Tuesday, March 31, 2009

Audio Clipping indicator.

It's possible to build a clipping indicator like accesory for amplifier which detects amplifier limitation, when output transistors are fully opened and signal is cutted close to power supply voltage. In this case is acoustic signal distorted in a power amplifier. Circuit as usually is from authors pages. I redraw them in a Eagle and I designed circuit board for two channels. I added place for two LEDs for power supply voltage indicators. This board have small pads, which is not much good. Eagle has these pads too small in default state.

Schematics diagram

Download this schematic

Semiconductor list datasheet download. (PDF Format)

1. BC639
2. BC640


First we must to test power supply part. Fuses F2 to F5 we leave out and for sure we check again circuit of rectifier and capacitor polarity. a zkontrolujeme pro jistotu zapojení usměrňovače a polaritu kondenzátorů. Possible error can be fatal. If is all OK, that on capacitors will be voltage about 51V. Exact voltage depends on used transformer and power line voltage. After disconnecting will be voltage on capacitor for a long time. We can discharge them with a resistor 100R 2W. It's possible, that with power-on blows fuse F1 even all is OK. In my situation is charging current too big, that I had place NTC thermistor in a series with primary transformer side. I get them from old PC power supply, where it has identical function. Better idea is to use "soft start" circuit, which is made from big resistor on primary side of transformer and relay, which short-circuit resistor after few seconds. I didn't found any circuit which I liked it.

When the power supply works correctly, we can go to test amplifier. First we set trmmer P1 to one end position with maximum resistance. In to the fuse holders for one channel we place resistors 100R 1/4W. With disconnected output and input we can power-on amplifier. On the resistor we would measure maximally 2.5V, which matches current 25mA. If is everything allright, we wait for discharging after power-off and replace resistor with fuses. Initially for testing we can use smaller values. I had switched two wires from power transistors on one channel and resistors smokes and smells. Really is better to everything double check.

Now we must set the bias current. Use amperemeter in place of F2. Turn the trimmer P1, until is current 100mA. How amplifier warming-up current is changing. Regulate current value when it is stabilized, which can be after 15 minutes. Identical procedure repeat for second channel.

With disconnected input we can measure DC offset on the output. In my example I measured 19mV on left channel and 22mV on right channel.

Now we can made regular tests and connects speakers and signal source. I tested with connecting of the amplifier input directly on the output of soundcard. You must carefully increase volume, because amplifier has enough power to destroy small speakers.

Monday, March 30, 2009

Power supply for the 40 W single chip amplifier.

Constructing the power supply for this amplifier is simple. As shown on the schematic above you need to wire up a 18-0-18 (center tapped) transformer in order to get the recommended +/- 25V. Be very careful since this construction involves mains wiring.

1-chip 40 watt amplifier.

This is a compact, easy to build amplifier that uses one IC only but delivers 40 watts of audio power. It is ideal for amplifying audio from your mobile CD player or iPod. The chip being used here is the TDA1514 originally brought to the market by Phillips/Valvo. The best characteristics of this chip is its high output power and robustness. It is available in a 9-pin SIL plastic package with a metal mount.

Its package has a heat resistance of less than 1.5K/W. This means that the heatsink must have a heat resistance of only 3.8K/W when the chip reaches its maximum power dissipation of 19W (at Ub = +/-27.5V, Tu = 500C).
One can see from the diagram that only a handful of passive elements are needed to build the chip into a powerful audio amplifier. The power supply as supplied must be able to deliver a current of at least 3 amperes. The standby current consumption is about 60 mA. The supply voltage must never go beyond 27.5 volts!

In building the circuit, keep the wires to the power supply and outputs as short as possible. The resistos R4 and R5 set the voltage gain at the feedback which, in this case, is between 20 and 46 dB.
For a single channel amplifier(mono), a 80 VA transformer (T1) should be sufficient. If you construct two channels (or stereo) amps, 120 VA is recommended. Capacitors Cx and Cy should be at least 4.700uF rated at 35V. It can be up to 10.000uF. Capacitors twice as large discharge slower giving better peak power potential resulting to better power output. Feel free to increase the capacitance but take note that you may not get much additional benefit for the price involved. Make sure they are connected the right way around too or they will blow and cause injury.

