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Electronics Engineering
Electronics Engineering is a branch of engineering that deals with practical applications of electronic components, devices, systems, or equipment. Electronics are devices that operate on low voltage sources, as in electron tubes, transistors, integrated circuits, and printed circuit boards and use electricity as part of its driving force.
24,372 Questions
What does open collector output mean?
Open collector output is normally used in logic circuits and can be viewed as a common emitter configuration for a BJT transistor and normally of type NPN. A typical common emitter configuration requires the emitter to be connected to the ground and a resistor Rc from Vcc to the collector. When the transistor becomes forward biased, the collector will pulled the voltage across the resistor down, from approximately Vcc down to almost 0V, normally in the order of 0.1V at the collector.
We can see that the output at the collector will swing between Vcc and ground. In open collector outputs the collector resistor Rc and Vcc have been left out. This enables the engineer to use any voltage and any pull-up resistor that will meet the specifications of the output transistor.
Normally it is acceptable in logic circuits that multiple inputs may be connected to one output, but not multiple outputs to one input due to the nature of the active outputs. With open collectors however multiple outputs may be connected to one input without damaging the device.
Low state will result in a lower impedance than a high state since the high state is obtained by current flowing from Vcc through the pull-up resistor Rc.
Open collector can be used to convert 5V logic to 8V or 12V logic or down to 3.3V since the logic high will be determined by the external supply to the pull up resistor.
Open collector also prevents component failure during output short-circuit or over-current. If an open collector is short circuited to the ground, it will cause no harm to the device since all the current will be supplied via the Rc resistor. Short circuit to a +supply rail can however damage the device.
Open collector is not used that commonly anymore but many variations of the same concept can be found in modern electronics. For example: micro processor devices that employ a I2C (Inter-Integrated Circuit) communications interface make use of a open-drain lines.
It appears to work very much in the same fashion with pull-up resistors and all. Open drain is associated with MOSFET transistors instead of BJT's. In this example an I2C interface will fail if pull-up resistors are not used. Like open collector, open drain lines are also passive and does not provide any active high output of its own. The High output is supplied by Vcc via the Rc or Rp pull-up resistors. The open collector or open drain will pull the pull-up resistor voltage down to the ground to create a low impendence, low logic state.
If you cant find a spec sheet, take out a multi meter, set it to ohm mode and measure the thing. If its a variable find something in the same range, if its fixed you should be able to find a suitable replacement. If its a big resistor make sure you get a power resistor and not a standard ceramic one.
Why do you connect a diode in parallel to a capacitor?
1. bec the capacitor not allow the current to pass through it after it has charged & it charged in no time ex:(10^-4 second).
2. because it is necessary to avoid wrong polarity by shorting the terminals of the capacitor and tripping the fuse.
What are the methods of producing emf?
Presently, there are six known methods for producing a voltage or electromotive force (emf). Some of these methods are more widely used than others, and some are used mostly for specific applications. Following is a list of the six known methods of producing a voltage.
1. FRICTION - Voltage produced by rubbing certain materials together.
2. PRESSURE (piezoelectricity) - Voltage produced by squeezing crystals of certain substances.
3. HEAT (thermoelectricity) - Voltage produced by heating the joint (junction) where two unlike metals are joined.
4. LIGHT (photoelectricity) - Voltage produced by light striking photosensitive (light sensitive) substances.
5. CHEMICAL ACTION - Voltage produced by chemical reaction in a battery cell.
6. MAGNETISM - Voltage produced in a conductor when the conductor moves through a magnetic field, or a magnetic field moves through the conductor in such a manner as to cut the magnetic lines of force of the field.
Solenoids are used in Car Starters, Rail road as electric switch. They are also used as valves to control the flow of fluid in appliance like washing machine.
What is wattage rating of microwave oven transformer also hi voltage from secondary?
The rating is about 1500W. This is for both the input and the output. Output voltage is usually 2,000 volts. Divide watts by input volts to get input current. And divide watts by output voltage to get output current. -Joe
How does an LED emits different colours?
LED stands for "light emitting diode".
An LED that is capable of emitting more than one color is actually composed of more than one diode.
For example, since diodes only transmit electricity in one direction, it's possible to make a green/orange/red LED with only two leads by connecting a red and green emitting diode to both leads, but "pointing" in opposite ways. When DC current is applied in one direction, the red diode emits red light. When it's applied in the opposite direction, the green diode emits green light. When AC current is applied, both diodes emit light part of the time; if the AC alternates quickly enough, your eye blends the red and green and you perceive it as orange (or amber, or yellow, depending on the relative strength of the light sources).
Alternatively, you can make an LED with three diodes (red, green, blue) with distinct leads (one side can be shared, if you want to minimize the number of leads) and depending on the percentage of time voltage is applied to each lead, the diode will appear to emit just about any color you want.
What is the hard black dot on small circuit boards?
The hard black dot on circuit boards is a drop of epoxy placed over small integrated circuit chips. The epoxy is specially formulated to draw heat away from the IC and is essentially a tiny heat sync for the chip.
What is the indication of arrow heap in the transistor?
it indicates the direction of flow of emitter current
The "LM" stands for Linear Monolithic" and is just part of the part-number that National decided to use for this famous timer IC.
The LM prefix is still used for a lot of medium complexity analog chips, like regulators and op-amps.
What are differences between broadside array and end fire array?
end fire array
A combination of identical and equally spaced antenna that radiate along the axis of the axis of the antenna array is known as an end fire array.
the elements are fed with a current of equal magnitude but opposite in phase.due to this variation in phase ,the radiation obtained is unidirectional.
broadside array
when the maximum radiation of an array is directed normal to the axis of array it is known as broadside array.
in a broadside array combination a number of identical antennas are set up along a line drawn perpendicular to their respective axis.
200KQ7W is the emission bandwidth of GSM 900/1800 network.
200K - 200KHz bandwidth
Q - The carrier is angle-modulated during the period of the pulse
7 - Two or more channels containing quantized or digital information.
W - Information to be transmitted- telegraphy, facsimile,telemetry, data transmission, telephony and television(video)
yes diode can be used as a switch as it conducts current in only one direction.it is a open switch when it reverse biased.and as aclosed switch when it is forward biased.but we consider diode as ideal .
no
What is a description of the loading effect of an ammeter?
loading of an ammeter in a circuit decreases the flow of current,so it has to be calculated to reduce expected errors in the operations
A z-diode is a diode that works almost the same as a normal ordinary diode. It has the same forward voltage drop.
The trick is that it has got a reverse voltage through point.
Z-Diodes comes with a lot of different values. Some 3.3Volt. Others 5.6, 7.2, 11.3 Volt.
The function of these diodes is that they will start conducting electricity the other way (reverse) if the voltage is higher than what it is marked for.
One particular use for this is as a voltage regulator. It can be used in series with a resistor in order to create a semi stable reference point of voltage. Together with an OpAmp, this can be utilized in order to regulate voltage very accurately.
A zener diode can also be used to protect logic low volt circuitry from high volt signals.
It has got many uses and only our imagination prevents us from finding more uses.
