LM7809 vs KM317T for a 12v to 9v regulated supply

S

Siddhartha Jain

Guest
Hi,

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?

- Siddhartha
 
Siddhartha Jain wrote:
Hi,

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?
Click to expand...
Sorry, thats LM317T (or even a LM350).
 
"Siddhartha Jain" <reach.siddhartha@gmail.com> wrote in message
news:1124359152.795268.323730@o13g2000cwo.googlegroups.com...
Siddhartha Jain wrote:
Hi,

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?

Sorry, thats LM317T (or even a LM350).
The 317T, is a variable voltage regulator, while the '78' family are fixed
Click to expand...
voltage. With the former, two resistors will also be present to set the
working voltage, while the 78 does not need these.
In both cases, the 'car' is a fairly nasty enviroment, and some
significant attempts will be needed to reduce spikes on the incoming
supply rail, if damage to the regulator, and player are to be avoided.
Also the control loop round the regulator has a very high gain, and care
has to be taken to decouple close to the output pin to avoid instability.
There are a lot of different 'variants' of 7809, and the original standard
versions were only rated for 1A. If (for example), you look at the version
from Fairchild (MC7809), this is still only a 1A device, while the 'On
semiconductor' version (MCT7809), is rated at 1.5A. The LM317T, is a 1.5A
device, and will probably be easier to source than the 9v 1.5A version of
the 78 chip.

Best Wishes
 
Roger Hamlett wrote:
"Siddhartha Jain" <reach.siddhartha@gmail.com> wrote in message
news:1124359152.795268.323730@o13g2000cwo.googlegroups.com...
Siddhartha Jain wrote:
Hi,

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?

Sorry, thats LM317T (or even a LM350).
The 317T, is a variable voltage regulator, while the '78' family are fixed
voltage. With the former, two resistors will also be present to set the
working voltage, while the 78 does not need these.
In both cases, the 'car' is a fairly nasty enviroment, and some
significant attempts will be needed to reduce spikes on the incoming
supply rail, if damage to the regulator, and player are to be avoided.
Also the control loop round the regulator has a very high gain, and care
has to be taken to decouple close to the output pin to avoid instability.
There are a lot of different 'variants' of 7809, and the original standard
versions were only rated for 1A. If (for example), you look at the version
from Fairchild (MC7809), this is still only a 1A device, while the 'On
semiconductor' version (MCT7809), is rated at 1.5A. The LM317T, is a 1.5A
device, and will probably be easier to source than the 9v 1.5A version of
the 78 chip.
Click to expand...
Thanks Roger. I checked the specs of the MP3 player in question and it
says:
# DC Power: Internal Power: Li-ion rechargeable battery 3.6V x 2(720mA)
# External Power: 12V adapter (1500mA)
# Supply Voltage: 9~18V
# Supply Current: working:12V(360mA) / standby :175mA
http://www.vosonic.co.uk/vp300.html#_specs

Also, I am currently running the player on 8 x 1.2v 2300mah NiMH
batteries since the internal Li-Ion one is almost dead. So the player
can run on 9.6v DC input.

- Does this mean that the player can tolerate an external DC supply
source from 9v to 18v and I can plug the player directly to the
cigarette adapter with a fuse in between?
- Would it be a good idea to keep the almost dead battery in the player
to act as some sort of protection against a spike?

Thanks,

- Siddhartha
 
Siddhartha Jain wrote:

Roger Hamlett wrote:
"Siddhartha Jain" <reach.siddhartha@gmail.com> wrote in message
news:1124359152.795268.323730@o13g2000cwo.googlegroups.com...
Siddhartha Jain wrote:
Hi,

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?

Sorry, thats LM317T (or even a LM350).
The 317T, is a variable voltage regulator, while the '78' family are fixed
voltage. With the former, two resistors will also be present to set the
working voltage, while the 78 does not need these.
In both cases, the 'car' is a fairly nasty enviroment, and some
significant attempts will be needed to reduce spikes on the incoming
supply rail, if damage to the regulator, and player are to be avoided.
Also the control loop round the regulator has a very high gain, and care
has to be taken to decouple close to the output pin to avoid instability.
There are a lot of different 'variants' of 7809, and the original standard
versions were only rated for 1A. If (for example), you look at the version
from Fairchild (MC7809), this is still only a 1A device, while the 'On
semiconductor' version (MCT7809), is rated at 1.5A. The LM317T, is a 1.5A
device, and will probably be easier to source than the 9v 1.5A version of
the 78 chip.

