reverse voltage protection with parallel diode

[markj...@gmail.com]

I have a diode 1N5402 connected in parallel reverse biased across the power supply for reverse polarity protection. The maximum absolute ratings of the load IC says -0.3V to +30V. If reverse power is applied, anything above diode's forward drop it will short circuit and break the fuse. No issue here. If, let's say, 0.5V is applied in reverse, the diode will not conduct and reverse supply of -0.5V will go directly to the load IC. Since it is below the min -0.3V, will it damage the IC?

-Markj

[TTman]

<markj...@gmail.com> wrote in message
news:c11b0d25-be76-4fd5...@googlegroups.com...

Probably not, but why not put the diode in series with the PSU feed ? Or a
PFET ?

[John Larkin]

On Sat, 21 Jul 2012 05:24:17 -0700 (PDT), markj...@gmail.com wrote:

>I have a diode 1N5402 connected in parallel reverse biased across the power supply for reverse polarity protection. The maximum absolute ratings of the load IC says -0.3V to +30V. If reverse power is applied, anything above diode's forward drop it will short circuit and break the fuse. No issue here. If, let's say, 0.5V is applied in reverse, the diode will not conduct and reverse supply of -0.5V will go directly to the load IC. Since it is below the min -0.3V, will it damage the IC?
>
>-Markj

-0.5 volts won't hurt most ICs.

But if you connect a chunky 30 volt supply backwards, until the fuse
blows the diode forward drop could be several volts.

What's your normal supply voltage, and what's the load current? What
IC is it?


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

[Jim Thompson]

On Sat, 21 Jul 2012 09:38:55 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:

>On Sat, 21 Jul 2012 05:24:17 -0700 (PDT), markj...@gmail.com wrote:
>
>>I have a diode 1N5402 connected in parallel reverse biased across the power supply for reverse polarity protection. The maximum absolute ratings of the load IC says -0.3V to +30V. If reverse power is applied, anything above diode's forward drop it will short circuit and break the fuse. No issue here. If, let's say, 0.5V is applied in reverse, the diode will not conduct and reverse supply of -0.5V will go directly to the load IC. Since it is below the min -0.3V, will it damage the IC?
>>
>>-Markj
>
>-0.5 volts won't hurt most ICs.
>
>But if you connect a chunky 30 volt supply backwards, until the fuse
>blows the diode forward drop could be several volts.
>
>What's your normal supply voltage, and what's the load current? What
>IC is it?

For sensitive applications, use an SCR fuse blower... and heavy traces
on the PCB... I've measured 100A+ during "quick-blowing" a 1A fuse.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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I love to cook with wine. Sometimes I even put it in the food.

[Mike]

Blowing fuses to save an ic is not a very good idea.

Can you put the dide in series with the load instead of in parallel across
the supply?

That way if the power supply leads are reversed, only the diode leakage
current will flow. This is sped'd at 5uA at room temperature, which should
not harm an ic.

[markj...@gmail.com]

On Saturday, July 21, 2012 10:08:55 PM UTC+5:30, John Larkin wrote:
> On Sat, 21 Jul 2012 05:24:17 -0700 (PDT), markjsunil wrote:
>
> &gt;I have a diode 1N5402 connected in parallel reverse biased across the power supply for reverse polarity protection. The maximum absolute ratings of the load IC says -0.3V to +30V. If reverse power is applied, anything above diode&#39;s forward drop it will short circuit and break the fuse. No issue here. If, let&#39;s say, 0.5V is applied in reverse, the diode will not conduct and reverse supply of -0.5V will go directly to the load IC. Since it is below the min -0.3V, will it damage the IC?
> &gt;
> &gt;-Markj
>
> -0.5 volts won&#39;t hurt most ICs.

>
> But if you connect a chunky 30 volt supply backwards, until the fuse
> blows the diode forward drop could be several volts.
>

> What&#39;s your normal supply voltage, and what&#39;s the load current? What

> IC is it?
>
>
> --
>
> John Larkin Highland Technology Inc
> www.highlandtechnology.com jlarkin at highlandtechnology dot com
>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom timing and laser controllers
> Photonics and fiberoptic TTL data links
> VME analog, thermocouple, LVDT, synchro, tachometer
> Multichannel arbitrary waveform generators

Thanks. The IC is TPA3111. Absolute max Vcc is -0.3 to 30V.

[Jim Thompson]

On Sat, 21 Jul 2012 17:49:31 GMT, Mike <sp...@me.not> wrote:

>markj...@gmail.com wrote:
>
>> I have a diode 1N5402 connected in parallel reverse biased across the
>> power supply for reverse polarity protection. The maximum absolute
>> ratings of the load IC says -0.3V to +30V. If reverse power is
>> applied, anything above diode's forward drop it will short circuit and
>> break the fuse. No issue here. If, let's say, 0.5V is applied in
>> reverse, the diode will not conduct and reverse supply of -0.5V will
>> go directly to the load IC. Since it is below the min -0.3V, will it
>> damage the IC?
>>
>> -Markj
>
>Blowing fuses to save an ic is not a very good idea.

