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Groups > sci.electronics.design > #447047 > unrolled thread
| Started by | Peabody <waybackNO584SPAM44@yahoo.com> |
|---|---|
| First post | 2017-02-09 13:16 -0600 |
| Last post | 2017-02-15 10:41 -0800 |
| Articles | 20 on this page of 67 — 17 participants |
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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
Page 3 of 4 — ← Prev page 1 2 [3] 4 Next page →
| From | rickman <gnuarm@gmail.com> |
|---|---|
| Date | 2017-02-14 01:52 -0500 |
| Message-ID | <o7u9c5$cp6$1@dont-email.me> |
| In reply to | #447375 |
On 2/12/2017 12:26 AM, 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. If there is very little current, the voltage drop on the Schottky is less, possibly as low as 200 mV. > Also, Schottkys aren't known for having all that great > reverse leakage values, which might make them problematical > for protecting against reverse polarity. Your circuit uses less current than the reverse leakage current of a Schottky diode? Wow! That's low. > 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. How many are you making? -- Rick C
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| From | Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> |
|---|---|
| Date | 2017-02-11 18:04 -0700 |
| Message-ID | <55dv9clb8afdcps9tk8i7lp3c2u0pjqe0i@4ax.com> |
| In reply to | #447341 |
On Sat, 11 Feb 2017 18:31:18 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> 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.
Did you miss...
Message-ID: <6equ9cdnov5br6kbmnd78i70o40ce75jma@4ax.com>
...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.
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| From | Peabody <waybackNO584SPAM44@yahoo.com> |
|---|---|
| Date | 2017-02-11 23:14 -0600 |
| Message-ID | <20170212-051417.120.0@Peabody.ssl.astraweb.com> |
| In reply to | #447347 |
Jim Thompson says... > Did you miss... > Message-ID: <6equ9cdnov5br6kbmnd78i70o40ce75jma@4ax.com> Yes I did. Thanks for asking. And for the circuit suggestion. But I think if I have to use two devices, then I would rather just use a P-channel mosfet for the polarity protection. It wouldn't need any additional parts since its gate would be tied directly to ground. Then the switch transistor could either be another mosfet, or just a simple PNP switch. With either choice, I wouldn't need the diodes or the extra resistor.
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| From | Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> |
|---|---|
| Date | 2017-02-12 08:18 -0700 |
| Message-ID | <atu0acps337l1cu0e8rshb76gnopdtd7pu@4ax.com> |
| In reply to | #447374 |
On Sat, 11 Feb 2017 23:14:17 -0600, Peabody
<waybackNO584SPAM44@yahoo.com> wrote:
>Jim Thompson says...
>
> > Did you miss...
>
> > Message-ID: <6equ9cdnov5br6kbmnd78i70o40ce75jma@4ax.com>
>
>Yes I did. Thanks for asking. And for the circuit
>suggestion.
>
>But I think if I have to use two devices, then I would
>rather just use a P-channel mosfet for the polarity
>protection. It wouldn't need any additional parts since its
>gate would be tied directly to ground.
>
>Then the switch transistor could either be another mosfet,
>or just a simple PNP switch. With either choice, I wouldn't
>need the diodes or the extra resistor.
>
Yep, like this...
<http://www.analog-innovations.com/SED/Peabody_Switch_PMOSx2.png>
I used this scheme about 20 years ago for a LiIon battery charge chip
design I did for California Micro Devices.
I don't know if I was the first to do so or not. I actually used only
one FET and switched the body connection... the chip was not only a
charger, but also a discharge controller.
