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.
Thursday, November 20, 2014
15W Stereo audio Amplifier using TDA 4935
TDA4935 2x15W audio amplifier is high quality Siemens IC. The IC can be used in stereo or bridge mode. In stereo mode can deliver 15W Stereo audio Amplifier using TDA 4935 per channel in bridge mode can deliver 30W to an 8 ohm load at the source of 30V. TDA4935 requires very few external components and has an ample supply voltage range. The IC operates in class B and has built-in protection circuits over temperature and overload protection.
Notes :
- The circuit must be assembled on a good quality PCB.
- TDA 4935 must be fitted with a proper heat sink.
- The supply voltage can be anything between 8 to 30V DC.
- Capacitors C1, C2, C8 are polyester capacitors.
- Capacitors C3, C4 and C6 are ceramic capacitors while C5 and C9 are electrolytic.
Lightning Protection ELCB
Lightning Protection ELCB (CIRCUIT BREAKER Earth Leakage)
Installation of a building usually equipped with a safety short circuit current and current limiters. In the event of a short-circuit the safety fuse will break, and when the series occurred over the current-limiting load (MCB) will open the circuit so that circuit current flow to the inside of the building to be disconnected.
If it occurs in an electrical installation safety is a leakage current and current-limiting fuses can not provide security so that the power loss will occur continuously. Apart from that, if there are power users have a leakage current and untouched by humans, the safety will not be decided so that the electrical circuit is quite dangerous it would be safe if the installation is already installed grounding.
But when man-voltage electrical power users then all these safety devices can not be secured. For that installed a safety device, called an Earth Leakage Circuit Breaker or ELCB. This tool is able to decide the relationship string of leakage current in the event of 30 MA in a time of 0.1 seconds. Leakage current is intended to be through electrical components in the normal state of no voltage or phase conductor directly touched by humans.
How it Works chain of ELCB
ELCB separate chain consists of a magnetic coil and switch. This switch can be manually controlled electric and magnetic fields. If the position of liaison ELCB switch is closed, then the source voltage will flow gets the load. Magnet coils which will open the circuit to work when there is an electric current flowing in the coil. Magnet coil circuit that will open, works when there is an electric current flowing in the coil. ELCB magnet coil also called z. Travo, which normally do not get the voltage. If there is leakage current is z. Travo will work to open the circuit by pulling the main chain of the switch should be set up in advance for reuse and so on.
Automatic Battery Charger Circuit
Basically the circuit designed above have a very simple way of working, where the circuit is designed so that does not happen short circuit or short circuit between the voltage supply with batteries that will be in-charge.
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It is true that if any one wants to try to direct mengghubungkan between supply with batteries then the batteries can be sure will be filled. But the current flowing through a charged battery can not be controlled and if the battery is full, the batteries will be damaged or worn out if it remains on the short circuit condition.
Working Principle Battery Charger
By the time we put an empty battery charging terminals, transistor Q1 will be activated immediately because the current flows through R1 and would trigger a transistor Q1 base. In this condition the flow that would fill the batteries mostly comes from the collector of Q1 is connected directly to the positive terminal of supply. Then during the charging process increases the battery voltage will increase the current flowing in Q2 base via 10 Kohm R5, VR1 and diode D2. VR1 is a component that is used as an initial calibration to determine the exact position in the planning process of switching circuit. For VR1 you can use a trimpot or potensio according to your taste. At the beginning of filling, arrange potensio at position D3 LED indicators on the condition of death, and the current flowing into the collector of Q1 is not too big and not too small.
If the battery is fully charged, the LED indicator will light up automatically because of an increase in voltage on the battery charge will cause the increase of current flowing at the base of transistor Q2 and will terminate the charging cycle due to transistor Q1 having a cut-off due to lack of base current. Why on condition Q1 base current will experience a shortage of this is because almost all the current flowing in R1 10 Kohm will switch to a diode D1 which is logically connected directly with ground experience due Q2 saturated.
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Component List
1. Resistors: R1 (10 Kohm), R2 (680 ohms), R3 (100 Kohm), R5 (10 Kohm) and VR1 (Potensio / trimpot = 100 Kohm)
2. Diodes: D1 & D2 (IN4002) and D3 (Led)
3. Transistors: Q1 and Q2 (2N3904)
4. 9 volt power supply
By the time we put an empty battery charging terminals, transistor Q1 will be activated immediately because the current flows through R1 and would trigger a transistor Q1 base. In this condition the flow that would fill the batteries mostly comes from the collector of Q1 is connected directly to the positive terminal of supply. Then during the charging process increases the battery voltage will increase the current flowing in Q2 base via 10 Kohm R5, VR1 and diode D2. VR1 is a component that is used as an initial calibration to determine the exact position in the planning process of switching circuit. For VR1 you can use a trimpot or potensio according to your taste. At the beginning of filling, arrange potensio at position D3 LED indicators on the condition of death, and the current flowing into the collector of Q1 is not too big and not too small.
