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Monday, January 26, 2015

Basics of Schmitt Trigger Circuits – Part 3

All Schmitt triggers are active devices relying on positive feedback to achieve their hysteresis action. The output goes to high whenever the input rises above a certain preset upper threshold limit, and goes to low whenever the input drops below a lower threshold limit.

The output retains its previous value (low or high), when the input is between the two threshold limits. This type of circuit is often used to clean up noisy signals, and convert an analogue waveform into a digital waveform (1’s and 0’s) with clean, fast edge transitions.

There are three methods typically used in implementing positive feedback to form a Schmitt trigger circuit. These methods are Parallel Feedback, Series Feedback, and Internal Feedback, and are discussed as follows. The parallel and series feedback techniques are actually dual versions of the same feedback circuit type.

Parallel Feedback

A parallel feedback circuit is sometimes called a modified input voltage circuit. In this circuit, the feedback is added directly to the input voltage, and does not affect the threshold voltage. As the feedback is added to the input when the output changes state, the input voltage has to shift by a greater amount in the opposite direction to cause further change in output.

If the output is low, and the input signal increases to the point where it crosses the threshold voltage and the output changes to high. Part of this output is applied directly to the input through a feedback loop, which “helps” the output voltage stay in its new state. This effectively increases the input voltage, which has same effect as lowering the threshold voltage. The threshold voltage itself is not changed, but the input now has to move farther in the downward direction to change the output to a low state. Once the output is low, this same process repeats itself to get back to the high state.

This circuit does not have to use a differential amplifier, as any single-ended non-inverting amplifier will work. Both the input signal and the output feedback are applied to the non-inverting input of the amplifier through resistors, and these two resistors form a weighted parallel summer. If there is an inverting input, it is set to a constant reference voltage. Examples of parallel feedback circuits are a collector-base coupled Schmitt trigger circuit or a non-inverting op-amp circuit, as shown:

Series Feedback

A dynamic threshold (series feedback) circuit operates in basically the same way as a parallel feedback circuit, except that the feedback from the output directly changes the threshold voltage instead of the input voltage. The feedback is subtracted from the threshold voltage, which has the same effect as adding feedback to the input voltage. As soon as the input crosses the threshold voltage limit, the threshold voltage changes to the opposite value. The input now has to change to a greater extent in the opposite direction to change the output state again.

The output is isolated from the input voltage and only affects the threshold voltage. Therefore, the input resistance can be made much higher for this series circuit compared to a parallel circuit.

This circuit is usually based on a differential amplifier where the input is connected to the inverting input and the output is connected to the non-inverting input through a resistor voltage divider. The voltage divider sets the threshold values, and the loop acts like a series voltage summer. Examples of this type are the classic transistor emitter-coupled Schmitt trigger and an inverting op-amp circuit, as shown here:

Internal Feedback

In this configuration, a Schmitt trigger is created by using two separate comparators (without hysteresis) for the two threshold limits. The outputs of these comparators are connected to the set and reset inputs of an RS flip-flop. The positive feedback is contained within the flip-flop, so there is no feedback to the comparators. The output of the RS flip-flop toggles high when the input goes above the upper threshold, and toggles low when the input goes below the lower threshold. When the input is between upper and lower thresholds, the output retains its previous state.

An example of a device that uses this technique is the 74HC14 made by NXP Semiconductors and Texas Instruments. This part consists of an upper threshold comparator and a lower threshold comparator, which are used to set and reset an RS flip-flop. The 74HC14 Schmitt trigger is one of the most popular devices for interfacing real world signals with digital electronics. The two threshold limits in this device are set at a fixed ratio of Vcc. This minimises the part count and keeps the circuit simple, but sometimes the threshold levels need to be changed for different kinds of input signal conditions. For example, the input signal range might be smaller than the fixed hysteresis voltage range. The threshold levels can be changed in the 74HC14 by connecting a negative feedback resistor from the output to input, and another resistor connecting the input signal to the input. This effectively reduces the fixed 30% positive feedback to some lower value, such as 15%. It is important to use high-value resistors for this (Mega-Ohm range) in order to keep the input resistance high.

Tuesday, November 18, 2014

Stereo Circuit Schematic of The ADAU1592 Audio Power Amplifier

Stereo Circuit Schematic of The ADAU1592 Audio Power Amplifier

This is a stereo circuit schematic of the ADAU1592, a 2-channel, bridge-tied amount (BTL) switching audio ability amplifier. You can administer ADAU1592 on collapsed console televisions, pc audio arrangement and/or mini-components applications.

According to the ADAU1592 datasheet, an alien aegis ambit is recommended to be added for applications that crave accumulation voltage (PVDD) >15 V, you can use RC snubber or Schottky diode for this purpose. To anticipate the exhausted frequencies of asynchronous clocks (if appliance assorted ADAU1592s) in the audio band, it is recommended to use alone one alarm antecedent if the ADAU1592s allotment the aforementioned ability supply.

