current - even though there is no base current.

So this effect appears to hold for all my bipolar
transistors so far.  What I don't know is whether the
voltage at which this current flow begins to happen is
related to any datasheet parameter.

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#447267

On Fri, 10 Feb 2017 20:49:08 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> wrote:

>Jim Thompson says...
>
> > You have R1 the wrong way around in the
> > emitter-toward-load mode.  And it should be about the
> > same value as the bias resistor.
>
> > And lose the diode.
>
>With the transistor in the backwards orientation, and V+ at
>12V:
>
>I made all three resistors 47K, and removed the diode.
>
>I still get C-E current with the base open.  If I move R1 to
>the emitter side, it INCREASES the OFF current from 75 uA to
>200 uA.  So that makes things worse.  
>
>I tested three NPN transistors the same way - connecting C
>or E to 12V through a 47K resistor with the other
>connected to ground, but with the base open, and got similar
>results.  If I connect C and E in normal polarity, no
>current flows (because there is no base current), but when I
>reverse the polarity of the C and E connections, I get
>current - even though there is no base current.
>
>So this effect appears to hold for all my bipolar
>transistors so far.  What I don't know is whether the
>voltage at which this current flow begins to happen is
>related to any datasheet parameter.
>

What is you load current?  I think you're doing something wrong...
don't open the friggin' base!
		
                                        ...Jim Thompson
-- 
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

     Thinking outside the box... producing elegant solutions.

[toc] | [prev] | [next] | [standalone]

#447302

Jim Thompson says...

 > https://s28.postimg.org/8tdthq4il/Peabody_breadboard.jpg

 > What is you load current?  I think you're doing
 > something wrong... don't open the friggin' base!

As I said, I changed all the resistors to 47K.  So the base
pullup resistor is 47K, the base resistor is 47K, and the
load resistor is 47K.  I removed the diode.  And the power
supply is 12V.

When I insert the transistor backwards, the ON performance
is essentially the same as when it's in normal orientation.
The base current is about .25mA, and load current is also
.25mA, both of which are right for 47K resistors.

The problem comes when I try to turn the transistor OFF by
disconnecting the base resistor from ground, leaving only
the base pullup resistor connected.  If the base pullup is
connected to the collector (i.e. - directly to the 12V power
supply), I still get 75 uA of current through the load.  If
instead I connect the pullup to the emitter as you suggest,
the load current increases to 190 uA.  The problem of course
is that with the base pullup tied high, the transistor
should be completely off, and there shouldn't be any load
current at all.

The OFF load current only happens if the transistor is in
the opposite orientation from normal, and even then only if
the power supply is above about 8V (for my 2N3906's at
least).

Even though this effect doesn't appear to involve the E-B
voltage, I do wonder if the Vebo rating of a transistor
affects the 8V threshhold.  But I don't have a high-Vebo
part to test.

If anyone actually breadboards this (not Spice) and
gets a different result, please let me know.

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#447303

On Sat, 11 Feb 2017 11:38:32 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> wrote:

>Jim Thompson says...
>
> > https://s28.postimg.org/8tdthq4il/Peabody_breadboard.jpg
>
> > What is you load current?  I think you're doing
> > something wrong... don't open the friggin' base!
>
>As I said, I changed all the resistors to 47K.  So the base
>pullup resistor is 47K, the base resistor is 47K, and the
>load resistor is 47K.  I removed the diode.  And the power
>supply is 12V.
>
>When I insert the transistor backwards, the ON performance
>is essentially the same as when it's in normal orientation.
>The base current is about .25mA, and load current is also
>.25mA, both of which are right for 47K resistors.
>
>The problem comes when I try to turn the transistor OFF by
>disconnecting the base resistor from ground, leaving only
>the base pullup resistor connected.  If the base pullup is
>connected to the collector (i.e. - directly to the 12V power
>supply), I still get 75 uA of current through the load.  If
>instead I connect the pullup to the emitter as you suggest,
>the load current increases to 190 uA.  The problem of course
>is that with the base pullup tied high, the transistor
>should be completely off, and there shouldn't be any load
>current at all.
>
>The OFF load current only happens if the transistor is in
>the opposite orientation from normal, and even then only if
>the power supply is above about 8V (for my 2N3906's at
>least).
>
>Even though this effect doesn't appear to involve the E-B
>voltage, I do wonder if the Vebo rating of a transistor
>affects the 8V threshhold.  But I don't have a high-Vebo
>part to test.
>
>If anyone actually breadboards this (not Spice) and
>gets a different result, please let me know.
>

What is "motor"?
		
                                        ...Jim Thompson
-- 
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

     Thinking outside the box... producing elegant solutions.

