Relay driver using transistor as switch

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. Both npn and pnp transistors can be used as switches. Now simply check the resistance of two side terminal of relay the side having three terminals, the resistance lies between 100ohms to 500ohm. Mar 21, 2017 the switch s1 and s2 control the relay 1 and relay 2 respectively. Can a transistor work as a switch for high ac voltage 220. Jun 12, 2012 if you are talking about replacing the small switch on a regular pc with an atx power supply or anything recent, where the switch is actually a soft switch that is, the bios monitors the switch state, then all you need is something very small to make a momentary contact. With a small circuit arrangement of a transistor able to energise the coil of the relay so that the external load connected to it is controlled. 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. Working of transistor as a switch npn and pnp transistors.

How to make 12v relay driver circuit using transistor. The first step is to determine the voltage and current of the load, the thing you are trying to control. A transistor relay circuit may be answered for you. Figure 82 shows a circuit using a pnp transistor as a high side switch. Npn transistor provides high driving current to electromechanical relay through the 12volt external power supply. In short, a transistor conducts current across the collectoremitter path only when a voltage is applied to the base. Usually, an npn transistor in a common emitter configuration used as a switch drives the relay. 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.

When using the mosfet as a switch we can drive the mosfet to turn on faster or slower, or pass high or low currents. Ssrs consist of an input logic to respond to an appropriate. When using the transistor as a switch, a small base current controls a much larger collector load current. Pnptransistor based dc relay drive make triggering. You can use a 5v relay to switch the 120240v current and use the arduino to control the relay. The difference in the pnp transistor from the npn is how power is biased to the transistor for it to function. They generally take more power than an arduino pin can deliver, and therefore they are often controlled by a transistor. The switch is on when the base is saturated so that collector current can flow without restriction. In many designs where switching is infrequent and the designer of the circuit doesnt know exactly what the user is going to want to switch, a relay is a nice choice as it will switch either ac or dc at a huge voltage and current range. The ncv7240 is an automotive eight channel low side driver providing drive capability up to 600 ma per channel. Its contact is closed when a current flows through a coil. Hence transistors are used to conduct current from vin pin of arduino to relay which is controlled using a pushbutton connected from digital pin to base terminal of transistor. Mosfet true switch bidirectional switch with nchannel mosfets an example. The coil of the relay needs a large current around 150ma to drive the relay, which an arduino cannot provide.

Analyzing a transistor relay driver electrical engineering. The relay circuits used for controlling relays often use semiconductor devices. Some types of transistors can switch in picoseconds almost 10 orders of magnitude faster. Any other kind of solid state switch bjt, scr, triac, igbt will have some resistance and drop some voltage. A transistor can be operated in three modes, active region, saturation region and cutoff region. Below is the circuit of a relay driver using the npn transistor bc 548. The microcontroller provides high or low input signals to npn transistors. This type solid state switching offers significant reliability and lower cost as compared with conventional relays.

Arduino dc motor speed and direction control using relays and. 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. When should i use a transistor, mosfet, and when should i. It is used to switch high loads or loads that needs ac current to operate. The ic uln2003a is a darlington transistor array which deals with highvoltage and highcurrent. Circuit design of 12v relay driver using transistor as a switch about this video. I can use a darlington as well using two 2n2222as if need be or whatever else works. The relay driver circuit using uln2003 is given below.

This ac relay driver ic circuit is a relay that runs with ac power and cannot be run with dc power. We will use the most widely used pnp transistor for our circuit, the 2n3906. This is a schematic diagram for a circuit that uses an npn. 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. A relay does give you galvanic isolation between the coil and the contacts. Can a transistor work as a swi tch for high ac voltage 220 v without using relay. The switch s1 and s2 control the relay 1 and relay 2 respectively. As we know that some circuit require fast switching onoff system e. In an ideal switch, the transistor should be in only one of two states. Transistors are capable of driving small relays without any problems. A typical relay switch circuit has the coil driven by a npn transistor switch, tr1 as shown depending on the input voltage level.

Consider the below circuit to know the operation of a transistor to energize the relay coil. 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. Driving relays with stm32f103 microcontroller using uln2003. How to wire a relay to a transistor explained through. Fet as a switch working of mosfet or jfet as a switch.

How to build a relay driver circuit learning about electronics. 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. Relay driver circuit using ic uln2003 with applications. A relay basically allows a relatively low voltage to easily control higher power circuits.