...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]
| From | John Larkin <jjlarkin@highlandtechnology.com> |
|---|---|
| Date | 2017-02-12 08:29 -0800 |
| Message-ID | <3b31acpje26dhs1o62mft8n4bupt828q55@4ax.com> |
| In reply to | #447374 |
On Sat, 11 Feb 2017 23:14:17 -0600, Peabody <waybackNO584SPAM44@yahoo.com> wrote: >Jim Thompson says... > > > Did you miss... > > > Message-ID: <6equ9cdnov5br6kbmnd78i70o40ce75jma@4ax.com> > >Yes I did. Thanks for asking. And for the circuit >suggestion. > >But I think if I have to use two devices, then I would >rather just use a P-channel mosfet for the polarity >protection. It wouldn't need any additional parts since its >gate would be tied directly to ground. > >Then the switch transistor could either be another mosfet, >or just a simple PNP switch. With either choice, I wouldn't >need the diodes or the extra resistor. > Why not use a series schottky diode? -- John Larkin Highland Technology, Inc lunatic fringe electronics
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| From | whit3rd <whit3rd@gmail.com> |
|---|---|
| Date | 2017-02-10 13:54 -0800 |
| Message-ID | <cf94a4d2-f84d-4027-bdc7-dc342e6e9ab5@googlegroups.com> |
| In reply to | #447157 |
On Friday, February 10, 2017 at 7:50:26 AM UTC-8, Jim Thompson wrote: > 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. > 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. This PNP transistor will have no problem with Vbe reverse breakdown <https://www.centralsemi.com/get_document.php?cmp=1&mergetype=pd&mergepath=pd&pdf_id=CMPT404A_R1.PDF>
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| From | Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> |
|---|---|
| Date | 2017-02-10 08:53 -0700 |
| Message-ID | <7eor9c92ul2nngqmojfh0sh9qtlce6n7bg@4ax.com> |
| In reply to | #447047 |
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.
The diode isn't needed. Should have checked that before posting :-[
...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]
| From | M Philbrook <jamie_ka1lpa@charter.net> |
|---|---|
| Date | 2017-02-10 18:08 -0500 |
| Message-ID | <MPG.33081208bded3ed898a00b@news.eternal-september.org> |
| In reply to | #447047 |
In article <20170209-191645.81.0@Peabody.ssl.astraweb.com>, waybackNO584SPAM44@yahoo.com says... > > 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 a Pmos as polarity protection and you can soft start the gate. Jamie
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| From | Lasse Langwadt Christensen <langwadt@fonz.dk> |
|---|---|
| Date | 2017-02-10 15:15 -0800 |
| Message-ID | <1fa742ba-1f65-4192-b9ad-fecf0b701d69@googlegroups.com> |
| In reply to | #447229 |
Den lørdag den 11. februar 2017 kl. 00.06.14 UTC+1 skrev M Philbrook: > In article <20170209-191645.81.0@Peabody.ssl.astraweb.com>, > waybackNO584SPAM44@yahoo.com says... > > > > 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 a Pmos as polarity protection and you can soft start the > gate. > Jamie soft starting the gate doesn't help much when the body diode is conducting you need two pfets
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| From | M Philbrook <jamie_ka1lpa@charter.net> |
|---|---|
| Date | 2017-02-10 18:34 -0500 |
| Message-ID | <MPG.33081815c1c2c698a00e@news.eternal-september.org> |
| In reply to | #447231 |
In article <1fa742ba-1f65-4192-b9ad-fecf0b701d69@googlegroups.com>, langwadt@fonz.dk says... > > > 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 a Pmos as polarity protection and you can soft start the > > gate. > > Jamie > > soft starting the gate doesn't help much when the body diode is conducting > > > Yes, I know, I miss understood the question, I thought he was looking for good protection and didn't see where he was also looking for switching. Anyway, I followed that up with another one after the fact. Thinking some more about this, somewhere in my history I remember using an protective switch IC, ready made.. But I guess he maybe looking for heavy loads too ? Jamie
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| From | Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> |
|---|---|
| Date | 2017-02-11 12:47 -0700 |
| Message-ID | <6equ9cdnov5br6kbmnd78i70o40ce75jma@4ax.com> |
| In reply to | #447047 |
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.
<http://www.analog-innovations.com/SED/Peabody_Switch_v2.png>
...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.
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| From | Jasen Betts <jasen@xnet.co.nz> |
|---|---|
| Date | 2017-02-14 06:13 +0000 |
| Message-ID | <o7u75m$e65$1@gonzo.alcatraz> |
| In reply to | #447047 |
On 2017-02-09, 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.
ok
> 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.
nah. backwards its just like a worse PNP.
VCE max may be 5V, Hfe takes a hit by a factor of 3 to 30
> 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.
it does does not protect.
current will flow from the base to the collector, turning the reversed PNP on.
