When I was in high school, I worked at a local fast food =
restaurant. =20
Rather than save the money I earned for college, or something else more=20
practical, I invested in something else - car audio.
I had a Toyota Corolla with a hatchback. It was a junker (a perfect =
first=20
car). Over the course of a couple of years, I saved and upgraded =
and=20
eventually had a stereo system in my car that was worth more than the =
car=20
itself. It was an impressive system and LOUD! I drove that =
car all=20
through college and for the first two years I worked at TI. =
Eventually, I=20
out grew the car and stereo system, but I still have a place in my heart =
high=20
performance car audio.
Aftermarket Car Audio system (not mine, but=20
similar!)
The main power source in a car system is the car battery and =
alternator. It=20
is a 12V system with an alternator that runs at approximately 14.4V. The =
sound=20
system environment is also pretty nasty in terms of voltage =
transients. In=20
order to make the windows shake, you will need a lot of power.
There are many components to a car audio system: head units, =
amplifiers,=20
equalizers, etc. All of these components require power. For =
the sake=20
of this blog, we are going to focus on the highest power devices, the=20
amplifiers. The newest amplifiers use class D power stages, which means, =
the=20
sound system requires a voltage that is higher than the battery or =
alternator=20
voltage in the car. In this case, a boost power supply makes the most =
sense. It=20
is not uncommon for a power amplifier to be capable of 500 to 1000W of =
output=20
power. Operating from a 12V input, the input current for the boost =
converter=20
with 1000W of output power is close to 100A!
A boost converter with 100A of input current is no simple task. =
To make=20
this task easier, you can use one of a number of PowerLab designs and ICs. In order to handle the =
amount of=20
power, a multiphase approach is necessary. I wrote a previous blog =
covering the advantages of a multiphase approach see it here. Based on the high output voltage and power =
levels, a=20
non-synchronous approach can be used and still achieve efficiencies over =
90%.=20
The TPS4009x family of controllers can be used in a 2, 3 or 4 phase =
boost=20
design. In some cases, a synchronous approach can provide better =
efficiency with=20
slightly more complexity. The LM5122 is a synchronous boost controller that is =
capable of=20
multiphase operation.
The block diagram shows a four phase design with 4 x LM5122=20
devices plus 8 x CSD18501 MOSFETs. This design is perfect for =
a high=20
efficiency car audio application. You can find this design in PowerLab along with several others for car audio=20
amplifiers:
PMP2445: TPS40090 + 2x UCC27324 =E2=80=93 This design generates 24V at 13A from 8 =
to 18.5V=20
input. This is a four phase non synchronous boost design.
PMP4538: TPS40090 + 4x UCC27201 =E2=80=93=20
This design generates 28V at 20A from 11 to 18V input2. This is a =
four=20
phase non synchronous boost design.
PMP7837: 4x LM5122 + 8x CSD18501 =E2=80=93 This design generates 24V at 450W from =
6 to 17V=20
input. This is a four phase synchronous boost design. The=20
synchronous operation allows for up 96% efficiency.
Do you ever build your own car audio systems? What has your =
experience=20
been? What do you think of these designs?
See all PowerLab Notes here.