Download this schematic diagram.

Semiconductor datasheet component. (PDF Format)

1. TDA 1514

TV Modulator (Exiter) with MC1374

The MC1374 includes an FM audio modulator, sound carrier oscillator, RF oscillator, and RF dual input modulator. It is designed to generate a TV signal transmitter from audio and video inputs. The MC1374’s wide dynamic range and low distortion audio make it particularly well suited for applications such as video tape recorders, video disc players, TV games and subscription decoders.

Download this schematic diagram.

Semiconductor list datasheet download. (PDF Format)

1. MC1374
2. MPN3404
3. IN914

The MC1374 contains an RF oscillator, RF modulator, and a phase shift type FM modulator, arranged to permit good printed circuit layout of a complete TV modulation system. The RF oscillator is similar to the one used in MC1373, and is coupled internally in the same way. Its frequency is controlled by an external tank on Pins 6 and 7, or by a crystal circuit, and will operate to approximately 105 MHz. The video modulator
is a balanced type as used in the well known MC1496. Modulated sound carrier and composite video information can be put in separately on Pins 1 and 11 to minimize unwanted crosstalk. A single resistor on Pins 12 and 13 is selected to set the modulator gain. The RF output at Pin 9 is a current source which drives a load connected from Pin 9 to VCC.

Saturday, March 28, 2009

Op Amp Radio

Here is a simple
radio that is easy to build and inexpensive. In fact, you probobly have all the parts you need in your junk box. You will be suprised at the great reception with this little set.


The antenna can be a piece of wire or a telescoping antenna. 18 inches is a good length for in the city.

The tuning capacitor is a regular broadcast band tuning capacitor. I got mine from a junked AM radio. I got the loopstick antenna from that same radio.

You can change L1 and C1 to recieve different bands (eg. Shortwave). To recieve shortwave, try this: Make L1 30 turns of 30 guage wire wound on a film can and make C1 a 10-365pf capacitor.

Combine this circuit and the 8 Watt Audio Amp for a really neat radio.

The circuit diagram for a 4 bit TTL counter, a type of state machine.

A circuit diagram (also known as an electrical diagram, wiring diagram, elementary diagram, or electronic schematic) is a simplified conventional pictorial representation of an electrical circuit. It shows the components of the circuit as simplified standard symbols, and the power and signal connections between the devices. Arrangement of the components interconnections on the diagram does not correspond to their physical locations in the finished device.

Unlike a block diagram or layout diagram, a circuit diagram shows the actual wire connections being used. The diagram does not show the physical arrangement of components. A drawing meant to depict what the physical arrangement of the wires and the components they connect is called "artwork" or "layout" or the "physical design."

Circuit diagrams are used for the design (circuit design), construction (such as PCB layout), and maintenance of electrical and electronic equipment.

Download this schematic diagram.

Semiconductor datasheet download. (PDF Format)

1. 74SL107D

2. 74LS08D

For detail, please visit http://en.wikipedia.org

Monday, March 23, 2009

Christmas Decoration Project

This project flashes 18 LEDs at three different rates and you can use these to create a Christmas decoration of your choice. The circuit is kept simple (and cheap!) by using the 4060B IC which is a counter and oscillator (clock) in one package. The circuit requires a 9V supply, such as a PP3 battery. It will not work with lower voltages and a higher voltage will destroy the LEDs.

The preset variable resistor can be used to adjust the oscillator frequency and this determines the flash rate of the LEDs. The IC limits the current to and from its outputs so the LEDs can be safely connected without resistors in series to limit the current. The stripboard part of the circuit is easy to build but the wiring for the LEDs needs care so detailed instructions are provided below.

