May 16, 2019 above figure shows a class a amplifier circuit that uses a darlington transistor configuration to have a high collector current. Transistor relay driver circuit circuit wiring diagrams. Basic transistor relay driver, actuated on high input npn this circuit will drive a relay coil from a low power output, usually from an ic like 555 or a ttlcmos. The driven relay can then operate as a switch in the circuit which can open or close, according to the needs of the circuit and its operation. During the transition of lighttemperature levels, the relay clicks which may cause sparking of contacts. Simple transistor relay circuit transistor as a switch youtube. Electronics tutorial about the relay switch circuit and relay switching circuits used to control a variety of. A typical relay switch circuit has the coil driven by a npn transistor switch, tr1 as shown depending on the input voltage level.
This tutorial will guide to to make simple circuit using npn transistor as a switch to turn on electrical appliances using relay. I have preformed the following tests with my voltage meter. We can use seven relays with relay driver circuit using uln2003 and the relay driver circuit using uln2803 enables to use eight relays. A relay driver circuit is disclosed in which a relay coil is operated by enabling the collectoremitter path of a switching transistor. However the low level signals from an electronic which may be derived from an ic stage or a low current transistor stage may be be pretty incapable of driving a relay directly. A transistor works best as a switch when it is connected with a common emitter configuration, meaning the.
Below is the circuit of a relay driver using the npn transistor bc 548. Introduction to bipolar junction transistors bjt the proliferation of the arduino, the raspberry pi, the ti msp430 launchpad, and various other embedded development platforms has led to a corresponding proliferation of a basic switch driver circuit based on an npn bipolar junction transistor. Npn relay switch circuit electronic schematics, electronics. This means that any device is switched via its negative terminal sinks rather than the positive sources, which is the conventional method. When voltage and current levels are in the correct range, the transistor acts like a highcurrent switch controlled by the. Its contains seven darlington pair of a transistor which have high voltage and high current carrying capability. Practical circuit relay driver using bipolar transistor how to design a practical relay driver circuit using bipolar transistor. A transistor works best as a switch when it is connected with a common emitter configuration, meaning the emitter of the bjt must be always connected directly with ground line. Optoisolated transistor drivers microcontroller interfacing. Relay driver ic uln2003 is high voltage and high current integrated ic which used darlington array. Rapid analysis of bjt switchdriver circuits technical. Operation of this 2way motor control circuit is simple. In this 4channel relay driver circuit we have used an optocoupler whic his triggered by active low signal, to trigger the npn transistor which further drives the relay. Relay driver circuit using ic uln2003 with applications.
Pick the configuration that suits your other needs best, or just reuse a transistor you also use elsewhere reusing the same part in several places in a circuit can lead to cost. Transistor relay driver circuit circuit diagram, relay. Can someone draw a small circuit showing me the transistor the resistors required. Rapid analysis of bjt switchdriver circuits technical articles. One of the serious problems in relay operated circuits is the relay clicking or chattering during the onoff of the relay driver transistor. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. Bipolar transistor biasing circuits worksheet discrete. One very useful inductordriving circuit is the relay driver, and a number of examples of this are shown in figures 3 to 7. Here is a bit of a description that can be used as a guide in designing tips or relay drivers using bipolar transistors. A transistor driver uses the transistor as a switch rather than an amplifier by saturating the inputs and outputs. The humble transistor q1 emitter e collector c base b transistor basics.
Dc current gain collector current ic base current ib applications. It is used to switch high loads or loads that needs ac current to operate. A classic example circuit using an pnp device, where the withdrawing or falling positive voltage level at some point of time becomes too low to keep the transistor reverse biased. This problem is severe if the input circuit is a lighttemperature sensor.
Practical circuit relay driver using bipolar transistor. If you go with a darlington pair configuration using a couple of transistors, the hfe of one multiplies the hfe of the 2nd transistor. But if someone comes up with a circuit schematic that mostly works, and all they need is a little help with the actual selection of the correct resistor to drive a particular transistor. When a transistor is saturated the collector current ic is determined by the supply voltage and the external resistance in the collector circuit, not by the transistor s current gain. The most diode will be diode that is in the general rectifier circuit is 1n4001 etc. This circuit adds a 2k2 resistor from base to emitter ground, something i do not usually see in other circuits. Here the ground refers to the negative line for an npn and the positive line for a pnp bjt.
Analyzing a transistor relay driver electrical engineering. Sometimes it is helpful for students to redraw the circuit using a transistor model showing the baseemitter junction as a diode. Fundamentals of mosfet and igbt gate driver circuits. The circuit shown in figure 1 will drive the relay through optocoupler in same circuit with same power supply. Uln2003 is a very famous relay driver integrated circuit. Design a sustainable relay driving circuit using bjt. Mar 21, 2015 below is the circuit of a relay driver using the npn transistor bc 548. And, the input current at output of a normal digital circuit is about 2 ma. These simple optocoupler relay driver circuits can be used in variety of electronic projects.