> 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.
through 100K the microcontroller should be safe, but the PNP collector
will be trying to pull current out of the voltage regulator.
pnp
-9 --+----. .------[VREG]--
| \ / |
| ------- |
| | ---+---
-->Z----|
5V |
100K
|
|
|
\|
NPN |-+-100K-+-uC
/| |
/ +--|<-+ ... uC protection diode.
| |
| |
----+-----------------+--
so you've got current flowing from the microcintroller,
through the base resistor and the NPN B-C junction
this turns the reverse NPN on as an emitter follower
since it's feeding the PNP B-E junction you get maybe 5V drop there
(avalanche breakdown, potentially damaging - shown as a zener diode)
and the rest in the two diodes and 2 resistors.
you get about 25uA in the main 100K and maybe 3 uA from the
microcontroller, A diode in series with the PNP base will fix that.
So the PNP is biased off but current may flow from the voltage
regulator through the collector to the base then through the
emitter. if it does you could destroy the PNP.
--
This email has not been checked by half-arsed antivirus software
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| From | whit3rd <whit3rd@gmail.com> |
|---|---|
| Date | 2017-02-14 00:52 -0800 |
| Message-ID | <e2e01b2c-6c26-49d9-85a1-bc2fe2d27073@googlegroups.com> |
| In reply to | #447620 |
On Monday, February 13, 2017 at 10:31:04 PM UTC-8, Jasen Betts wrote: > On 2017-02-09, 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 > > ... current will not flow backwards from collector to emitter of > > a PNP so long as the transistor's voltage rating is not exceeded. > > But the absolute maximum base-emitter reverse voltage for this transistor > > (BC560C) is 5V. So, use a PNP with higher base-emitter reverse voltage. This one is good to 25V: <http://www.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkeyCMPT404A-TR>
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| From | Peabody <waybackNO584SPAM44@yahoo.com> |
|---|---|
| Date | 2017-02-14 22:26 -0600 |
| Message-ID | <20170215-042650.84.0@Peabody.ssl.astraweb.com> |
| In reply to | #447623 |
whit3rd says... > So, use a PNP with higher base-emitter reverse voltage. > This one is good to 25V: > http://www.mouser.com/search/ProductDetail.aspx? R=0virtualkey0virtualkeyCMP T404A-TR Yes, someone else also recommended that one. It's not clear to me that the Vebo rating necessarily matters in this case. I mean, you certainly would think it would matter, but I'll have to order one at some point and see what happens. At this point, though, I've been using through-hole parts from Digikey, so the surace mount item from Mouser is a bit off the trail. But I do need to test it. But you know, the world is not full of PNPs with that kind of Vebo rating, or even something as modest as 10V, which would be enough for me.
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| From | Peabody <waybackNO584SPAM44@yahoo.com> |
|---|---|
| Date | 2017-02-14 22:16 -0600 |
| Message-ID | <20170215-041622.132.0@Peabody.ssl.astraweb.com> |
| In reply to | #447620 |
Jasen Betts says... > you get about 25uA in the main 100K and maybe 3 uA from > the microcontroller, A diode in series with the PNP base > will fix that. Yes it will, but - > So the PNP is biased off but current may flow from the > voltage regulator through the collector to the base then > through the emitter. if it does you could destroy the > PNP. Detroy the PNP and all the 9V unregulated circuitry outside the regulator and controller. I was hoping that with the base protected by the diode, or even open, no current would flow from collector to emitter, thus protecting everything from reverse battery connection. And that does work at 5V or 6V, but not at 9V. In my tests, current began to flow at 8V, so it wouldn't protect against a backwards 9V battery. I've seen a lot of descriptions of the Zener effect when you backward bias the B-E junction of a PNP, but what I'm seeing is the same Zener effect from C to E, although at a higher voltage, no matter what's happening with the base - it can be open, or tied high, and C-E current still flows. After a couple hours of Googling and reading, I've yet to find any discussion of this phenomenon or why that happens. It's a shame the reverse protection doesn't work at 9V (or actually 9.6V with a new battery), because then the single PNP could both switch the power on and protect against reversal, which is what I wanted to do.