Download this schematic diagram.

Parts Required

  • resistors: 10k, 470k
  • preset: 47k (this could be 100k if necessary)
  • capacitor: 0.1µF
  • 4060B IC
  • 16-pin DIL socket for IC
  • LEDs × 18, 5mm diameter, any mix of colours: red, orange, amber, yellow or green
  • on/off switch
  • battery clip for 9V PP3
  • stripboard 13 rows × 18 holes
Download list datasheet semiconductor parts. (PDF Format)

1. CD4060B

Voltage Regulator 5V-20V Project.

If you are looking for a low drop voltage regulator that is able to provide a power supply of 1A with an output voltage of between 5V and 20V DC, National Semiconductor LM2941 Low Dropout Adjustable Regulator is one that you can choose to use. It has a typical dropout voltage of 0.5V which means that the input supply need only have to be 0.5V DC more than the desired output voltage. Its other features include internal short circuit current limit and reverse battery protection. As shown in the schematic below, the regulator has 5 pins which consists of the ON/OFF control, Input Voltage, Output Voltage, Ground and Adjustable pins. ON/OFF is used for the purpose of switching on and off of the regulator. The capacitors C1 and E1 are to be placed as close as possible to the regulator.

Download this schematic diagram.

The output of the circuit can be varied by varying the value of potentiometer VR1 from 5V DC to 20V DC. The input voltage is limited from 5.5V DC to 30V DC. Resistor R1 must be greater than 1K. The value of the VR1 that needs to be set is calculated from the formula given below:

VR1 = R1[(Vout/1.275) - 1] ohm

If R1=1K, Vout = 5V, VR1 should be set to 2.9K ohm.

If R1=1K, Vout = 20V, VR1 should be set to 14.7K ohm

Datasheet semiconductor component download. (PDF Format)

1. LM2941CT

Electronic Timer Switch.

This electronic timer switch project is a good project to build to simulate the presence of occupants in a house. In these days when security is becoming more of a concern when no one is at home, having this device will deter the thief from breaking in. When power up, after 60 minutes, the relay will turn ON for 100 secs, OFF for the next 100 secs, and ON again for 100 secs before OFF again for the next 60 mins. This sequence will be repeated. A device such as a lamp that is connected to the relay will turn ON and OFF according to this timing.

Schematic Diagram

The schematic of the project is as shown below.

Download this schematic diagram.

Parts List

Download datasheet semiconductor component. (PDF Format)

1. CD4060B
2. IN4148
3. IN4003
4. 2SC2002

Sunday, March 22, 2009

Vox Amplifier model AC100 Schematic Diagram

Vox Amplifier model AC100 circuit diagram

Download this schematic diagram.

For detail this circuit, visit schematics.ca

Sunday, March 15, 2009

Resistor color code

The calculator above will display the value, the tolerance and performs a simple check to verify if the calculated resistance matches one of the EIA standard values. Select the first 3 or 4 bands for 20%, 10% or 5% resistors and all 5 bands for precision (2% or less), 5-band resistors. Hover above the tolerance for min. and max. range values.

If you want to find out the color bands for a value, use the tool on the left. Enter the value, select the multiplier (Ω, K or M), the desired precision and hit 'Display resistor' or ENTER. You can also type in resistor values in shorthand notation like 1k5, 4M7 or 100R.

Resistor color code chart
Standard EIA Decade Resistor Values:

E6 series: (20% tolerance)
10, 15, 22, 33, 47, 68

E12 series: (10% tolerance)
10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82

E24 series: (5% tolerance)
10, 11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68, 75, 82, 91

E48 series: (2% tolerance)
100, 105, 110, 115, 121, 127, 133, 140, 147, 154, 162, 169, 178, 187, 196, 205, 215, 226, 237, 249, 261, 274, 287, 301, 316, 332, 348, 365, 383, 402, 422, 442, 464, 487, 511, 536, 562, 590, 619, 649, 681, 715, 750, 787, 825, 866, 909, 953

