> It is not clear to me where you are driving this from, i.e. how you 
> are
> deriving the V+ and V- from the PWM.

H-bridge is made from two IRF9540 and two IRF540. Driven by Microchip 
TC4469 as per Application note AN807. The TC4469 is driven by PWM and 
a direction signal from a PIC18F4520.

 PWM  |--------|
  O---| TC4469 |----o V     +12V   ----  ----  --
      |   &    |                   |  |  |  |  |   (Square wave)
 Dir  |   H    |                   |  |  |  |  |
  O---| Bridge |----o V     -12V ---  ----  ----
      |--------|


> pair of high current FETS ... into a buck regulator type filter

I am not very familiar with SMPS design... Wouldn't a buck regulator 
filter really be an LC filter? I need to change directions of the 
current flow in the peltier, so choose the topology shown in my 
original post.

Mohit.

----- Original Message ----- 
From: "Alan B. Pearce" <A.B.Pearce@rl.ac.uk>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Monday, October 02, 2006 6:36 PM
Subject: Re: [PIC] Capacitor suggestions


> >I am designing a peltier heater/cooler using PWM (10kHz, 12VDC @ 
> >8A)
>>and an H-bridge. To filter the ripples across the peltier, I plan to
>>use an LC filter:
>>
>>                        ____ Peltier
>>                   ----|____|----
>>                   |            |
>>                   |            |
>>               L   |       C1   |   L
>>              ___  |     ||     |  ___
>>       V+ o---UUU--o-----||-----o--UUU---o V-
>>                   |     ||     |
>>                   |            |
>>                   |            |
>>               C2 ---          --- C2
>>                  ---          ---
>>                   |            |
>>                  ^^^          ^^^
>>                  GND          GND
>
> It is not clear to me where you are driving this from, i.e. how you 
> are
> deriving the V+ and V- from the PWM.
>
>>I am able to get multi-layer ceramic capacitors 16V,10uF in SMD1210
>>package from Kemet/Murata. I have a few questions regarding these...
>>
> ...
>>
>>4. If not, can anybody suggest alternate filtering methods for 
>>peltier
>>coolers? The manufacturer (and past discussions on this list) say 
>>less
>>than 10% ripple across the cooler.
>
> I would suggest a single PWM drive into a device such as a UC1715, 
> with a
> pair of high current FETS (IRF530 or similar) into a buck regulator 
> type
> filter as used for switch mode power supplies. You can then use 
> switch mode
> supply application notes to calculate the required components for 
> the
> filter. A normal switchmode type filter will easily reach the 10% 
> figure.
>
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