Electronics > Projects, Designs, and Technical Stuff
Help with how this PSU works. (With revised design)
jaycee:
Jumping in VERY late on this, but essentially the regulator circuit used here is a very common one, I believe Harrison Labs developed it first, and the concept is used in quite a lot of power supplies including the Mastech ones. The neat trick is that the opamp supplies float around the main regulator's +ve output.
Tap switching is simplest and best done by a relay. A simple circuit using a comparator checking the output voltage can be used to know when to switch taps. My own power supply switches between 9VAC and 18VAC taps using a simple two transistor circuit. You would adjust R20/R47 accordingly. "VRAW" in this case is the raw voltage fed to the pass transistor
xavier60:
It might be interesting to know that current sourcing PSU designs such as this aren't immediately damaged by applied reverse polarity.
The output transistors might experience much higher than usual dissipation and the output capacitor will eventually burst.
I'm not saying that there is no need for the diode across the output. An example for its need is when PSUs are connected in series.
aheid:
Just a thought but one thing I've been missing in my bench supply, which I'm considering hacking in, is a way to have external voltage probes. Idea was to be able to switch from sensing voltage at the output terminals to have sense terminals, to compensate for voltage drop in cables etc.
It'd require an extra opamp control circuit, but can be diode-OR'ed as well so should be relatively easy to add such a design.
Maybe not for rev1 but perhaps something for rev2?
jaycee:
--- Quote from: aheid on May 13, 2020, 11:47:16 pm ---Just a thought but one thing I've been missing in my bench supply, which I'm considering hacking in, is a way to have external voltage probes. Idea was to be able to switch from sensing voltage at the output terminals to have sense terminals, to compensate for voltage drop in cables etc.
It'd require an extra opamp control circuit, but can be diode-OR'ed as well so should be relatively easy to add such a design.
Maybe not for rev1 but perhaps something for rev2?
--- End quote ---
Strictly this doesnt require extra opamps, it does require careful routing though. Using separate opamps for sense and error does make it easier though. My own PSU has separate sense amps, and has voltage sense right up to the terminals, but I used separate sense amps primarily because I wanted to feed the output of those to ADC's for metering purposes.
The Elektor "Precison PSU" from 1982 is the only diagram I've seen which shows single opamps and how to correctly do remote voltage sense. Ignore the 723 in this circuit, it is used only as a voltage reference (a bit of a bizarre choice!) - IC2 is doing the voltage control, IC3 is doing the current control
xavier60:
--- Quote from: aheid on May 13, 2020, 11:47:16 pm ---Just a thought but one thing I've been missing in my bench supply, which I'm considering hacking in, is a way to have external voltage probes. Idea was to be able to switch from sensing voltage at the output terminals to have sense terminals, to compensate for voltage drop in cables etc.
It'd require an extra opamp control circuit, but can be diode-OR'ed as well so should be relatively easy to add such a design.
Maybe not for rev1 but perhaps something for rev2?
--- End quote ---
You could break the connections where R15 and R24 connect to 0V and -output. Then insert something like a 10Ω, 10uF and back to back 1A didoes all in parallel. There will be a small voltage change depending on if the sense leads are used or not.
Are you simulating the present design?
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version