12v dropping to 11.92v at 4amp loadThere is a slight improvement even now on the 4amp draw at 12v output....earlier the 12v dropped to 11.89v...........now 11.92v
12v dropping to 11.92v at 4amp loadThere is a slight improvement even now on the 4amp draw at 12v output....earlier the 12v dropped to 11.89v...........now 11.92v
yes as above12v dropping to 11.92v at 4amp load
I have to go to bed.....It's 00:50 my time Ireland.yes as above
Why reduce the opamp's supply voltage? It has a low output current then it does not get hot. Its absolute maximum allowed supply voltage is 44V. It is the TIP41 transistor and output transistors that have the high current and any extra voltage above about 17V makes them very hot.Hello again, Can I use a zener to lower the voltage to 18.3V supply for the op amp?
Yes. Like a high-end Zener diode but much better.(Some text removed for clarity)
Is it the reference shunt?
The last time I saw something like that it turned out that were was a ground loop that affected the feedback.2 amp load 4.39v, 4 amp load 4.35v
If you had the reference connected to the non-inverting input and the rest of the circuit was "right" it should not affect stability. Your voltage reference is stable to within 100 parts per million per °C. The voltage drop across the 2N2222 is about 2 millivolts/°C of the 5V reference for 400 parts per million per °C. In other words, you are cheating yourself out of the thermal stability you paid for the LM1440 by adding that transistor's thermal dependency.I tried using the zener directly to op-amp input but its stability suffered under load, I added the transistor to achieve some stability
The last time I saw something like that it turned out that were was a ground loop that affected the feedbackOn thermal stability:
Yes. Like a high-end Zener diode but much better.
The last time I saw something like that it turned out that were was a ground loop that affected the feedback.
If you had the reference connected to the non-inverting input and the rest of the circuit was "right" it should not affect stability. Your voltage reference is stable to within 100 parts per million per °C. The voltage drop across the 2N2222 is about 2 millivolts/°C of the 5V reference for 400 parts per million per °C. In other words, you are cheating yourself out of the thermal stability you paid for the LM1440 by adding that transistor's thermal dependency.
Glad to see it you got it working better.Still thinking about lowering the voltage and maybe lowering the reference voltage.
20k have to get my little head around that, what about lowering the overall 23v, any thoughtsGlad to see it you got it working better.
Not sure if I would lower the reference voltage unless you want to go below 4 volts on the output.
Only other recommendation would be to replace the two 10K pots with a single 20K. Center tap to -input.
See diagram about the pot.20k have to get my little head around that, what about lowering the overall 23v, any thoughts
Yes I see the error thanks.See diagram about the pot.
Reducing the voltage to the output transistors will lower their power dissipation. It depends on the maximum output voltage you require.
As you have it designed now I calculate the dissipation on Q2,Q3 at appx.18 watts each at 4 amps. Based on a 12 volt output and the input voltage dropping to 21 volts at 4 amps to be exact. Q1 at appx .6 watt.
Noticed an error in your schematic. The collectors of Q1-Q3 should be connected together.
Q2,Q3 are rated 150 watts and properly heatsinked should not be a problem.
View attachment 225669
I see what you mean, will 20k drive the current too low? meant to sayYes I see the error thanks.
I see what you mean, will 20k drive the current too?
I measured the resistance of each earlier, at 12v vr1 is 2500ohm and vr2 is 3500ohms thats @ 1.4:1 ratio, with 20k vr1-12k and vr2 8k.
Incidentally what is the real function of your capacitor across the pot wiper, is it cleaning the suppply
I don't think so but you probably could just use one of the10K pots you have now. Adjusting the one pot will get you the same ratio of 1.4 somewhere in it's range.I see what you mean, will 20k drive the current too low?
My error, should show the cap from pin 2 to negative. Purpose is to eliminate any noise on that pin. Will correct schematicIncidentally what is the real function of your capacitor across the pot wiper, is it cleaning the suppply
I will try and see what happens,I thi
I don't think so but you probably could just use one of the10K pots you have now. Adjusting the one pot will get you the same ratio of 1.4 somewhere in it's range.
Any drop at pin 3 is going to show up on the output. However a 18 volt output requires the output of the chip to be 19.4 volts. If the supply is dropping to 21 volts there may not be enough "overhead" to sustain a 18 volt output. The specs indicated the max output of the chip is the supply voltage minus 1 volt.is this a tiny drop at pin 3 multiplying
I know this is a silly question, how do you arrive at an exact 1.4 v loss at 19.6vAny drop at pin 3 is going to show up on the output. However a 18 volt output requires the output of the chip to be 19.4 volts. If the supply is dropping to 21 volts there may not be enough "overhead" to sustain a 18 volt output. The specs indicated the max output of the chip is Vcc+ minus 1 volt.
The output from the chip goes through two base emitter junctions. Q1 and the parallel combo of Q2,Q3. You lose appx .7 volt per junction. Just as you lose voltage through diodes, same principal.how do you arrive at an exact 1.4 v loss at 19.4v
Yes it would or more depending on the current. At 4 amps that would dissipate appx 4.8 watts. dropping the transistor dissipation to under16 watts per transistor at 12 volt out.question no.2 would connecting two power diodes in series drop the 23v by 1.2v
I only got a chance to try out the previous suggestion of combining vr1 and vr2 into one 10k, and then 20k by Sghioto today. Happy holidays.The common mode voltage range of only 2.9V is when its supply is only 5V. When the supply is +/-15V then the common mode voltage range is -15V to +12.9V. The bases of its PNP input transistors stop working then they are higher than 2V below the positive supply voltage like the PNP input transistors in an LM324 and LM358.