How should the circuit be adjusted in order to have 0-5v output?
Opamp is LM741CN, BJT are BD139 and BD140.
Opamp is LM741CN, BJT are BD139 and BD140.
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Yes. It's a R/2nR DAC with buffer to drive 25 ohm load.Your resistor network of R2 through R9 should be more like an R-2R ladder. Google that name and see what you find.
The opamp is connected improperly. Look up "non-inverting amplifier". Since your input range is 0v-3.5v and you require an output of 0v-5v, you will need a gain of ~1.4286.
The 741 opamp is not rail-to-rail, so you will need a negative supply as well as a positive supply. This is also true of your Q1/Q2 current amplifier; it won't reach the power rails.
However, you have Q2 connected upside-down, D1/D2 are shorted out, R15, R10 and R11 should not be there, and your opamp needs to take its' feedback from the junction of the Q1/Q2's emitters.
Change the R17/R13 pair to 5k/20k and ditch the LM741 as it will not be able to output below about 1.5V which will keep the transistor switched on. Use an LM358/LM324, or even better, a modern RRIO op-amp such as MCP6002 (available for around 20 pence.)Yes. It's a R/2nR DAC with buffer to drive 25 ohm load.
The circuit has been changed. But output could only reach 3.1V.
What should be done?
A resistor connected to the collector is needed? Then change the gain of the opamp?That's looking MUCH better.
Did you check to make sure that the gain of the opamp is now proper?
Did you notice that you are exceeding the power limitations for Q1?
Do you have any ideas how you could reduce the power dissipation in Q1, without changing Vcc?
If you insert a resistor in series with the transistors' collector, it will help to take the power dissipation away from the transistor.A resistor connected to the collector is needed?
No, I asked you if you checked to make certain that the opamp gain is correct.Then change the gain of the opamp?
It's a DAC circuit which converts 8 bits 3.5V TTL into 0-5V analog voltage.You should be able to go up to 33 Ohms with R12.
It should be rated for at least 2 Watts.
I don't know what you're doing with all of the resistors and voltage sources on the left, but that's OK. If it works for you, that's fine.
so LM324 needs to be replace by TL081? i have tried the circuit,which is very unstable. sometimes output was 5V,sometimes was 3.6V.I don't know what the current source/sink capability of the NI data acquisition box is.
If the DAC is entirely contained within the NI box, then you don't really have to worry about it, as the opamp will have a fairly high input impedance and won't load the analog signal much.
If the NI box output is digital, then you should increase your resistor values very significantly. I suggest using 10k and 20k, as they are standard values that are easy to obtain, and won't load the digital outputs very much. However, you may need to use an opamp with a much higher input impedance to get accurate results, like a TL071 or newer JFET-input opamp.
by Duane Benson
by Duane Benson
by Duane Benson
by Duane Benson