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| From | John Larkin <jjlarkin@highlandtechnology.com> |
|---|---|
| Date | 2017-02-14 21:42 -0800 |
| Message-ID | <b9q7achk2hr8ubb8ak8g74t54h2o1h99ec@4ax.com> |
| In reply to | #447709 |
On Tue, 14 Feb 2017 22:16:22 -0600, Peabody <waybackNO584SPAM44@yahoo.com> wrote: >Jasen Betts says... > > > you get about 25uA in the main 100K and maybe 3 uA from > > the microcontroller, A diode in series with the PNP base > > will fix that. > >Yes it will, but - > > > So the PNP is biased off but current may flow from the > > voltage regulator through the collector to the base then > > through the emitter. if it does you could destroy the > > PNP. > >Detroy the PNP and all the 9V unregulated circuitry outside >the regulator and controller. > >I was hoping that with the base protected by the diode, or >even open, no current would flow from collector to emitter, >thus protecting everything from reverse battery connection. >And that does work at 5V or 6V, but not at 9V. In my tests, >current began to flow at 8V, so it wouldn't protect against >a backwards 9V battery. > >I've seen a lot of descriptions of the Zener effect when you >backward bias the B-E junction of a PNP, but what I'm seeing >is the same Zener effect from C to E, although at a higher >voltage, no matter what's happening with the base - it can >be open, or tied high, and C-E current still flows. After a >couple hours of Googling and reading, I've yet to find any >discussion of this phenomenon or why that happens. The c-b junction is forward biased, in series with the b-e zener. So c-e zeners about 0.6 volts higher than b-e. Some transistors magically become 6.2 volt "reference zeners", super low TC zener diodes, used backwards c-e with base open. But longterm, zenering a b-e junction damages the part. > >It's a shame the reverse protection doesn't work at 9V (or >actually 9.6V with a new battery), because then the single >PNP could both switch the power on and protect against >reversal, which is what I wanted to do. > Why not use a series schottky diode, instead of complicated circuits? -- John Larkin Highland Technology, Inc lunatic fringe electronics
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| From | Peabody <waybackNO584SPAM44@yahoo.com> |
|---|---|
| Date | 2017-02-15 00:21 -0600 |
| Message-ID | <20170215-062109.685.0@Peabody.ssl.astraweb.com> |
| In reply to | #447714 |
John Larkin says... > Why not use a series schottky diode, instead of > complicated circuits? I just wanted to avoid even that voltage drop. Any drop just means the battery has to be replaced sooner. Also, a P-channel mosfet requires no additional parts, has essentially no voltage drop, and in case it even matters, only costs a little more that a Schottky diode. One other possible problem is that Schottky diodes tend to have larger reverse leakage currents than regular diodes, and I'm just not sure how much reverse current my circuit can withstand. This may be a non-problem. I just don't know.
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| From | Jasen Betts <jasen@xnet.co.nz> |
|---|---|
| Date | 2017-02-15 11:44 +0000 |
| Message-ID | <o81eum$3dj$4@gonzo.alcatraz> |
| In reply to | #447717 |
On 2017-02-15, Peabody <waybackNO584SPAM44@yahoo.com> wrote: > John Larkin says... > > > Why not use a series schottky diode, instead of > > complicated circuits? > > I just wanted to avoid even that voltage drop. Any drop > just means the battery has to be replaced sooner. Also, a > P-channel mosfet requires no additional parts, has > essentially no voltage drop, and in case it even matters, > only costs a little more that a Schottky diode. if preserving the battery is important, why are you using "9V", which is one of the most expensive forms? or is that 6 AA cells in series? -- This email has not been checked by half-arsed antivirus software
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| From | Peabody <waybackNO584SPAM44@yahoo.com> |
|---|---|
| Date | 2017-02-15 08:15 -0600 |
| Message-ID | <20170215-141523.978.0@Peabody.ssl.astraweb.com> |
| In reply to | #447725 |
Jasen Betts says... > if preserving the battery is important, why are you > using "9V", which is one of the most expensive forms? or > is that 6 AA cells in series? Part of the circuit needs unregulated 9-ish volts, and the 9V battery is just easier to deal with for size and weight than multiple AAs.
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| From | makolber@yahoo.com |
|---|---|
| Date | 2017-02-15 09:30 -0800 |
| Message-ID | <b28f5528-8f74-4ef0-903d-292cf596d5d0@googlegroups.com> |
| In reply to | #447733 |
one more question.... for the reverse polarity protection function, why is 100uA leakage a problem? Reverse polarity protection is just to keep the magic smoke in if someone momentary connects the battery backwards... ...no? 100uA is not going to blow anything... Mark
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