E96 series: (1% tolerance)
100, 102, 105, 107, 110, 113, 115, 118, 121, 124, 127, 130, 133, 137, 140, 143, 147, 150, 154, 158, 162, 165, 169, 174, 178, 182, 187, 191, 196, 200, 205, 210, 215, 221, 226, 232, 237, 243, 249, 255, 261, 267, 274, 280, 287, 294, 301, 309, 316, 324, 332, 340, 348, 357, 365, 374, 383, 392, 402, 412, 422, 432, 442, 453, 464, 475, 487, 491, 511, 523, 536, 549, 562, 576, 590, 604, 619, 634, 649, 665, 681, 698, 715, 732, 750, 768, 787, 806, 825, 845, 866, 887, 909, 931, 959, 976

E192 series: (0.5, 0.25, 0.1 and 0.05% tolerance)
100, 101, 102, 104, 105, 106, 107, 109, 110, 111, 113, 114, 115, 117, 118, 120, 121, 123, 124, 126, 127, 129, 130, 132, 133, 135, 137, 138, 140, 142, 143, 145, 147, 149, 150, 152, 154, 156, 158, 160, 162, 164, 165, 167, 169, 172, 174, 176, 178, 180, 182, 184, 187, 189, 191, 193, 196, 198, 200, 203, 205, 208, 210, 213, 215, 218, 221, 223, 226, 229, 232, 234, 237, 240, 243, 246, 249, 252, 255, 258, 261, 264, 267, 271, 274, 277, 280, 284, 287, 291, 294, 298, 301, 305, 309, 312, 316, 320, 324, 328, 332, 336, 340, 344, 348, 352, 357, 361, 365, 370, 374, 379, 383, 388, 392, 397, 402, 407, 412, 417, 422, 427, 432, 437, 442, 448, 453, 459, 464, 470, 475, 481, 487, 493, 499, 505, 511, 517, 523, 530, 536, 542, 549, 556, 562, 569, 576, 583, 590, 597, 604, 612, 619, 626, 634, 642, 649, 657, 665, 673, 681, 690, 698, 706, 715, 723, 732, 741, 750, 759, 768, 777, 787, 796, 806, 816, 825, 835, 845, 856, 866, 876, 887, 898, 909, 920, 931, 942, 953, 965, 976, 988


Saturday, March 14, 2009

Infrared Modulation Identifier

This is the schematic of Infrared Modulation Identifier Via Remote Control.

Download this schematic diagram.

Download datashet semiconductor component. (PDF Format)

1. BC549C

The circuit illustrates how the modulated carrier of infrared is measured by displaying the waveform on a frequency counter after the signal received is amplified.

Current Expanded Regulated Power Supply

Actually, this is ordinary regulated power supply, but the current expander using a transistor make this power supply become powerful.

Based on the datasheet, the stabilizer IC’s can deliver up to 1A output current. For example 78xx series regulators are available in different voltage ratings, but in any case the current should not exceed 1A.

The transistor Q1 (2N 29055) used here has 5A current capacity. The resistor R1 is used to keep the current through regulator IC below 300mA. When the current through R1 increases the base current of Q1 (2N 29055) also increases & the load required load current flows through this transistor. By this way a current greater than the capacity of the regulator IC can be delivered to the load. The C1 is used to filter the ripples off the rectifier output.

Download this schematic diagram.


  1. Assemble the circuit on good quality PCB.
  2. T1 can be a 230V primary,15V/1A secondary, step down transformer.
  3. If 1 A bridge is not available, make one using four 1N 4007 diodes.
  4. The series regulator IC should be selected according to the desired output voltage.
  • IC 7805 for 05V
  • IC 7806 for 06V
  • IC 7809 for 09V
  • IC 7812 for 12V
Semiconductor datasheet download. (PDF Format)

1. LM78XX
2. 2N2955

Friday, March 13, 2009

Digital Volume Controller

If you need digital volume control, then this circuit will great for you. Just press the button and you will be able to increase and decrease the volume level. This circuit is for 1 kanal only. For stereo audio, you need to build 2 similiar circuit and use push button switch which have double input and double output.