Thanks Roger. I checked the specs of the MP3 player in question and it
says:
# DC Power: Internal Power: Li-ion rechargeable battery 3.6V x 2(720mA)
# External Power: 12V adapter (1500mA)
# Supply Voltage: 9~18V
# Supply Current: working:12V(360mA) / standby :175mA
http://www.vosonic.co.uk/vp300.html#_specs

Also, I am currently running the player on 8 x 1.2v 2300mah NiMH
batteries since the internal Li-Ion one is almost dead. So the player
can run on 9.6v DC input.

- Does this mean that the player can tolerate an external DC supply
source from 9v to 18v and I can plug the player directly to the
cigarette adapter with a fuse in between?
- Would it be a good idea to keep the almost dead battery in the player
to act as some sort of protection against a spike?
Click to expand...
Given that your mp3 player can tolerate a wide input voltage range it might be
best just to power it direct from the car supply via a 'surge protector' to stop
the nasty automotive electrical transients getting into it.

Graham
 
Pooh Bear wrote:
Siddhartha Jain wrote:

Roger Hamlett wrote:
"Siddhartha Jain" <reach.siddhartha@gmail.com> wrote in message
news:1124359152.795268.323730@o13g2000cwo.googlegroups.com...
Siddhartha Jain wrote:
Hi,

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?

Sorry, thats LM317T (or even a LM350).
The 317T, is a variable voltage regulator, while the '78' family are fixed
voltage. With the former, two resistors will also be present to set the
working voltage, while the 78 does not need these.
In both cases, the 'car' is a fairly nasty enviroment, and some
significant attempts will be needed to reduce spikes on the incoming
supply rail, if damage to the regulator, and player are to be avoided.
Also the control loop round the regulator has a very high gain, and care
has to be taken to decouple close to the output pin to avoid instability.
There are a lot of different 'variants' of 7809, and the original standard
versions were only rated for 1A. If (for example), you look at the version
from Fairchild (MC7809), this is still only a 1A device, while the 'On
semiconductor' version (MCT7809), is rated at 1.5A. The LM317T, is a 1.5A
device, and will probably be easier to source than the 9v 1.5A version of
the 78 chip.

Thanks Roger. I checked the specs of the MP3 player in question and it
says:
# DC Power: Internal Power: Li-ion rechargeable battery 3.6V x 2(720mA)
# External Power: 12V adapter (1500mA)
# Supply Voltage: 9~18V
# Supply Current: working:12V(360mA) / standby :175mA
http://www.vosonic.co.uk/vp300.html#_specs

Also, I am currently running the player on 8 x 1.2v 2300mah NiMH
batteries since the internal Li-Ion one is almost dead. So the player
can run on 9.6v DC input.

- Does this mean that the player can tolerate an external DC supply
source from 9v to 18v and I can plug the player directly to the
cigarette adapter with a fuse in between?
- Would it be a good idea to keep the almost dead battery in the player
to act as some sort of protection against a spike?

Given that your mp3 player can tolerate a wide input voltage range it might be
best just to power it direct from the car supply via a 'surge protector' to stop
the nasty automotive electrical transients getting into it.
Click to expand...
Could you please suggest a good/simple surge protection circuit?

- Siddhartha
 
Siddhartha Jain wrote:

Pooh Bear wrote:
Siddhartha Jain wrote:

Roger Hamlett wrote:
"Siddhartha Jain" <reach.siddhartha@gmail.com> wrote in message
news:1124359152.795268.323730@o13g2000cwo.googlegroups.com...
Siddhartha Jain wrote:
Hi,

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?

