For the regulator it may be a better idea to wire together a binch of resistors to make a DAC. Only down side is to get 8 bit resolution you need 8 pins.
But if you have a scope you could just try out different values and see how clean the output is.
For the regulator it may be a better idea to wire together a binch of resistors to make a DAC. Only down side is to get 8 bit resolution you need 8 pins.
It gives no advantage, you have to buffer the R2R anyway, so it's as easy to use a LPF on a PWM output, and you get 10 bit resolution rather than 8 bit.
It's also a VERY widely used technique, used in countless millions of TV sets, for generating the varicap tuning voltage (with great precision), plus lower resolution channels for volume, brightness etc.
PWM Duty Cycle * Vcc (5V, 3.3V, whatever) = DC voltage after lowpass. Pick a regulator with a control input pin OR scale the DC voltage by some gain factor (you can do this in the LPF at the same time and save an op amp) and connect it to the ADJ pin on a variable regulator.
It will not work. The LM317 is actually regulating the 1.2V and uses the current through that resistor to raise itself up on another while sending it's own 5mA of operating current to it's output.
You need an additional reference to compare the output to and regulate it with an additional transistor. Switching in resistors would require 40V transistors since the 30V when you try to disable one would blow out anything less.
No 12 of then will give you 12 bit accuracy that means 2^12 and that is 4096 different levels of output. This means you can control the output in 0,007V steps.
It will not work!!! You need to set your max voltage with the normal circuit (a resistor from out to sense and a resistor to GND) and then put a transistor in the GND line.
Then put a BIG cap from sense to GND, the value is determined by the response time you need.
It will not work!!! You need to set your max voltage with the normal circuit (a resistor from out to sense and a resistor to GND) and then put a transistor in the GND line.
Then put a BIG cap from sense to GND, the value is determined by the response time you need.