Schematic Volt: stage

Wednesday, October 29, 2014

Error Correction Output Stage for Mosfet and BJT Power Amplifier

For best results, any active device with the exception of the output transistors operating in class A. This is to avoid bias to saturate or block the entrance to all the clipping level, should be selected. This raises some difficulties for a BJT amplifier, where (to stay in Class A) driver stage collector currents, the base of BJT output current at maximum output current (ie in our case some of 10A) No is not exceeded. Therefore, the overall bias regime redesigned to allow space for the swing base BJT output current.

Even in these circumstances, the power dissipation in the driver’s relevant and it is doubtful if a heat sink on board (as in our design side MOSFET included) help, if maximum performance is desired 200W into 4 ohms. It is therefore assumed that the power BJT design based on our application can not be more than one goal and 100W/4ohm 50W/8ohm. Of course, for such relatively modest achievements, it is not necessary to install three pairs of output devices, a pair of (ex) MJL4281/MJL4302 or equivalent work will be done.

Adjusting the balance Hawks Word is a double potentiometer (minimum of ten rounds) with more than 0.5% of correspondence between the sections. We replaced R20 and R81 with a 2K potentiometer Bourns 10 turns and adjusted for minimum distortion 20kHz Open Loop. You will find that the minimum is strongly dependent on the frequency, always adapting to at least the higher frequency in the audible range. At low frequencies, the feedback loop gain in reducing DHT levels to help you. Measured values ??and replace the potentiometer with fixed resistors.

The minimum is usually very close, if you need 0.5% or better precision resistors. The aim should be to bring the open-loop THD-20 below 0.01% to 10 Vrms input level. We built four previous CE FPO advice and got the last open-loop THD-20-values ??at 0.0065% 0.0075% 0.0090% and 0.012% (the latter, we can not source of precision resistors required values).

The network output Zobel is the stability amps together. For the same reasons, shoud not be 2UH air core output inductor.

The error amplifier frequency compensation C17 is the signal ground of the amplifier that takes full power to the ground. It is for reasons of stability and provide a grounding shield for feedback (output port).

Four Stage FM Transmitter

This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1), a preamplifier built around transistor BF200 (T2), a driver built around transistor 2N2219 (T3) and a power amplifier built around transistor 2N3866 (T4). A condenser microphone is connected at the input of the oscillator.

Four-Stage FM Transmitter Circuits diagram :

Four-Stage FM Transmitter Circuits Diagram

Working of the circuit is simple. When you speak near the microphone, frequency-modulated signals are obtained at the collector of oscillator transistor T1. The FM signals are amplified by the VHF preamplifier and the pre-driver stage. You can also use transistor 2N5109 in place of 2N2219. The preamplifier is a tuned class-A RF amplifier and the driver is a class-C amplifier. Signals are finally fed to the class-C RF power amplifier, which delivers RF power to a 50-ohm horizontal dipole or ground plane antenna. Use a heat-sink with transistor 2N3866 for heat dissipation. Carefully adjust trimmer VC1 connected across L1 to generate frequency within 88-108 MHz. Also adjust trimmers VC2 through VC7 to get maximum output at maximum range.

Regulator IC 78C09 provides stable 9V supply to the oscillator, so variation in the supply voltage will not affect the frequency generated. You can also use a 12V battery to power the circuit.

Assemble the circuit on a general-purpose PCB. Install the antenna properly for maximum range. Coils L1 through L5 are made with 20 SWG copper-enamelled wire wound over air-cores having 8mm diameter. They have 4, 6, 6, 5 and 7 turns of wire, respectively.

EFY note. This transmitter is meant only for educational purposes. use of this transmitter with outdoor antenna is illegal in most parts of the world. The author and EFY will not be responsible for any misuse of this transmitter.

Author : Pradee G. - Copyright : EFY

Wednesday, October 29, 2014

Error Correction Output Stage for Mosfet and BJT Power Amplifier

Wednesday, October 22, 2014

Four Stage FM Transmitter