Easy Discrete Low Drop Regulator

This circuit was designed to ensure that an amplifier circuit containing a TDA1516Q would not exceed its maximum supply voltage when the load is small. This amplifier is used in a PC to increase the audio power somewhat. The PC power supply, however, created so much interference that an additional power supply was required.

Discrete Low-Drop Regulator Circuit Diagram

The power supply has its own power trans-former with a secondary voltage of 12 V AC. After rectification and filtering this results in a DC voltage of about 16 V. The regulator consists of a P-channel MOSFET SJ117, the gate of which is driven via a voltage divider connected to T2. The base of T2 is held at a constant voltage by LED D2, so that the volt-age across emitter resistor R2 is also constant and therefore carries a constant cur-rent. 

When the output voltage is higher than about 13.5 V, zener diode D1 will start to con-duct and supply part of the current through R2 — as a result the MOSFET will be turned on a little less. In this way there is a balance point, where the output voltage will be a little over 13.5 V (1.5 V across R2 plus the 12 V zener voltage). The regulator is capable of deliver-ing up to about 2 A — in any case it is a good idea to fit the MOSFET with a heatsink.

It is possible to add an optional potentiometer in series with the 12-V zener diode, which will allow a small amount of adjustment of the output voltage.The relay at the AC powerline input ensures that the power supply is only turned on when the PC is turned on. This relay is driven from a 4-way power supply connector from the PC.

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A Low Cost Hearing Aid Circuit

Small and portable unit, Useful for old men and old women

This low-cost, general-purpose electronic hearing aid works off 3V DC (2x1.5V battery). The circuit can be easily assembled on a veroboard. For easy assembling and maintenance, use an 8-pin DIP IC socket for TDA2822M.

Circuit Diagrams:

 A Low Cost hearing Aid Circuit

Parts:
P1 = 10K
R1 = 2.2K
R2 = 330K
R3 = 680R
R4 = 33R
R5 = 100R
R6 = 4.7R
R7 = 4.7R
R8 = 220R
C1 = 0.01uF-10V
C2 = 100nF-63V
C3 = 47uF-10V
C4 = 10uF-10V
C5 = 0.01uF-10V
C6 = 100uF-10V
C7 = 100nF-63V
C8 = 100nF-63V
D1 = Red LED
Q1 = BC547
IC1 = TDA2822M
EP1 = Mono Earphone 32R
SW1 = On-Off Switch

Circuit Operation:

In this circuit, transistor Q1 and associated components form the audio signal preamplifier for the acoustic signals picked up by the condenser microphone and converted into corresponding electrical signals. Resistor R5 and capacitor C3 decouple the power supply of the preamplifier stage. Resistor R1 biases the internal circuit of the low-voltage condenser microphone for proper working. The audio output from the preamplifier stage is fed to the input of the medium-power amplifier circuit via capacitor C2 and volume control P1.

The medium-power amplifier section is wired around popular audio amplifier IC TDA2822M (not TDA2822). This IC, specially designed for portable low-power applications, is readily available in 8-pin mini DIP package. Here the IC is wired in bridge configuration to drive the 32-ohm general-purpose monophonic earphone. Red LED (D1) indicates the power status. Resistor R8 limits the operating current of D1. The audio output of this circuit is 10 to 15mW and the quiescent current drain is below 1 mA.

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Low Loss Step Down Converter Circuit Diagram

This circuit arose from the need of the author to provide a 5 V output from the 24 V battery of a solar powered genera-tor. Although solar power is essentially free it is important not to be wasteful especially for small installations; if the battery runs flat at midnight you’ve got a long wait before the sun comes up again. The basic requirement was to make an efficient step-down converter to power low voltage equipment; the final design shown here accepts a wide input voltage from 9 to 60 V with an output current of 500 mA. The efficiency is very good even with a load of 1 mA the design is still better than a standard linear regulator. The low quiescent current (200 µA) also plays a part in reducing losses. 

Some of the components specified (particularly the power MOSFET) are not the most economical on the market but they have been deliberately selected with efficiency in mind.

Low Loss Step Down Converter Circuit diagram :

Low Loss Step Down Converter Circuit Diagram

When power is applied to the circuit a reference voltage is produced on one side of R2. D1 connects this to the sup-ply (pin 7) of IC1 to provide power at start-up. Once the circuit begins switching and the output voltage rises to 5 V, D2 becomes forward biased and powers the IC from the output. Diode D1 becomes reverse biased reducing current through R1. When the circuit is first powered up the voltage on pin 2 of IC1 is below the reference voltage on pin 3, this produces a high level on output pin 6. The low power MOSFET T1 is switched on which in turn switches the power MOSFET T3 via R5 and the speed-up capacitor C4, the output volt-age starts to rise. 