If the battery is fully charged, the LED indicator will light up automatically because of an increase in voltage on the battery charge will cause the increase of current flowing at the base of transistor Q2 and will terminate the charging cycle due to transistor Q1 having a cut-off due to lack of base current. Why on condition Q1 base current will experience a shortage of this is because almost all the current flowing in R1 10 Kohm will switch to a diode D1 which is logically connected directly with ground experience due Q2 saturated.
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Component List
1. Resistors: R1 (10 Kohm), R2 (680 ohms), R3 (100 Kohm), R5 (10 Kohm) and VR1 (Potensio / trimpot = 100 Kohm)
2. Diodes: D1 & D2 (IN4002) and D3 (Led)
3. Transistors: Q1 and Q2 (2N3904)
4. 9 volt power supply
Wednesday, November 19, 2014
Surround Power Amplifier LM3886
Audio Power Amplifier is an important part in the reproduction of sound in a sound system. Audio Power Amplifier LM 3886 with power IC Audio Power Amplifier is a highly capable and able to produce 68 Watts with power rata2 4Ohm load and capable of producing power 38 Watt with 8Ohm load.
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With good sound reproduction capabilities of 20Hz-20kHz is also included on this LM3886 Audio Power Amplifier. LM3886 Audio Power Amplifier is equipped with spike protection that will protect the output circuit from overvoltage, undervoltage, overloads, konrsleting power supply, thermal runawaydan peak temperature. Audio Power Amplifier LM3886 also features a noise reduction system which can keep the audio from the noise well.
Basic Audio Power Amplifier Series LM3886
Audio Power Amplifier LM3886
Feature owned LM3886 Audio Power Amplifier
68W cont. avg. output power into 4Ω at VCC = ± 28V
38W cont. avg. output power into 8Ω at VCC = ± 28V
50W cont. avg. output power into 8Ω at VCC = ± 35V
135W instantaneous peak output power capability
Signal-to-Noise Ratio ≥ 92dB
An input mute function
Output protection from a short to ground or to the supplies via internal current limiting circuitry
Output over-voltage protection against transients from inductive loads
Supply under-voltage protection, not allowing internal biasing to occur Pls | VEE | + | VCC | ≤ 12V, Thus eliminating turn-on and turn-off transients
11-lead TO-220 package
Wide supply range 20V - 94V
Application of Audio Power Amplifier LM3886
Stereo audio system
Active Speaker
High End Audio Power TV
Suround Power Amplifier
Power Supply with tube
Power supply with Z2C tubes are designed specifically to provide power supply voltage to the EL-34 tube amplifier push-pull in the previous article. Power supply with Z2C tube to tube power amplifier is made with a tube rectifier Z2C. Just as the power supply for power amplifier tube earlier, power supply also uses a filter 3 levels with kapsitor electrolyte. Circuit power supply with tube rectifier Z2C can give +210 VDC output voltage. A complete range of power supply for power amplifier tube can be seen in thethe following figure .
| Power Supply with tube |
Z2C on the rectifier tube in power supply with tube above require a supply voltage for the filaments taken from the other side of the transformer secondary. Power supply with Z2C tube is a power supply that dapt used as a substitute power supply for power amplifier tubes .
Flash Converting ADC 207
ADC 207 is the first to use Flash Converting An Advanced High Speed VLSI 1.2 micron CMOS process. The process that is able to do the ADC 207 as mentioned earlier is very great and makes the ADC 207 is unique. The speed of the process of this ADC has a good linearity and have a stable temperature. ADC 207 has a lower power consumption is 250 mW. ADC is working with +5 VDC voltage source and at a frequency of 20 MHz. ADC 207 has a small sampling time is 12nS, thus making the ideal sampling results. ADC 207 has 128 features auto balanced comparators with each conversion that serves to offset temperature and dynamic effects that exist. Resistor ladder in the ADC 207 has a mid point that is connected to an external voltage source and function in the conversion of 7-bit linearity. ADC 207 has 3 levels of output that is easy to connect it with external components.
ADC 207 Architecture
Feature ADC 207
- 7-bit flash A / D Converter
- Sampling frequency of 20 MHz
- Low power consumption (250mW)
- VCC 5 VDC
- 1.2 micron CMOS technology
- 7 bits with 3 levels of output gates and overflow bits
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