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overvoltage #u3s and protective circuit #u3s

 

I just fried my U3s with 12 supply. ?At a min I should have had it fused.
Engineer friend noted that since this is a not uncommon problem for kit builders the U3s and other devices
probably should have an "axehandle" over voltage/over current protection circuit as an option.

In my case I lost just the eeprom and the QLG1 GPS. Could have been worse.

Anyone have a suitable design for QRPLab kits?

Tom ?KJ6MKI
 

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Axe Handle?
Google "over voltage crowbar circuits"
The MC3423 IC was common in linear power supplies,
it's probably being replaced by something bigger (smaller) and better


Alan

On 30/07/2018 22:20, Thomas Yarish wrote:

I just fried my U3s with 12 supply. ?At a min I should have had it fused.
Engineer friend noted that since this is a not uncommon problem for kit builders the U3s and other devices
probably should have an "axehandle" over voltage/over current protection circuit as an option.

In my case I lost just the eeprom and the QLG1 GPS. Could have been worse.

Anyone have a suitable design for QRPLab kits?

Tom ?KJ6MKI
 

开云体育

Yes, Crowbar. ?mixing metaphors.
Thanks.
t

On Jul 30, 2018, at 2:39 PM, Alan de G1FXB via Groups.Io <g1fxb@...> wrote:

Axe Handle?
Google "over voltage crowbar circuits"
The MC3423 IC was common in linear power supplies,
it's probably being replaced by something bigger (smaller) and better


Alan

On 30/07/2018 22:20, Thomas Yarish wrote:
I just fried my U3s with 12 supply. ?At a min I should have had it fused.
Engineer friend noted that since this is a not uncommon problem for kit builders the U3s and other devices
probably should have an "axehandle" over voltage/over current protection circuit as an option.

In my case I lost just the eeprom and the QLG1 GPS. Could have been worse.

Anyone have a suitable design for QRPLab kits?

Tom ?KJ6MKI
 

开云体育

It's not obsolete, the MC3423 IC is still available in through hole & now surface mount :-)

In the early days of 5v TTL logic IC's
Designers used the "undesirable" feature that zener diodes posess? to their advantage, to protect those "new fangled" IC's.
Unless current limited, applying a voltage exceeding the zener point causes them to fail short circuit.

A Crowbar in it's most basic form is therefore a zener diode and a fuse.
Don't forget a carefully chosen value fuse, you need that to be the weak link......
The enhanced solution is a resettable crowbar, an SCR.

We used wirewrapped back planes,
they make poor substitutes for a fuse that has being replaced by the incorrect type / value, or silver paper.

Alan



On 30/07/2018 22:53, Thomas Yarish wrote:

Yes, Crowbar. ?mixing metaphors.
Thanks.
t

On Jul 30, 2018, at 2:39 PM, Alan de G1FXB via Groups.Io <g1fxb@...> wrote:

Axe Handle?
Google "over voltage crowbar circuits"
The MC3423 IC was common in linear power supplies,
it's probably being replaced by something bigger (smaller) and better


Alan

On 30/07/2018 22:20, Thomas Yarish wrote:
I just fried my U3s with 12 supply. ?At a min I should have had it fused.
Engineer friend noted that since this is a not uncommon problem for kit builders the U3s and other devices
probably should have an "axehandle" over voltage/over current protection circuit as an option.

In my case I lost just the eeprom and the QLG1 GPS. Could have been worse.

Anyone have a suitable design for QRPLab kits?

Tom ?KJ6MKI
 

Anyone have a suitable design for QRPLab kits?
Tom,

An interior 5V regulator and a series diode to prevent reversed voltage damage.

73 Alan G4ZFQ
 

In fact I already have those measures in place. I simply connected 12 v to the wrong side of the regulator.
A fuse likely would have helped if it was sized right. Alas… A crowbar would have been better.

Note that Analog Devices analysis of the LTM4641 over voltage regulator demonstrates that SCR/thyristors do not
act fast enough to prevent damage to modern logic devices. They recommend mosfet switches instead. Hype?

However, there is no substitute for human error. You know it when you see it.

Now reordering more U3s components.