This article looks at three alternative circuits and the tradeoffs each offers in complexity. The required current to run the relay coil is more than can be supplied by various integrated circuits like opamp, etc. Driving an electromechanical relay from a lowvoltage digital io line is a common situation, but there are. Mar 10, 2008 hi, i am working to create a circuit in which i can control a light using my computers parallel port. Drivers, relays, and solid state relays drivers, relays, and solid state relays.
The relay in the npn driver circuit in figure 3 can be activated via a digital input or via switch sw1 it turns on when the input signal is high or sw1 is closed, and turns off when the input signal is low or sw1 is open. When uses as an amplifier the dc current gain of the transistor can be calculated by using the below formulae. In the circuit below is most transistor relay driver circuit. Darlington transistor darlington pair electronics hub. In this case no current flows to the base of transistor, hence transistor remains off acts like an open switch due to which no current flows to relay coil from vin pin of arduino. In order to avoid damage to the transistor from voltages induced in the relay coil when the relay is turned off, an isolating semiconductor device is inserted between the transistor and the relay coil.
The post also explains the formula for calculating relay drivers transistor base resistor value. Relay drivers if the basic figure 1 switching circuit is used to drive inductive loads such as coils or loudspeakers, etc. Analyzing a transistor relay driver electrical engineering stack. Transistor relay driver circuit with formula and calculations. The previous npn transistor relay switch circuit is ideal for switching small loads such as leds and miniature relays. An electronic circuit will normally need a relay driver using a transistor circuit stage in order to converter its low power dc switching output into a high power mains ac switching output.
If you connect the scope ground to the circuit ground, probe to the transistor collector, and turn the relay off you should see the transistor collector voltage rise to one diode drop above the 12v supply briefly then settle back to the supply voltage. So, my guess is the relay needs a current of 563 79ma. The advantage of relays is that it takes a relatively small amount of power to operate the relay coil, but the relay itself can be used to control ac circuits and devices. A relay driver ic is an electromagnetic switch that will be used whenever we want to use a low voltage circuit to switch a light bulb on and off which is connected to 220v mains supply. A relay driver circuit is a circuit which can drive, or operate, a relay so that it can function appropriately in a circuit. We will use the most widely used pnp transistor for our circuit, the 2n3906. It is good to know about power transistor basics, characteristics and construction before proceeding further. Driving power bjt this post will explain about the power transistor base drive circuit. The post also explains the formula for calculating relay drivers transistor. It is difficult to use a number of relays with transistors, so, relay driver ic uln2003a can be used for availing more relays. If you think this model would help some of your students understand the concept here, have another student draw the transistor model on the whiteboard, and use that drawing as a discussion aid.
Transistor bc547 is probably the most elementary of the available electronic active components and yet becomes the basic, vital building block in most electronic circuits. But the circuit shown in figure 2 is completely isolated from. Circuit options explore issues, solutions for relay drivers. The output pulse from the digital circuit to biased the transistor is on. Pnptransistor based dc relay drive make triggering. The relay is connected between the positive rail and the collector of the transistor. Pin diode drive circuits optimized for fast switching. The mosfet symbol in figure 2a represents the channel resistance and the.
How to wire a relay to a transistor explained through. When the signal from the transistor s collector is taken and used to drive another circuit as shown in the figure on the right, a minute dark current flows to the relay even if the transistor is off. The peak current that could flow through the collector pin is 200ma, this combined with the high gain value makes it an ideal choice for audio amplification applications. In order to avoid damage to the transistor from voltages induced in the relay coil when the relay is turned off, an isolating semiconductor device is inserted between the transistor and the relay. With bipolare transistors you must perhaps use darlington transistors as well. The condition provides more negative bias to the base of the bc557 transistor and switches on the led assembly, indicating an undesirable voltage condition of the. Applications of relays in electronic circuits automation.
Electronics club transistor circuits functional model. When the input signal passes through the i k resistor to the base of the transistor, it conducts and pulls the relay. The first model in figure 2 is based on the actual structure of the mosfet device and can be used mainly for dc analysis. High side toggle switch driver, low side toggle switch driver, bipolar npn transistor driver, darlington transistor driver, nchannel mosfet driver, and uln2003 driver. Analysis of the topics in the premier conference on power.
Darlington transistor offers a gain that equal to the product of two individual gains. When the base voltage of the transistor is zero or negative, the transistor is cutoff and acts as an open switch. In this circuit diagram, the pic microcontroller is providing a signal to 4 relays through relay driver ic uln2003. In this article we will comprehensively study a transistor relay driver circuit and learn how. You may recall the tlc555 relay driver circuit that i recently posted, it too is a low side driver. Output control is via a spi port and offers convenient reporting of faults for open load or short to ground, over load, and over temperature conditions. When a transistor is saturated the collectoremitter voltage v ce is reduced to almost 0v. An common emitter amplifier circuit has a load resistance, r l of 1. One of the serious problems in relay operated circuits is the relay clicking or chattering during the onoff of the relay. This wont matter in most cases but take care when connecting any polarised device to ensure the supply to it is the correct way round.