You can additionally body a archetypal address appliance ambit of the ADAU1592 by affairs pin 11 (MO/ST) to argumentation high, with abundant account in the datasheet.

Monday, November 17, 2014

Protection of the Mosfet in flyback power supply

PKC-136 PEAK CLAMP CHARACTERISTICS VBR 160Vdc VDRM 700Vdc P 1.5W. See Circuits Diagram below :

Protection of the Mosfet in flyback power supply

Feature :
- Protection of the Mosfet in flyback power supply
- TRANSIL™ and blocking diode in a single package BENEFITS
- Accurate voltage clamping regardless load
- Reduced current loop
- Reduced EMI emission
- High integration
- Fast assembly
- Reduced losses in stand by mode

Friday, October 31, 2014

LM317 to create constant current of 2mA

I have a circuit where I want to have a constant current of 2mA through a variable resistor. Ive been told that I could probably use a LM317 as a current regulator, with one resistor on the ouput. But Ive read some places that the LM317 takes minimum 5-10mA load to function correctly.

How can I achieve a constant current output of 2mA when I dont know the resistance of the variable resistor?

The input voltage is about 2.755V. Output voltage doesnt matter, just the current.

Heres an image to my feeble attempt at a schematic:

The LM317 with the single series resistor between output and adjust input is actually a fixed current source, not a current limiter. You dont need the LM317 to create a current limiter, a few discrete components will do:

For a limiting at 2mA you select a 330Ω resistor for RSENSE. If there flows 2mA through it Q2 will start to conduct and reduce the base voltage of Q1, so that its current is cut off.

edit (re changed question)

Maybe youre focusing too much on the LM317. If you need a constant current you could use the LM234 which is a programmable current source for up to 10mA. You set the current with a resistor.

Monday, October 27, 2014

Different types of TV TUNER

TV tuner that is used on older models and new models of television there are some differences. Therefore, understanding the different types of tuner would be useful if we want to replace the tuner with the other models.

Supply voltage tuner.

Tuner older models generally use a supply voltage of 12v, the new models are commonly used 5V supply voltage. Some use a 9V voltage, but very rare.

TV TUNER

Voltage Synthesizer tuner (VS tuner)

Tuner that uses a tuning control (VT or BT) with a voltage between 0 to 33V Voltage Synthesizer tuner named. TV can be found on the aircraft models, old and new

Based on how the control band-switch, Tuner VS then there are 2 kinds, namely

Using 3-Band input sw, the VL-VH-U

Using 2-Band input sw, the Band SW1 and SW2 Band. This tuner is actually similar to the type of band 3-sw. For control-sw 2 band is in the tuner will still be converted into 3-sw bands.

Frequency Synthesizer tuner (FS tuner) or the type of PLL

Tuner wherein the tuning voltage and the voltage controlled band switching the digital communication through SDA and SCL. This tuner has a supply voltage Vcc, which is

5V is used for the digital tuner circuit control and

33V (fixed voltage or fixed) is used to control the voltage supplied to the tuning in the digital circuits within the tuner.

(Tuner old) sometimes there are additional circuit voltage of 12V to the tuner.

Frequency band.

Based on the wide range of revenue-frequency band, there are three kinds of tuner

Normal tuner

Superband tuner

Tuner hyperband

Normal tuner, the tuner that can receive broadcasts "on-air" (terrestrial) TV in the frequency band:

Frequency of VHF Band I - VL 41-68 Mhz
Band III - VH 174-230 Mhz
Frequency UHF Band IV - U 470-581 Mhz
Band V - U 582-960 Mhz
Band II 87.5 - 104 MHz is used for FM radio broadcasting
VL and VH bands used for broadcast channels 2 through 12
U bands used for broadcast channels 21 to 69

Superband Tuner and Hyperband, the tuner can receive broadcast as normal tuner plus the ability to receive broadcasts "off air" CATV (cable television).

S band using frequency band between VL and VH
H-band using a frequency band between VH and U
Superband Tuner can receive the broadcast band S
Hyperband tuner can receive broadcast band and S band H

Based on the IF frequency out

IF frequency tuner out there who have 38/38.9/45.75 Mhz frequency. In Indonesia generally use 38.9Mhz frequency, but sometimes there is a use 38.0Mhz

Based on the pin-out

There are several kinds of tuner long pin-out configuration. But now almost all the tuner is already using an international standard 11-pin

Universal tuner

China is now producing "universal tuner" 11-pin. Indonesia was just the market we do not know whether it exists or not. This tuner can be used to substitute for the various types of tuners and tuner can adjust to this direct voltage of 5, 9, or 12v.

