Electronics > Projects, Designs, and Technical Stuff
Bench CC/CV PSU Based on Daves uSupply (Not Anymore)
KC0PPH:
--- Quote from: imo on March 17, 2019, 06:49:33 am ---With the red leds use R2=220ohm (220-250ohm) for 4mA.
C3/4/5/6 are critical (compensation), do not use 100n there.
Most probably you have to play with the best values based on the parts used for an optimal performance. With a lower capacitor's values - the control loop will be unstable and may oscillate, with too high values - the control loop will be slow.
--- End quote ---
OK I will wait until Tuesday to power up. I ordered an assortment of smaller value caps. Ill adjust R2.
Thank you for your assistance.
not1xor1:
--- Quote from: imo on March 16, 2019, 10:16:43 am ---Here are the simulation sources.
The baroque .wav file has to be provided yourself.
Enjoy..
:D
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that's wrong
It just doesn't make sense to use the same compensation network for different feedback loops (single vs. double opamps).
Besides that LM358/324 isn't a good choice for differential amplifiers. An OP07 might be better for that purpose and is still quite cheap.
LT1056 although a bit slower than LT1022 has slightly better features regarding CMMR, PSRR, offset, etc.
LT1013 although as slow as the common LM358 has a wider input/output range and better precision than the above mentioned LT devices.
Of course there are plenty of other suitable devices.
Kleinstein:
The TIP120 is a darlington transistor. So it would replace the 2N3055 and the BD139 directly in front.
The BD139 used for the constant load at the low side sees quite some power. So with a small 2N3904 one might have to reduce the current a little (larger resistor at the emitter).
The fast current limit shown in last Spice files is still flawed - the collector should go to the base of the darlington circuit, not just the 2N3055. One would have to do that change with the TIP120 anyway, but should also do it if BD139+2N3055 are used.
For the OPs the LM358 is not really accurate, but not that bad. For the difference amplifier at the shunt the resistors are still the larger problem than the CMRR of the LM358. The LT1013 is usually a good replacement for the LM358/324 in a simulation and the model is standard with LTspice. Usually one would not need that precision with a lab supply and the LT1013 (and OP07) are still quite slow. The LM358 has the additional cross over distortion that can be a problem, that might not be included in the simulations.
The current limiting might want a little more speed than the LM358, though no need for a really fast OP like the LT1022.
For the breadboard one could consider the RC4558 and similar OPs. 1 or 2 MHz should be fast enough.
iMo:
Sure, a darlington pass transistor simplifies the schematics.
Here is a simulation of FastCC (set to about 4A) acting upon a "short" (Vout=15V, I_load=100mA, I_limit=1A).
The pass transistor is the TIP120.
We may simulate and discuss this wiring forever, indeed. Hopefully, there is a reader who will try with it in hardware finally :D
Some points to repeat/add:
1. the BD139 current source has to be put on a small heat-sink, its max loss could be 0.6W.
It is currently set to 20mA, you may lower it to 10mA (R22=120ohm) or so.
2. the max output voltage is limited by V+max of the opamps used.
When using a lower V+ for the opamps and a higher one for Vp, the max Vout will still be limited by the max opamp's output.
Thus, for example, a setup, where the Vp=40V and V+=15V, will work up to only Vout=13V with this wiring.
It simulates nice with 2x ADA4700 opamps, TIP122 and powered at V+=95V and V-=5V, btw.
3. the compensation - it needs to be adjusted based on the opamp's type used.
jaycee:
I hadn't thought I'd get so much feedback on the circuit, thanks guys :)
The fast current limit transistor is definitely worthwhile.. it gives better current limit response and means that the compensation on the current error amp can be made faster. This will definitely be a bonus on the next power supply I'm working on.
I'm not sure why the BC368P is being chosen here, it seems to be obsolete. It doesnt seem to be shunting a lot of current, so a BC817 seems to work well too. I guess if more current and more dissipation was required, a BC639 could work.
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