circuit harness wiring

Showing posts with label circuit. Show all posts

Showing posts with label circuit. Show all posts

Thursday, January 9, 2014

100Khz Multiple Output Switching Power Supply Circuit Diagram

The 100Khz Multiple Output Switching Power Supply Circuit Diagram uses two VN4000A 400-V MOSPOWER FETs in a half-bridge power switch configuration. Outputs available are + 5 Vat 20 A and Â±15 V (or Â±12 V) at 1 A. Since linear three-terminal regulators are used for the low-current outputs, either Â±12 V or Â±15 V can be made available with a simple change in the transformer secondary windings.

A TU94 switching regulator IC proVides pulse-width modulation control and drive signals for the power supply. The upper MOSPOWER FET, Q7. in the power switch stage is driven by a simple transformer drive circuit. The lower MOS. Q6, since it is ground referenced. is directly driven from the control !C.

100Khz Multiple Output Switching Power Supply Circuit Diagram

100Khz Multiple Output Switching Power Supply Circuit Diagram

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Friday, December 27, 2013

Build a 5v And 12V Ac Powered Switching Supply Circuit Diagram

How to Build a 5v And 12V Ac Powered Switching Supply Circuit Diagram? This supply uses an SGS-Thomson UC3842 IC in an off-line flyback regulator, providing + 5 V at 4 A and Â± 12 V at 300 mA. This enables a small high-frequency (50 kHz) transformer, to handle large amounts of power that are normally handled by a 60-Hz transformer.

Q1 is a 5-A 500-V MOSFET, and the diodes are fast-recovery types. T1 has a 45-turn primary winding of #26 wire. The 12-V windings are each 9 turns of #30 wire, bifilar wound. The 5-V winding is 4 turns of four bifilar #26 wires. The control (feedback) winding is two bifilar, parallel 10-turn, #30 windings. The core is Ferroxcube EC35-3C8 with a 3/s` center leg.

5v And 12V Ac Powered Switching Supply Circuit Diagram

5v And 12V Ac Powered Switching Supply Circuit Diagram

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Thursday, December 26, 2013

Simple Micro volt probe Circuit Diagram

The current tracer helps locate a defective IC that is loading down the power supply. The tracer amplifies the small voltage drop caused by current flow along a fraction of an inch of PC wiring and drives an ordinary microammeter. Needle-point test probes are used to contatt the edge of a PC trace and to follow the current to determine which branch the current takes.

One-half of a dual 741 op amp forms a dc amplifier with ac feedback to prevent oscillations and hum-pickup problems.It drives a 50-to-100 Âµ meter. The other op amp provides a center tap for the 9 V battery supply and zero adjustment with R4. Two diodes protect the meter. Resistor Rl eliminates the necessity for shorting the probes when the meter is zeroed. The value of 1 ohm is large when compared with the resistance of the meter leads plus the bridged portion of PC wiring.

Micro-volt probe Circuit Diagram

Micro-volt probe Circuit Diagram

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Tuesday, December 24, 2013

Build a High voltage Bucking Regulator Circuit Diagram

This High voltage Bucking Regulator Circuit Diagram is basically tbe classic bucking regulator, except it uses a TMOS N-channel power FET for the chopper and creates its own supply for the gate control. Tht unique aspect of this circuit is how it generates a separate supply for the gate circuit, which must be greater than Vvv.

When power is applied, C2 charges, through D2, to +12 V. At this time, Q1 is off and the voltage at point A is just below zero. When the pulse-modulated signal is applied, the optoisolator transistors, Q2 and Q3, supply a signal to Q1 that turns it on. The voltage at point A then goes to Vvn. C2 back-biases D2, and the voltage at point B becomes 12 V above VnnÂ· After Q1 is turned on, current starts to flow through L1 into C1, increasing until Q1 turns off.

High voltage Bucking Regulator Circuit Diagram

High voltage Bucking Regulator Circuit Diagram

The current still wants to flow through Ll, so the voltage at point A moves toward negative infinity, but is clamped by D1 to just below zero. Current flows less and less into C1, until Q1 turns on again. Q2 and Q3 drive Q1 `s gate between the voltages at point A and B, which is always a12 V swing, so Vcs max. is never exceeded. For proper operation, the 12-V supply has to be established before the pulse-width modulator signal is applied.

