Top Circuits Page 6
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A single transistor makes a simple phase shift oscillator. The output is a sine wave with distortion of about 104. The sine wave purity can be increased by putting a variable resistor (25 ohms) in the emitter lead of Q1 (x). The resistor is adjusted so the....
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Timing resistor R may be adjusted to any value between 10 K and 50 M to obtain a frequency range from 400 kHz to 100 Hz. Returning the timing resistor to the collector of Q1 ensures that Q1 draws its base current only from the timing capacitor Ct. The timing....
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This circuit generates sinusoidal, square, and triangle waveforms simultaneously. Set the frequency to a particular value or vary it, as-shown above. An op amp can be added for extra drive capability and simplified amplitude adjustment. ..
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The circuit"s frequency of oscillation is/= 2.8/ [C1 x (R1 + R2)]. Using the values shown, the output frequency can be varied from 60 Hz to 20 kHz by rotating potentiometer R2. A portion of IC1"s output voltage is fed to its noninverting input at pin 3.....
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Germanium transistor Ql is used as a noise generator in the audio range. Ul acts as a high-gain amplifier. Ql is not ..
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This circuit produces a 20-MHz clock phase locked to a 10-MHz clock present in the Apple MAC II. To generate..
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Two gates, U1A and U1B O/3 of a 4049 hex inveter), are connected in a VFO circuit. Components Rl, R3, and CI set the frequ..
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Capacitor CI charges through resistor Rl, and when the gate level established by potentiometer R2 is high enou..
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A VOX is a voice-operated switch that is often used as a substitute for the press-to-talk switch on" a microphon..
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The frequency of this sine-wave oscillator is determined by a direct voltage, U" of 0 to 15 V. The distortion on..
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This keyer uses skin conductivity to simulate the old-fashioned mechanical CW bug keyer. When the dit paddle is touched the bias on the inverter, ICl-a is shunted to ground, and it produces a logic high, causing oscillator sections CD to generate a....
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Referring to the simplified schematic in A, the AFG is made up of 10 relatively simple circuit elements. ICl-c and ICl-d arc configured as unity-gain noninverting buffer amplifiers. The summing (L+R) amplifier, IC2-c, combines equal amounts of the left and....
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Perfect pitch, which is based on the 8751 microprocessor, is an inexpensive and easy-to-build instrument tuner/frequency counter with a built-in headphone amplifier and a visual metronome. Perfect pitch converts the audio signal from your instrument to a....
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The precision audio-frequency-generator consists of several sub circuitsan audio-amplifier/filter circuit, an automatic level control, a variable voltage-controlled oscillator, a frequency divider circuit, an integrator, and an audio output amplifier. An....
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For use with low-power transmitters with a positive keying voltage. Q1/Q2/Q3 form a switching amplifier. When the key is pressed, the collector of Q3 goes to ground, turning on Q5 and activating IC1, an audio oscillator. Q4 drives the speaker...
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One section of the precision audio frequency generator uses an electret microphone element to pick up audio from the piano. That signal is then processed and sent to one channel of a dual-trace oscilloscope. The other section of the circuit is used to....
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Charging is accomplished with a constant current of 60 mA for AA cells to a cutoff voltage of 2.4 V per cell at which point the charge must be terminated. The charging system shown is designed for multi-cell battery packs of 2 to 6 series-connected cells or....
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One way to charge Ni-Cad batteries rapidly without abuse is to measure cell temperature and taper the charge accordingly. The circuit uses a thermocouple for this function. A second thermocouple nulls out the effects of ambient temperature. The temperature....
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A diac is used in the gate circuit to provide work for the signal being applied to the gate. R1 a threshold level for firing the triac. C3 and R4 is selected to limit the maximum charging cur-provide a transient suppression network..
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This circuit charges the battery at 75 mA battery can be left in the charger indefinitely, until the battery is charged, then it reduces the To set the shut-off point, connect a 270-ohm, current to a trickle rate..
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This circuit uses constant current LEDs to adjust charging current. It makes use of LEDs that pass a constant current of about 15 mA for an applied voltage range of 2-18 V. They can be paralleled to give any multiple of 15 mA and they light up when current....