Thanks.

t





On Jul 30, 2018, at 10:05 PM, Alan G4ZFQ <alan4alan@...> wrote:


Anyone have a suitable design for QRPLab kits?
Tom,

An interior 5V regulator and a series diode to prevent reversed voltage damage.

73 Alan G4ZFQ
 

You are correct; crowbar has been the accepted term for decades. Using a word like axehandle, perhaps in an attempt to be amusing, or because you can't remember the correct word, is very poor practise. These post are read by amateurs all over the world, by people whose first language is not english (or american), and using the wrong word causes confusion and misunderstanding.

For the same reason, it is important to read your message before you post it, as the number of typos and missing words I see is indicative of a serious lack of care. For example, leaving "not" out of a sentence dramatically changes its meaning. Teacher told you to do that in primary school, don't you remember. Read your next message, and if you don't find a single mistake, give yourself a pat on the back, and if you do find an error, correct it, and continue to read your messages before posting.

No-one is a perfect typist; I have made several correction to this post, and still cannot promise that it is all correct.
 

In fact I already have those measures in place. I simply connected 12 v to the wrong side of the regulator.
Tom,

So actually an error while experimenting? I've many certificates for that club:-)
A fuse likely would have helped if it was sized right.
A fuse is too slow, the damaged parts would blow the fuse.
A crowbar would have been better.
Yes, but getting complicated. The document linked by KJ6MKI shows that. This is not usually seen even in high-priced commercial rigs, just some form of reverse voltage protection.

73 Alan G4ZFQ
 

A simple circuit I use on all my rigs is:- series fuse and in4001 diode -10uF cap to GND - 7805 regulator in - 7805 Gnd - 7805 out- 10uF cap to Gnd, parallel led in series with 680ohms to gnd.
This allows approx 9-16v input (choose input cap voltage to be say 25v version), a 5 volt output to U3. AND gives reverse voltage protection.?

Bolt the 7805 to the U3 metal case to provide the heatsinking.

Ken G4APB
 

Hello Alan,

Just to prove your last sentence to be so correct Alan ;)

1: Practise should be practice (noun)

2: ... as the number of typos and missing words I see is
indicative... Should be ARE indicative

3: ..... don't you remember This has no following question mark

4: I have made several correction.... Should be corrections


We have a pot calling a kettle black amongst us. Lines or a fine? ;)

Tuesday, July 31, 2018

You are correct; crowbar has been the accepted term for decades.
Using a word like axehandle, perhaps in an attempt to be amusing, or
because you can't remember the correct word, is very poor practise.
These post are read by amateurs all over the world, by people whose
first language is not english (or american), and using the wrong
word causes confusion and misunderstanding.
For the same reason, it is important to read your message before
you post it, as the number of typos and missing words I see is
indicative of a serious lack of care. For example, leaving "not" out
of a sentence dramatically changes its meaning. Teacher told you to
do that in primary school, don't you remember. Read your next
message, and if you don't find a single mistake, give yourself a pat
on the back, and if you do find an error, correct it, and continue
to read your messages before posting.
No-one is a perfect typist; I have made several correction to this
post, and still cannot promise that it is all correct. _._,_._,_





--

2E0ILY
Best regards,
Chris mailto:chris@...
--
Best regards, Chris Wilson (2E0ILY)
 

2. Actually "the number" is singular so "is indicative" is correct.
 

On Tue, Jul 31, 2018 at 02:13 AM, Chris Wilson wrote:
Hello Alan,

Just to prove your last sentence to be so correct Alan ;)

1: Practise should be practice (noun)

2: ... as the number of typos and missing words I see is
indicative... Should be ARE indicative

3: ..... don't you remember This has no following question mark

4: I have made several correction.... Should be corrections


We have a pot calling a kettle black amongst us. Lines or a fine? ;)

Tuesday, July 31, 2018
Thanks, Chris, you reinforce my point beautifully.

Can I take a slapped wrist instead? Please!

Best wishes

Alan
 


2. Actually "the number" is singular so "is indicative" is correct.

Yes, I agree, but Idon't want to start World War III, just a bit more care.

Thanks for your support, though.

Alan

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