[toc] | [prev] | [next] | [standalone]

#447335

On 2/11/2017 1:07 PM, Jim Thompson wrote:
> On Sat, 11 Feb 2017 11:38:32 -0600, Peabody
> <waybackNO584SPAM44@yahoo.com> wrote:
>
>> Jim Thompson says...
>>
>>> https://s28.postimg.org/8tdthq4il/Peabody_breadboard.jpg
>>
>>> What is you load current?  I think you're doing
>>> something wrong... don't open the friggin' base!
>>
>> As I said, I changed all the resistors to 47K.  So the base
>> pullup resistor is 47K, the base resistor is 47K, and the
>> load resistor is 47K.  I removed the diode.  And the power
>> supply is 12V.
>>
>> When I insert the transistor backwards, the ON performance
>> is essentially the same as when it's in normal orientation.
>> The base current is about .25mA, and load current is also
>> .25mA, both of which are right for 47K resistors.
>>
>> The problem comes when I try to turn the transistor OFF by
>> disconnecting the base resistor from ground, leaving only
>> the base pullup resistor connected.  If the base pullup is
>> connected to the collector (i.e. - directly to the 12V power
>> supply), I still get 75 uA of current through the load.  If
>> instead I connect the pullup to the emitter as you suggest,
>> the load current increases to 190 uA.  The problem of course
>> is that with the base pullup tied high, the transistor
>> should be completely off, and there shouldn't be any load
>> current at all.
>>
>> The OFF load current only happens if the transistor is in
>> the opposite orientation from normal, and even then only if
>> the power supply is above about 8V (for my 2N3906's at
>> least).
>>
>> Even though this effect doesn't appear to involve the E-B
>> voltage, I do wonder if the Vebo rating of a transistor
>> affects the 8V threshhold.  But I don't have a high-Vebo
>> part to test.
>>
>> If anyone actually breadboards this (not Spice) and
>> gets a different result, please let me know.
>>
>
> What is "motor"?

I believe that is "meter", the thing in series with the voltage source 
on the left.

-- 

Rick C

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#447304

On Sat, 11 Feb 2017 11:38:32 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> wrote:

>Jim Thompson says...
>
> > https://s28.postimg.org/8tdthq4il/Peabody_breadboard.jpg
>
> > What is you load current?  I think you're doing
> > something wrong... don't open the friggin' base!
>
>As I said, I changed all the resistors to 47K.  So the base
>pullup resistor is 47K, the base resistor is 47K, and the
>load resistor is 47K.  I removed the diode.  And the power
>supply is 12V.
>
>When I insert the transistor backwards, the ON performance
>is essentially the same as when it's in normal orientation.
>The base current is about .25mA, and load current is also
>.25mA, both of which are right for 47K resistors.
>
>The problem comes when I try to turn the transistor OFF by
>disconnecting the base resistor from ground, leaving only
>the base pullup resistor connected.  If the base pullup is
>connected to the collector (i.e. - directly to the 12V power
>supply), I still get 75 uA of current through the load.  If
>instead I connect the pullup to the emitter as you suggest,
>the load current increases to 190 uA.  The problem of course
>is that with the base pullup tied high, the transistor
>should be completely off, and there shouldn't be any load
>current at all.
>
>The OFF load current only happens if the transistor is in
>the opposite orientation from normal, and even then only if
>the power supply is above about 8V (for my 2N3906's at
>least).
>
>Even though this effect doesn't appear to involve the E-B
>voltage, I do wonder if the Vebo rating of a transistor
>affects the 8V threshhold.  But I don't have a high-Vebo
>part to test.
>
>If anyone actually breadboards this (not Spice) and
>gets a different result, please let me know.
>

Oooops!  I misunderstood your original post.  I only tried reverse
voltage protection, not turn-off via the transistor.

Do you really need to turn off via the transistor rather than just a
switch at the battery?
		
                                        ...Jim Thompson
-- 
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

     Thinking outside the box... producing elegant solutions.

[toc] | [prev] | [next] | [standalone]

#447341

Jim Thompson says...

 > Oooops!  I misunderstood your original post.  I only
 > tried reverse voltage protection, not turn-off via the
 > transistor.

 > Do you really need to turn off via the transistor rather
 > than just a switch at the battery?

Yes.  The whole point is not having to use a manual switch.

Besides, it appears reverse polarity protection doesn't work
if the power supply is more than 8V, which would include a
9V battery.

Well, I'll keep working on this, but for now it looks like
two P-channel mosfets will be needed, as others have
suggested.

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#447344

On 2/11/2017 7:31 PM, Peabody wrote:
> Jim Thompson says...
>
>  > Oooops!  I misunderstood your original post.  I only
>  > tried reverse voltage protection, not turn-off via the
>  > transistor.
>
>  > Do you really need to turn off via the transistor rather
>  > than just a switch at the battery?
>
> Yes.  The whole point is not having to use a manual switch.
>
> Besides, it appears reverse polarity protection doesn't work
> if the power supply is more than 8V, which would include a
> 9V battery.
>
> Well, I'll keep working on this, but for now it looks like
> two P-channel mosfets will be needed, as others have
> suggested.