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Saturday, December 21, 2013

Build a High Voltage Dc Generator Circuit Diagram

High Voltage Dc Generator Circuit Diagram. In the miniature high-voltage dc generator, the input to the circuit, taken from a 12-Vdc power supply, is magnified to provide a 10,000-Vdc output causing a pulsating signal, of opposite polarity, to be induced in Tl`s secondary winding.

The pulsating dc output at the secondary winding of Tl (ranging from 800 to 1000 V) is applied to a 10-stage voltage-multiplier circuit, which consists of D1 through D10, and C3 through C12. The multiplier circuit increased the voltage 10 times, producing an output of up to 10,000 Vdc. The multiplier accomplishes its task by charging the capacitors (C3 tlirough C12); the output is a series addition of the voltages on all the capacitors in the multiplier. In order for the circuit to operate efficiently, the frequency of the square wave, and therefore the signal applied to the multiplier, must be considered.

The output frequency of the oscillator (Ul-a) is set by the combined values of Kv Rr>, and C{ (which with the values specified is approximately 15 kHz). Potentiometer R5 is used to fine tune the output frequency of the oscillator. The higher the frequency of the oscillator, the lower the capacitivc reactance in the multiplier. Light-emitting diode LED1 serves as an input-power indicator, and neon lamp NE1 indicates an output at the secondary of Tl. A good way to get the maximum output at the multiplier is to connect an oscilloscope to the high-voltage output of the multiplier, via a high-voltage probe, and adjust potentiometer R5 for the maximum voltage output.

High Voltage Dc Generator Circuit Diagram

High Voltage Dc Generator Circuit Diagram

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Sunday, October 6, 2013

Amplifier Timer Circuit Diagram

Turns-off your amplifier when idle for 15 minutes, Fed by amplifier tape-output

This circuit turns-off an amplifier or any other device when a low level audio signal fed to its input is absent for 15 minutes at least. Pushing P1 the device is switched-on feeding any appliance connected to SK1. Input audio signal is boosted and squared by IC2A & IC2B and monitored by LED D4. When D4 illuminates, albeit for a very short peak, IC3 is reset and restarts its counting. Pin 2 of IC3 remains in the low state, the two transistors are on and the relay operates. When, after a 15 minutes delay, no signal appeared at the input, IC3 ends its counting and pin 2 goes high. Q1 & Q2 stop conducting and the relay switches-off. The device is thus completely off as also are the appliances connected to SK1. C5 & R9 reset IC3 at power-on. P2 allows switch-off at any moment.

Parts:

R1,R8___________1K 1/4W Resistors
R2,R3___________4K7 1/4W Resistors
R4_____________22K 1/4W Resistor
R5______________4M7 1/4W Resistor
R6,R9__________10K 1/4W Resistors
R7______________1M5 1/4W Resistor
R10___________100K 1/4W Resistor
R11____________15K 1/4W Resistor
R12____________10M 1/4W Resistor
R13_____________1M 1/4W Resistor
R14_____________8K2 1/4W Resistor
R15_____________1K8 1/4W Resistor
C1____________470µF 25V Electrolytic Capacitor
C2,C3,C6______100nF 63V Polyester Capacitors
C4,C5__________10µF 25V Electrolytic Capacitors
D1_____Diode bridge 100V 1A
D2,D7________1N4002 100V 1A Diodes
D3__________Red LED 5mm.
D4_______Yellow LED 5mm.
D5,D6________1N4148 75V 150mA Diodes
IC1___________78L12 12V 100mA Voltage regulator IC
IC2___________LM358 Low Power Dual Op-amp
IC3____________4060 14 stage ripple counter and oscillator IC
Q1____________BC557 45V 100mA PNP Transistor
Q2____________BC337 45V 800mA NPN Transistor
J1______________RCA audio input socket
P1_____________SPST Mains suited Pushbutton
P2_____________SPST Pushbutton
T1_____________220V Primary, 12V Secondary 3VA Mains transformer
RL1___________10.5V 270 Ohm Relay with SPST 5A 220V switch
PL1____________Male Mains plug
SK1__________Female Mains socket

Notes:

Simply connect left or right channel tape output of your amplifier to J1.
You can employ two RCA input sockets wired in parallel to allow pick-up audio signals from both stereo channels.
The delay time can be varied changing R13 and/or C6 values.
Needing to operate a device not supplied by power mains, use a double pole relay switch, connecting the second pole switch in series to the device supply.

