Regulator Design Topology Suggestions.

[Joe G \(Home\)]

Hi All,

My radio device requires the following Vin Specifications

Vin range 3v2 to 4v5 nominal 3v6
Current 2amps peak
Ripple less than 250mV up to 10KHz,
Ripple less than 40mV from 10kHz to 100kHz and
Ripple less than 5mW greater than 100KHz

From the outside world I would like to supply my radio devices with a
voltage range 9 - 36V

What can you suggest for regulator options?

Should a use a two step approach.... a pre-regulator to drop the voltage
down to 9-12V then a very low ripple DC-D regulator.

Should I add DC capacitive filtering to achieve the ver low ripple
requirements


What can you suggest?


Thanks in advance.

Joe

 

[Phil Allison]

"Joe G (Home)"

From the outside world I would like to supply my radio devices with a
voltage range 9 - 36V

** More details needed.

What is the supply of voltage ?

An old car battery charger ??

Solar cells ??

Bicycle dynamo feeding a bridge ??



..... Phil

 

[Joe G \(Home\)]

Hi All,

My radio device requires the following Vin Specifications

Vin range 3v2 to 4v5 nominal 3v6
Current 2amps peak
Ripple less than 250mV up to 10KHz,
Ripple less than 40mV from 10kHz to 100kHz and
Ripple less than 5mW greater than 100KHz

Assuming no ripple on the input and a switcher running at
100KHz, the ripple values below 100KHz are all easily met.

The best design is likely to be a fairly simple bucker.

To get the low ripple, you need to be careful with where the
ripple currents end up flowing.


L1 ---------- L2 L3
IN-+--))))---+---! Switcher !---+---))))--+--))))--+--
! ! ---------- ! ! !
===C1 ===C2 ! ---D1 ===C3 ===C4
! ! ! ^ ! !
! ! ! ! ! !
! ---------+---+---- ! !
! ! GND1 ! !
! --------------+ !
! GND2 ! !
---+--------------------------------------+--------+----

You need to bring the ground end of C2 and D1 together directly
Move the parts around until they almost touch

The next priority is to get C3 to ground near the same point.

If this is a multilayer PCB, a GND1 can be an internal layer that
on other parts of the PCB is a trace layer. The whole idea here is
to keep the ripple currents local to the circuit.

If this is a stand alone item, the GND2, input and output should
all be in one small area. Don't put them on opposite ends of the
PCB as would seem intuitive.

The connection between C1 and C4 should be also as short as you can
make it.

L1 and L3 are basically large RF beads. They need to be lossy.


All the capacitors are actually collections of capacitors as
needed to get the ESR and ESL numbers low enough.

From the outside world I would like to supply my radio devices with a
voltage range 9 - 36V

What can you suggest for regulator options?

Should a use a two step approach.... a pre-regulator to drop the voltage
down to 9-12V then a very low ripple DC-D regulator.

Should I add DC capacitive filtering to achieve the ver low ripple
requirements

What can you suggest?

Thanks in advance.

Joe

Regs
Joe

 

[Joe G \(Home\)]

Google on "buck regulator".

...Jim Thompson
--

Yes... but after googling buck regulator... the search results give too
many buck regulator options.

Only some buck regulators offer up ripple specifications - Linear Tech is
one.

I was after an "executive summary" an pointer in the right direction...
which is why I made my question quite specific.

Some else has replied with a detail answer in few lines.... I many need a PI
filter and careful PCB design.

Regs
Joe