Need help in understanding a circuit

Hi,

I'm relatively new to electronics and I'm trying to understand the
following circuit:

http://elm-chan.org/works/vlp/ldpctl2.png

It's to control a laser galvanometer X/Y.

I see that a 12-bit DAC is being used to create the output voltages,
but why are they then passed through an op-amp (TA75072) stage?

Also is the following multiplexer (TC74HC4053) only to provide
"emergency off"?

What does the LM358 section do? It's tied to the inverting input of
the TA75072, but I'm not sure why.

Finally, why does the section with the Schmitt triggers below this not
seem to be connected to anything?

Thanks,
Dave

 

[John Popelish]

kasterborus@yahoo.com wrote:

Hi,

I'm relatively new to electronics and I'm trying to understand the
following circuit:

http://elm-chan.org/works/vlp/ldpctl2.png

It's to control a laser galvanometer X/Y.

I see that a 12-bit DAC is being used to create the output voltages,
but why are they then passed through an op-amp (TA75072) stage?

The DAC produces output voltage only between its reference
input voltage and ground. The opamps offset the signal
based on the reference voltage, so that the output is at
zero volts when the DAC output is at half scale. So they
convert the signal from Vref to ground range to +- 1/2 Vref
range.

Also is the following multiplexer (TC74HC4053) only to provide
"emergency off"?

Can't say anything about emergencies, but it provides a
choice of either the offset DAC output or ground.

What does the LM358 section do? It's tied to the inverting input of
the TA75072, but I'm not sure why.

It just buffers the voltage reference source, so that the
gain divider loads from the two output opamps dies not shift
the voltage.

Finally, why does the section with the Schmitt triggers below this not
seem to be connected to anything?

They are the source of the negative supply voltage AVEE.
They constitute a square wave oscillator and charge pump
rectifier.

 

Oh I get it...

Thanks - I couldn't think of a better term than "emergency off"