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Saturday, October 5, 2013

Logic Probe With Sound Circuit

This logic probe can be selected to operate on TTL or CMOS logic levels, depending on switch S1. A string of resistors associated with switch S1 sets the threshold levels for a window comparator comprising IC1a and IC1b. Depending on whether the level applied to the probe is high or low, the window comparator turns on LED1 (high) or LED2 (low). The 1.2M and 680k resistors set the probe signal to a midrange value when the probe is open-circuit, thereby preventing either LED from being lit.

Circuit diagram:

Logic Probe With Sound Circuit digram

If a pulse signal is present, the output of IC1a will toggle the clock input of flipflop IC2a. This drives LED3 which either lights for each pulse or continuously, depending on the setting of switch S2. Finally, the outputs of IC1a & IC1b are connected by diodes D5 & D6 to the base of transistor Q1 which is connected to the Reset input of flipflop IC2b. This has a piezo sounder (not buzzer) connected between its Q and Q-bar outputs so that it produces a sound which echoes the input pulse signal.

Author: Tom Hughes Copyright: Silicon Chip Electronics

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Friday, October 4, 2013

Aviation Intercom Circuit

Before its move offshore, I was lucky enough to be involved in developing the avionics system for the Flightship Ground Effect FS8 craft (see www.pacificseaflight.com/craft.shtml). Although officially classed as a boat, it has wings and can travel at 180km/h some three metres above the water. The communications system was adapted from an aircraft unit and was a particular problem. It was expected to allow speech between the two pilots and radio, as well as receive audible warnings from the onboard computers and feed sound to the onboard data logger. Initially, the system was very noisy due to ground loops and incompatibility problems.

A circuit similar to that shown here was the solution. Although optimised to suit Softcom brand headphones with active noise reduction, it should be suitable for most aviation sets. The plugs indicated are standard aviation types but are insulated from the instrument panel to eliminate earth loops. The inputs from the two pilots microphones are summed and amplified by transistors Q1 & Q2. When one pilot presses his or her transmit key (mounted on the yoke), the transmit relay (RLY1) closes, muting the other pilot’s microphone via the optocoupler (OPTO1).

Circuit diagram:

Aviation Intercom Circuit Diagram

The outputs from the microphone preamp, computer audio transformer (T1) and radio speaker transformer (T2) are summed via 10kΩ resistors and applied to the input of IC1, an LM386 audio amplifier. Note that transformers are used here to avoid creating additional earth loops. The output of the LM386 drives the pilots’ headphones via transformers T3 & T4, which are needed for impedance matching. Each audio source has its own level control (VR1, VR3 & VR4). The main volume control (VR5) is included to allow for ambient noise level. VR2 is used to set the signal level for the data logger.

Author: Gary Smith Copyright: Silicon Chip Electronics

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Monday, September 30, 2013

Bass Booster Circuit

Increase the bass output of your present instrument at modest cost!

Bass Boost is todays sound... whether its the driving, gut-vibration pulsation of disco, or the solid bass line of soft, hard, or laid-back rock. One way to get the modern bass-boost sound without running out and buying an all-new expensive piece of equipment is to use a Bass Booster between your guitar, electronic organ or what-have-you, and the instrument amplifier. A bass booster strips the highs from the instruments output signal and amplifies low frequencies, feeding on "all-bass" sound to the instrument amplifier. Naturally, the bigger the speaker used with the amp, the more powerful the bass: use 15-inchers with the Bass Booster and you can rattle the windows. Bass Booster is powered by an ordinary 9 volt transistor radio battery. It can be assembled on a small printed board or on a veroboard using point to point wiring. The booster connects between your instrument and its amplifier through two standard RCA Jacks.

