On Gentoo I needed to point the configure script at libbfd.so. On my
system it is in
./configure --prefix=/usr/local/ --with-bfd=/usr/lib/binutils/x86\_64-pc-linux-gnu/2.22/
The transistors in the current mirror, and differential amplifier will benefit from having thermal contact, to keep the temperature difference as small as possible, thereby minimising the DC output offset. I have taken the best picture I could, of this coupling for one channel, in my amplifier.
I have found this tool indespensible, when finding unforseen errors in complex makefiles.
I have built and tested, the revised version of, both the positive, and the tracking negative regulator. The new version is here:
I have not included Q12, since it was part of the original current limiting circuit. The pass transistors Q5 and Q7, are mounted off-board, on a suitable heat sink. R18 adjusts the maximum output voltage, and R17 adjusts the voltage of the negative tracking regulator.
I will do some more testing of the power supply under different load conditions, and post the results.
I started a thread on diyAudio, here. Some of the feedback, I got, made me revise the circuit, to accommodate an off-board current limiting circuit. Along the way, I adjusted a couple of things, and added current mirrors to the differential amplifiers, since I could cram them in there, and they should better the performance. I have designed and etched a PCB, and tested the positive half of the circuit.
When testing is done, I will post the revised schematic, and PCB. Stay tuned.
This is the final schematic, everything is now tested, and working. Had a little trouble, until I realized I had put a PNP transistor in place of Q6.
Refering to the figure in LAB Power Supply taking shape here is the run down on the last parts.
- is the current limiting circuit on the positive rail. When the voltage across the current sense resistor R1 rises above 0.65V the transistor, Q3, will begin to conduct, stealing base current from the pass transistor. This will make the output voltage fall, until the voltage loss in R1 is back at 0.65V. The value of resistor R1 sets the current limit, using Ohms law it is easy to calculate resistor value for a 1A current limit, (R=U/I), R1=0.65V/1=0.65Ω. The closest value is 0.56Ω, which gives a current of 0.65V/0.56Ω=1.16A.
- is the negative current limiting circuit. Q10 and R14, is the mirror circuits of Q3 and R1. Since the negative rail tracks the positive one, the negative voltage will drop, when the positive current limit kicks in. The positive rail, is not tracking the negative, and the positive voltage, will not drop, when the negative current limiter kicks in. Arguably, there will be no over-current problem, on the positive rail, if the positive current limit is not activated. For completeness, Q6 will turn down the voltage of the positive rail, when the difference between the positive and negative rail becomes large enough to make the voltage at the junction R9, R13 more than 0.65V
Well it seems the power supply is working, I have made a PCB design,
that I will perfect, and publish when done.
I have tested the negative tracking regulator today, it differs from the positive regulator, in that it it measures the voltage at the positive output, and adjusts the negative rail accordingly.
Referring to the block diagram in the last post, I will describe the new blocks.
- is a differential amplifier just like 2. The first input is taken from ground, the second from the voltage divider H, that samples the midway point between the positive and negative rail. The midway point is essentially 0V, as the positive and negative real should have equal opposite voltages. The difference amplifier will keep this midway point close to zero, by controlling, through the pass transistor 7, the voltage of the negative rail.
- is a darlington pass transistor like 3.
- is the voltage divider creating the midway voltage for 6.
Everything is working, and the next step is to test the current limiters, which is hopefully going to happen at the beginning of next week.
Generated on 2018-05-03 01:14:21.835342