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The circuit is capable of charging a 12 volt component selection. When the battery voltage battery at up to a six ampere rate..
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The circuit disconnects the battery from the load when output voltage falls below a preset level. Cl charges through R1 and turns on Q2. Collector current flows through R2 turning Ql on and battery is connected to the load..
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This circuit monitors car battery voltage. It provides an indication of nominal supply voltage as well as low or high voltage. RV1 and RV2 adjust the point at which the red/yellow and yellow/green LEDs are on or off. For example the red LED comes on at 11V,....
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A short-circuit-proof battery charger will provide an average charging current of about 8 A to a 12-V lead/acid storage battery. The charger circuit has an additional advantage; it will not function nor will it be damaged by improperly connecting the....
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This circuit furnishes an initial voltage of 2.5 V per cell at 25° C to rapidly charge a battery. The charging current decreases as the battery charges, and when the current drops to 180 mA, the charging circuit reduces the output voltage to 2.35 V per....
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When power is applied to the circuit, SCRl is off, so there is no bias-current path to ground; thus, L~317 acts as a current regulator. The LM317 is umnected to the battery through steering diode Dl, limiting resistor Rl, and bias resistor R2. The....
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This circuit will not work unless the battery to be charged is connected with proper polarity. The battery voltage controls the charger and when the battery is fully charged, the charger will not supply current to the battery. The battery charging the....
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This circuit was designed to charge NiCad battery packs in the range of 4.8 to 15.6 V from a convenient remote power source, such as an automobile battery. When power is first applied to the circuit, a small bias current supplied by Rl via winding Wl,....
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The charger"s output voltage is adjustable and regulated, and has an adjustable constant-current charging circuit that makes it easy to use with most NiCad batteries. The charger can charge a single cell or a number of series-conoected cells up to a....
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A voltage divider consisting of Rl, R2, and R3 is used to set the input reference voltage below which the batteries are to be replaced. That reference voltage, at point A, is varied by Rl. With the voltage divider shown in Fig. 9-7, a range of 2 to 3.5 Vis....
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The portable charger is intended primarily to give model enthusiasts the opportunity of charging their Nicad batteri..
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This high-performance charger quickly charges gelled lead-acid batteries, and turns off at full charge. At first, the charg..
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This circuit provides up to 20 V output from a 12-V automotive supply, to enable constant current charging o..
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The circuit furnishes an initial charging voltage of 2.5 V per cell at 25°C to rapidly charge a batt..
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Two simple circuits permit Nicad charging of a battery based on temperature differences between t..
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This type of charger couples RF from L2 to an external pickup coil. The pickup coil connects to a rectifier and battery to be charged. This idea is handy because no wire or contacts are required. L2 is 10T #24 wire and L3 is 10T #30 wire...
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The circuit is capable of supplying either a trickle (50 mA) or high-current (1-A) charge. You can select either charging method or an automatic mode that will first trickle charge a battery if it is particularly low before switching to high-current....
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Lamp LI will glow brightly and the LED will be out when the battery is low and being charged, but the LED will be bright and the light bulb dim when the battery is almost ready. Ll should be a light bulb rated for the current you want (usually the battery....
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This circuit is a small +5V power supply, which is useful when experimenting with digital electronics. Small inexpensive wall tranformers with variable output voltage are available from any electronics shop and supermarket. Those transformers are easily....
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The amplifier feeding to the final amplification stage is performed with unstabilized voltage. The output stage, due to push-pull operation, has a large rejection of the supply voltage. The various other steps, however, do not have the same rejection and....
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The power supply circuitry consists of a 220/2 * 18V / 3.5A transformer, a rectifier, a smoothing filter, a power amplifier, LM301, and two regulators LM317 and LM337. The theoretical of the circuit is shown in the figure. The voltage from the transformer is....
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At the left side (input AC) goes the secondary of a 220 volt (primary) 18 Volt (secondary) / 3 Ampere mains transformer. The alternating voltage of 18 volts from its secondary transformer is rectified by the diodes D1, D2, D3 and D4, which are connected to a....