Circuit Diagram:

Bass Booster Circuit Diagram

Parts:

P1 = 50K
P2 = 100K
R1 = 22K
R2 = 470K
R3 = 47K
R4 = 10K
R5 = 470R
R6 = 1K
Q1 = 2N2222
C1 = 2.2uF-25v
C2 = 100nF-63v
C31 = 00nF-63V
C4 = 3.3uF-25v
C5 = 470uF-25v
D1 = 5mm. Red Led
Q1 = 2N2222
B1 = 9v Battery
J1 = RCA Audio Input Socket
J2 = RCA Audio Output Socket
S1 = On-Off Switch

Using Bass Booster:

Connect your electronic guitar or other electronic instrument to input jack J1; Connect output jack J2 to your instruments amplifiers normally-used input. With power switch S1 off, key S2 so the instrument feeds directly to the instrument amplifier. With P2 set full counter-clockwise (Off), turn power switch S1 on, key S2 once, and advance P2 for the desired Bass Boost level. To cut back to natural sound just stomp down on S2 and key the Bass Booster out. Dont worry about leaving power switch S1 on for several hours of a gig. The circuit pulls less than 1mA from the battery, so battery will last many, many months.

source :www.extremecircuits.net

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Wednesday, September 4, 2013

Electronic Security Door Key Circuit

Circuit Diagram

Description

A different circuit of electronic lock very simple, one and does not need a lot of materials in order to it is manufactured. The right keys of code should be stepped with the right line, so that is activated the optocupler IC2. If from error is stepped switch that does not belong in the combination, then the lock is trapped. In order to we restore the regular operation of lock, it should we press switches S1 or S12. Switch S1 makes Reset of lock externally and the S12 internally, the door. The Code the circuit as he is connected it is 147 and it can change, very easily, changing the connections in the switches of keyboard. The optocupler IC2, can drive any exterior circuit as Relay etc, ensuring simultaneously electric isolation the two circuits. The circuit can be also supplied from a battery 9V..

Part List

R1-7-9=1Kohm
R2-3-4-5=100Kohm
R6 =10Kohm
R9 =47Kohm
IC1 = 4066
IC2 =4N25
Q1-2=BC550
S1...11=Push button sw or keyboard
S12=Push button normal closed
All resistors is 1/4W 5%

Source Sam Electronic Circuits

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Sunday, September 1, 2013

24 Second Shot Clock Circuit

Description:
This is a circuit intended to be used in basketball shot clock
Circuit Diagram

Notes:
To start in 24 seconds; 24s LOAD SW and Reset SW should be push simultaneously. If not, the count will start in 99. Pulse input can be connected to 555 astable multivibrator but must be calibrated for real time clock. The PAUSE SW must have a Switch Debouncer so that the counter will count normal when counting is paused and then turn-on.
When the count reach 00, the NOR gate will have an output of logic1 that will turn on the two transistor. The buzzer will rung and light will turn on. The two transistors are continuously turn-on not until LOAD SW and Reset SW is push. All have a +5v power supply.

Author: Milardo de Guzman
E-mail: milardo_dg@yahoo.com
Source: http://www.zen22142.zen.co.uk

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Wednesday, August 14, 2013

Build a Low pass filter Circuit Diagram

This Low-pass filter Circuit Diagram is useful where fast signal acquisition and high precision are required, as in electronic scales. The filters time constant is set by the 2 ohm resistor and the 1 Âµ capacitor until comparator No. 1 switches. The time constant is then set by the 1.5 ohm resistor and the 1 jtF capacitor. Comparator No. 2 provides a quick reset. The circuit settles to a final value three times as fast as a simple 1.5 ohmâ€”1 ÂµÂ¥ filter, with almost no dc error.