When the output approaches 5 V the voltage fed back to the inverting input of IC1 becomes positive with respect to the non inverting input (reference) and switches the output of IC1 low. T1 and T3 now switch off and C3 transfers this negative going edge to the base of T2 which conducts and effectively shorts out the gate capacitance of T3 thereby improving its switch off time. 

The switching frequency is not governed by a fixed clock signal but instead by the load current; with no load attached the circuit oscillates at about 40 Hz while at 500 mA it runs at approximately 5 kHz. The variable clock rate dictates that the output inductor L1 needs to have the relatively high value of 100 mH. The coil can be wound on ferrite core material with a high AL value to allow the smallest number of turns and produce the lowest possible resistance. Ready-made coils of this value often have a resistance greater than 1 ? and these would only be suitable for an output load current of less than 100 mA. 

The voltage divider ratio formed by R4 and R3 sets the output voltage and these values can be changed if a different out-put voltage is required. The output volt-age must be a minimum of 1 V below the input voltage and the output has a minimum value of 4 V because of the supply to IC1. 

A maximum efficiency of around 90 % was achieved with this circuit using an input voltage between 9 and 15 V and supplying a current greater than 5 mA, even with an input voltage of 30 V the circuit efficiency was around 80 %. If the circuit is used with a relatively low input voltage efficiency gains can be made by replacing D4 with a similar device with a lower reverse breakdown voltage rating, these devices tend to have a smaller for-ward voltage drop which reduces losses in the diode at high currents. At higher input voltage levels the value of resistor R1 can be increased proportionally to reduce the quiescent current even further. 

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1V Low Power Stereo Headphone Amplifier with Shutdown MAX9725

The MAX9725A–MAX9725D fixed-gain, stereo headphone amplifiers are ideal for portable equipment where board space is at a premium. The MAX9725E offers the flexibility to adjust the gain with external input and feedback resistors. The MAX9725A–MAX9725E use a unique DirectDrive® architecture to produce a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors, saving cost, board space, and component height. Fixed gains of -2V/V (MAX9725A), -1.5V/V (MAX9725B), -1V/V (MAX9725C), and -4V/V (MAX9725D) further reduce external component count. The adjustable gain of the MAX9725E DirectDrive headphone amplifier allows for any gain down to -1V/V using external resistors.

The MAX9725 delivers up to 20mW per channel into a 32Ω load and achieves 0.006% THD+N. An 80dB at 1kHz power-supply rejection ratio (PSRR) allows the MAX9725 to operate from noisy digital supplies without an additional linear regulator. The MAX9725 includes ±8kV ESD protection on the headphone output. Comprehensive click-and-pop circuitry suppresses audible clicks and pops at startup and shutdown. A low-power shutdown mode reduces supply current to 0.6µA (typ).

The MAX9725 operates from a single 0.9V to 1.8V supply, allowing the device to be powered directly from a single AA or AAA battery. The MAX9725 consumes only 2.1mA of supply current, provides short-circuit protection, and is specified over the extended -40°C to +85°C temperature range. The MAX9725 is available in a tiny (1.54mm x 2.02mm x 0.6mm) 12-bump chip-scale package (UCSP™) and a 12-pin thin QFN package (4mm x 4mm x 0.8mm). 

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AC Inverter Low cost 12VDC to 120 220V

This inverter will sufficiently power any of your 115VAC (or 220VAC)small appliances। T1 choice of amperage is yours to make, but if you can salvage a heavy-duty unit from somewhere, use it. The least expensive method to get a larger transformer would be to remove the old 2000v primary and then re-wind an old microwave transformer. Most of these transformers are rated 1KW or better. Your local TV or Electronics repair shop may have one or dig one up from the dumpster. Just in case you dont know, micro-wave transformers can keep their charge (via the connected electronics) for a long time, so be careful!R1 and R2 are 10 ohm, wire-wound, and at least 5 watts. Wattage/cooling should be increased accordingly if you decide to beef up the output. For D1 and D2 you can use any power diode like the 1N4002 to 1N4005.If you live in Europe, Australia, or any other country with a 220VAC system, the only different is the transformer. This particular circuit can be constructed to handle up to 1 KiloWatt (1000 watt). If there is enough interest, I can modify this circuit to include a crow-bar circuit, battery backup, or more output in watts, or everything.The power output is determined by transformer T1, and power transistors Q1 & Q2. Assume a transformer of about 15A and the chosen transistors of 2N3055 (15A) type, the inverter can supply about 300 watts with the parts shown. If you are good with electronics all you have to do is replace the 2N3055s and T1 accordingly for more output. It is imperative to mount Q1 and Q2 on large coolribs. If you intend to beef everything up with a couple kilowatts a standard (5") cooling fan will also be required. If this is the case, the 2N3771 power transistor is a good choice at 30Amps. NTEs replacement, NTE181, is an improved version of the 2N3771 and carries 90volts instead of the 40 volts and can dissipate 200W instead of 2N3771s 150W.It is mandatory to include at least one suitable fuse and enclose this project in the correct casing. To be really safe you may want to include a primary and secundary fuse for your own protection. You are dealing with 120VAC or 220VAC at respectible amperage so be careful. The powercord also needs to be secured to prevent accidents.The 68uF Tantalum capacitors were chosen for their endurance. Normal electrolytic capacitors would overheat and explode. Somesort of cooling fan inside the project case may be a good choice, I myself use a ball-bearing cpu-fan from an old computer. New they dont cost that much either, about 3 bucks or so.

