Transistor relay driver circuits

How to make a simple relay circuit relay driver using transistor. I used a bjt bipolar junction transistor npn transistor. How to build a relay driver circuit learning about electronics. 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. Jul 21, 2016 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. 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.

Referring to the above circuit diagram we see that the configuration only. They are frequently found on, but they are not the driver of choice for three reasons as follows. The sensitivity and current gain of a relay switch circuit can be greatly increased by using a darlington pair of transistors in place of a single switching transistor. B weve added ammeters to measure the base and collector currents as well as voltmeters to measure the voltage across the transistor and the relay coil. Sensitivity can be further increased by using a darlington pair of. Its contains seven darlington pair of a transistor which have high voltage and high current carrying capability. The transistor is typically and solely employed for operating the relay in response to the commands received from the preceding control stage. Relay switch circuit and relay switching circuit electronicstutorials. It is generally used to isolate high voltage circuit to low voltage circuit using a relay. A cheap generalpurpose transistor such as the bc548 is capable of controlling a small relay with a. Electronics club transistor circuits functional model. The uln2003a is a highvoltage, highcurrent darlington transistor array consisting of seven npn darlington pairs that feature highvoltage outputs with commoncathode clamp diodes for switching inductive loads.

Transistors can even get too hot and burn out, if the circuit is not designed correctly. During the transition of lighttemperature levels, the relay clicks which may cause sparking of contacts. It is generally used to isolate high voltage circuit to low voltage circuit using a. Here we have used 12v 10amp relay in this pcb board, but you can also use 5v relays. It turns the relay itself into a voltage threshold detection devicewhile it may work, it was not designed for this function and the threshold may vary greatly from device to device. Also note the concept of sinksource as we go along. Relay driver circuit using ic uln2003 with applications. Applications of relays in electronic circuits automation. In this instructable you will make a transistor relay driver. Npn transistor provide high driving current to electro mechanical relay through 12 volt external power supply.

In electronics, a driver is a circuit or component used to control another circuit or component, such as a highpower transistor, liquid crystal display lcd, and numerous others they are usually used to regulate current flowing through a circuit or to control other factors such as other components, some devices in the circuit. Using relay general the majority than to use a power supply that has. This is a straight forward circuit, in that the transistor turns on, and the relay coil gets energized. These characteristics make it suitable for driving the coil of a small relay of 24vd. On this page we will look at transistor driver circuits using both bipolar transistors and power mosfets and will use them as electrical switches. A relay driver is nothing but an additional transistor stage attached with the relay which needs to be operated. Thus, this is all about bc547 transistor and it is an npn bjt. This means that any device is switched via its negative terminal sinks rather than the positive sources, which is the conventional method. Because we can use the generally available devices. One of the serious problems in relay operated circuits is the relay clicking or chattering during the onoff of the relay driver transistor. These simple optocoupler relay driver circuits can be used in variety of electronic projects. There are various types of relay driver ics such as a high side toggle switch, low side toggle switch, bipolar npn transistor, darlington transistor, nchannel mosfet, uln2003 driver ic. Due to the relay coil current, the difference in the voltage at point p when t 2 is conducting and at point p when t 1 is conducting creates hysteresis in the detection capability of schmitt circuit, and care must be taken in setting the values.

A small amount of current at the base terminal of the transistor will control the high current at collector and emitter terminals of the transistor. But the circuit shown in figure 2 is completely isolated from. A relay switch circuit can be designed using npn transistor. A relay is an electromagnetic switch operated by a relatively. I want to use raspberry pi gpio pins to control a few relays. 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. In this project, we will go over how to build a relay driver circuit which is a circuit. Usually, an npn transistor in a common emitter configuration used as a switch drives the relay. Below is the circuit of a relay driver using the npn transistor bc 548. For example in a transistor power amplifier circuit, typically the driver circuit requires current gain, often the ability to discharge the following transistor bases rapidly, and low output impedance to avoid or minimize distortion. The difference in the pnp transistor from the npn is how power is biased to the transistor for it to function. Relay driver circuit using ic uln2003 and its working. Can someone draw a small circuit showing me the transistor the resistors required. Your attempt at using a voltage divider was a kludge that depends on the characteristics of the actual transistor being used.