You can also notice a diode connected across the coil of the relay, this diode is called the. The article presents a comprehensive discussion regarding these tiny electronic devices in a very lucid style, explaining bc547 datasheet, their operating principle and how to implement bc547 and the associated parts into. After downloading circuits, they should be copied into the circuits directory of the app. So now that weve gone over the basics of pnp transistors, we can now go over how to connect a pnp transistor in a circuit to provide switching andor amplification. Calculate the maximum collector current ic flowing through the load resistor when the transistor is switched fully on saturation, assume vce 0. Mar 26, 2018 this is where a pnp transistor differs from a npn transistor. When the load must be at ground potential, and the microcontroller cannot supply enough current, a pnp transistor can be used to switch the load from the vcc side. Be sure the transistor can handle the voltage and current requirements. I will revise the circuit and post it again based on your suggested values just as soon as i get some free time. A high current, high voltage relay needs a power transistor to driving it. This video pnp transistor based 12v dc relay control drive simple make it, this type transistor is a semiconductor device used to switch electronic.
Dc biasing of bjtsbjt dc analysis bjt dc analysis 1. The ncv7240 is an automotive eight channel low side driver providing drive capability up to 600 ma per channel. Aug 02, 2018 the above diagram is for relay triggering circuit. As shown in the diagram, the section basically consists of a transistor t1, resistor r1 and a flyback diode d1 connected across the relay coil. All the relay driver circuit above are the pulse output of the digital circuit to control a transistor works and drive relay as onoff switch for circuit or external devices next, to using it now selected to suit the circuit. The pnp transistor, like almost all transistors, is a 3lead device. Bjt dc analysis dc biasing circuits fixedbias circuit emitterstabilized bias circuit voltage divider bias circuit dc bias with voltage feedback various di erent bias circuits pnp ransistotrs bias stabilization stability factors stability of ransistotr circuits with active components practical applications relay driver ransistotr switch. I can use a darlington as well using two 2n2222as if need be or whatever else works. This problem electrical projects electrical engineering electronics projects dc circuit circuit diagram tech updates computer hardware home automation model trains. Driving an electromechanical relay from a lowvoltage digital io line is a common situation. In part 1 we looked at a number of bipolar transistor and mosfet driver circuits. The relay driver circuit using uln2003 is given below.
A voltage or current applied to one pair of the transistor s terminals controls the current through another pair of terminals. Draw the dc equivalent circuit signal frequency is zero, i. Drive relay by digital circuit circuit wiring diagrams. The relay will be actuated when the input of the circuit goes high. Jul 21, 2016 technical article rapid analysis of bjt switchdriver circuits july 21, 2016 by robert keim this technical brief explains a quick, straightforward procedure for evaluating a switchdriver circuit based on an npn bipolar junction transistor. You are not here to create my circuits for me, and i should learn something from the process. I understand that the inductive effect of the relay coil causes a backward voltage spike to occur as the magnetic field collapses, and the diode protects the transistor from too large a reverse spike. How to build a relay driver circuit learning about electronics. I will consider your sugestion for a nonzener transistor drive circuit, but im mostly interested in your original explanation with the zener transistor constant current source driver. This page covers just about all the options for driving a relay with transistors. Relay driver circuit using uln2003 and its applications. Using npn transistors, your output can be amplified by the hfe of the transistor and you can sink the load of the relay s coil. Oct 24, 2018 if the circuit power supply is a 9v battery, the baseemitter voltage would need to be no more than 8. The circuit analysis is almost identical to using an npn transistor except that the polarities are all reversed.
But sometimes it is required to switch larger relay coils or currents beyond the range of a bc109 general purpose transistor and this can be achieved using darlington transistors. Pic 16f54 needs to drive a 5v relay i am using a pic 16f54 and need to trigger a 5v relay. To power a relay or configure it with an electronic circuit, a small output circuit is generally incorporated and is known as the relay driver circuit. They had a flaw of having to be electrically connected to low voltage digital circuits. Ee times ee times europe power electronic news ebn elektroda. Therefore, with a small base current, the output current at the collector terminal is very high. The humble transistor q1 emitter e collector c base b transistor basics emitter to base junction is forward biased normally collector to base junction is reverse biased normally transistors are current operated devices, so. Driver modules like relay driver, led driver etc amplifier modules like audio amplifiers, signal. For relay control, i always see a flywheel diode across the relay, with anode at transistor collector and cathode at vcc, as shown in this diagram. In this project, we will build a relay driver for both dc and ac relays. What others are saying the post explains how to calculate understand and make relay driver circuit stage.
For switching we are using a transistor as a switching device. All the relay driver circuits above are the pulse output of the digital circuit to control a transistor works and drive relay as an onoff switch for circuit or external devices next, to using it now selected to suit the. Here we have used 12v 10amp relay in this pcb board, but you can also use 5v. The relay circuit considerations can be split into two main areas. The description and notes about circuits can be found at the bottom of circuit pages. Relay driver circuit using ic uln2003 and its working. How to make simple electronic circuits using transistor bc547. A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. A transistor that is full on with r ce 0 is said to be saturated.