RF antenna input connector

Form the antenna input connector there are two kinds, namely:

RCA type connectors
Antenna RF connector

Tuner modules

Tuner is a tuner module inside there are all Video IF amplifier circuit and the FM-detector. This kind of tuner is using VS and some are using the FS.

Tuner module has output like:

RF AGC-out
RF AFC-out
Audio-out
Video-out
Base band out, the signal to be processed into stereo sound circuit.

Except that in tuner is also sometimes diperlengkapa with audio-switch to TV / AV-in. Therefore, to the sound of the AV-in connected via Audio-in found on the tuner module. Sometimes the sound volume to be controlled in the tuner module.

SONY tuner module 1
SONY tuner module 2
Toshiba tuner module

Impedance input / output

Impedance tuner has all kinds of input / output 75 ohm.

How to distinguish 2-band tuners VS sw with PLL tuner FS

In all these circumstances and the removable pin 11 feet was not cut, it is sometimes difficult to distinguish between two band-tuner tuner sw with FS.

Some models have a tuner pin legs partially emptied. FS Tuner has a location pin 30V voltage 3 numbers from the back (of the IF pin out).

Sunday, October 5, 2014

How to calculate the value of a resistor using the color coded stripes on the resisto

To calculate the value of a resistor using the color coded stripes on the resistor, use the following procedure.

Step One: Turn the resistor so that the gold or silver stripe is at the right end of the resistor.

Step Two: Look at the color of the first two stripes on the left end. These correspond to the first two digits of the resistor value. Use the table given below to determine the first two digits.

Step Three: Look at the third stripe from the left. This corresponds to a multiplication value. Find the value using the table below.

Step Four: Multiply the two digit number from step two by the number from step three. This is the value of the resistor n ohms. The fourth stripe indicates the accuracy of the resistor. A gold stripe means the value of the resistor may vary by 5% from the value given by the stripes.

Resistor Color Codes (with gold or silver strip on right end)

Follow the above procedure with the examples below and soon you will be able to quickly determine the value of a resistor by just a glance at the color coded stripes.

Examples

Example1:
You are given a resistor whose stripes are colored from left to right as brown, black, orange, gold. Find the resistance value.

Step One: The gold stripe is on the right so go to Step Two.

Step Two: The first stripe is brown which has a value of 1. The second stripe is black which has a value of 0. Therefore the first two digits of the resistance value are 10.

Step Three: The third stripe is orange which means x 1,000.

Step Four: The value of the resistance is found as 10 x 1000 = 10,000 ohms (10 kilohms = 10 kohms).

The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 9,500 ohms and 10,500 ohms. (Since 5% of 10,000 = 0.05 x 10,000 = 500)

Example2:
You are given a resistor whose stripes are colored from left to right as orange, orange, brown, silver. Find the resistance value.

Step One: The silver stripe is on the right so go to Step Two.

Step Two: The first stripe is orange which has a value of 3. The second stripe is orange which has a value of 3. Therefore the first two digits of the resistance value are 33.

Step Three: The third stripe is brown which means x 10.

Step Four: The value of the resistance is found as 33 x 10 = 330 ohms.

The silver stripe means the actual value of the resistor mar vary by 10% meaning the actual value will be between 297 ohms and 363 ohms. (Since 10% of 330 = 0.10 x 330 = 33)

Example3:
You are given a resistor whose stripes are colored from left to right as blue, gray, red, gold. Find the resistance value.

Step One: The gold stripe is on the right so go to Step Two.

Step Two: The first stripe is blue which has a value of 6. The second stripe is gray which has a value of 8. Therefore the first two digits of the resistance value are 68.

Step Three: The third stripe is red which means x 100.

Step Four: The value of the resistance is found as 68 x 100 = 6800 ohms (6.8 kilohms = 6.8 kohms).

The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 6,460 ohms and 7,140 ohms. (Since 5% of 6,800 = 0.05 x 6,800 = 340)

Example 4:
You are given a resistor whose stripes are colored from left to right as green, brown, black, gold. Find the resistance value.

Step One: The gold stripe is on the right so go to Step Two.

Step Two: The first stripe is green which has a value of 5. The second stripe is brown which has a value of 1. Therefore the first two digits of the resistance value are 51.

Step Three: The third stripe is black which means x 1.

Step Four: The value of the resistance is found as 51 x 1 = 51 ohms.

The gold stripe means the actual value of the resistor mar vary by 5% meaning the actual value will be somewhere between 48.45 ohms and 53.55 ohms. (Since 5% of 51 = 0.05 x 51 = 2.55)

Other Resistor Information

There are some more rules that may be useful when working with resistors. You do not need to know them but if you need a resistor with a value that you do not have, you my be able to use the following information to create the value of resistor you need.