Download this schematic diagram.

Datasheet semiconductor download. (PDF Format)

1. DS1669

Loudspeaker System Crossover Network

Building a crossover for your speaker system is easy. Here the schematic diagram:


  • Capacitor must be non-polar capacitor types with a voltage rating of 50 volt or more (preferably 100 volt).
  • Capacitor may be paralled to achieve specified values.
  • Inductors should be air core. Do not mount inductors in top of each other.
  • Resistors should be 100 Watts or more.

Download the schematic diagram in PDF format

800W Audio Amplifier with MOSFET

Here the schematic diagram of 800 watt audio amplifier with MOSFET.

This amplifier can be used for practically any application that requires high power, low noise, distortion and excellent sound. Examples would be Sub-woofer amp, FOH stage amplifier, One channel of a very high-powered surround sound amplifier etc.

For detail explanation about how this circuit works include the large schematic diagram, power supply schematic diagram and complete component listing, download this complete article


Power Supply 1.3 - 32 V / 5A with Short Circuit Protection

This is a very easy to build power supply that is based on LM338 5A adjustable voltage regulator. I am using the supply for a long time, have no problem yet. Only current adjust is missing but I overcome this situation by using an LCD panel ampermeter. There is no PCB for the circuit. I took a 3x16 copper plate and strip the unused areas by a knife. If you want you can use analog meters instead of LCD panels.

Download this schematic diagram.

Download datasheet semiconductor component. (PDF Format)

1. LM338

2. IN4002


  1. Use thick wires for connections.
  2. When connecting the LM338 to the heatsink use thermal paste.
  3. Use external supplies for LCD panels. They can be 9V batteries. The panels I use draws 1mA current and the batteries last sufficiently long time. If you have small transformers which can supply regulated 9V, you can use them. You need separate transformers for each panel!
  4. The transformer should be 100 Watt but if you don't need high current you can try transformers that you already have. (I can draw 6A from 100Watt transformer.)
  5. If you have multi winding transformer you can use the diode connections shown in schematic. Diodes must be 10-15 A.
  6. Be careful while connecting LM338. Don't put it inverse.
  7. Output of your transformer mustn't exceed 25V AC...

60 Watt Amplifier using TDA2052

This is HiFi audio amplifier system. This amplifier is AB class amplifier and has very low distortion that's why this amplifier can be used for HiFi audio system. TDA2052 has mute and st-by functions so it can be controlled by external digital circuits. Very high temperature and output short circuit protections are included. You should use a heatsink to dissipate the excess heat.

Download this schematic diagram.

Download datasheet semiconductor component. (PDF Format)

1. TDA2052

Functions of the Components:

  1. R1 - Input Impedance
  2. R2,R3 - Gain (32dB)
  3. R4 - Input Impedance in Mute Mode
  4. R5 - Standby Transition Time
  5. R8 - Output Frequency Balancing
  6. R9,R10 - Discharge Resistors
  7. C1 - Input Coupling Capacitor
  8. C3 - Feedback Coupling Capacitor
  9. C4 - Standby Transition Time
  10. C5 - Output Frequency Balancing
  11. C6,C7 - Supply Stabilizing Capacitors
  12. C9,C10 - Supply Filter Capacitors

Component List:

Component Value
R1,R2,R4,R5 11k ¼ W 4
560, ¼ W 1
7.5 K, ¼ W 1
1 K, ¼ W 1
4.7 , ¼ W 1
1.2 K, ¼ W 2
2 uF/25 V 1
C3,C4 10 uF/25 V 2
100 nF 3
1000 uF/40 V 1
TDA2052 1

10 Band Graphic Equalizer

Download this schematic diagram.

This is 10 band graphic equalizer for one channel (mono) audio system. You need build 2 similiar circuits for 2 channel (stereo) audio system.

