Hi everyone,
I am researching the Agilent E363xA power supply and came across their Digital-Analog Converter circuit and was wondering if anyone could help shed light on the operation of this circuit?
I am kinda lost trying to understand what is going on and how they generate the references for the CV & CC loops.
My guess is they use the 74HC4051 to choose (by using the 74HC4094 parallel-out data, kinda like a GPIO expander) which OP-AMP will be connected to the AD1851, then they set the relevant output voltage of the DAC to the desired level of CC/CV_REF they want. I am just not sure if this is correct or not.
that is a scanning DAC system. The opamps are sample and hold circuits. The 4051 is an analog multiplexer.
The load one value in the dac (U12) , select the channel where they want to send that value using the ABC inputs of the 4051 and then pulse the INHIBIT line of the 4051. The moment they pulse that isngal the dac output is essentially connected through the 215 ohm resistor and charges the 0.22uf capacitor of the selected channel./ The TL074 is nothing but a buffer opamp. since it has JFET inputs it does not form a load for the capacitor.
They scan the channels in a loop. If you attach a scope probe to Pin 9 or 10 of the DAC you will see a staircase waveform where each step represents the value of a channel.
This saves them 7 DACs... they can use one and some cheap opamps. Many multichannel DAC's are internally built like that. Back in the day when these machines were deigned such dacs did not exist. That AD1851 is pretty pricey ... it is a 16 bit Pulse code modulation DAC originally intended for Audio. Back then 16 bit DAC were a rarity. Being a PCM system it can be made perfectly linear
That is great explanation, thank you very much!
Do you know if in todays world, this solution is viable or there are better solutions to save up on DACs?