Low-pass filter Circuit Diagram

Low-pass filter Circuit Diagram

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Sunday, August 11, 2013

Input Impedance Booster Circuit

The input resistance of a.c.-coupled op amp circuits depends almost entirely on the resistance with which the d.c. setting is determined. If CMOS op amps are used, the input resistance is normally high, currently up to 10 MΩ. If a higher value is needed, a bootstrap circuit may be used. This enables the input resistance to be boosted artificially to a very high value, indeed In the circuit shown in the diagram, resistor R1 sets the d.c. point for IC1a. The terminal of the resistor linked to pin 7 of IC1 would normally be at earth potential, so that the input impedance would be 10 MΩ. Connecting the other terminal of the resistor to earth via IC1a and network C2-R3-R2 as far as d.c. is concerned results in the requisite d.c. setting of the op amp.

Circuit diagram:

Input Impedance Booster II Circuit Diagram

As far as alternating voltages are concerned, the input signal is fed back so that only a tiny alternating current flows through R1. Therefore, Rin=R1[(R2+R3)/R3]. With resistor values as specified, Rin is about 1 GΩ. One aspect must be borne in mind: the numerical value of (R2+R3)/R3 must not exceed 0.99. This means that the value of R3 cannot be less than 100 kΩ if the value of R2 is 10 MΩ. If these conditions are not met, the circuit will become unstable.

http://www.ecircuitslab.com

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Thursday, August 8, 2013

USB Battery Charger Circuit Rise

In recent years, the use of USB or Universal Serial Bus as a reliable communications interface in plenty of electronic devices have increased due to its increased speed, size and flexibility. It fundamentally consists of terminals VBUS(+5V supply), GROUND, D+ and D-. As plenty of of the devices run on rechargeable battery, it is now the trend to design the charging circuit that makes use of the power supply from the USB port to charge the rechargeable battery. This feature will make the devices more convenient to the users as the devices will get their power from the bus and requires no outside plug or cables.

USB Bus Powered Functions

Theres fundamentally three classes of USB functions on power that can be derived from the port.

High-Power Bus The high power bus powered functions derived all its power from the VBUS and cannt draw over 100mA until its been configured. One time configured, it can draw up to five unit loads(500mA) by requesting it in its descriptor. At full load, it must be able to work between the VBUS voltage of four.75V and five.25V.

Low-Power Bus The low power bus powered functions derived all its power from the VBUS and must not draw over one unit load (100mA) according to the USB standard. It must even be able to work between the VBUS voltage of four.40V and five.25V.

Self-Power Self power functions can draw up to 100mA from the VBUS and the rest from its outside source. This is the most simplest to design.

USB Port Powered Battery Charger

This application circuit makes use of the MCP73853/MCP73855 linear charge management controllers for cost sensitive applications. They are specially designed for USB applications and adhere to all the USB specifications governing the USB power bus. The circuit below makes use of the MCP73855 to design a USB powered Lithium Ion/Lithium Polymer battery charger by deriving the power from the USB port.

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Wednesday, August 7, 2013

Protectors Circuit on SMPS power supply

The simplest example SMPS which still uses 3 transistors (C3807, A1015 and power transistors) classic problem that often occurs is: - Problem in the feedback circuit can cause the output voltage B + over so that it can endanger the aircraft as a whole. For example elco erupted, pcb burnt burnt by over-heated, horizontal transistor short.

- Problem on feedback circuits may cause power regulator transistor is damaged due to over current transistor (eg, due to the 47k resistor transistor circuit on the secondary error detector value is delayed).

- If the input ac voltage drops can cause the power regulator transistor is damaged, due to over current transistor If the secondary there is a power transistor short can cause damage over current regulator.

- Protectors are designed to make the SMPS SMPS "reliable will not be damaged" if there are things that go wrong as mentioned above.

Switching Mode Power Supply protect Circuit

SMPS Circuit

SMPS circuit using IC systems generally are designed with a surge protector, which include:

Over voltage protector (OVP)
Over current protector (OCP)
Over load protector
Short circuit protector
Over temperature protector

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Tuesday, August 6, 2013

170W AMPLIFIER BTL LM4651 LM4652 CIRCUIT DIAGRAM

170W AMPLIFIER BTLLM4651 & LM4652 CIRCUIT DIAGRAM

IC LM4651 is a integrated conventional pulse width modulator driver IC. The IC contains short circuit, under voltage, over modulation, and thermal shut down protection circuitry. The LM4651 also contains a standby function which shuts down the pulse width modulation minimizing supply current.

