Malajas Payment We accept Paypal only. Learn More — opens in a new window or tab International shipping and import charges paid to Pitney Bowes Inc. Please enter a valid ZIP Code. Minimum monthly payments are required. Sign in to check out Check out as guest.
|Published (Last):||19 July 2012|
|PDF File Size:||7.66 Mb|
|ePub File Size:||18.40 Mb|
|Price:||Free* [*Free Regsitration Required]|
Non tested Regulated DC power supply, short circuit safe, and with current limiter. This PSU has been especially designed for current-hungry ham radio transceivers. It delivers safely around 20Amps at For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added.
Let us see what we have got here. The power transformer should be capable to deliver at least 25A at The lower the voltage, the lower power dissipation. This capacity can be built up by several smaller capacitors in parallel. The base of this design is a simple 12V regulator The output voltage can be brought to desired value here The one that has been tested and proven here is the 2N The current limiting resistance RL, for the maximum output of 20 Amps should be 0.
Therefore the R4 is inserted, as to limit the IC1 current to 15mA. This makes it possible to run the IC1 without any cooling aid. There is an adjustable current limiter in parallel to the fixed output, thus providing adjustable current source for smaller currents. This circuit is very simple too. You will notice that there is no current sensing resistor.
But it is really there, in a form of the Rds-on resistance of the N-channel FET, which actually handles the load cutoff from the source. The function of the FET is shown in the diagram 2. When the current Id is rising, the tension Uds over the resistance Rds rises very slowly in the beginning, but very fast after the knick. This means, that before the knick the FET behaves as a resistor but after it, works as constant current source. However, to enable the FET1 to open, there is certain gate voltage necessary, which in this case is brought up by the voltage divider consisting of R8, Z1, P1 and R9.
So the maximum Gate voltage will be the one of the Z1, and the minimal will be around 3V6. Within the designed limits, the P1 will limit the current output in the range of 15mA to 20A.
You can use both output simultaneously, but the total output current will be limited by the value of the RL. This PSU can be built also for higher outputs, as long as the transformer will handle the current requirements, and you provide sufficient cooling for the Q3. If somebody will be interested, there is a PCB design ready. I have received several requests for some modifications, and the one I find useful is the addition of an amp meter.
Therefore the slightly modified diagram is included in this revision. All elements within the dotted border are now placed on the pcb. There is also elements placement design included. Should one have an 25Amp instrument on hand, there is nothing easier.
Just mount it in line and there it goes. No problem. As already known from before, there is a voltage drop of 0V7 over the resistor at current flow of 20A. What we now have to do, is to simply measure the voltage drop over the resistor, and co-relate it with the current.
Let us say that our instrument has an internal resistance of 13R, and has a full scale reading of 60mV. The voltage drop over the RL is 0V7 for 20Amps. Therefore, we need another resistance in line with the instrument, that would bring the 0V7 to 60mV, or an voltage drop of mV. The formula is simple:.
2N3955 SPEC PDF
Non tested Regulated DC power supply, short circuit safe, and with current limiter. This PSU has been especially designed for current-hungry ham radio transceivers. It delivers safely around 20Amps at For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added. Let us see what we have got here.
13.8V 20A power supply
Many people thought this situation would always stay that way, and the TESLA management thought so too. How typical for Ebay. Then they keep just this value no matter how long hours or days I let the tester run. Well ok, JJ is new production, so I thought this was the explanation. These are little jewels. I sold this lot where it belongs: Only the machines are the same, and in the Tesla days they were new, and now they are old.