Under Voltage Lockout for Buck Circuit Using LM2575

This is a implementation for buck boost configuration. This circuit is control by LM2575. This is the figure of the circuit.


In some applications it is desirable to keep the regulator off until the input voltage reaches a certain threshold. These circuits keep the regulator off until the input voltage reaches a predetermined level.
VTH ≈ VZ1 + 2VBE (Q1)

Negative Booster Regulator

This is a circuit for the variation on the buck-boost topology is the negative boost configuration. This circuit is based on LM2575-12. This is the figure of the circuit.


The circuit accepts an input voltage ranging from −5V to −12V and provides a regulated −12V output. Input voltages greater than −12V will cause the output to rise above −12V, but will not damage the regulator. Because of the boosting function of this type of regulator, the switch current is relatively high, especially at low input voltages. Output load current limitations are a result of the maximum current rating of the switch. Also, boost regulators can not provide current limiting load protection in the event of a shorted load, so some other means (such as a fuse) may be necessary. [Circuit’s source: National Semiconductor Notes].

Inverting Buck Boost Circuit Using LM2575

This is a design circuit for inverter circuit. The circuit is built by LM2575. This is the figure of the circuit.


LM2575-12 in a buck-boost configuration to generate a negative 12V output from a positive input voltage. This circuit bootstraps the regulator's ground pin to the negative output voltage, then by grounding the feedback pin, the regulator senses the inverted output voltage and regulates it to −12V. For an input voltage of 12V or more, the maximum available output current in this configuration is approximately 0.35A. At lighter loads, the minimum input voltage required drops to approximately 4.7V. The switch currents in this buck-boost configuration are higher than in the standard buck-mode design, thus lowering the available output current. Also, the start-up input current of the buck-boost converter is higher than the standard buck-mode regulator, and this may overload an input power source with a current limit less than 1.5A. [Circuit’s source: National Semiconductor Notes].

Low Voltage Synchronous Buck Feedback

This is one of the application for low voltage feedback in PWM. This circuit is called as synchronous buck feedback. This circuit is proposes an alternate method for feeding back an output voltage lower than the PWM internal error amplifier reference voltage. This is the figure of the circuit.


Normally the output voltage is higher than the error amplifier reference, and so a simple resistive divider between VOUT and ground sets the regulated voltage at the non-inverting input of the PWM error amplifier. However, when VOUT is less than the error amplifier reference voltage, the feedback voltage must be divided up instead of down. Dividing up implies that some additional voltage must be added to the feedback from another regulated voltage source.[Schematic’s source: Texas Instrument Notes].

0 - 28V / 6 - 8A Power Supply Circuit

This is the complete design power supply circuit. This circuit has stable, clean and regulator 0-28V 6/8 Amp output voltage. This circuit is using transistor 2N3055. Although you could use this design to deliver 20 amps (with almost no modifications and with a proper transformer and a huge heat sink with a fan), it didn’t need much power. This is the figure of the circuit.


Although the 7815 power regulator will kick in on short circuit, overload and thermal overheating, the fuses in the primary section of the transformer and the fuse F2 at the output will secure your power supply. The rectified voltage of: 30 volt x SQR2 = 30 x 1.41 = 42.30 volt measured on C1. So, all the capacitors should be rated at 50 volts. Caution: 42 volt is the voltage that could be on the output if one of the transistors should blow. P1 allows you to 'regulate' the output voltage to anything between 0 and 28 volts. The LM317 lowest voltage is 1.2 volt. To have a zero voltage on the output I've put 3 diodes D7,D8 and D9 on the output of the LM317 to the base of the 2N3055 transistors. The LM317 maximum output voltage is 30 volts, but using the diodes D7,D8 & D9 the output voltage is approx 30v - (3x 0.6v) = 28.2volt. Calibrate your build-in voltmeter using P3 and, of course, a good digital voltmeter. P2 will allow you to set the limit of the maximum available amps at the output +Vcc. When using a 100 Ohm/1watt varistor the current is limited to approx. 3 Amps @ 47 Ohm and +- 1 Amp @ 100 Ohms.

Single Op Amp Band Pass Filter

This is a circuit design for a band pass filter. A band pass filter passes a range of frequencies while rejecting frequencies outside the upper and lower limits of the pass band. The range of frequencies to be passed is called the pass band and extends from a point below the center frequency to a point above the center frequency where the output voltage falls about 70% of the output voltage at the center frequency. This is the figure of the circuit.


The filter bandwidth (BW) is the difference between the upper and lower pass band frequencies. The quality factors, or Q of the filter is a measure of the distance between the upper and lower frequency points and is defined as (Center Frequency / BW) so that as the pass band gets narrower around the same center frequency, the Q factor becomes higher. For a single op-amp band pass filter with both capacitors the same value, the Q factor must be greater than the square root of half the gain, so that a gain of 98 would require a Q factor of 7 or more.

