# reverse voltage protection with parallel diode

Started by July 21, 2012
```I have a diode 1N5402 connected in parallel reverse biased across the power=
supply  for reverse polarity protection. The maximum absolute ratings of t=
he 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 her=
e. If, let's say, 0.5V is applied in reverse, the diode will not conduct an=
d reverse supply of -0.5V will go directly to the load IC. Since it is belo=
w the min -0.3V, will it damage the IC?=20

-Markj
```
```<markjsunil@gmail.com> wrote in message
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
Probably not, but why not put the diode in series  with the PSU feed ? Or a
PFET ?

```
```On Sat, 21 Jul 2012 05:24:17 -0700 (PDT), markjsunil@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.

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

>On Sat, 21 Jul 2012 05:24:17 -0700 (PDT), markjsunil@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.
>
>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/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

I love to cook with wine.     Sometimes I even put it in the food.
```
```markjsunil@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.

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.
```
```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:
>=20
> &gt;I have a diode 1N5402 connected in parallel reverse biased across the=
power supply  for reverse polarity protection. The maximum absolute rating=
s 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. Si=
nce it is below the min -0.3V, will it damage the IC?=20
> &gt;
> &gt;-Markj
>=20
> -0.5 volts won&#39;t hurt most ICs.
>=20
> But if you connect a chunky 30 volt supply backwards, until the fuse
> blows the diode forward drop could be several volts.
>=20
> What&#39;s your normal supply voltage, and what&#39;s the load current? W=
hat
> IC is it?
>=20
>=20
> --=20
>=20
> John Larkin                  Highland Technology Inc
> www.highlandtechnology.com   jlarkin at highlandtechnology dot com  =20
>=20
> 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.
```
```On Sat, 21 Jul 2012 17:49:31 GMT, Mike <spam@me.not> wrote:

>markjsunil@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
--
| James E.Thompson, CTO                            |    mens     |
| 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  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

I love to cook with wine.     Sometimes I even put it in the food.
```
```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

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.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
```
```On Sat, 21 Jul 2012 11:17:25 -0700, Fred Abse
<excretatauris@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
>
>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 ;-)

...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| 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  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

I love to cook with wine.     Sometimes I even put it in the food.
```
```On Sat, 21 Jul 2012 17:49:31 GMT, Mike <spam@me.not> wrote:

>markjsunil@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.
```