Build a 100W V-MOSFET Power Amplifier Circuit

Description

A design that is being developed, utilising the POWER VMOS FET from the series [ 2SK134 or 2SK135 ] [ 2SJ49 or 2SJ50 ], these transistors are not produced anymore by Toshiba and finding them is difficult. They can be substituted with [ 2SK1530 in the place of 2SK135 ] and [ 2SJ201 in the place of 2SJ50 ]. These new transistors are housed in a plastic case ΤΟ-3Ρ and are not TO-3, they operate with a higher supply voltage and possess a positive temperature coefficient. This indicates that as temperature increases, the current flowing through the transistor also increases, consequently affecting its power. The use of diodes D2 until D5 in combination with the resistances R17-19, they protect the gates of transistors v-fet from exceeds the voltage ± 14V and it creates perforation in very thin layer SiO2, that is used as insulation in the gate. This way of protection is common in all the amplifiers that use these transistors. The total gain of amplifier is 32.6, regulated from the R18, R6 and R8, in the negative feedback. Also is used enough the use of local feedback for stabilisation of operation under all the conditions. Because the transistors v-fet have positive factor of temperature, with result with the increase of temperature is increased also their resistance. This increase has as result the reduction of current that via the transistor, hence also his power. The use of separated supply in the stages of drive and exit, ensures stability and reject of distortion of intermodulation.

Circuit diagram

Part List

*polyester or mylar