This equalizer build based on TL074 low noise JFET op-amp which will give you high quality audio output.

Thursday, March 12, 2009

Transistorized Inverter 60W 12V DC to 230V AC

Download this schematic.

Download datasheet semiconductor component. (PDF Format)

1. BC548
2. BD140
3. 2N6107
4. 2N3055

This is low cost fully transistorised inverter circuit capable of driving medium loads of the order of 40 to 60 watts using battery of 12V, 15 Ah or higher capacity.

Transistors T1 and T2 (BC548) form a 50Hz multivibrator. For obtaining correct frequency, the values of resistors R3 and R4 may have to be changed after testing. The complementary outputs from collectors of transistors T1 and T2 are given to PNP darlington driver stages formed by transistor pairs T3-T4 and T6-T7 (utilising transistors BD140 and 2N6107). The outputs from the drivers are fed to transistors T5 and T8 (2N3055) connected for push-pull operation.

Somewhat higher wattage can be achieved by increasing the drive to 2N3055 transistors (by lowering the value of resistors R7 and R8 while increasing their wattage). Suitable heatsinks may be used for the output stage transistors. Transformer X1 is a 230V primary to 9V-0-9V, 10A secondary used in reverse.

Inverter 100W, 12V DC to 220V AC

Here is 100 Watt Inverter 12V DC to 220V AC schematic diagram.

Download this schematic diagram.

Download datasheet semiconductor component. (PDF Format)

1. CD4047
2. TIP122
3. 2N3055

Low Impedance Microphone Amplifier

You can download the schematic, pcb layout and component list from here

Download this schematic diagram.

This circuit is a microphone amplifier for use with low impedance (~200 ohm) microphones.
It will work with stabilized voltages between 6-30VDC. If you don’t build the impedance adapter part with T1, you get a mic-amp for higher impedance microphones. In this case, you should directly connect the signal to C7.

Component list:

C1= 3k9
U1= TL081
R2= 150k
C2= 100u
D1= 1N4148
R3= 2k2
C3= 22u
R4= 820
C4= 4u7

R6= 10k
C5= 470u

R7= 10k
C6= 10u

P1= 1M
C7= 100n


2000W Stereo Audio Power Amplifier

Click here for download this schematic diagram.

Download datasheet semiconductor component. (PDF Format)

1. BF245A

2. BF256C

3. BC639

4. BC640

5. BC550

6. BC560

7. BD711

8. BD712

9. BF871

10. BF872

11. BD139

12. BD140

13. MJE340

14. MJE350

15. 2SC5171

16. 2SA1930

17. 2SA1987

18. 2SC5359

This is linear amplifier which need advance knowledge in electronics since the schematic diagram is very complex for hand made circuit.

Download the zipped schematic here

DipTrace Free 1.30

Design & Photo 3D Modeling & CAD
Type: Freeware
Cost: $0.00 US
Size: 22813 K



DipT race is an advanced PCB design software application that consists of 4 modules: PCB Layout with efficient auto-router, Schematic Capture, Component and Pattern Editors that allow you to design your own component libraries. Besides being very easy-to-use, which is rare for a PCB design tool, this software possesses a very intuitive user interface and many innovative features. Output formats are DXF, Gerber, N/C Drill and G-code.

Wednesday, March 11, 2009

60W Power Audio Amplifier with 2N3055

Download this schematic diagram.

Download darasheet semiconductor component. (PDF Format)

1. 2N3055
2. BC286
3. BC287
4. BC187
5. BC717

This is a class B amplifier, this means, that a current must flow through the end transistors, even if there is no signal on the input. This current can be regulated with the 500Ω trimmer resistor. As this current incrases, the sound of the amplifier gets better, but the end transistors are more heating. But if this current decrases, the transistors are not heating so much, but the sound gets worse.

TV Transmitter.

Download this schematic diagram.

Semiconductor datasheet component download.