How to make simple electronic circuits using transistor. In this tutorial, we will learn about field effect transistors or fet, its working, regions of operation and see the working of a fet as a switch. Using mosfets as general switches electronic product design. The opposite of the low side switch is the high side switch. The relay driver circuit using an npn transistor is given below. Going from a back view, the first lead is the emitter, the second lead is the base, and the third lead is the collector. We will see both how both jfet and mosfet can be used in switching applications. This video pnp transistor based 12v dc relay control drive simple make it, this type transistor is a semiconductor device used to switch electronic signals and electrical power onoff control than. When the input signal passes through the i k resistor to the base of the transistor, it conducts and pulls the relay. For a long time i was afraid of the issues of static damage and i steered away for fets in general for switchesdrivers. Lowcost ac solidstate relay with mosfets 1 system overview 1. Design a sustainable relay driving circuit using bjt. This page covers just about all the options for driving a relay with transistors.

How to use transistor as relay npn transistor as dc switch. How to use a transistor as a switch in different applications. The bc547 have a maximum collector current ic rating of 100ma, seems fine for the 70ma. 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. When using transistors to switch inductive loads such as relays and solenoids, a flywheel diode is used.

Using a transistor as a relay electronics forum circuits. Using relay general the majority than to use a power supply that has. 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. In order to run an ac relay, enough ac voltage is required tp rate the relay and transient suppressor. The output pulse from the digital circuit to biased the transistor is on. By using a simple tip, this problem can be avoided. A relay accomplishes this by using the 5v outputted from an arduino pin to energize the electromagnet which in turn closes an internal, physical switch to turn on or off a higher power circuit. Here the ground refers to the negative line for an npn and the positive line for a pnp bjt. When voltage and current levels are in the correct range, the transistor acts like a highcurrent switch controlled by the lower current digital logic signal.

One way around this problem is to use the microcontroller to drive a transistor, which in turn controls the load. Relay driver circuit using uln2003 and its applications. In ac relay circuit we cannot use a diode to remove voltage spikes. One channel relay driver using bc547 transistor circuit. A cheap generalpurpose transistor such as the bc548 is capable of controlling a small relay with a holding current of less than 300 ma. A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a. Like any transistor, a pnp provides amplification andor switching capabilities to turn a load on or off connected to it. A relay, as we all know is an electromechanical device which is used in the form of a switch. A relay accomplishes this by using the 5v outputted from an arduino pin to energize the electromagnet which in turn closes an internal, physical switch to. I was planning to use a 3904 npn transistor with a 330 ohm resistor on the base of the 3904 and a fly back diode across the coil of the relay just as shown in the attached image. This tutorial will guide to to make simple circuit using npn transistor as a switch to turn on electrical appliances using relay. Jul 26, 2006 pic 16f54 needs to drive a 5v relay i am using a pic 16f54 and need to trigger a 5v relay.

There are also solid state relays, which have a triac like a transistor in them. One channel relay driver using bc547 transistor 24082016 raj sharma 2 comments single channel relay project is a simple and convenient way to interface a relay for switching application in your project. Transistor relay driver circuit with formula and calculations. Leds on or off by using a transistor in its saturated or cutoff state when used as an ac signal amplifier, the transistors base biasing voltage is applied in such a way that it always operates within its active region, that is the linear part of the output. Using pnp transistors is essentially the same as npn transistors, except the polarities are reversed. Because of how transistors work, these can be a little more difficult to use in an arduino or raspberry pi circuit.

The transistor is off when theres no bias voltage or when the bias voltage is less than 0. Drive relay by digital circuit circuit wiring diagrams. The arrow in the emitter of a pnp transistor points in the opposite direction than in an npn transistor. The wire used in coils have fixed resistance in range of few 100s ohm. 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. Designers need to know more about the switched device than when using a relay. One of the most common uses for transistors in an electronic circuit is as simple switches.

Relays use a magnet to control the position of a metal switch. The transistor will be in off state when the when the pin p2. In this project the npn transistor 2n2222 drives the relay when the npn junction gets saturated. Wide variety of advantages such as high input impedance, simple fabrication, simple operations, etc. A generalpurpose bipolar junction transistor bjt works fine for small relay loads, however, for larger relays a twotransistor darlington circuit provides better performance.

