Relay driver using pnp transistor

Part 8 showed how to use a pnp transistor allowing the load to be at ground potential, as is sometimes necessary. Nov 16, 2014 the output transistor of a 4n25 is still a low power device, so we must use it to drive higher power components for greater loads. Mar 26, 2018 bc558 is a pnp transistor hence the collector and emitter will be closed forward biased when the base pin is held at ground and will be opened reverse biased when a signal is provided to base pin. A cheap generalpurpose transistor such as the bc548 is capable of. You must set the port pin low to turn on the pnp transistor. The advantage of relays is that it takes a relatively small amount of power to opera. The most commonly used transistor switch is the pnp variety shown in figure 1. This video pnp transistor based 12v dc relay control drive simple make it, this type transistor is a semiconductor. Further the pin 8 is 2n906 to relay with pnp transistor 2n and a diode with some resistor as in the image.

Optoisolated transistor drivers microcontroller interfacing. As well as switching relay coils and other such loads with npn bipolar transistors, we can also switch them using pnp bipolar. Learn how to construct npn and pnp relay drivers on a stripboard. Analyzing a transistor relay driver electrical engineering stack. Notice that the emitter is connected to the positive voltage. Transistor relay driver circuit with formula and calculations. 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. Often your relay driver can be very simple, using little more than an npn or pnp transistor to control the coil current. Last months edition of this transistor cookbook series described practical ways of using bipolar transistors in useful commoncollector voltage follower circuit applications, including those of relay drivers, constantcurrent generators, linear amplifiers, and complementary emitter followers.

Another possible issue, not related to the reliability of the drive circuit, is that clamping with a diode slows the relay release and thus shortens the life of the relay somewhat. Now that were using a transistor to drive the relay, we can use considerably less power to get the relay driven. Analyzing a transistor relay driver electrical engineering. Also note the concept of sinksource as we go along. When to use npn transistors, and when to use pnp transistors for switching i want to be able to use a transistor to turn on and off a light, such that writing digitalwritepin, high will allow current to flow through the light, and digitalwritepin, low will stop the flow of current and turn the light off again. Lab iii voltage comparator and relay drivers by using bjts. Well, theoretically yes old germanium pnp is better because they have a lower resistance when open also they need a lower tension to open them 0. Transistors are capable of driving small relays without any problems. There is no problem when i connect raspberry pi with laptop usb port as power. A cheap generalpurpose transistor such as the bc548 is capable of controlling a small relay with a holding current of less than 300 ma. The transistor is a 2n2222a the relay a 5 volt axicom d3009 with 30. The arrow in the emitter of a pnp transistor points in the opposite direction than in an npn transistor. Protect the transistor with a snubbing diode if the load is a relay, solenoid, motor or otherwise inductive.

On the tp3200 the relay driver pnp transistors operate between bgnd and a negative, ring function, the other two are general purpose. If you want to design circuits with transistors, its really worth knowing about this type of transistor. Here the ground refers to the negative line for an npn and the positive line for a pnp bjt. The main issue in this circuit was the maximum voltage that was being applied to the base of the transistor wasnt enough to compared to the emitter. 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. How to use a transistor as a switch in different applications. The relay driver uln2003 ic is a high voltage and current darlington array ic, it comprises of 7open collector darlington pairs with common emitters. The resulting excess base current when the input is at 12v should not be a problem. You need a better transistor and you have damaged the one you. Protect the transistor with a snubbing diode if the load is a relay, solenoid, motor or otherwise. With bipolare transistors you must perhaps use darlington transistors as well. Voltage comparator and relay drivers by using bjts. This page covers just about all the options for driving a relay with transistors. When a switch supplies a voltage on the hot side such as a household light switch, we say the switch sources the voltage.

May 16, 2019 a darlington transistor is a back to back connection of two transistors that comes as a complete package with three leads base, emitter and collector as equivalent to the single transistor. Relay driver ic uln2003 the relay driver uln2003 ic is a high voltage and current darlington array ic, it comprises of 7open collector darlington pairs with common emitters. In this example i will be using the 5 v version of the g5la relay because it is the cheapest and there seems to be plenty of documentation regarding its specifications. 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. 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.

