Circuit Diagram

VARACTORLESS_HF_MODULATOR

Published:2009/6/23 4:36:00 Author:Jessie

Traditionally, high-frequency oscillators are frequency-modulated by using a varactor. However, varactors usually require a large voltage change to achieve a reasonable capacitance change-a prob-lem in many battery-powered systems.Such a problem can be overcome by employing base-charging capacitance modulation. Resistor RI establishes Q1's current, and R2 allows control of the collector bias current byVmod The trans-mission line (T1) in the negative resistance-type oscillator determines the frequency of oscillation. T1 is a high-quality, low-loss, ceramic coaxial shorted quarter-wave transmission line. Under proper terminal impedances, a negative resistance is seen at Q1's base. T1 reacts with this negative resis-tance to produce sustained oscillations.Frequency modulation is accomplished by changing Q1's collector bias current and thus chang-ing Q1's base-charging capacitance. This effect is seen at Q1's base and causes a frequency shift in the resonators quarter-wave node.   (View)

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33_V_FROM_5_V_LOGIC_SUPPLIES

Published:2009/6/23 4:36:00 Author:Jessie

Microprocessor chip sets and logic families that operate from 3.3-V supplies are gaining acceptance in both desktop and portable computers. Computing rates, and in most cases, the energy consumed by these circuits, show a strong improvement over 5-V technology. The main power supply in most systems is still5 V, necessitating a local 5-V to 3.3-V regulator. Linear regulators are viable solutions at lower (IO≤1 A) currents, but they must have a low dropout voltage in order to maintain regulation with a worst-case input of only 4.5 V. The ftgure shows a circuit that converts a 4.5-V minimum input to 3.3Vwith an output tolerance of only 3% (100 mV). The LT1129-3.3 can handle up to 700 mA in surface-mount conftgurations, including both 16-μA shutdown and 50-μA standby currents for system sleep modes. Unlike other Iinear regulators, the LT1129-3.3 combines both low-dropout and Iow-voltage operation. Small input and output capacitors facilitate compact, surface-mount designs.   (View)

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SIMPLE_AUDIO_MIXER

Published:2009/6/23 3:45:00 Author:May

A single transistor is used as an audio mixer, the transistor serving as a feedback amplifier.   (View)

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SAWTOOTH_GENERATOR

Published:2009/6/23 4:35:00 Author:Jessie

A sawtooth waveform generator circuit using a 555 IC is shown. The IC is connected in an astable oscillator circuit with the majority of the output contained in the positive portion of the cy-cle. The negative output is a very brief pulse.Capacitor C2 charges through R3 in a positive direction during the time that the IC's output (at pin 3) is high. When the output goes negative, C2 is rapidly discharged through Dl and the IC's out-put.Peak-to-peak sawtooth output is about 1 V. The linearity of this circuit is best when R3 is as large as possible. The oscillator's frequency is about 200 Hz and can be increased by lowering either the value of R1 or C1 to decrease the frequency, increase the values of those components.   (View)

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FAST_33_V_REGULATOR

Published:2009/6/23 3:45:00 Author:May

New high-performance microprocessors require a fresh look at power-supply transient response.The LT1585 linear regulator features 1% initial accuracy, excellent temperature drift and load regulation, and virtually perfect line regulation. Complementing superb dc characteristics, the LT1585 exhibits extremely fast response to transients. Transient response is affected by more than the regulator itself. Stray inductances in the layout and bypass capacitors, as well as capacitor ESR dominate the response during the first 400 ns of transient.The ftgure shows a bypassing scheme developed to meet all the requirements for the Intel P44C-VR microprocessor. Input capacitors C1 and C2 function primarily to decouple load transients from the 5-V logic suppJy. The values used here are optimized for a typical 5-V desktop computer silver box powersupply input. C5 to C10 provide bulk capacitance at low ESR and ESL, and C11 to C20 keep the capacitance at low ESR and ESL low at high (>100 kHz) frequencies. C4 is a damper and it minimizes ringing during setting. Trace C is the load current step, which is essentially flat at 4 A with a 20-ns rise time.Trace A is the output settling response at 20 mV per division. Cursor trace B marks －46 mV relative to the initial output voltage. At the onset of load current, the microprocessor socket voltage dips to －38 ntV as a result of inductive effects in the board and capacitors, and the ESR of the capacitors. The inductive effects persist for approximately 400 ns. For the next 3 μs, the output droops as the load current drains the bypass capacitors. The trend then reverses as the LT1585 catches up with the load demand, and the output settles after approximately 50 μs. Running 4 A with a 1.7-V drop, the regulator dissipates 6.8 W.   (View)