The ic uln2003a is a darlington transistor array which deals with highvoltage and highcurrent. Microcontroller provides high or low input signals to npn transistor. Not having that, what you are looking for is a low enough resistance with out the transistor being on just remove the transistor for now that the relay driver circuit will just turn on the relay. If an ic cannot provide this much current, a transistor is used as a switch to trigger the relay as shown below. In case of npn transistor as shown in fig when v1 is 0v or turn off then base current ib will not flow. Here the ground refers to the negative line for an npn and the positive line for a pnp bjt.

Im mostly concerned about transistor q1 which is supposedly a constant current source. Uln2003a darlington transistor array circuit examples. The resistor is used to provide biasing to the transistor. I can use a darlington as well using two 2n2222as if need be or whatever else works.

Relay driver circuit using pnp bjt 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. In figure 3 is the driver relay circuit by use input voltage to feed to the relay coil, but has some voltage junction base and emitter lead of transistor. First lets look at a standard relay circuit in figure 1. Oct 07, 2019 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 circuit. Transistor is used to amplify the current so that full current from the dc source 9v battery can flow through a coil to fully energies it. Types of relays and relay driver circuit buchholz relay. In the above circuit, the 555 timer is in monostable multivibrator mode. The figure 6 circuit raises a relays current sensitivity by a factor of about 200 the current gain of transistor q1, and greatly increases its. Rapid analysis of bjt switchdriver circuits technical articles. With an hbridge circuit, the polarity across a load can be altered in both directions. Can someone tell me if the circuit in the link below will work. The circuits shown in figures 3 and 4 effectively increase the relay current sensitivity by a factor of about 200 the h fe value of q1, e.

I was planning to use a 3904 npn transistor with a 330 ohm resistor on the base of the 3904. 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. You may recall the tlc555 relay driver circuit that i recently posted, it too is a low side driver. Analyzing a transistor relay driver electrical engineering stack. Jan 22, 2020 a relay driver is nothing but an additional transistor stage attached with the relay which needs to be operated. 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 circuit. The part numbers are not given in the schematic for mosfet, bjt and diodes. The relay is always configured by using a small driver circuit which consists a transistor, diode and a resistor. Relay driver circuit using uln2003 and its applications. Circuit design of 12v relay driver using transistor as a switch about this video. Dont avoid the protection diode d1 shown in circuit as it will protect transistor from back emf induced in relay coil. Transistor relay driver transistor relay driver nuke101 electrical op 25 sep 03 01. Transistor relay driver demo the basic transistor relay driver circuit is shown in fig.

A transistor relay circuit may be answered for you. When a switch supplies a voltage on the hot side such as a household light switch, we say the switch sources the voltage. Relay driver circuit is one of the most used circuits in electronics. Figures 6 through 8 show examples of such circuits. A relay based dc motor controller works with an hbridge arrangement. Its mean uln3002 can drive up to seven relays at a time. The common emitter resistor r e must have a value sufficiently small compared with the resistance of the relay coil 2.

How to control a load with a digital circuit like arduino. When you startup your microcontroller, the gpios will be a weak high. An npn transistor is required because the relay coil must be on when the ic output is high. 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. Then pick a even lower resistance to make sure the relay will stay on despite noise on the power line. The design and types of relay switching circuits is huge, but many small electronic projects use transistors and mosfets as their main switching device as the transistor can provide fast dc switching onoff control of the relay coil from a variety of input sources so here is a small collection of some of the more common ways of switching relays. In dual spdt motor driver circuit, the dc motor terminals are connected between the common poles of the two relays. How to make simple electronic circuits using transistor. Uln2003 is a very famous relay driver integrated circuit. High side toggle switch driver, low side toggle switch driver, bipolar npn transistor driver, darlington transistor driver, nchannel mosfet driver, and uln2003 driver. 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. Transistor relay driver circuit circuit wiring diagrams. Transistor relay driver circuit in digital circuit, dc.

