Electronic Repairing: Circuits

Constant Current Regulator Circuit Diagram

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<tr><td class="tr-caption" style="text-align: center;"><i>Constant Current Regulator Circuit Diagram</i></td></tr>
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This fixed 1-mA current source delivers a fixed current to a load connected between Q1's collector and ground; the load can be anywhere in the range from 0 n to 14 n. The circuit is powered from a regulated 15-V supply , and the R1/R2 voltage divider applies a 14-V reference to R3. The op amp's output automatically adjusts to provide an identical voltage at the junction of R4 and R5. That produces 1 V across R5 ,r esulting in an R5 current ofl rnA. Because that current is derived from Q1's emitter, and the emitter and collector currents of a transistor are almost identical, the circuit provides a fixed-current source. The output current can be doubled by halving the value of R5.</div>
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Constant Current Regulator Circuit Diagram

Constant Current Regulator Circuit Diagram This fixed 1-mA current source delivers a fixed current to a load connected between Q1'...

Active Antenna Circuit Schematic

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<tr><td class="tr-caption" style="text-align: center;"><i><span style="color: #666666;">Active Antenna Circuit Schematic</span></i></td></tr>
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<span style="color: #666666;">This circuit is designed to make a short pull-up aotenna perform like a long wire aotenna, while offering no voltage gaio. The circuit boosts the receiver's performaoce only if the signal at the antenna is of sufficient level to begio with.This circuit takes a short pull-up antenna that has a high output impedaoce aod couples it to the receiver's low input impedaoce through a two-traosistor impedaoce-matching network. Traosistor Q1's high input impedaoce and high-frequency characteristics make it a good match for the short antenna, aod Q2's low output impedaoce is a close match for the receiver's input. This circuit is usable over the raoge from 100kHz to 30 MHz.</span></div>

Active Antenna Circuit Schematic

Active Antenna Circuit Schematic This circuit is designed to make a short pull-up aotenna perform like a long wire aotenna, while off...

Switch Mode Voltage Regulator Circuit Diagram

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<tr><td class="tr-caption" style="text-align: center;"><i><span style="color: #666666;">Switch Mode Voltage Regulator Circuit Diagram</span></i></td></tr>
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<span style="color: #666666;">Switch-mode power supplies offer the benefit of a much greater efficiency than obtainable with a traditional</span></div>
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<span style="color: #666666;">power supply. The switch-mode regulator presented here has an efficiency of around 85%. An input voltage of 12 to 16 V dc is converted into a direct voltage of exactly 5 V. The use of a MAX638CPA enables the design and construction of the regulator to be kept fairly siruple: only nine additional components are needed to complete the circuit. Resistors R1 and R2 are used to indicate when the battery voltage becomes low: as soon as the voltage on pin 3 becomes lower than 1.3 V, D1 lights. With values as shown for the potential divider, this corresponds to the supply voltage getting lower than about 6.5 V. The output of the IC is shunted by a siruple LC filter formed hy L1, C3 and D2. The oscillator on board the IC generates a clock frequency of around 65 kHz and drives the output transistor via two NOR gates. The built-in error detector, the ''battery low'' indicator or the voltage comparator can block the clock frequency , which causes the transistor to switch off. The IC compares the output voltage of 5 V with a built-in reference (FET). Depending on the load, the FET will be switched on for longer or shorter periods. The maximum current through the FET is 375 rnA, which corresponds with a maximum output current of 80 rnA.</span></div>

Switch Mode Voltage Regulator Circuit Diagram

Switch Mode Voltage Regulator Circuit Diagram Switch-mode power supplies offer the benefit of a much greater efficiency than obtainab...

Short circuit protection circuit diagram

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<span style="color: #666666; font-size: large;"><i>Short circuit protection circuit diagram</i></span></div>
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<tr><td class="tr-caption" style="text-align: center;">Short circuit protection circuit diagram</td></tr>
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<b><i><span style="color: #666666;">Circuit Description</span></i></b></div>
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<span style="color: #666666;">When Sl is pressed, the coil of K1 is energized, closing its normally open contacts. If the regulated de input is between 1 and 24 V, that voltage feeds the base of Q1 through Rl, turning on the transistor, and latching the relay. When that occurs, LED2 glows indicating that all is okay. If there is a short to ground at the circuit's output (i.e., in the device being powered), the voltage that feeds the base of Q1 goes to zero, turning off the transistor. Then, LEDl glows because K1 is de-energized to indicate the short circuit.</span></div>

Short circuit protection circuit diagram

Short circuit protection circuit diagram Short circuit protection circuit diagram Circuit Description When Sl is pressed, the coil ...

