| Electronics > Beginners |
| Problem with first lab power supply |
| << < (3/4) > >> |
| Kleinstein:
The circuit does not look like it is a good idea. A agree in forgetting about that circuit, though for different reasons: The biggest problem is that chances are high that the current regulation can, likely will oscillate with some loads. Stability could be a problem in CV mode too. The current limit would not work below some 20 mV - so a dead short could damage the regulator. The NPN transistor does have a small residual CE voltage. There is a realtively cheap kit that is quite often discussed. https://www.banggood.com/0-30V-2mA-3A-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-p-958308.html?cur_warehouse=UK It is not perfect and has some issues, however with a few modifications that are discussed in several threads here and other forums, the circuit is useful. The main point is to reduce the transformer voltage to some 18-20 V - thus it would fit the 18 V transformer. With a few additions one might be able to get some 20 V at low current and with nominal grid voltage. At 1 A it is likely more like 16 V max. |
| not1xor1:
--- Quote from: Eldi4 on June 22, 2018, 01:36:37 pm ---I'm sorry, but the circuit actually perform well when i power it with my 25V SMPS, and no problem really noticable, it's output voltage can reach 23.5V and the current limiting are pretty precise, so i will use SMPS instead, because my transformator seems to have some problem (it's output voltage drop is really high even on 1 amp?), i don't think i will need really low noise power supply, as i will just power some simple circuit, testing led, and some un-sensitive load. I don't really have precise measuring instrument to perfect-ing the circuit, i don't have oscilloscope (planning to buy soon!), my multimeter is 10 year old manual ranging multimeter, but it pretty fullfil my little need. And i use darlington transistor as series pass transistor, because my maximum output current will be 5A, which will overload the op-amp if i'm not using darlington transistor as series pass transistor. The only problem that is left now is just tingling when i touch the power supply, probably earthing the ground will fix this problem, not a real problem. And if you really have some another simple circuit suggestion please let me know, or suggestion to this circuit. --- End quote --- I guess you just got a wrong feeling it works. Typically an LM324 with 3mA of load can't get closer than 3V to the positive rail so while you might be lucky and get 23.5V without load, I bet you would not be able to get more than 21V (with really poor regulation) at the maximum load. Besides that you can't tell anything about oscillations, transient stability, PARD, etc without an oscilloscope. |
| exe:
--- Quote from: not1xor1 on June 22, 2018, 03:35:28 pm ---PARD --- End quote --- What is PARD? Partnership on Religion and Sustainable Development? |
| schmitt trigger:
Periodic And Random Noise. |
| not1xor1:
--- Quote from: Kleinstein on June 22, 2018, 03:23:21 pm ---The circuit does not look like it is a good idea. A agree in forgetting about that circuit, though for different reasons: The biggest problem is that chances are high that the current regulation can, likely will oscillate with some loads. Stability could be a problem in CV mode too. --- End quote --- I just preferred to focus on easier to understand issues (and did not even mention all them) --- Quote from: Kleinstein on June 22, 2018, 03:23:21 pm ---There is a realtively cheap kit that is quite often discussed. https://www.banggood.com/0-30V-2mA-3A-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-p-958308.html?cur_warehouse=UK It is not perfect and has some issues, however with a few modifications that are discussed in several threads here and other forums, the circuit is useful. The main point is to reduce the transformer voltage to some 18-20 V - thus it would fit the 18 V transformer. With a few additions one might be able to get some 20 V at low current and with nominal grid voltage. At 1 A it is likely more like 16 V max. --- End quote --- For low voltage values, single winding transformer PSUs, I think that a circuit like the one I quickly drew and tested on ltspice is more suitable (but I would use TL431s rather than zeners and LM385s) It is just a plain power DC amplifier with a darlington buffer and a basic constant current sink as down programmer. Voltage doublers are used to get two additional rails for the opamp which can work within the granted input/output limits. From the transient test it looks like the circuit might even work without a compensation network. Of course real circuit are always different than simulated ones. Besides that I sketched it in haste and it is likely that there are a few mistakes. BTW R6/R7 should be a V reg potentiometer while R9/R10 should be the current reg pot (with additional resistor to reduce the maximum current). |
| Navigation |
| Message Index |
| Next page |
| Previous page |