I'm working on a project and requires 4-bits of data from a micro-controller to connect to a DAC using R-2R. I chose R to equal 1k ohms and the max V_out from the DAC (V_R-2R) without the amplifier measures around 1.6V and the current is about 0.8mA. When I connect the amplifier (LM386n-1 powered by a 5V source) according to a schematic below, with resistor R_f value 2k ohms, I expect V_o to equal 3.2V. Rather my measured values are: current is about 15mA and voltage is about 0.9V (yes it goes down). In all honesty, R_f does nothing because I get the same reading on my Voltmeter if I remove that resistor. What am I doing wrong?
PS: The link to the schematic shows a Theveninized R-2R connected to the amplifier.
PS: The link to the schematic shows a Theveninized R-2R connected to the amplifier.
An externally hosted image should be here but it was not working when we last tested it.
I don't see any ladder.
Guessing what you have done: the LM386 on 5V outputs 2.5V DC. The opamp "+" input is at zero Volts? Then the opamp output should be at -5V. (Show how you figure "3.2V".) However it is at 0.9V. Above zero? Is there a negative power rail on the opamp? If not, if just powered +5V(?) and zero, sure it can not go below the rail and typically not much closer than a volt.
Guessing what you have done: the LM386 on 5V outputs 2.5V DC. The opamp "+" input is at zero Volts? Then the opamp output should be at -5V. (Show how you figure "3.2V".) However it is at 0.9V. Above zero? Is there a negative power rail on the opamp? If not, if just powered +5V(?) and zero, sure it can not go below the rail and typically not much closer than a volt.