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The special feature of the circuit shown below is the low consumption. With voltage n 9 at the entrance and no exit load, absorbs current 50 ma, which is certainly very small compared with a quiescent current 78L05. The components that comprise it are....
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Indicator provides an accurate comparison of two voltages by indicating their degree of balance (or imbalance). Detecting small variations near the null point is difficult with the basic Wheatstone bridge alone. Amplification of voltage differences near the....
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This supply is powered by a transformer operating from 120 Vac on the primary and providing approximately 20 Vac on the primary, and providing approximately 20 Vac on the secondary. Four 10-A diodes with a 100 PIV rating are used in a full-wave bridge....
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Intended for extreme temperature, radiation-hardened environments, this linear supply is capable of supplying 28 Vdc at 125 A from an ac-driven power unit. In operation, power supply output voltage is sensed by the voltage divider consisting of R24 to R28....
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The output current is set by the resistor R in the collector of Tr2, which may be varied to offer a range of output currents from 100 mA to 2 A with fine control by means of VR3 which varies the reference voltage to the non-inverting input of the op amp...
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A tapped transformer drives a diode bridge (D1-D4) and two 2500 µ¥ filter capacitors (Cl and C2), that provide a no-load voltage of 37 or 47 volts, depending upon the position of switch S2a. The unregulated dc is then fed to a pre-regulator stage composed....
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To prevent loss of data when a CMOS RAM is switched from normal operation (Vcc = 5 volts) to stand-by mode (Vcc = VBAT) it must be ensured that the CS pin goes near the Vcc rail at all times. Ac coupling to the chip select is made through capacitor C,....
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When using a regulated supply to reduce a supply voltage there is always the danger of component failure in the supply and consequent damage to the equipment. A fuse will protect when excess current is drawn, but might be too slow to cope with overvoltage....
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This circuit provides for accurate half wave rectification of the incoming signal. For positive signals, the gain is 0; for negative signals, the gain is — 1. By reversing both diodes, the polarity can be inverted. This circuit provides an accurate output,....
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The circuit provides accurate full wave rectification. The output impedance is low for both input polarities, and the errors are small at all signal levels. Note that the output will not sink heavy current, except a small amount through the 10K resistors.....
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A simple means of generating a low-power voltage supply of opposite polarity from the main supply. Self oscillating driver produces pulses at a repetition frequency of 100 kHz. When the VMOS device is off, capacitor C is charged to the positive supply. When....
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A16 V power supply can be synthesized as shown using IN1692 rectifiers. A shift pulse input saturates the 2N2714 depriving the Darlington combination (2N2714 and 2N2868) of base drive..
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This circuit provides a simple means of obtaining phase shifts between zero and 170°. The transistor operates as a phase splitter, the output at point A being 180° out of phase with the input. Point B is in phase with the input phase. Adjusting Rl provides....
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Each stage provides 0° to 180° phase shift. By ganging the two stages, 0° to 360° phase shift is achieved This circuit is under:, power supplies, ac dc dc dc, 0° To 360° phase shifter l12884. By ganging the two stages, 0° to 360° phase shift is achieved The....
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The circuit is essentially a constant source modified by the feedback components R2 and R3 to give a constant voltage output. The output of the ZN424E need only be 2 volts above the negative rail, by placing the load in the collector of the output transistor....
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Many countries have 115 volts mains supplies. This can be a problem if your electric shaver is designed for 220/240 volts only. This simple rectifier voltage doubler enables motor driven 240 volt shavers to be operated at full speed from a 115 volt supply.....
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This simple circuit gives a positive and negative supply from a single transformer winding and one full-wave bridge. Two zener diodes in series provide the voltage division and their centerpoint is grounded..
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This simple mobile voltage regulator circuit may save your two meter or CB transceiver if the voltage regulator fails. The 2N3055 should be heat sinked if current drawn by the rig is in excess of 2 A on transmit..
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This circuit may be used where a high current is required with a low ripple voltage (such as in a high powered class AB amplifier when high quality reproduction is necessary), Ql, Q2, and R2 may be regarded as a power darlington transistor. ZDl and Rl....