1. BC547


A VHF band TV transmitter using negative sound modulation and PAL video modulation. This is suitable for countries using TV systems B and G.

The frequency of the transmitter lies within VHF and VLF range on the TV channel, however this circuit has not been tested at UHF frequencies. The modulated sound signal contains 5.5 -6MHz by tuning C5. Sound modulation is FM and is compatible with UK System I sound. The transmitter however is working at VHF frequencies between 54 and 216MHz and therefore compatible only with countries using Pal System B and Pal System G.

13 Volt 20 Amp PSU

Download this schematic diagram.

Download datasheet semiconductor component. (PDF Format)

1. BC557
2. BD330
3. 2N5683
4. BC547
5. BUZ11


This PSU has been especially designed for current-hungry ham radio transceivers. It delivers safely around 20Amps at 13.8V. For lower currents, a separate current limiting output, capable of 15ma up to a total of 20A has been added.

The power transformer should be capable to deliver at least 25A at 17.5 to 20V. The lower the voltage, the lower power dissipation.

The rectified current will be “ironed” by the C1, whose capacity should not be less than 40.000uF, (a golden rule of around 2000uF/A), but we recommend 50.000uF. This capacity can be built up by several smaller capacitors in parallel.

The base of this design is a simple 12V regulator (7812). The output voltage can be brought to desired value (here 13.8V) by two external resistors (R5 and R6) using this formula:

U= 12(1+R5/R6)

The low currents (here 15mA) will keep the 7812 in its regular function. As soon as the current rises over 15ma, the voltage drop on R4 will “open” the Q3, actually handling the high output current. This is a PNP transistor (Ic>25) and current amplification factor of at least 20. The one that has been tested and proven here is the 2N5683.

The current limiting resistance RL, for the maximum output of 20 Amps should be 0.03 Ohms, rated at least 15W. You can use the resistance wire or switch several resistors in parallel, totaling the resistance/power values. Values for other currents can be calculated by the rule:


The RL and Q2 (3A PNP such as BD330) form a short circuit “automatic fuse”. As soon as the maximum current reaches 20Amps, the voltage drop over the resistor RL will open Q2, and thus limit the B-E Current of Q3. Parallel to Q2 is Q1, which lights the LED 1 whenever the current limiting circuit is active. When the “fuse” is active, the Q2 bridges the R3, so the full current would flow through the IC1, and damage it. Therefore the R4 is inserted, as to limit the IC1 current to 15mA. This makes it possible to run the IC1 without any cooling aid.

The LED 2 will light up every time the PSU is switched on.

There is an adjustable current limiter in parallel to the fixed output, thus providing adjustable current source for smaller currents.

This circuit is very simple too. You will notice that there is no current sensing resistor. But it is really there, in a form of the Rds-on resistance of the N-channel FET, which actually handles the load cutoff from the source. The function of the FET is shown in the diagram 2. When the current Id is rising, the tension Uds over the resistance Rds rises very slowly in the beginning, but very fast after the knick.

This means, that before the knick the FET behaves as a resistor but after it, works as constant current source.

The D2, R3 and B-E connection of the Q4 will sense the Uds voltage of the FET1. When the voltage rises enough, the Q4 will shortcut the FET1 gate to mass, and cut the current flow through the FET 1 off.

However, to enable the FET1 to open, there is certain gate voltage necessary, which in this case is brought up by the voltage divider consisting of R8, Z1, P1 and R9. So the maximum Gate voltage will be the one of the Z1, and the minimal will be around 3V6.

The Z1 voltage (Uz1) will thus determine the max current flowing through the FET 1.

The diagram 2 will show that for 5 Amps the Uz1 should be 5V6, and for 20Amps around 9V6.

The Capacitor C4 will determine the “velocity” or the reaction time of the limiter. 100 uF will make the reaction time to be around 100ms, and 1n will make it 1us.

Within the designed limits, the P1 will limit the current output in the range of 15mA to 20A.