5 volt variable power supply circuit

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<tr><td class="tr-caption" style="text-align: center;">5 volt variable power supply circuit </td></tr>
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<span style="color: #666666;"><b><i>Circuit Description</i></b></span></div>
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<span style="color: #666666;">Although linear-regulator !Cs are frequently used in variable power-supply applications, they might noLalways be the best choice. At low output voltages, power losses in these regulators can cause headaches for designers. For example, if an output current of 1.25 A is required at 1.25 V from an input of 8 V. a regulator (such as the LT317) dissipates more than 10 W. The figure depicts a de-de converter that functionally replaces a linear regulator in the just described application. The converter not only eliminates the problem of power loss, but it can be adjusted for output voltages (as low as 25 mY) while delivering an output current of 1.5 A. The circuit uses a basic positive-buck topology with one exception. A control voltage is applied through R4 to the feedback summing node at pin 1 of the LT1076 regulator JC, making it possible to adjust the output from 0 V to approximately 6 V. This range encompasses the 3.3-V and 5-V logic supply voltages for portable and desktop equipment, as well as battery-pack combinations of one to four cells. As R4 is driven from 0 to 5 V by the buffer (Ul), more or less current is required from R2 to satisfy the loop's desire to hold the feedback swmning point at 2.37 V. This forces the converter's output to swing over the range of 0 to 6 V. The LT1076 is capable of 1.75-A guaranteed output current in this application, ;md 2 A is typical. If more current is required, the LTl 07 4 can be substituted for the 1:1'1076.</span></div>

5 volt variable power supply circuit

5 volt variable power supply circuit Circuit Description Although linear-regulator !Cs are frequently used in variable power-supply ...

12v power supply circuit

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<b><span style="color: #666666; font-size: large;"><i>12V Power Supply Circuit Diagram</i></span></b></div>
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<tr><td class="tr-caption" style="text-align: center;">12v power supply circuit</td></tr>
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<b><i><span style="color: #666666;">Description</span></i></b></div>
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<span style="color: #666666;">This 12-V power supply is easy-to-build, and it produces a smooth output. D1 is a 14-V, \1-W Zener diode. The voltage can be varied by a few volts up or down to change the output voltage.</span></div>

12v power supply circuit

12V Power Supply Circuit Diagram 12v power supply circuit Description This 12-V power supply is easy-to-build, and it produces a ...

Low battery indicator circuit diagram

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<tr><td class="tr-caption"><i>Low battery indicator circuit diagram</i></td></tr>
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<b><i><span style="color: #666666;">Description</span></i></b></div>
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<span style="color: #666666;">The sensing circuit consists of a 741 op amp set up as a voltage comparator, using a zener diode as a voltage reference. The op amp is inserted as a bridge between two resistance ladders, one which contains the zener reference, and the other a high-value linear potentiometer. When the voltage at the wiper of the potentiometer drops below the voltage set by the zener, the output of the op amp becomes low; that turns on the LED connected between it and Vee. The circuit can be adapted to work with battery-powered circuits that require between 6 and 18 V; the only changes needed would be a lower-voltage zener and a smaller current-limiting resistor in the case of voltage below 9 V, and a larger resistor for higher voltages.</span></div>

Low battery indicator circuit diagram

Low battery indicator circuit diagram Description The sensing circuit consists of a 741 op amp set up as a voltage comparator, usin...

8w audio amplifier circuits

This audio power amp (built around an LM383 8-W, audio power amplifier) can be used to boost an audio signal to a sufficient level so that it can be heard in a high-noise environment. Note that LM383 should be heatsinked.<br />
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<i>Audio Amplifier Circuit</i></div>
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<tr><td class="tr-caption" style="text-align: center;">8w audio amplifier circuits</td></tr>
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8w audio amplifier circuits

This audio power amp (built around an LM383 8-W, audio power amplifier) can be used to boost an audio signal to a sufficient level so that i...