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These short-circuit protected regulators give 6, 7, and 9 V from an automobile battery supply of 13 V nominal; however, they will function just as well if connected to a smoothed dc output from a transformer/rectifier circuit. Two types are shown for both....
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This circuit combines a 555 timer with a 2N2222 transistor and an external potentiometer. The pot adjusts the output voltage to the desired value. To regulate the output voltage, the 2N2222 varies the control voltage of the 555 IC, increasing or decreasing....
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ICs requiring 3 or 6 volts can be run from a battery or fixed regulated supply of a higher voltage by using the circuit shown. The transistor should be mounted on a heatsink as considerable power will be dissipated by its collector. Additional filtering can....
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The circuit behaves like a zener diode over a large range of voltages. The current passing through the voltage divider R1-R2 is substantially larger than the transistor base current and is in the region of 8 mA. The stabilizing voltage is adjustable over the....
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This circuit enables transistorized items such as radio, cassettes, and other electrical devices to be operated from a car"s electrical supply. The table gives values for resistors and specified diode types fordifferent voltage. Should more than one voltage....
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This circuit gives a regulated output of between 5 V and 15 Vdc, adjusted and set by a preset resistor. Current output up to about 350 mA..
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This circuit utilizes the quasi-complementary output stage of the popular LM380 audio power IC. The device is internally biased so that with no input the output is held midway between the supply rails Rl, which should be initially set to mid-travel, is used....
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For positive protection of electrical or electronic equipment, use this against excessive supply voltage. Due to improper switching, wiring, short circuits, or failure of regulators, an electronic crowbar circuit can quickly place a short circuit across the....
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To safeguard portable, emergency power repeaters from reverse or excessive voltage, Dl prevents incorrect polarity damage, and zener voltage determines the maximum voltage that will reach the rest of the circuitry..
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These circuits provide overvoltage protection in case of voltage regulator failure or application of an external voltage. Intended to be used with a supply offering some form of short circuit protection, either foldback, current limiting, or a simple fuse.....
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Zener diode ZD1 senses the supply, and should the supply rise above 6 V, Ql will turn on. In turn, Q2 conducts clamping the rail. Subsequent events depend on the source supply. It will either shut down, go into current limit or blow its supply fuse. None of....
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When using a regulated power supply to reduce a supply voltage, there is always the danger that component failure in the power supply might lead to a severe overvoltage condition across the load. To cope with overvoltage situations, the circuit is designed....
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The circuit will produce the current relationship to within 2% using 1% values for Rl through R5. This includes variations in Rl from 100 ohm to 2000 ohm. The use of large resistors for Rl through R4 minimizes the error due to Rl variations..
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In this circuit, a TU31 shunt regulator is used to sense the output voltage. The TU31 drives the LED of a 4N28 optocoupler which provides feedback to the MAX641 while maintaining isolation between the input, +12 V, andJhe output, +15 V. ..
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Positive output step-up and step-down de-de converters have a common limitation in that neither can handle input voltages that are both greater than or less than the output. For example, when converting a 12-V sealed lead/acid battery to a regulated +12 V....
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This linear post regulator provides 12 V at 3 A. It employs TL431 reference Ul which, without additional amplification, drives TMOS MTP3055A gate Ql series pass regulator. Bias voltage is applied through Rl to Q1"s gate, which is protected against....
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The diagram is a power supply circuit using the isolated feedback capabilities of the TL3103 for both current and voltage sensing. This supply is powered fromthe ac power line and has an output of 5 Vat 1.5 A. Both output voltage and current are sensed and....
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This de adapter provides a regulated 9-V source for operating a Kenwood TR-2500 hand-held transceiver in the car. The LM317T"s mounting tab is electrically connected to its output pin, so take this into account as you construct your version of the adapter. ..
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A MAX634 inverting regulator is combined with a MAX630 to provide a dual tracking ±15 output from a 12-V battery. The reference for the -15 V output is derived from the positive output via R3 and R4. ..
