Recent Post

Power Current Limiter 13v 20A Circuit

Power Current Limiter 13v 20A Circuit

This PSU has long been particularly created for current-hungry ham radio transceivers. It delivers safely around 20Amps at thirteen.8V. For reduced currents, a separate existing limiting output, able to 15ma as much as a total of 20A has long been extra. The energy transformer should be able to provide at least 25A at 17.5 to 20V. The decrease the voltage, the reduce energy dissipation.

The rectified existing will be "ironed" by C1, whose capacity will need to not be less than 40.000uF, (a golden rule of close to 2000uF/A), but we suggest fifty.000uF. This capacity could be constructed up by many smaller capacitors in parallel. The base of this design is a basic 12V regulator (7812). The output voltage might be introduced to ideal value (here thirteen.8V) by two exterior resistors (R5 and R6) using this formula: U= 12(1+R5/R6). The very low currents (here 15mA) will maintain the 7812 in its normal perform. As quickly because the present rises over 15ma, the voltage drop on R4 will "open" the Q3, basically handling the high output present. This is actually a PNP transistor (Ic > 25) and current amplification factor of a minimum of twenty. The one which has been tested and confirmed right here is the 2N5683. The existing limiting resistance RL, for that maximum output of twenty Amps must be 0.03 Ohms, rated a minimum of 15W. You possibly can make use of the resistance wire or swap numerous resistors in parallel, totaling the resistance/power values. Values for other currents could be calculated by the rule: RL=0.7/Imax

The RL and Q2 (3A PNP which include BD330) form a brief circuit automated fuse. As quickly as the maximum current reaches 20Amps, the voltage drop more than the resistor RL will open Q2, and thus restrict the B-E Existing of Q3. Parallel to Q2 is Q1, which lights the LED one when the present limiting circuit is active. Once the fuse is active, the Q2 bridges the R3, so the full present would circulation by way of the IC1, and harm it. As a result the R4 is inserted, as to limit the IC1 existing to 15mA. This may make it feasible to run the IC1 without having any cooling aid. The LED two will light up every single time the PSU is switched on.

There is an adjustable current limiter in parallel for the fixed output, thus supplying adjustable present source for scaled-down currents. This circuit is incredibly straightforward also. You might discover that there is no current sensing resistor. But it is definitely there, inside a type of the Rds-on resistance of the N-channel FET, which basically handles the load cutoff from the supply. The perform of the FET is proven in the diagram 2. When the existing Id is rising, the pressure Uds over the resistance Rds rises especially gradually in the starting, but especially quick immediately after the knick. This means, that just before the knick the FET behaves as being a resistor but right after it, works as continuous existing source. The D2, R3 and B-E connection of the Q4 will feeling the Uds voltage with the FET1. When the voltage rises sufficient, the Q4 will shortcut the FET1 gate to mass, and reduce the current circulation via the FET 1 off.

Nonetheless, to allow the FET1 to open, there is particular gate voltage required, which with this case is brought up through the voltage divider consisting of R8, Z1, P1 and R9. So the optimum Gate voltage will probably be the one with the Z1, along with the minimal is going to be around 3V6. The Z1 voltage (Uz1) will therefore establish the max current flowing via the FET one. The diagram two will indicate that for 5 Amps the Uz1 really should be 5V6, and for 20Amps close to 9V6.The Capacitor C4 will determine the “velocity” or the reaction time with the limiter. a hundred uF will make the response time to be about 100ms, and 1n will allow it to be 1us. Inside the created limits, the P1 will restrict the existing output within the array of 15mA to 20A.
You possibly can use each output simultaneously, but the complete output current will be restricted by the value of the RL. This PSU can be built also for greater outputs, as long as the transformer will deal with the present needs, and also you provide adequate cooling for your Q3.

Stumble This Fav This With Technorati Add To Digg This Add To Reddit Add To Facebook Add To Yahoo