Video amplifier splitter by transistor BD137-BC547-BC557

This is Video amplifier splitter circuit or the video splitter circuit, it is designed to take video signal is stronger. Compensate for the loss of signal, and is video splitter video, which can connect up to three outputs.

So it is suitable for display on several television screens, or video tapes recording at the same time too. (Now may will no video tape.) The advantage of this circuit is cheap, easy and the more detail in the circuit below.

How it works


Technical specifications

  • Increasing rate Typically, the circuit video amplifier is designed to have low amplifier rates. (it different with the common pre-amp circuit) For our, the circuit has the maximum gain ratio is only 4 times.
  • Impedance is 75 ohms on both the input and output.
  • The bandwidth of this circuit is wide of 5 Mhz.

The circuit contains only three transistors. By Q1 (BC547), Q2 (BC557) acts as a signal amplifier, and Q3 (BD139 or BD137) serves as the output circuit of the common emitter follower.

The input impedance of the circuit is determined by the value of R1. The input signal enters through C2 to the base of Q1. By the VR1 is the set the level of the signal swing.

The output of Q1 is connected directly to the base of Q2. The amplified gain of the circuit is determined by adjusting VR2. Which is in the feedback circuit, between collector pin of Q2 and emitter pin of Q1.

However, the rate of increase (gain) depends on the ratio between the resistance of R5 and R6, R8, VR2, C3. The based on the used components in the circuit, we can get the gain of 1.95 to 8.7 times. Thus, if the load is 75 ohms load will reduce the gain of final amplifier section is half. The output signal is only 1-4 times.

The R9 that may change to suit the application. For example, if only single channel networks that use the 150 ohms. If the second channel is used for network 82 ohms, the current in the circuit will decrease.

The LM7812 is main of Dc voltage Regulator circuit in this project. I think you still to know about it very well for popular IC.

The building
We can All can assemble all components on a PCB as the figure below. You should put carefully the device in the circuit. Points of caution are that capacitors, diodes, and transistors put always the correct way. Otherwise, the circuit does not work and damage.

Figure 2 Single-sided PCB layout(Above) and The components layout (Below

The detail parts
R1, R10, R11, R12__________75 ohm____ 1/4W Resistor
R2_____________________10K_______ 1/4W Resistor
R3_____________________8.2K_______ 1/4W Resistor
R4_____________________1K_________ 1/4W Resistor
R5, R8__________________180 ohm____ 1/4W Resistor
R6_____________________3.3K_______ 1/4W Resistor
R7_____________________470 ohm___ 1/4W Resistor
R9_____________________56 ohm____ 5W Resistor
VR1, VR2________________2.2K_______Potentiometer
C1, C3__________________ 10uF 16V__ Electrolytic Capacitors
C2, C8, C9_______________ 0.1uF 50V_Polyester Capacitor
C4, C5, C6_______________ 100uF 16V Electrolytic Capacitors
C7______________________ 470uF 25V Electrolytic Capacitors
D1_______________________ 1N4148___ 75V 150mA Diodes
D2, D3, D4, D5_____________ 1N4001___100V 1A Diodes
Q1___________________ BC547b ,BC546 45V 100mA NPN Transistor
Q2___________________ BC557b, BC556 45V 100mA PNP Transistor
Q3______________________ BD137, BD139 __NPN transistor
IC1______________________ LM7812__12VDC voltage regulator IC

The customization of circuit
When certain that circuit is complete.  Next, enter the power to the circuit to testing by the following method.

Adjusting VR1 done two ways.

First of all, Adjust VR1 until the voltage at the base of Q1 is equal to 1 volt. And has a voltage drop across R7. (no input signal.) approximately 0.75 volts.

Second, Adjust VR1 in the middle, Enter the input signal is 1Vp-p then adjust VR2 to have the lowest rate of increase.

Then, connect the TV or monitor to output. And, adjust VR1 until the test signal without distortion.

Keep reading: ‘Simple video amplifier circuit’ »


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