Power amplifier electronic circuits-tube audio rf amplifiers

Electronic Amplifier Circuits-Power amplifier, audio amplifier designs and circuits

May 7th, 2010

25 Volt Adjustable Voltage Regulator Circuit

Circuit Description

The circuit diagram of 25V Adjustable Regulator has been given here. This circuit is based on LM 117 IC which is the central part of this circuit. The LM117 IC is an adjustable 3-terminal positive voltage regulator. This voltage regulator is able to provide in excess of 0.5A over a 1.2V to 37V output range. The added advantages of this circuit is that the ease of handling and the use of only two external resistors for setting the output voltage.

In this circuit, voltage adjustment is done by using the resistors R1 and R2. This power supply for this circuit is able to deliver a maximum of 0.5A current. By adjusting the potentiometer R2, required voltage can be obtained. To reduce min output voltage from 1.2 volt to 0V, connect two IN4007 diodes in series to the output.

Circuit Diagram

25 Volt Adjustable Voltage Regulator Circuit

25 Volt Adjustable Voltage Regulator Circuit

LM 117 Pin Diagram

lm117 pin diagram

lm117 pin diagram

Notes

  • For getting a 1.2A output current replace LM117 with LM317.
  • This circuit is easy to assemble and provides great results.
  • Adequate heat sink should be provided for IC LM 117.
  • To get a 1.2A output current replace LM117 with a LM317.
  • You can use as less as 5V DC as input voltage. Here a minimum 28V, 2A DC input is needed for the IC as shown in figure.
  • If exact value components are not available then try the nearest ones.
May 7th, 2010

Dual Adjustable Power Supply Circuit

Circuit Description

The circuit diagram of Dual adjustable power supply has been given here. This circuit is based on two ICs namely LM 317 and LM 337. Among these ICs, LM 337 is the negative complement of LM317. These ICs work at voltage range between 1.2 V and 30V and are capable of delivering 1.5A current. One of the most advanced features of these ICs is the short circuit protection.

This circuit gives an output dual DC voltage in the range of -15V to +15V. Filtering and ripple rejection in this circuit is accomplished by the series of capacitors from C1 to C8. The job of controlling the output is done by resistors R1, R2, R3 and R4 (R1 and R2 for LM 317 and R3 and R4 for LM 337).

Parts List

Capacitors:

C1, C2 (2200 uF 50V)
C3, C4, C5, C7 (2.2 uF 50V)
C6, C8 (100 uF 50V)

Resistors:
R1, R4 (5K Potentiometer)
R2, R3 (220 Ohms 1/4 W Resistor)

Active Components:
D1 to D4 IN 4007 Diodes
U1 LM317 U2 LM337

T1 (24 0 24 Center Tapped 2 Ampere Transformer)
S1 (SPST 2 Ampere Switch)

Circuit Diagram

Dual Adjustable Power Supply Circuit
Dual Adjustable Power Supply Circuit

Notes

  • This circuit is a must on an electronic hobbyist’s workbench.
  • The transformer should be produce a min of 3 A with (24 0 24) output voltage.
  • Resistors R1 and R4 can be turned to vary the positive and negative voltages.

Adequate heat sinks should be provided for ICs.

May 7th, 2010

Long Range FM Transmitter Circuit

Circuit Description

The circuit diagram of Long Range FM transmitter having a power output in the range of 0.5 -2W has been explained here. High power transmitters are required if the transmission path contains many obstacles or the transmission distance is very high. A micro transmitter can produce a power of a few thousandths of a watt. The battery using here should be of the alkaline high power type, because the current drain will be high when compared to micro transmitter current drain. The power output of the device can be altered by changing the value of the resistor R6. This can be done by putting a variable resistor of 1K in series with R6 so that it can be adjusted to get a variable output power.

The audio input to the power oscillator is formed by TR2 and associated components, is derived from a piezoelectric microphone. This is used to drive the simple audio frequency amplifier TR1. Potentiometer R1 is used to control the input of the audio amplifier which is done by selecting the correct amount of voltage that is generated by the piezoelectric microphone. Then this signal is connected to the base of TR1 by means of capacitor C7. RF feed back problem due to large RF field is solved by employing a metal enclosure for transmitter and keeping internal wirings short.

Component listing for 1 watt transmitter

Resistors: R1 (27K), R2 (330K), R3 (56K), R4, R5 (10K), R6 (100 ohm).

Semiconductors and other Devices: TR1 (BC547), TR2 (2N2219) fitted, MIC (piezoelectric microphone), L (6 turns 22 gauge enameled wire wound on 3⁄16″ former)

Capacitors: C1, C2, C3, C8 (330 pF), C4 (2–10 pF trimmer), C5 (47 pF), C6 (1 nF), C7, C8 (40uF).

Circuit diagram

Long Range FM Transmitter Circuit
Long Range FM Transmitter Circuit

Notes

  • DC power supply ranging from 6V to 30V can be used in this circuit
  • The variable resistor must not be a wire wound device since this would act as an inductor which will cause feedback problems.
  • It is possible to use an electret microphone instead of piezoelectric microphone.
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