Re: quad 1/2 bridge

john larkin <JL@gct.com> wrote:

On Mon, 23 Sep 2024 14:59:25 GMT, Jan Panteltje <alien@comet.invalid>
wrote:
 

On a sunny day (Mon, 23 Sep 2024 07:15:43 -0700) it happened john larkin
<JL@gct.com> wrote in <abt2fj53dcek89n4f9b67c9ca0a1nd8cgn@4ax.com>:
 

 
https://www.digikey.com/en/products/detail/texas-instruments/DRV8962DDWR/18724317
 
Four half-bridge switchers for about $5. Current and thermal limiting.
I was about to dremel and test my own half-bridge driver, but won't
now. I guess I'll have to shuffle up the abstraction stack.
 
There must be something cool that these could be used for. A
16-channel power supply?

 
4 channel audio amp?

 
Half-bridge audio amps can be tricky. At that price, may as well go
full-bridge. A half-bridge switcher can pump power uphill, back into
the power supply.
 
I wonder if we can get our little RP2040 cpu chip to do a multichannel
closed-loop supply, and maybe generate spread-spectrum PWM on 8
channels.
 
Phil, the 8962 data sheet discusses driving TECs.

Thanks.

I rarely have the luxury of using a barefoot switcher for TECs. The
capacitance from the supply to the cold plate is tens of nanofarads, and
anyway a small TEC runs way under 5V in normal use, so it usually needs a
buck.

We have a couple of nice canned designs that use variations on Class H,
i.e. a fast buck switcher with a very low-Vsat linear stage that gets rid
of the ripple. 

The switcher control is stupid simple. The MCU DAC is summed with the
switcher feedback network. The MCU very slowly drops the output voltage
until the analog loop rails, bumps it up by 200mV or so, then starts
dropping it again.  You wouldn’t do that with an audio amp, but it works
great for thermal control.

For cooling-only, we use a two-pole BJT current source (like a BJT gyrator
but with two poles).

For use near ambient, as with diode lasers, we use a slightly more
complicated thing, an asymmetrical BJT bridge. One side is a complementary
current conveyor (current in, current out) and the other is a regular
voltage-output complementary class-B that keeps the load terminals moving
symmetrically.   (All that is to say that one side comes out the collectors
and the other comes out the emitters.)

This approach allows current sensing in all four legs, which turns out to
be very handy—besides short circuit protection, it also lets you have
different current limits in the heating and cooling directions.

The other trick is choosing the polarity so the voltage-output side is
sourcing current when cooling. The control amp runs off the higher rail, so
the NPN’s  V_CE can go way into saturation. This isn’t an issue on the
current conveyor side.

Both fit into under a square inch, including pours, and can drive the usual
2-3A TECs to their limits.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics