Interesting mosfet voltage regulator IRF3205

  The mosfet used was the IRF3205 Enhancement Mosfet. Its function is to boost the current induced into the transmitting coil to increase its distance level. Mosfet ratings; Peak Drain to Source Voltage (VDS)= 55V On Resistance = 8.0 ohm Peak current = 110A when VDS = 10V So the current used was derived using the equation; ION = k (VDS(on) – VDS(th))2 Using the ratings to get the constant k we have, K = 110A/ (10V – 4V)2 K= 110/62 K = 110/36 K = 3.10AV2 Having gotten the constant k as 3.10AV2, we can derive our drain current as; I = 3.10 x (9V – 4V)2 I = 3.10 x 25 I = 77.50A

  The inductance of the inductor to use is derived using the equation; L = n2 x R2/ 9R + 10x Where, L is the inductance N is the number of turns R is the radius of coil X is the distance of turns To get the required reactance of the coil to use, we divide the DC supply Voltage by the Drain Current of the MOSFET. Therefore, XL = 21.21/77.50 XL = 0.27ohm If Reactance of an inductor XL = 2 x 3.142 x f x L, then 0.27 = 6.284 x 50 x L L = 0.27 / 314.2 L = 0.0008593H RECEIVING CIRCUIT: The receiving circuit has basically the receiving coil, half wave rectifier circuit/filter and the voltage capacitor. The value of R is used to set the charging current to a fixed value which is determined by the Charging voltage/ charging current. For this project, the charging voltage was 5V DC. And the charging current required was 500mA. Therefore the value of R will be; R = 5/0.5 = 10ohm

BS170 - is used for the QRP rig PA

The 2N7000 PA was described in my blog message sometime ago. The BS170 by Fairchild can be also used for QRP rig PA. It is N-Channel Enhancement Mode FET. The Maximum Power Dissipation Pd is 830mW, therefore it can be suitable for QRP rig PA. The transmitter section of ADC-40 is the dual BS170 and it generates about 4watts with 13.8V power supply. The small heatsink is required to use BS170s for PA because it will be hot and drops the power. The PFR-3A is the triple BS170 for PA and generates 5 Watts with 12V power supply.