600 Volt Power Supply

This circuit is design for power supply that can produces 600 volt. This circuit is descript a full wave voltage doubler. The output voltage is twice the input voltage. For 230V AC input the output will be nearly 600 Volts. This is the figure of the circuit.


How is the circuit work? Resister R1 is used to limit the initial high voltage and high currents. Capacitor C1, C2, C3 together with coils L1 and L2 form input line filter. The capacitors C4 and C5 protect diodes from high voltage transients on the AC line as well as reduce inter carrier hum modulation of the R.F picked up by the mains. Capacitors C6 and C7 provides enough filtering for the output DC Voltage.

Part:
C1, C2, C3 - 0.1 mf 630V
C4, C5 - 0.01 mf 630V
C6, C7 - 100 mf 450V
R1 - 10E 5W Wire Wound
R2, R3 - 220KE 2Watts
D1, D2 - BY127
D3, D4 - BY127
L1, L2 - 12 Turns 18 SWG

12 Volt Off Line Power Supply

This is a simple circuit for switching power supply. This circuit is using converter concept. This is the figure of the circuit.

This circuit can work over an universal input AC line voltage range 90-240 VAC and provides 12 VDC output when over 4A loaded. Line and load regulation is better than 0,5%. This circuit has over current, over temperature, over voltage protection. The output ripple is approximately 0,2Volt peak to peak.

10 Amp 13, 8 Volt Power Supply

This is a design for power supply. This circuit is using LM723 for voltage regulator. This is a simple design circuit. This is the figure of the circuit.

The circuit even has a current limiting feature which is a more reliable system than most commercial units have. The circuit uses 3 pass transistors which must be heat sink. Resistor R9 allows the fine tuning of the voltage to exactly 13.8 volts and the resistor network formed by resistors R4 through R7 controls the current limiting. The LM723 limits the current when the voltage drop across R5 approaches .7 volts. To reduce costs, most commercial units rely on the HFE of the pass transistors to determine the current limiting. The fault in that system is that the HFE of the pass transistors actually increases when the transistors heat up and risks a thermal runaway condition causing a possible failure of the pass transistors. Because this circuit samples the collector current of the pass transistors, thermal runaway is not a problem in this circuit making it a much more reliable power supply.

The only adjustment required is setting R9 to the desired output voltage of anywhere between 10 and 14 volts. You may use a front panel mounted 1K potentiometer for this purpose if desired. Resistor R1 only enhances temperature stability and can be eliminated if desired by connecting pins 5 and 6 of IC-1 together. Although it really isn't needed due to the type of current limiting circuit used, over voltage protection can be added to the circuit by connecting the circuit of Figure 2 to Vout. The only way over voltage could occur is if transistors Q2 or Q3 were to fail with a collector to emitter short. Although collector to emitter shorts do happen, it is more much more likely that the transistors will open up when they fail.

PLL FM Demodulator Circuit Module

This is a circuit about PLL system that can be used to implement an FM demodulator. Since the VCO output tracks the FM signal, and the VCO input voltage is proportional to the VCO output frequency, then the VCO input will be equal to the demodulated signal. This circuit is based on phase comparator and VCO. This is the figure of the circuit.


For this example, an FM signal consisting of a 10-kHz carrier frequency was modulated by a 400-Hz audio signal. The schematic diagram shows the connections of the CD4046B as an FM demodulator. The total FM signal amplitude is 500 mV, therefore, the signal must be ac coupled to the signal input (terminal 14). Phase comparator I is used for this application because a PLL system with a center frequency equal to the FM carrier frequency is needed. Phase comparator I lends itself to this application also because of its high signal-input-noise-rejection characteristics.

Pierce XTAL Oscillator Circuit Using JFET

This circuit is conventional “Pierce” type oscillator that uses a JFET. The circuit uses fundamental mode crystals. It has decent performance and reliability if we use a low noise JFET. This is the figure of the circuit.


The feedback is controlled by the C1 Capacitance from drain to ground. Adjusting the frequency can be done by adjusting a shunt capacitance C2 across the crystal. The crystal works in parallel mode. This circuit is suitable where some crystals should be switched in and out to select the frequency, as there’s no tuning required.

Linear Thermo Electric Cooler Driver

This circuit is becoming popular because of its robustness and maintenance free characteristic. This driver is capable of delivering ±2A into a TEC. This circuit operates on a single +5V supply and drives the TEC in the most preferred “constant-current” mode. This is the figure of the circuit.


This TEC driver amplifier is a voltage-controlled current source. Constant current drive eliminates the effect of thermal “back EMF” on current through the TEC under dynamic temperature control conditions. Constant-current drive also assures that TEC drive current is independent of production variations in TEC junctions or long-term aging.

Current Loop Transmitter Circuit for Temperature Sensor

This circuit provide current loop transmitter for temperature sensor. Current loop interface has been widely used in industrial environment because it’s robustness. This is the figure of the circuit.


The temperature measurement is done by LM35 temperature sensor chip. You can use general silicone diode such as 1N4001. The current controller function is done by LM317 current/voltage regulator. This circuit will draw a consistent current proportional to the temperature being measured, regardless the supply voltage variation caused by noise or long wire’s temperature-dependent resistance variation.