It's a long thread, maybe this was stated.  Is there a reason why a 
Schottky diode can't be used for reverse polarity protection?  That 
seems simpler than adding two transistors.  Maybe not.  Two of the same 
line item can be easier in fabrication than two line items.

-- 

Rick C

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#447353

On 12/02/17 11:50, rickman wrote:
> On 2/11/2017 7:31 PM, Peabody wrote:
>> Jim Thompson says...
>>
>>  > Oooops!  I misunderstood your original post.  I only
>>  > tried reverse voltage protection, not turn-off via the
>>  > transistor.
>>
>>  > Do you really need to turn off via the transistor rather
>>  > than just a switch at the battery?
>>
>> Yes.  The whole point is not having to use a manual switch.
>>
>> Besides, it appears reverse polarity protection doesn't work
>> if the power supply is more than 8V, which would include a
>> 9V battery.
>>
>> Well, I'll keep working on this, but for now it looks like
>> two P-channel mosfets will be needed, as others have
>> suggested.
>
> It's a long thread, maybe this was stated.  Is there a reason why a
> Schottky diode can't be used for reverse polarity protection?

Sometimes you simply can't spare 400mV, such as in single-cell applications.

A MOSFET that will pass (say) 10amps is a lot smaller and cheaper than a 
Schottky that will.

Clifford Heath.

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#447375

Clifford Heath says...

 >> It's a long thread, maybe this was stated.  Is there a
 >> reason why a Schottky diode can't be used for reverse
 >> polarity protection?

 > Sometimes you simply can't spare 400mV, such as in
 > single-cell applications.

 > A MOSFET that will pass (say) 10amps is a lot smaller
 > and cheaper than a Schottky that will.

I need very little current, so a Schottky would be cheaper.
But it's mainly the voltage drop.  Anything that produces a
voltage drop just shortens the life of the battery -
assuming the circuit will only operate properly down to a
certain supply voltage.

Also, Schottkys aren't known for having all that great
reverse leakage values, which might make them problematical
for protecting against reverse polarity.

From everything I've read, the P-channel mosfet, installed
backwards, is the school-approved solution for reverse
polarity protection.  They are more expensive, but for my
needs, the TP2104 should work fine, and it's 60 cents at
Digikey, versus maybe 40 cents for a Schottky.

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#447385

On 12/02/17 16:26, Peabody wrote:
> Clifford Heath says...
>  >> It's a long thread, maybe this was stated.  Is there a
>  >> reason why a Schottky diode can't be used for reverse
>  >> polarity protection?
>
>  > Sometimes you simply can't spare 400mV, such as in
>  > single-cell applications.
>
>  > A MOSFET that will pass (say) 10amps is a lot smaller
>  > and cheaper than a Schottky that will.
>
> I need very little current, so a Schottky would be cheaper.
> But it's mainly the voltage drop.  Anything that produces a
> voltage drop just shortens the life of the battery -
> assuming the circuit will only operate properly down to a
> certain supply voltage.
>
> Also, Schottkys aren't known for having all that great
> reverse leakage values, which might make them problematical
> for protecting against reverse polarity.
>
> From everything I've read, the P-channel mosfet, installed
> backwards, is the school-approved solution for reverse
> polarity protection.  They are more expensive, but for my
> needs, the TP2104 should work fine, and it's 60 cents at
> Digikey, versus maybe 40 cents for a Schottky.

I have some IRLML6302 that I bought for soft power-switches
and reverse protection in single-LiPo applications. $0.37
in singles from Digikey.

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#447414

Den søndag den 12. februar 2017 kl. 06.26.22 UTC+1 skrev Peabody:
> Clifford Heath says...
> 
>  >> It's a long thread, maybe this was stated.  Is there a
>  >> reason why a Schottky diode can't be used for reverse
>  >> polarity protection?
> 
>  > Sometimes you simply can't spare 400mV, such as in
>  > single-cell applications.
> 
>  > A MOSFET that will pass (say) 10amps is a lot smaller
>  > and cheaper than a Schottky that will.
> 
> I need very little current, so a Schottky would be cheaper.
> But it's mainly the voltage drop.  Anything that produces a
> voltage drop just shortens the life of the battery -
> assuming the circuit will only operate properly down to a
> certain supply voltage.
> 
> Also, Schottkys aren't known for having all that great
> reverse leakage values, which might make them problematical
> for protecting against reverse polarity.
> 
> From everything I've read, the P-channel mosfet, installed
> backwards, is the school-approved solution for reverse
> polarity protection.  They are more expensive, but for my
> needs, the TP2104 should work fine, and it's 60 cents at
> Digikey, versus maybe 40 cents for a Schottky.

if you don't need the gnd and battery negative to be the same 
you can use nfets on the low side instead

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