IC LM4652 is a fully integrated H-bridge power MOSFET IC in a TO-220 power package. The LM4652 has a temperature sensor built in to alert the LM4651 when the die temperature of the LM4652 exceeds the threshold. Together, these two ICs form a simple, compact high power audio amplifier solution complete with protection normally seen only in Class AB amplifiers. Few external components and minimal traces between the ICs keep the PCB area small and aids in EMI control.

Absolute Maximum Ratings LM4651 & LM4652

Supply Voltage ± 22V
Output Current (LM4652) 10A
Power Dissipation (LM4651) 1.5W
Power Dissipation (LM4652) 32W
ESD Susceptibility (LM4651) 2000V,
ESD Susceptibility LM4652 (pins 2,6,10,11) 500V
ESD Susceptibility (LM4651) (Note 5) 200V
ESD Susceptibility LM4652 (pins 2,6,10,11) 100V
Junction Temperature 150°C
Soldering Information N, TA and TF Package (10 seconds) 260°C
Storage Temperature -40°C to + 150°C

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Saturday, August 3, 2013

Door Handle Alarm Circuit Using Transistor

The automatic door handle alarm circuit gives a audible alarm and glows a LED when somebody touches the handle of the door. The circuit is latching type and continues to produce sound until it is switched off.

The transistor Q1 is wired as an astable multi vibrator whose output is used to bias transistor Q2 to conduction. As a result the transistor q3 and LED are in OFF state. When someone touches the handle, the capacitance of the human body damps the oscillations of Q1.The cuts the biasing of Q2 and it goes OFF.As a result the current flows to the base of Q3 , it conducts and LED glows. If the switch S1 is ON the transistor pairs Q4&Q4 which is wired in the latching mode is triggered and the Buzzer Z1 is activated. When the person removes his hand from door handle the LED goes OFF but the buzzer continues to beep. The only way to mute the buzzer is to open the switch S2. All capacitors must be rated 15V.

A 9V battery or 9V DC power supply can be used to power the circuit. To make L1 wind 25 turns of 0.4 mm enameled copper wire on resistor R2 and solder the ends of the wire to the resistor leads. This unit will stand for the R2 as well as L1 because both are parallel in the circuit. A readily available 10mH inductor can be used for L2. Connect the point A in the circuit to the door handle using a long wire.

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Thursday, August 1, 2013

Super Ni Cd Battery Charger 12 18V Circuit Diagram

A clever charger circuit that safely can charge any Ni-Cd battery. Offers charge current sellection, polarization detection and protection and the ability to connect many batterys in siries. Ni-Cd bateries can be recharged more than 1000 times before become useless. the charging current shoud be the 1/10 of the (Ah) of the battery. The bateries need 14 hours to be fully charged.Swhitch S2 is the current selection as folows: 50mA, 200mA and 400mA. LED D10 is the indicator for proper batery connection and/or wrong polarity checking. LED D9 is the charging indicator. The transformer is a 220V/2x12V 0.5A.

Super Ni-Cd Battery Charger 12-18V Circuit Diagram

Super Ni-Cd Battery Charger 12-18V Circuit Diagram

PARTS LIST

R1,R4,R5=10K

R2,R3=100K

R6,R8,R10=1K

R7=820

R9=100

R11=15

R12=3,9

R13=1,8

C1=1000uF/40v

C2=470pf

D1-D4,D6=1n4001-7 D7,D8=1n4148

D9,D10=LED IC=741

TR1=BC548

TR2=BD137

TR3=2N3055

Datasheet file1: Click here to download LM741.pdf datasheet.

Datasheet file2: Click here to download BC548.pdf datasheet.

Datasheet file3: Click here to download BD137.pdf datasheet.

Datasheet file4: Click here to download 2N3055.pdf datasheet.