AC/DC converter circuit

AC/DC converter circuit

AC/DC converter circuit A de level is produced that corresponds to the ac input rms value (if sine wave). i; set the gain of IC2 to 1.1...

12V BATTERY CHARGER CIRCUIT

<span style="color: #666666;">This high-performance charger quickly charges gelled lead-acid batteries, and turns off at full charge. At first, the charge current is held at 2 A, but as battery voltage rises, current decreases. When current falls to 150 rnA, the charger automatically switches to a lower float voltage to keep from overcharging. When you hit full charge, transistor Qllights the LED to indicate that status.</span><br />
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<tr><td class="tr-caption" style="text-align: center;">12V BATTERY CHARGER CIRCUIT</td></tr>
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12V BATTERY CHARGER CIRCUIT

This high-performance charger quickly charges gelled lead-acid batteries, and turns off at full charge. At first, the charge current is held...

DIGITAL ENTRY LOCK

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<span style="color: #666666;">A keypad enters a four-digit access code, which is programmed via jumpers on a 24-pin plug-in header and socket. Ul is an LST220. which detects a four-digit sequential data input. When the correct data is entered into the keyboard, pin 13 of Ul goes high, which activates Ql and Kl. Kl drives an external electric lock solenoid, etc.</span></div>

DIGITAL ENTRY LOCK

A keypad enters a four-digit access code, which is programmed via jumpers on a 24-pin plug-in header and socket. Ul is an LST220. which...

TRANSISTOR TESTER

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<span style="color: #666666;">A 555 timer drives Ql through Q4 with a square wave. LEDl and LED2light when an npn or pnp transistor respectively, are connected to the text terminals. If LED3 and LED4 light equally as LEDl and LED2, the transistor is functional. If LED3 and LED4 are brighter than LEDl or LED2, the transistor is shorted.</span></div>
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<span style="background-color: white; font-family: Verdana, Geneva, sans-serif; font-size: 12px; line-height: 19.200000762939453px;"><span style="color: #666666;">(Source: Encyclopedia of electronic circuits volume 4)</span></span></div>

TRANSISTOR TESTER

A 555 timer drives Ql through Q4 with a square wave. LEDl and LED2light when an npn or pnp transistor respectively, are connected to the ...

Electronic Ignition Circuit Diagram

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This electronic ignition circuit is intended to be inserted into a car's conventional ignition system. In<br />
effect, it replaces tbe original I2-V switching circuit in tbe primary winding of tbe coil by one generating<br />
more tban IOO V. It thereby converts a current circuit, which is upset by lead and stray resistance, into a<br />
voltage circuit that is much more efficient.<br />
The pulses emanating from the contact breaker, shown at tbe extreme lower left-hand side of the diagram,<br />
are applied to transistor Tl and subsequently differentiated by R3/CI. This causes a negligible ignition<br />
delay. The current through the contact-breaker points is determined by the value of Rl. This value has<br />
been chosen to ensure tbat tbe points remain clean.<br />
Transistor TI is followed by two monostables, !CIA and !CIB, which are both triggered by the output<br />
pulses of Tl. However, whereas !CIA is triggered by tbe trailing edge, ICIB is triggered by the leading<br />
edge.<br />
Monostable !CIA passes a pulse of about 1.5 ms (determined by R4/C2) to NAND gate IC2A. This<br />
gate switches off high-voltage Darlington T3 via gates IC2B, IC2C and IC2D, and driver T2, for the duration.<br />
of tbe pulse. Gate IC2 ensures that T3 is switched on only when the engine is running, to prevent a<br />
current of some amperes flowing through the ignition coil.<br />
As long as pulses emanate from the contact breaker, I ClB is triggered and its Q output remains logic<br />
high. The mono time of this stage is about I s and is determined by R5/C3.<br />
Darlington T3 is switched on via T2 and IC2A through IC2D as long as !CIA does not pass an ignition<br />
pulse. When the engine is not running, the Q output of IC2B goes low after I s and this causes T2 and T3<br />
to be switched off. The two series-connected ISO-V zener diodes protect the collector of tbe BU932R<br />
against too high of a voltage. The Darlington must be fitted on a suitable heatsink.<br />
(Source: Encyclopedia of electronic circuits volume 4)

Electronic Ignition Circuit Diagram

This electronic ignition circuit is intended to be inserted into a car's conventional ignition system. In effect, it replaces tbe ori...