First Rule for Resistors : Series Connection

When two resistors are connected in series, as shown in Figure 1, the new resistance between points A and B is R1 + R2.

Figure 1

The resistors add together. For example if R1 = 500 ohms and R2 = 250 ohms then the resistance between points A and B would be R1 + R2 = 500 + 250 = 750 ohms.

Second Rule for Resistors : Parallel Connection

When two resistors are connected in parallel, as shown in Figure 2, the new resistance is smaller than either R1 or R2. The new resistance between points A and B is (R1 x R2) / (R1 + R2).

Figure 2

For example, if R1 = 500 and R2 = 250 then the resistance between points A and B = (500 x 250) / (500 + 250) = (125,000) / (750) = 167 ohms. If R1 = R2 then the new resistance is just R1 / 2.

Sunday, September 21, 2014

Power Supply with principle of UPS

For UPS Power Supply circuit consists of lowering the voltage, rectifier, charger, batery and regulators. The technique is applied from UPS on the power supply is the use of batery and charger is connected dengang direct coupling with a series diode. For more details can be seen with the following image.

Friday, September 19, 2014

Central Junction Fuse Panel Diagram Of 2004 Ford Focus ZXW

The following circuit shows about Central Junction Fuse Panel Diagram Of 2004 Ford Focus ZXW. The parts fuse panel consist of: heating and ventilation, anti lock control, electronic engine control, vehicle speed control, daytime running lamp, instrument cluster, anti theft active, speakers, exterior lighting, air conditioning, engine cooling charging n control, starting system, engine ignition, module communication network, horn, generator and regulator, audio unit, interior lighting.

Thursday, September 18, 2014

LM317 to create constant current of 2mA

How can I achieve a constant current output of 2mA when I dont know the resistance of the variable resistor?

The input voltage is about 2.755V. Output voltage doesnt matter, just the current.

Heres an image to my feeble attempt at a schematic:

enter image description here

For a limiting at 2mA you select a 330

Ω resistor for

RSENSE. If there flows 2mA through it Q2 will start to conduct and reduce the base voltage of Q1, so that its current is cut off.

edit (re changed question)

Maybe youre focusing too much on the LM317. If you need a constant current you could use the LM234 which is a programmable current source for up to 10mA. You set the current with a resistor.

Saturday, August 16, 2014

The New Technology of Auto Sound Systems

So what kind of auto sound system really seems to float your boat? Are you the type of person who wants the simplest sound system on the market today? Will you be content with talk radio and a few FM radio stations? Do you need an 8-track? How about a cassette player? I hate to say it, but if you are still living in the past, you will have a rather difficult time finding an audio system for your car that can accommodate your desire to hold technology behind the current trends. These things simply do not sell. You may find an occasional auto sound system that still has a cassette player but for the most part you will find that the market for this device is almost as limited as the quality of the device itself.

Todays auto sound systems are more sophisticated than they have ever been before. Gone are the days when you had to turn a dial to find a radio station. Today you can set your car to scan the stations until you find one you like. You can even set them to scan radio stations by type. For me, that was a great invention as I find country music rather sad and always end up finding the one song that will bring uninvited torrents of tears while flipping through the stations mindlessly as I drive. Being someone that hates to cry on any given day it is bad enough to cry. Add to that the fact that Im probably driving at about 75 or so miles an hour and you can probably see where this is problematic. I do best whenever I can avoid country music stations all together.

Another great technological advance when it comes to the auto sound system is individual volume control. No longer do you have to listen to your mothers, brothers, sisters, or Aunt Sallys music blaring, you can slide on your headphones and mute out the noise of the rest of the world. If your vehicle has a truly sophisticated sound system, you can even change the radio station in order to find music that is much more suitable for your musical tastes.

You should also be aware that todays auto sound systems are much more user friendly than those of days past. Most displays are digital and easy to read. You might even notice that many can read the local radio stations codes and formats and will list the songs that are playing for you. Youll never have to wonder about the name of that great song you just heard or even who sang it again. Its right before your eyes as you are driving along and listening to awesome tunes.

The best auto sound systems offer not only CD options to drivers and passengers alike but also the ability and capability of reading and interpreting MP3 data as well. More and more people are turning to MP3s for their primary source of music. It takes up far less space than your average CD holder and holds a lot more music. You can download only the songs you like without purchasing an entire CD full of songs only to find that you only liked one song on the entire CD. You can put your favorite songs on a memory stick and bring them along for the ride. Its a great way to enjoy music in this day and age. Im quite literally surprised that I havent seen an iPod auto sound system pop up on the radar yet and am seriously expecting to see one any day now, literally.

Regardless of whether or not you wish to enter the modern era of music and music listening its upon us. However, if you are truly opposed we could always find you a nice supply of Sinatra in MP3 format in order to make the transition a little more comfortable for you.