Sorry, thats LM317T (or even a LM350).
The 317T, is a variable voltage regulator, while the '78' family are fixed
voltage. With the former, two resistors will also be present to set the
working voltage, while the 78 does not need these.
In both cases, the 'car' is a fairly nasty enviroment, and some
significant attempts will be needed to reduce spikes on the incoming
supply rail, if damage to the regulator, and player are to be avoided.
Also the control loop round the regulator has a very high gain, and care
has to be taken to decouple close to the output pin to avoid instability.
There are a lot of different 'variants' of 7809, and the original standard
versions were only rated for 1A. If (for example), you look at the version
from Fairchild (MC7809), this is still only a 1A device, while the 'On
semiconductor' version (MCT7809), is rated at 1.5A. The LM317T, is a 1.5A
device, and will probably be easier to source than the 9v 1.5A version of
the 78 chip.

Thanks Roger. I checked the specs of the MP3 player in question and it
says:
# DC Power: Internal Power: Li-ion rechargeable battery 3.6V x 2(720mA)
# External Power: 12V adapter (1500mA)
# Supply Voltage: 9~18V
# Supply Current: working:12V(360mA) / standby :175mA
http://www.vosonic.co.uk/vp300.html#_specs

Also, I am currently running the player on 8 x 1.2v 2300mah NiMH
batteries since the internal Li-Ion one is almost dead. So the player
can run on 9.6v DC input.

- Does this mean that the player can tolerate an external DC supply
source from 9v to 18v and I can plug the player directly to the
cigarette adapter with a fuse in between?
- Would it be a good idea to keep the almost dead battery in the player
to act as some sort of protection against a spike?

Given that your mp3 player can tolerate a wide input voltage range it might be
best just to power it direct from the car supply via a 'surge protector' to stop
the nasty automotive electrical transients getting into it.

Could you please suggest a good/simple surge protection circuit?
Click to expand...
Not really my area. I just know you need one. I expect someone will offer assistance.
I gather you need to protect against possible polarity reversal ( easy - a diode ) and
high voltage transients. I guess a small series R and a TVS.

Graham
 
"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:430471FA.55D94476@hotmail.com...
Siddhartha Jain wrote:

Pooh Bear wrote:
Siddhartha Jain wrote:
[snip]
Given that your mp3 player can tolerate a wide input voltage range it
might be
best just to power it direct from the car supply via a 'surge
protector' to stop
the nasty automotive electrical transients getting into it.

Could you please suggest a good/simple surge protection circuit?

Not really my area. I just know you need one. I expect someone will offer
assistance.
I gather you need to protect against possible polarity reversal ( easy - a
diode ) and
high voltage transients. I guess a small series R and a TVS.
Click to expand...
If you value your MP3 player at all, you're probably best off with a
regulated supply. There's really only one sure-fire way to know if your
surge suppression circuitry is up to the task or not...

While a 7809 or LM317 will work, they are not usually the first choice for
an automotive application. I'd recommend an automotive grade regulator -
they are designed to accept the harsh transients routinely encountered.
Infineon's TLE 4274 regulator is a three-terminal type that is similar to
the 78xx, and is available in 8.5V and 10V fixed output voltages. The TLE
4274 incorporates reverse voltage protection internally (78xx and LM317 need
an external diode), has a low dropout voltage, and is able to accept up to
40V at the input continuously.

TJL
 
On Thu, 18 Aug 2005 02:22:12 -0700, Siddhartha Jain wrote:

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?
Click to expand...
You could see if you could get something like one of these:
http://www.radioshack.com/search.asp?find=dc+adapter&hp=search&image1.x=0&image1.y=0&SRC=1

Good Luck!
Rich
 
In article <pan.2005.08.23.22.54.02.398607@example.net>, richgrise@example.net
opined thusly:
On Thu, 18 Aug 2005 02:22:12 -0700, Siddhartha Jain wrote:

I was looking for a 12v to 9v power power supply circuit to run an MP3
player in my car. The MP3 player has a 2.5" hard disk (the hdd uses 1A
@ 5v) inside so I want something that won't fry the HDD. Most circuits
I came across either use the LM317T or the LM7809. Can someone tell me
which one is better suited to my particular requirement?
Click to expand...
Neither one will make a difference to your HDD if you use it right. But they
come in different current ratings, the "T" version wildo an amp but you're on
the limit of its spec. The nore heat sinking you give it the more reliable it
will be.

If you look at the power supply circuit inside the player you'll probably find
it is all regulated anyway, so you could just use a bunch of diodes in series
to drop a few volts off the car's supply, which isn't 12V at all, it's closer
to 14V.
 
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