You can use both output simultaneously, but the total output current will be limited by the value of the RL. This PSU can be built also for higher outputs, as long as the transformer will handle the current requirements, and you provide sufficient cooling for the Q3.

AM Transmitter

Download this schematic diagram.

Datasheet semiconductor component. (PDF Format)

1. BC109C

This ircuit is deliberately limited in power output but will provide amplitude modulation (AM) of voice over the medium wave band.
The circuit is in two halfs, an audio amplifier and an RF oscillator. The oscillator is built around Q1 and associated components. The tank circuit L1 and VC1 is tunable from about 500kHz to 1600KHz. These components can be used from an old MW radio, if available. Q1 needs regenerative feedback to oscillate and this is achieved by connecting the base and collector of Q1 to opposite ends of the tank circuit. The 1nF capacitor C7, couples signals from the base to the top of L1, and C2, 100pF ensures that the oscillation is passed from collector, to the emitter, and via the internal base emitter resistance of the transistor, back to the base again. Resistor R2 has an important role in this circuit. It ensures that the oscillation will not be shunted to ground via the very low internal emitter resistance, re of Q1, and also increases the input impedance so that the modulation signal will not be shunted. Oscillation frequency is adjusted with VC1.

Q2 is wired as a common emitter amplifier, C5 decoupling the emitter resistor and realising full gain of this stage. The microphone is an electret condenser mic and the amount of AM modulation is adjusted with the 4.7k preset resistor P1. An antenna is not needed, but 30cm of wire may be used at the collector to increase transmitter range.

Tuesday, March 10, 2009

35W RMS x 3-Channel Power Amplifier System.

Design Objectives This design is intended to drive the rear (stereo) and center channel speakers for surround-sound applications. This project combined with the 60W+60W power amplifier, which will drive the main stereo (front) speakers, gives a full 5 channel surround sound systems (Total power = 225W RMS). The power supply circuitry, PCB size and dimension should be designed to match nicely with the 60W+60W power amplifier so that later they may be nicely cased togather.

System Operation & Description The LM4781 3-channel audio power amplifier are configured as non-inverting amplifier which has a gain of 20V/V per channel, which is high enough to maintain stability and not too high until increasing the noise and THD+N performance. The inputs are taken from the RCA jacks which then feed to three high quality 1uF metallized polyester capacifor with 63V rating. The outputs are wired to the speaker terminals directly.

The schematic diagram is taken straight out from the National Semiconductor's referance PCB design schematic. However I have omitted the muting switch and replaced it with the soft start circuit, as explaned in the LM4781 datasheet. I have also added the L//R network (L=0.7uH, R=10 ohms 2W) at all the outputs.

For detail all discription, click here.

Thursday, March 5, 2009

Radio waves.

Radio waves were first predicted by mathematical work done in 1865 by James Clerk Maxwell. Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. He then proposed equations that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887, Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed, making practical the use of radio waves to transfer information through space.

Nikola Tesla and Guglielmo Marconi are credited with inventing systems to allow radio waves to be used for communication. for details, click here or visit on wikipedia website

source: wikipedia

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300W Subwoofer Power Amplifier

There are some important updates to this project, as shown below. Recent testing has shown that with the new ON Semi transistors it is possible to obtain a lot more power than previously. The original design was very conservative, and was initially intended to use 2SA1492 and 2SC3856 transistors (rated at 130W) - with 200W (or 230W) devices, some of the original comments and warnings have been amended to suit.

Download this schematic diagram.

Datasheet semiconductor component. (PDF Format)

1. MPSA42
2. MJE15032
3. MJE15033
4. MJL4302A
5. MJL4281A
6. IN4004

170W Audio Power Amplifier

The combination of the LM4651 driver IC and the LM4652 power MOSFET Class D power amplifier IC provides a high efficiency amplifier solution, suitable for self-powered speakers, subwoofers and quality car boosters.

Download this schematic diagram.

Download datasheet semiconductor component. (PDF Format)

1. LM4651
2. LM4652