Since T1, and Q1/Q2 are NOT part of the PCB, these few parts can easily be used on a piece of Vero or experimenters board. Radio Shack and Tandy have these boards also available at a very reasonable price. The receptacle(s) on T1s output will be part of the case (obviously). I Just a small note about the 12 Volt battery, this circuit and others similar can draw huge amounts of current and will drain your battery in hurry so dont let your battery go dead! Thats why a wind/solar power combination would be an excellent future addition. For those interested in a PCB, I have included one below with a layout. As soon as I get my digital camera I will include pictures of the finished project. Read More

Digital High Low Logic Tester Circuit diagram

1. 
   When the input signal is logic 1, the display shows H’ and the loudspeaker emits a note which is an octave higher than the low’ tone. Operation of the circuit can be seen from the circuit diagram in figure 1 and the truth table in figure 2. When the input signal is 1, transistor T1 conducts taking the input of gate N2 above the trigger threshold and the trigger output goes to logic 0.
2. This is not our first high and low tester, but the present circuit offers something new: a seven-segment display which shows ’H or ’L’ and at the same time a small loudspeaker emits a corresponding tone.
3. lf required, the loudspeaker can be switched on by means of S1. The switch can, of course, be omitted if the audio tone is always required. lf you have an ear for music, R10 and R12 may be replaced by a 220 Q resistor and a 2509 preset potentiometer so that the tone can be adjusted to your particular liking.!
4. And all that at very reasonable cost.
5. When the supply is switched on, the decimal point of the display lights and indicates that the unit is ready For use. lf this is not the case, or an undefined signal is applied to the input, the display, apart from the decimal point, remains dark and the loudspeaker remains silent. lf the input signal is logic O, the display shows ’L’ and the loudspeaker emits a low note.
6. When the input signal is logic 0, T1 is cut off and T2 conducts. The voltage at the inputs of gates N1 and N2 are below the trigger threshold and both outputs are logic 1, switching on transistors T3 and T4; the emitter voltage of T4 rises and cuts off diodes D4 and D5. This causes a current to flow through segments d, e and f, diodes D2 and D3, resistor R6 and transistor T3.
7. With non-defined inputs (between 0.8.. . 2.15 V) and an open circuit input, both input transistors are cut off, The output of N1 is then logic 0 and that of N2 is logic 1: no current can therefore flow through any of the segments. As regards the drive for the two oscillators, suffice it to say that during low inputs N3 is driven by the output of N1 and during high in- puts N4 is driven directly by T1.
8. Transistor T2 (PNP!) is cut off, the input of gate N1 is also above the trigger threshold and this trigger output is therefore also logic 0. Both switching transistors T3 and T4 are off and a current flows through the corresponding segments (b, c, e, f, g), diodes D4 and D5 and R7. 

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Delay and Music Power Supply Circuit with High and Low Voltage

Delay and Music Power Supply Circuit with High and Low Voltage

Voltage variations and ability cuts abnormally affect assorted equip- ment such as TVs, VCRs, music systems and refrigerators. This simple ambit will assure the cher accessories from aerial as able-bodied as low voltages and the voltage surges (when ability resumes). It additionally gives a accordant tune back mains ability resumes. Back mains voltage is normal, the DC voltage at the cathode of zener diode D4 is beneath afresh 5.6V. As a aftereffect transistor T1 is in off state. The DC voltage at the cathode of zener diode D5 is greater than 5.6V and as a aftereffect transistor T2 is in on state. Consequently, broadcast RL1 gets energised, which is adumbrated by lighting up of blooming LED. Under aerial mains voltage condition, transistor T1 switches to on accompaniment because the voltage at cathode of zener diode D4 becomes greater than 5.6V. Consequently, transistor T2 switches to off state, authoritative the broadcast to de-energise Under low mains voltage condition, transistor T1 switches to off accompaniment and as a aftereffect transistor T2 additionally switches to off state, authoritative the broadcast to de-energise.