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SIMPLE_12_V_POWER_SUPPLY

Published:2009/6/23 4:35:00 Author:Jessie

This 12-V power supply is easy-to-build，and it produces a smooth output，D1 is a 14-V，1/2-W Zener diode. The voltage can be varied by a few volts up or down to change the output voltage   (View)

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SIMPLE_FLOOD_ALARM

Published:2009/6/23 3:43:00 Author:May

A common collector amplifier drives a 2N3904 switch to sound alarm BZ1. The wire leads to wa-ter sensor or surnp pit, level switch, etc. and used to allow the alarm to operate and be mounted in a dry place.   (View)

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OP_AMP_LINEAR_SAWTOOTH_GENERATOR

Published:2009/6/23 4:34:00 Author:Jessie

Q1 is connected in a simple constant-current generator circuit. The value of Q1's emitter resistor sets the constant-current level flowing from the transistor's collector to the charging capacitor, C1.One op amp of an LM324.quad op-amp IC, UI-a, is connected in a voltage-follower circuit. The input impedance on the voltage follower is very high and offers little or no load on the charging cir-cuit. The follower's output is connected to the input of UI-b, which is configured as a voltage com-parator. The comparator's other input is tied to a voltage-divider setting the input level to about 8 V.The output of UI-b at pin 7 switches high when the voltage at its positive input, pin 5, goes above 8 V. That turns on Q2, discharging C1. The sawtooth cycle is repeated over and over as long as power is applied to the circuit.The sawtooth's frequency is determined by the value of C1 and the charging current supplied to that capacitor. As the charging current increases, the frequency also increases, andvice versa, To in-crease the generator's frequency range, decrease the value of C1, and to lower the frequency, in-crease the value of C1. The output is about 3 to5V.   (View)

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Drive LED Circuit of Voltage Dropping Model DC／DC Converter

Published:2011/7/23 8:23:00 Author:Michel | Keyword: DC／DC Converter, Drive LED Circuit

The dropping voltage model DC/DC converter drive LED circuit is showed as above.In this circuit,DC/DC converter(ZXSC310) works in dropping voltage model.More high system voltage can be provided by increasing the value of the R2 and the R2's value should be changed into 2.2kΩ if we want to get 24V voltage.At the same time capacitance C1 should also need the higher rated voltage. The circuit's basic work principle is as follows.When VT1 turns on, current flows through the white LED, capacitance and inductance L1 C1 .When both ends' voltage of R1 redcue to the threshold voltage of SENSE pin,VT1 shuts off and maintains a fixed time,the current in inductance flows through VZ and white LED.VT1 turns off again after the fixed time and the process repeats again and again. Picture:Drive LED Circuit of Voltage Dropping Model DC／DC Converter   (View)

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WATER_ACTIVATED_ALARM

Published:2009/6/23 3:42:00 Author:May

When sensor gets wet, it conducts, forward-biases Q1, and activates audio oscillator U1. A tone is heard from the speaker.   (View)

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POSITIVE_REGULATO_WITH_o_TO_70_V_OUTPUT

Published:2009/6/23 4:34:00 Author:Jessie

The op amp has one input at ground and a reference current drawn from its summing junction. With this arrangement, the output voltage is proportional to setting resistor R2. A negative supply is used to operate the op amp within its common-mode range, providing zero output with sink current and power a low-voltage bandgap reference, D1. The current drawn from this supply is under 150 mA, except when sinking a load current. The output load capacitor, C2, is part of the op-amp frequency compensation.   (View)

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SIMPLE_TLO82_VCO

Published:2009/6/23 4:32:00 Author:Jessie

This circuit uses a dual operational amplifier (TL082) to form a voltage-controlled oscillator (VCO). With the component values shown, the output-frequency range is 100 Hz to 10 kHz when the input control voltage is between 0.05 and 10 V.   (View)

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DIODELESS_PEAK_HOLD_CIRCUIT

Published:2009/6/23 3:38:00 Author:May

The input pulse is fed into the sample-and-hold amplifier (an inexpensive AD582), as well as the comparator U3. The SHA's output also is fed into the comparator. If the input pulse is higher in am-plitude than the SHA's output, the comparator output goes low and the 4538 one-shot produces a l0-ps pulse that is fed back to cause the SHA to sample and then hold the voltage. Subsequent input voltages that are less than the held value won't cause the one-shot to fire again.Gates U4A and U4B are used to inhibit the sampling when necessary. Gates U4C and U4D, at the one-shot's output, can force the AD 582 into the sample mode. This feature is useful to reset the output to zero by forcing a sample when the input to the AD582 is zero. The polarity of the peak-hold circuit can be easily changed from positive-to-negative peak hold by reversing the inputs of the comparator.   (View)