10 Watt Linear Amplifier Circuit

This is a 10 watt linear amplifier that is capable of delivering over 15 watts into 50 ohms and uses cheap plastic transistors that are used in CB equipment. This circuit is based on transistor. This is the figure of the circuit.


The bias generator transistor, TR4, is marked TIP31 in the circuit diagram, but here you can use just about anything that will fit. You could even use another 2SC2078, if you had money to burn, but more practical components would be TIP41, TIP3055, MJE3055. All that matters is that it will pass up to 1 Ampere and have the correct base details in a TO220 case. The amplifier has a wide bandwidth, from 1.8 MHz through to over 30 MHz. The drive level required is only about 2 - 5 mW under 14 MHz, rising to 10 mW at 30 MHz. You can therefore make a good QRP CW rig with nothing more than this PA and a simple crystal oscillator. [Schematic source: Harry Lythall Notes]

Automatic 12V Lead-Acid Battery Charger Circuit

This is design for charger circuit that is suitable for lead-acid battery, including flooded, gel, and AGM types. This circuit is simple design. This is the figure of the circuit.


The automatic term means that this charger will stop charging automatically when the battery voltage reach a certain pint, indicating that the battery has been fully charged, and charging will be restarted if the battery voltage falls below that threshold. A LED indicator is provided to show you when the battery is fully charged. This automatic battery charger can be left connected to a battery indefinitely to maintain full charge safely.

How is the circuit work?
1. R2 is used to adjust the final voltage when the charger should stop charging. For flooded and gel type, the batteries are usually charged to 13.8V. For cycling the battery (AGM or gel), 14.5V to 14.9V is usually recommended by battery manufacturers. Set the R2 pot to midpoint, turn on the charger and connect a battery to its output. Monitor the charge with a voltmeter until the battery reaches the proper end voltage, then adjust the pot until the LED glows constantly. To charge different types of batteries, you can mount the pot on the front of the case and mark each position of every battery types ending voltage.
2. Install proper heat sink for Q1. A small fan might be necessary and can generally be powered right off the output of D1 If the circuit is mounted in a case.
3. Choose T1 transformer which is appropriate for your local line voltage (120V, 220V, etc.) with 12 Volt secondary output.
4. If the circuit is powered off, you should disconnect the battery because the circuit will drain the battery slowly, and this could damage your battery if the battery is drained while it’s voltage falls below about 10V.

High Frequency Waveform Generator

This is the circuit of waveform generator. Waveform generator is very useful in electronic experiment and design. This circuit is generates sine wave oscillation, but actually we can modify the circuit to generate triangle or square wave function. This is the figure of the circuit.


This circuit is based on MAXIM IC. This integrated circuit chip gives complete function to build a waveform generator/function generator. Here some of modifications that can be used to build a complete waveform generator circuit:

· The circuit can be used to generate square wave, triangle, or sine wave by programming the pin inputs (A0: pin 3, A1:pin 4).
o A0 A1 WAVEFORM
o X 1 Sine wave
o 0 0 Square wave
o 1 0 Triangle wave

· The frequency can be controlled using current. If we disconnect the 20k RIN from REF (pin 1) and connect it to a DAC, then we can control the frequency using microcontroller or digital interface. We can even control the chip using a quartz crystal (PLL) by controlling the current using a phase comparator output that compares the sync output (pin 14 of MAX038) and a reference clock from quartz crystal oscillator.

Indoor and Outdoor Temperature Controller

This is a design controller for indoor and outdoor temperature. This circuit is intended for controlling a heating system or central heating plan, keep room temperature constant despite changes in the external one. This is the figure of the circuit.


In principle of work this circuit is when the Q1 to the ground voltage by less than half of supply voltage (determined by R7 & R9), the voltage generated in the R8 and the driver transistors Q2 & Q3-switch on the relay. Two sensors required, one placed outside the home, to sense an external temperature. When Q1 Base voltage to the ground more than half of the voltage supply, caused when one of NTC thermistor low value because of the increase in temperature, voltage does not appear in the R8 and the Relay is not active. C3 allows clean switching of Relay. P1 functions as the main temperature control.

Part:
P1 = 1K Linear Potentiometer
R1 = 10R
R2 = 1K
R3 = 3K3 @ 20°C n.t.c. Thermistor
R4 = 2K2 @ 20°C n.t.c. Thermistor
R5 = 10K
R6 = 3K3
R7,R9 = 4K7
R8 = 470K
R10 = 10K
C1,C2 = 470µF 25V
C3 = 1µF
D1,D2,D4 = 1N4002
D3 = LED Red
Q1 = BC557
Q2 = BC547
Q3 = BC337
RL1 = Relay with SPDT 2A @ 220V switch
Coil Voltage 12V. Coil resistance 200-300 Ohm
T1 = 220V Primary, 12 + 12V Secondary 3VA Mains transformer