When I was involved in such things, power supplies were unreliable,
and uP chips were _very_ expensive. The fuse blower apparatus added
pennies to the unit cost.

>
>Can you put the dide in series with the load instead of in parallel across
>the supply?
>
>That way if the power supply leads are reversed, only the diode leakage
>current will flow. This is sped'd at 5uA at room temperature, which should
>not harm an ic.

[Jim Thompson]

On Sat, 21 Jul 2012 11:17:25 -0700, Fred Abse
<excret...@invalid.invalid> wrote:

>On Sat, 21 Jul 2012 11:02:04 -0700, Jim Thompson wrote:
>
>> When I was involved in such things, power supplies were unreliable, and uP
>> chips were _very_ expensive. The fuse blower apparatus added pennies to
>> the unit cost.
>

>I still won't incorporate a bought-in PSU in a piece of equipment, without
>adding an in-house made crowbar-and-fuse protector.
>
>I just don't like the idea of my four-, or five-figure gizmo at the mercy
>of a two- or three-figure rice bowl.
>
>The field tech swaps out the PSU, and changes a fuse. I get to sleep
>soundly.

Me too ;-)

[k...@att.bizzzzzzzzzzzz]

On Sat, 21 Jul 2012 17:49:31 GMT, Mike <sp...@me.not> wrote:

>markj...@gmail.com wrote:
>
>> I have a diode 1N5402 connected in parallel reverse biased across the
>> power supply for reverse polarity protection. The maximum absolute
>> ratings of the load IC says -0.3V to +30V. If reverse power is
>> applied, anything above diode's forward drop it will short circuit and
>> break the fuse. No issue here. If, let's say, 0.5V is applied in
>> reverse, the diode will not conduct and reverse supply of -0.5V will
>> go directly to the load IC. Since it is below the min -0.3V, will it
>> damage the IC?
>>
>> -Markj
>
>Blowing fuses to save an ic is not a very good idea.

Why? I generally have used PTCs instead of fuses and TVSs instead of diodes
but the idea is the same.

>Can you put the dide in series with the load instead of in parallel across
>the supply?

>That way if the power supply leads are reversed, only the diode leakage
>current will flow. This is sped'd at 5uA at room temperature, which should
>not harm an ic.

For low currents, this works, as long as you don't need the voltage or
regulation. It doesn't protect against over-voltage, though.

[bloggs.fred...@gmail.com]

On Saturday, July 21, 2012 8:24:17 AM UTC-4, markj...@gmail.com wrote:
> I have a diode 1N5402 connected in parallel reverse biased across the power supply for reverse polarity protection. The maximum absolute ratings of the load IC says -0.3V to +30V. If reverse power is applied, anything above diode&#39;s forward drop it will short circuit and break the fuse. No issue here. If, let&#39;s say, 0.5V is applied in reverse, the diode will not conduct and reverse supply of -0.5V will go directly to the load IC. Since it is below the min -0.3V, will it damage the IC?
>
> -Markj

http://www.ti.com/lit/an/slva139/slva139.pdf

[miso]

If you can tolerate schottky reverse bias leakage, that would provide a
better clamp.

You don't indicate if the user is plugging in an external supply, or the
supply is hard wired. I'm not sure why you would expect a hard wired
supply to go negative. [OK, maybe from one of those home brew switcher
designs, which is of course why you should always buy a controller IC.]

I have a break out box I use for mobile applications to distribute 12vdc
from a marine type battery (AGM). I use a fuse and parallel Schottky in
the box. Actually a few Schottky diodes. Due to current hogging, I
expect the diodes to turn on individually, so paralleling them doesn't
do much in terms of current handling. My guess was the first diodes to
turn on might fail before the fuse pops, so as each diode fails, a new
one will take over. I added some junk box standard silicon diodes as
well. Needless to say I haven't tested this! I just tossed in the parts
because I had them handy and I couldn't see how it would hurt.

Regarding damage to ICs, you would really have to reach a diode turn on
voltage to get the chip to draw significant current. The manufacturer is
just guardbanding this by specing 0.3V.

With static DC, there are two way to damage an IC. Overvoltage will
break down diode junctions. Reverse voltage will "melt" the metal trace
in the path of the current.

This leads to a classic problem in IC metal fuse popping. If upon
popping the fuse the voltage on the test pad spikes upwards, as can
happen with a sudden di/dt as the fuse pops, the overvoltage can break
down an internal junction and cause it to leak. Generally is it better
to set up the fuse popper so it forward biases a junction after the fuse
is popped. Given that the energy to pop the fuse is stored in a
capacitor, you can predict how quickly the cap will discharge and thus
predict the time the metal trace will have to conduct high current.
Basically you can engineer around the potentially damaging situation.
Add protection diodes and insure a sufficient metal width to them.