Most convenient/efficient/straight-forward method of producing 12-bit, 20 kHz PWM

Thread Starter

PaulEE

Joined Dec 23, 2011
423
Hahaha. Apparently, they make their drawing available. :)

I would've thought the inductors were bigger.
 

Thread Starter

PaulEE

Joined Dec 23, 2011
423
Hahaha. Apparently, they make their drawing available. :)

I would've thought the inductors were bigger.
As a matter of fact, I don't think those inductors form the filter everyone thinks they do. There is no way you can drag 10 amps through those and not have them pop.

As far as the bigger L4, it is out of the way and connected to an LM2574 simple switcher regulator. Nothing to do with an LC filter for the peltiers.

This is a capacitor only board I believe.
 

Ron H

Joined Apr 14, 2005
7,012
As a matter of fact, I don't think those inductors form the filter everyone thinks they do. There is no way you can drag 10 amps through those and not have them pop.

As far as the bigger L4, it is out of the way and connected to an LM2574 simple switcher regulator. Nothing to do with an LC filter for the peltiers.

This is a capacitor only board I believe.
That was my thought too.
I wonder if that board can be programmed for Vmax limiting.
 

Thread Starter

PaulEE

Joined Dec 23, 2011
423
That was my thought too.
I wonder if that board can be programmed for Vmax limiting.
That is a very good question.

If my assumption is correct about what the capacitors are doing (smoothing out the PWM to a DC signal), perhaps it uses a standard voltage that is beneath most peltier modules and sources current accordingly. The controller has a 30 amp fuse on it; the specs say it can handle many watts of power control.

I do know that it comes with a serial port adaptor and a simple form application to tweak the PID loop coefficients, as well as a few other things; proportional band, etc. Maybe there is a control for this voltage.

I'm going to check tomorrow - now that you mention it.
 

THE_RB

Joined Feb 11, 2008
5,430
They just use unfiltered PWM to the peltier device like most manufacturers, you only need filtered PWM if it is less than about 4kHz to reduce thermal cycling shock.

PaulEE said:
...
However, I also agree that it can be done with on/off control, but the equivalent switching frequency would end up being the same as my pulse-width modulation signal!
...
I wasn't talkng about on/off control but about high speed delta-sigma modulation.

Basically the same result as PWM (and similar high frequency output) but not limited to a low resolution, and the resolution is fully under your control, so if you need resolution of 1 million, or 10 million etc its up to you and just needs changing one constant in your code.

You can have a very high resolution power adjustment to the heater load (which makes the precision temperature PID so much easier).
 

Thread Starter

PaulEE

Joined Dec 23, 2011
423
They just use unfiltered PWM to the peltier device like most manufacturers, you only need filtered PWM if it is less than about 4kHz to reduce thermal cycling shock.



I wasn't talkng about on/off control but about high speed delta-sigma modulation.

Basically the same result as PWM (and similar high frequency output) but not limited to a low resolution, and the resolution is fully under your control, so if you need resolution of 1 million, or 10 million etc its up to you and just needs changing one constant in your code.

You can have a very high resolution power adjustment to the heater load (which makes the precision temperature PID so much easier).
I'll have to look into this. I did look at whether Vmax limiting was present on the controller...and it seems that it is up to the user to supply only the Vmax that is needed. I think Ron_H inquired about that a day or so ago.
 
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