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The supply receives + 20 Vdc from the rectifier/filter section. This is applied to pins 11 and 12 of the uA723, as well as to the collector of the 2N3055 series-pass transistor. The output voltage is sampled through R1 and R2, providing about 7 V with....
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The supply receives -20 V from the rectifier/filter which is fed to the collector of the Darlington pnp pass transistor, a TIP105. The base drive to the TIP105 is supplied through resistor R5. The base of the TIP105 is driven from Vz terminal at pin 9,....
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This power supply delivers plus and minus 9 V to replace two 9-V batteries. The rectifier circuit is actually two separate full-wave rectifiers fed from the secondary of the transformer. One full-wave rectifier is composed of diodes D1 and D2, which....
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The supply 6-66 can be used for supply output voltages from 1 to 35 V. The line transformer should be selected to give about1.4 times the desired output voltage from the positive side of filter capacitor C1 to ground. Potentiometer R2 sets the output....
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This circuit generates three supply voltages using a minimum of components. Diodes D2 and D3 perform full-wave rectification, alternately charging capacitor C2 on both halves of the ac cycle. On the other hand, diode D1 with capacitor C1, and diode D4 with....
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Many systems require one or more relatively low-current voltage sources which can be programmed tna few predetermined levels. The circuit shown above produces positive output levels, but could be modified for negative or bipolar outputs. Q1 is the series....
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It is usually desirable to have the remote transmitter of a 4 to 20 mA current loop system powered directly from the transmission line. In some cases, this is not possible because of the high-power requirements set by the remote sensor/transmitter....
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This circuit consists of an astable multivibrator driving a push-pull pair of transistors into the transformer primary. The multivibrator frequency should~equal around 1 or 2kHz. ..
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The IC8211 provides the voltage reference and regulator amplifier, while Ql is the series pass transistor. Rl defines the output current of the IC8211, while Cl and C2 provide loop stability and also act to suppress feedthrough of input transients to the....
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A TMOS power FET, Ql, and an LM393 comparator provide a high-efficiency rectifier circuit. When V,. exceeds V,, Ul"s output becomes high and Ql conducts. Conversely, when VB exceeds V,., the comparator output becomes low and Ql does not conduct. The....
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In the circuit shown, a CMOS op amp controls the current through a p-channel HEXFET power transistor to maintain a constant voltage across RL The current is given by: 1 ~ VREF/Rl. ..
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One v;ay to provide good negative-voltage regulation is with a low-dropout positive-voltage regulator operating from a well-isolated secondary winding of switch-mode circuit transformer. The technique works with any positive-voltage regulator, although....
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In this circuit. a negative output voltage de-de converter generates a -5 V output at pin A. In order to generate -5 Vat point A, the primary of the transformer must fly back to a diode drop more negative than -5 V. If the transformer has a tightly coupled....
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In the circuit, Ql and Q2 are connected in the classic SCR or thyristor configuration. Where higher input voltages or minimum component count are required, the circuit for thyristor boost can be used. The thyristor is running in a linear mode with its....
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This circuit provides a continuous supply of regulated + 5 V, with automatic switch-over between line power and battery backup. When the line-powered input voltage is a + 5 V, it provides 4A V to the MAX630 and trickle charges the battery, If the....
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Ul, an LM317 adjustable regulator provides short-circuit protection and automatic current limiting at 1.5 A. The input voltage to the regulator is supplied by DBl, a 4-A 100 PIV full-wave bridge rectifier. Capacitor Cl provides initial filtering. Ul....
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The circuit powers the load via the regulator"s input instead of its output. Because the regulator"s output sees constant dummy load R1, it tries to consume a constant amount of current, no matter what the voltage across the actual load really is. Hence,....
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The variable voltage regulator lets you adjust the output voltage of a fixed de power supply between 1.2 and 37 V de, and will supply the output current in excess of 1.5 A. The circuit incorporates an LM117K three-terminal adjustable output positive....
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This circuit uses two comparator pairs from an LM339N quad comparator; one pair drives the yellow positive (+)and negative (-)indicators, the other jointly drives the red warn LED3. The circuit draws its power from the unregulated portion of the power....