Timer IC 555 in the ambit is configured to accomplish in a monostable mode. The beating amplitude is about 10 abnormal with the timing basic ethics acclimated in the schema. Back the ability resumes afterwards a break, pin 2 of IC 555 goes low briefly and this triggers it. Its achievement makes music IC UM66 to accomplish through transistor T3. Simultaneously, transistor T1 additionally gets advanced biased as the monostable IC1 achievement is affiliated to its abject via diode D8 and resistor R7. As a result, transistor T1 conducts and biases transistor T2 to cut off. Thus broadcast RL1 charcoal de-energised for the continuance of address beating and the amount is adequate adjoin the voltage surges.

To acclimatize presets VR1 and VR2, you may use a manually capricious auto-transformer. Set the achievement of auto-transformer to 270V AC and affix it to the primary of agent X1. Acclimatize preset VR1 such that broadcast RL1 aloof de-energises. Next set the achievement of auto-transformer to 170V AC. Now acclimatize preset VR2 such that broadcast RL1 afresh de-energises. Aggregate ascendancy VR3 may be adapted for the adapted achievement aggregate of the tune generated by IC UM66

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Digitally tuned low power active filter

This constant gain, constant Q, variable frequency filter provides simultaneous low-pass, bandpass, and high-pass outputs with the component values shown, the center frequency will be 235 Hz and 23.5 Hz for high and low logic inputs.

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Tone Control Subwoofer Low Pass Filter IC

• CMOS Technology
• 2 - Channel Input
• 3 - Channel Output (Including 1 stereo Output and Subwoofer Output)
• Low Total Harmonic Distortion (THD<0.01%, Subwoofer THD<0.2%)
• High S/N Ratio (S/N Ratio <-87dB, A-weighting)
• Least External Components
• Adjustment of Frequency response by changing the value of the external component
• Single Power Supply: 3 to 8.5 Volts
• Available in 20 pins, DIP or SO Package
• Multi-Media 3D Satellite Speaker and Subwoofer System
• Car Audio
• Audio Equipment
• Sound Card
• Other Electrical Audio Equipment

Tone Control Subwoofer Low Pass Filter IC

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Battery Switch With Low Dropout Regulator Wiring diagram Schematic

This is a simple Battery Switch With Low-Dropout Regulator Circuit Diagram. In the form of the LT1579 Linear Technology (www.linear-tech.com) has produced a practical battery switch with an integrated low-dropout regulator. In contrast to previous devices no diodes are required. The schema is available in a 3.3 V version (LT1579CS8-3.3) and in a 5 V version (LT1579CS8-5), both in SO8 SMD packages. There is also an adjustable version and versions in an SO16 package which offer a greater range of control and drive signals. The main battery, whose terminal voltage must be at least 0.4 V higher than the desired output voltage, is connected to pin IN1. The backup battery is connected to pin IN2. The regulated output OUT can deliver a current of up to 300 mA. The LDO regulator part of the IC includes a pass transistor for the main input voltage IN1 and another for the backup battery on IN2.

The IC will switch over to the backup battery when it detects that the pass transistor for the main voltage input is in danger of no longer being able to maintain the required output voltage. The device then smoothly switches over to the backup battery. The open-drain status output BACKUP goes low to indicate when this has occurred. When neither battery is able to maintain the output voltage at the desired level the open-drain output DROPOUT goes low. The LT1579 can operate with input voltages of up to +20 V from the batteries. The regulator output OUT is short-schema proof. The shutdown input switches off the output; if this feature is not required, the input can simply be left open.

Streampowers

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Low Voltage Cut Out

Low Voltage Cut-Out Circuit diagram. This schema will detect when the voltage of a 12v battery reaches a low level. This is to prevent deep-discharge or maybe to prevent a vehicle battery becoming discharged  to a point where it will not start a vehicle. This schema is different to anything previously presented. It has HYSTERESIS. Hysteresis is a feature where the upper and lower detection-points are separated by a gap. 

Low Voltage Cut-Out Circuit diagram :

Low Voltage Cut-Out Circuit Diagram

Normally,  the schema will deactivate the relay when the voltage is 10v and when the load is removed. The battery voltage will rise slightly by as little as 50mV and turn the schema ON again. This is called "Hunting." The off/on timing has been reduced by adding the 100u. But to prevent this totally from occurring, a 10R to 47R is placed in the emitter lead. The schema will turn off at 10v but will not turn back on until 10.6v when a 33R is in the emitter. The value of this resistor and the turn-on and turn-off voltages will also depend on the resistance of the relay. 

Author : Colin Michel - Copyright : 200 Transistor Circuits

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Low Noise operational amplifier

Low noise balanced input is can also call for the circuit schematic above , because it has a very small noise output and balanced on each input. The noise output is only  117.0 dBu, its very small maybe even not at all out noise. The schematic based on IC5532 , to maintain ic remain good and avoid damage, you should install heatsink in every IC. If the circuit is finished and ready to use, then connect circuit in final befor going out to other components . Because this circuit is also suitable as a buffer amplifier.

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