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Wednesday, June 12, 2013

Playback Amplifier For Cassette Deck circuit schematic with explanation

For some time now, there have been a number of tape cassette decks available at low prices from mail order businesses and electronics retailers. Such decks do not contain any electronics, of course. It is not easy to build a recording amplifier and the fairly complex magnetic biasing circuits, but a playback amplifier is not too difficult as the present one shows. The stereo circuits in the diagram, in conjunction with a suitable deck, form a good-quality cassette player. The distortion and frequency range (up to 23 kHz) are up to good standards. Moreover, the circuit can be built on a small board for incorporation with the deck in a suitable enclosure. Both terminals of coupling capacitor C1 are at ground potential when the amplifier is switched on.

Circuit diagram:

Cassette Deck Playback Amplifier Circuit Diagram

Cassette Deck Playback Amplifier Circuit Diagram

Because of the symmetrical ±12 V supply lines, the capacitor will not be charged. If a single supply is used, the initial surge when the capacitor is being charged causes a loud click in the loudspeaker and, worse, magnetizes the tape. The playback head provides an audio signal at a level of 200–500 mV. The two amplifiers raise this to line level, not linearly, but in accordance with the RIAA equalization characteristic for tape recorders. Broadly speaking, this characteristic divides the frequency range into three bands:

Up to 50 Hz, corresponding to a time constant of 3.18 ms, the signal is highly and linearly amplified.
Between 50 Hz and 1.326 kHz, corresponding to a time constant of 120 µs, for normal tape, or 2.274 kHz, corresponding to a time constant of 70 µs, for chromium dioxide tape, the signal is amplified at a steadily decreasing rate.
Above 1.326 kHz or 2.274 kHz, as the case may be, the signal is slightly and linearly amplified. This characteristic is determined entirely by A1 (A1’). To make the amplifier suitable for use with chromium dioxide tape, add a double-pole switch (for stereo) to connect a 2.2 kΩ resistor in parallel with R3 (R3’). The output of A1 (A1’) is applied to a passive high-pass rumble filter, C3-R5 (C3’-R5’) with a very low cut-off frequency of 7 Hz. The components of this filter have exactly the same value as the input filter, C1-R1 (C1’-R1’). The second stage, A2 (A2’) amplifies the signal ´100, that is, to line level (1V r.m.s.).

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LM4906 Boomer Audio Power Amplifier circuit and epxlanation

The well-known LM386 is an excellent choice for many designs requiring a small audio power amplifier (1-watt) in a single chip. However, the LM386 requires quite a few external parts including some electrolytic capacitors, which unfortunately add volume and cost to the circuit. National Semiconductor recently introduced its Boomer® audio integrated circuits which were designed specifically to provide high quality audio while requiring a minimum amount of external components (in surface mount packaging only). The LM4906 is capable of delivering 1 watt of continuous average power to an 8-ohm load with less than 1% distortion (THD+N) from a +5 V power supply. The chip happily works with an external PSRR (Power Supply Rejection Ratio) bypass capacitor of just 1 µF minimum.

In addition, no output coupling capacitors or bootstrap capacitors are required which makes the LM4906 ideally suited for cellphone and other low voltage portable applications. The LM4906 features a low-power consumption shutdown mode (the part is enabled by pulling the SD pin high). Additionally, an internal thermal shutdown protection mechanism is provided. The LM4906 also has an internal selectable gain of either 6 dB or 12 dB. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage. Four times the output power is possible as compared to a single-ended amplifier under the same conditions (particularly when considering the low supply voltage of 5 to 6 volts).

Circuit diagram:

LM4906 Boomer Audio Power Amplifier circuit schematic

Boomer Audio Power Amplifier Circuit Diagram

When pushed for output power, the small SMD case has to be assisted in keeping a cool head. By adding copper foil, the thermal resistance of the application can be reduced from the free air value, resulting in higher PDMAX values without thermal shutdown protection circuitry being activated. Additional copper foil can be added to any of the leads connected to the LM4906. It is especially effective when connected to VDD, GND, and the output pins. A bridge configuration, such as the one used in LM4906, also creates a second advantage over single-ended amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across the load.

This eliminates the need for an output coupling capacitor which is required in a single supply, single-ended amplifier configuration. Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 100 Hz to 150 Hz. Thus, using a large input capacitor may not increase actual system performance. Also, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be minimized.

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