This is a highside driver accomplished by an emitter follower transistor. Transistor relay driver circuit circuit diagram, relay. 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. It is used to switch high loads or loads that needs ac current to operate. Mar 21, 2015 one of the serious problems in relay operated circuits is the relay clicking or chattering during the onoff of the relay driver transistor. Relay driver ic uln2003 is high voltage and high current integrated ic which used darlington array. The circuit shown in figure 1 will drive the relay through optocoupler in same circuit with same power supply. All the 3 circuits can be build quickly with minimal changes at output side. 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. Relay driver circuit using npn transistor is given below. This problem is severe if the input circuit is a lighttemperature sensor. How to make a simple relay circuit relay driver using. Aug 12, 2017 one of the serious problems in relay operated circuits is the relay clicking or chattering during the onoff of the relay driver transistor. Transistor relay driver cbarn24050 industrial 2 oct 03 04.

Here we will explore using the versatile uln2003a darlington transistor array with a typical microcontroller such as arduino. A transistor driver uses the transistor as a switch rather than an amplifier by saturating the inputs and outputs. The basic digital circuits of figures 1 through 4 can be used as efficient relay drivers if fitted with suitable diode protection networks. Jul 26, 2006 pic 16f54 needs to drive a 5v relay i am using a pic 16f54 and need to trigger a 5v relay. Depending upon a relay s coil rating, some may require current greater than 100ma. Dec 28, 2017 the relay is always configured by using a small driver circuit which consists a transistor, diode and a resistor. Here we have used 12v 10amp relay in this pcb board, but you can also use 5v. Analyzing a transistor relay driver electrical engineering. The transistor is a 2n2222a the relay a 5 volt axicom d3009 with 30. Design a sustainable relay driving circuit using bjt. The relay is connected between the positive rail and the collector of the transistor. Like any transistor, a pnp provides amplification andor switching capabilities to turn a load on or off connected to it.

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. So, my guess is the relay needs a current of 563 79ma. How to make simple electronic circuits using transistor bc547. The required current to run the relay coil is more than can be supplied by various integrated circuits like opamp, etc. You need to deal with that for whatever relay driver you use. Pic 16f54 needs to drive a 5v relay i am using a pic 16f54 and need to trigger a 5v relay. Transistor relay driver circuit with formula and calculations. The advantages of bjts over mosfet transistors are being able to handle a high range of input voltages due to rb resistor with. There are various types of relay driver ics such as a high side toggle switch, low side toggle switch, bipolar npn transistor, darlington transistor, n.

A transistor is usually used for amplifying current. This is a relay driver circuit which can be driven by either ac or dc input voltage. Rapid analysis of bjt switchdriver circuits technical. 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. If you want to implement a 10 relay operation in that case you can configure the transistor relay driver stages across all the 10 output pins of the ic. Typically the driver stage s of a circuit requires different characteristics to other circuit stages. The normally closed terminal of both relays is connected to negative or. The output pulse from the digital circuit to biased the transistor is on. The transistor has to dissipate the power vi across its ce. Arduino relay control tutorial with code and circuit diagram. The relay circuit considerations can be split into two main areas. How to make 12v relay driver circuit using transistor proteus. And unlike the other circuits, a specific voltage, such as the rated voltage values we used to drive the others, does not need to be used. Dec 11, 2017 read about what is the best way to drive a relay.

Jan 12, 2018 relay driver circuit is one of the most used circuits in electronics. 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. The last relay driver circuit we will show is one which can be driven by an arbitrary control voltage. Also, bjt transistors cost less money are could be easily found in old electronic circuits. Drive relay by digital circuit circuit wiring diagrams. A relay driver circuit is a circuit which can drive, or operate, a relay so that it can function appropriately in a circuit. Most circuits have only the one diode across the relay, but some also have one from the emitter to the collector. A cheap generalpurpose transistor such as the bc548 is capable of controlling a small relay with a holding current of less than 300 ma. Mar 21, 2017 a relay based dc motor controller works with an hbridge arrangement. Resistor pullupdown problems with relay driving circuit. Mosfets are still a bit rare because they are only used for switching. Here is a simple circuit that uses a bipolar junction transistor bjt to drive a small 5 v relay coil. The bc547 is a cheapaschips general purpose npn transistor, which has a collector current of 100ma maximum, and a collectortoemitter voltage of 65vdc maximum.