The relay will be actuated when the input of the circuit goes high. 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. 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. You can use a transistor to allow one signal to switch a larger load, but its not entirely independent. How to drive a relay using microcontrollers vishnus blogs. Transistor switches can be used to switch a low voltage dc device e. You can also identify the coils pin using multimeter. Arduino dc motor speed and direction control using relays. In the case of the motor, if you know where it came. It has seven darlington pairs inside, each capable of driving loads up to 50v and 500ma. In this circuit diagram, the pic microcontroller is providing a signal to 4 relays through relay driver ic uln2003. Uln2003 relay driver ic the world of electronic parts and. A common bjt without any further parts would not work with ac.

The code in this project can be used with any of the relay board containg uln2003, uln2803, optocouplers or individual transistors as relay drivers. 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. Can someone draw a small circuit showing me the transistor the resistors required. 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. You can get mosfets with very very small rdson, which will result in nearzero voltage drop. Remember, the negative or the ground line of the external voltage must be connected with the transistor ground line or the emitter, otherwise the external voltage will have no effect on the transistor. Say you wanted to drive a 5v70ma rated electromagnetic relay by one io port of your microcontroller, and it can cater a maximum current of 20ma at 5v.

But you could achieve that by using an opto coupler t drive the triac. However if the ac is first rectified, the bjt is connected across a bridge rectifier, it would make. Ensure that the ratings of the transistor, far exceed the coil ratings of the relay meaning, the ce voltage must be much larger than 5v dc and the collector current must be much larger than 40ma. The required current to run the relay coil is more than can be supplied by various integrated circuits like opamp, etc. If the circuit uses the bipolar transistor as a switch, then the biasing of the. Notice that the emitter is connected to the positive voltage. This video npn transistor based 12v dc relay control drive simple make it, this type transistor is a semiconductor device used to switch electronic signals a.

Although the simplest relay circuits would simply involve a switch closing a circuit, the applications of relays often require a small signal, possibly from some form of a microcontroller circuit or other device to actuate the relay. When large currents or voltages need to be controlled, darlington transistors can be used. A transistor switch is used to allow a 12 volt relay to be operated turned on and off by a small input voltage, e in. Relay driver circuit using ic uln2003 and its working. Vin pin of arduino cannot easily supply this much current for both relay. It also could prevent damage to the transistor from applied negative voltage.

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. In the circuit diagram shown, the switch s1 is on and switch s2 is off. How to use a transistor as a switch teach me to make. Many components such as relays, solenoids, high power leds, buzzers and others require more drive current andor higher voltages than the microcontroller outputs can handle. A generalpurpose bipolar junction transistor bjt works fine for small relay loads, however, for larger relays a two transistor darlington circuit provides better performance. A transistor is used for switching operation for opening or closing of a circuit. Dec 11, 2017 merrick, when it comes to switching a load i. Relays have unique properties and are replaced with solid state switches that are strong than solidstate devices. How to use a transistor a switch work in progress 1. The relay is connected between the positive rail and the collector of the transistor.

Relays can usually switch more current than either a transistor or a mosfet. So, my guess is the relay needs a current of 563 79ma. Sep 07, 2017 if the relay is attached parallel to a switch in some external device such as a remote control, closing the relay is like closing the switch. A relay switch circuit can be designed using npn transistor. A relay driver circuit is a circuit which can drive, or operate, a relay so that it can function appropriately in a circuit. I want to use raspberry pi gpio pins to control a few relays.

How to make relay switch circuit engineering projects. Pic 16f54 needs to drive a 5v relay i am using a pic 16f54 and need to trigger a 5v relay. The transistor is a 2n2222a the relay a 5 volt axicom d3009 with 30. In this type of circuit, the purpose of the transistor is to behave as a switch to energise the relay coil.

By has various resistorr limit proper current for circuit. To control smaller devices that use dc, a transistor based driver circuit can be used to boost the current to the levels needed for the device. Is there a specific reason you dont want to use a relay. Lets assume you want to switch a motor or a light bulb. In case of npn transistor as shown in fig when v1 is 0v or turn off then base current ib will not flow. It has a draintosource resistance when conducting rdson and at low voltages, the voltage drop should be very small. I have already explained in one of my earlier posts regarding how to make a transistor driver circuit. The voltage level of the input can be changed by sliding the black arrow head up and down on this vertical scale. This ability to turn the power mosfet on and off allows the device to be used as a very efficient switch with switching speeds much faster than standard bipolar junction transistors. When no base voltage is present, the switch is off. Transistor switch driving a relay download for macintosh or for pc. If the circuit uses the bjt transistor as a switch, then the biasing of the transistor, either npn or pnp is arranged to operate the transistor at the both sides of the iv characteristics curves shown below. Rapid analysis of bjt switchdriver circuits technical articles.