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MODEL_RAILROAD_CROSSING_FLASHER

Published:2009/6/23 4:27:00 Author:Jessie

Gate U1-c is set up as an oscillator whose frequency is determined by C1 and R1. Gates U1-b and U1-d are set up as an RS flip-flop that is gated on by U1-a. Gate U1-a in conjunction with Q1 operates as the control gate for the flip-flop. Components D1, C2, and lR5 act as a delay circuit to compensate for anylight getting throughthe gaps between cars as theypass over the phototransistors. The light-emitting diodes are connected so that they operate alternately, depending on the outputs of U1-d and U1-b.Basically, R6 is adjusted so that ambient room-light striking Q1(and any other phototransistors connected in series)keeps the output of U1-a at pin 3 low. When a car passes over the phototransis-tor, which is installed between ties in the track, pin 3 goes high, allowing a high to be placed on pins 5 and 13. That allows the high output of UI-c at pin 10 to enable pin 12, which in turn allows pin 11 to go low. That makes a complete path for LED2 to operate. When pin 10 goes low, pin 11 goes high.That makes pin 5 high, and thus, enables pin 4 to go low and completes the circuit for LED1. That alternates the LEDs, which are installed in a railroad-crossing signal.   (View)

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ACID_RAIN_MONITOR

Published:2009/6/23 3:37:00 Author:May

The drain-to-source resistance of Q1 varies depending on the acidity of the sample presented to Q1's gate circuit. That variable resistance varies the current flowing through the bridge; that current is proportional to pH.   (View)

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MODEL_RAILROAD_TRACK_CONTROL_SIGNAL

Published:2009/6/23 4:30:00 Author:Jessie

When a train passesS1 (a red switch), a small magnet glued to the underside operates Sl and causes UI to generate a pulse, activating relay K1 and changing the signal from green to red. After a time determined by RI and C1 (see table), the relay de-energizes and the signal goes back to green.   (View)

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BIRD_FEEDER_MONITOR

Published:2009/6/23 3:35:00 Author:May

The first amplifier circuit is a bird phone. In this circuit, the electret mike (MIC1) is mounted in the neck of a large plastic funnel. The amplifier, built around an MC34119 (which is available from D.C. Electronics, P.O. Box 3203, Scottsdale, AZ 85271-3203; Tel. 800-467-7736, and elsewhere), is then placed outside of the funnel with the pick-up facing a nearby bird feeder. The output of the amplifier is then connected to a 16-Ω speaker. The amplifier's voltage gain is determined by the values of the input resistor (R1) and the feed-back resistor (R3 and R4, respectively). The differential gain of the amplifier is given by: R3 + R4/R1 × 2. With the component values shown, the maximum voltage gain is about 270. This permits listening to the activity at the bird feeder.   (View)

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LOW_NOISE_5_V_SUPPLY

Published:2009/6/23 4:23:00 Author:Jessie

Standard three-terrrtinal regulator ICs can be noisy. The key is the noise over the 10-Hz to 10-kHz band; measurements revealed a 40-dB improvement over standard three-terminal regulators.The regulator is built around a 5-V buried-Zener reference. It's the buried Zener's inherently low noise that makes the finished supply so quiet. Measured over a 10-Hz to 10-kHz band, the 5-V out-put contains just 7 μV rms of noise at full load. The 10-Hz to 10-kHz noise can be further reduced to 2.5 μV rms by adding a 100-p,H, 1000-μF output filter. The noise characteristics of the reference are tested and guaranteed to a maximum of 11 μV over the band of interest.An extemal boost transistor, the ZBD949, provides gain to meet a 200-mA output current requirement. Current limiting is achieved by ballasting the pass transistor and clamping the base drive.Although the oscillator only requires 200 mA, it's possible to extend the output current to at least 1 A.   (View)

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DUAL_TONE_GENERATOR_FOR_AUDIO_SERVICING

Published:2009/6/23 3:34:00 Author:May

This dual-tone generator can insert a distinctive tone in the audio section of a circuit under test.That way, you can work your way back from the speaker, stage-by-stage, to locate a faulty section.   (View)

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GROUND_LOOP_PREVENTER

Published:2009/6/23 3:32:00 Author:May

Ground loops are caused by improper grounding. Ground-loop voltages can interfere with test rrteasurements because the voltages in a ground loop can be larger than the signals you're trying to measure. To prevent ground loops, use two wire plugs to provide the line power to the test instru-ments and a separate wire to bring the input grounds of the instruments to a common ground.   (View)

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