A relay driver circuit is a circuit which can drive, or operate, a relay so that it can function appropriately in a circuit. The overall current gain of the darlington pair will be. 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. We can also use the pnp transistors as a switch, the difference this time is that the load is connected to ground 0v and the pnp transistor switches the power to it. 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. However, when using a transistor to turn on a relay coil, it is very important to use a 1n4001 diode reversed biased in parallel with the relay coil as in figure 3. Current gain hfe first transistor gain hfe 1 second transistor gain hfe 2. Using pnp transistor as a swichto drive a relay actually the output is given to a module which has a relay and an open close gate arrangement. To utilize the opencollector oc output on lenzeac tech drives, a separate relay must be inserted between the drive and the intended control or indicating device monitor or plc. Like the common emitter circuit, this one too can use a pnp transistor, but with the diode polarity and supply reversed. This issue can be solved using a darlington transistor. It is also possible to control the relay operation using a transistor. Want to automatically turn on a light when it gets dark. One of the most fundamental applications of a transistor is using it to control the flow of.

Here is a simple circuit that uses a bipolar junction transistor bjt to drive a small 5 v relay coil. Apr 10, 2018 a relay basically allows a relatively low voltage to easily control higher power circuits. Learn how to construct opamp comparator on a stripboard. Using relay general the majority than to use a power supply that has. This is met by using 2 npn and 2 pnp transistor as shown below. Because a transistor is an amplifier, we just have to make sure that the base lead gets enough current to cause a larger current to flow from the emitter of the transistor to the collector. A generalpurpose bipolar junction transistor bjt works fine for small relay loads, however, for larger relays a two transistor darlington circuit provides better performance. The two npn transistors t1 and t2 are connected together in an order where, t1 and t2s collectors are connected. The arrow points out for an npn transistor and in for a pnp transistor. Relay driver circuit using ic uln2003 and its working.

The arrows direction identifies the transistor type in data sheets and schematic diagrams. The output transistor of a 4n25 is still a low power device, so we must use it to drive higher power components for greater loads. It is similar to others i have seen, though it appears to have two extra parts that others do not have. You also need an emitter resistor to define the constant. How to connect transistors bjt and mosfet with arduino. Aug 17, 2019 although, a relay becomes the best option for operating heavy loads via a transistor driver, when mechanical switching becomes an undesirable factor, upgrading bjts becomes a better choice for operating high current dc loads, 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. A transistor works best as a switch when it is connected with a common emitter configuration, meaning the. 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. You can do this with one transistor and a couple 10k resistors, as shown. How to build a relay driver circuit learning about electronics. We must also select our supply voltage, so for this example we will use 12 volts. The voltage divider circuit seem to do the trick but it was also decided that i could put a p channel mosfet in the place of the pnp transistor and the relay and the circuit has been performing great. 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.

Ensure the pnp transistor can handle the current required by the load. A pair of darlington is an arrangement of two bipolar transistors. The first transistor t1 providing the required base. To turn the pnp transistor operating as a switch on, the base terminal is connected to ground or zero volts low as shown. Alternatively, we can use a pnp transistor to create a highside switch. A high current, high voltage relay needs a power transistor to driving it. Q1 is not a constant current source your current will vary with input voltage. Nov 17, 20 one more thing one can do with an npn transistor is use it as a relay. Dec 11, 2017 a high current, high voltage relay needs a power transistor to driving it. Design a sustainable relay driving circuit using bjt. I have already explained in one of my earlier posts regarding how to make a transistor driver circuit. 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. Pnptransistor based dc relay drive make triggering source. Using a diode plus resistor, zener in series with a diode, or zener across the transistor tvs may take the place of a zener diode can allow the relay coil voltage.

Going from a back view, the first lead is the emitter, the second lead is the base, and the third lead is the collector. This is because the classic single transistor source produces a constant current in the collector circuit not the emitter using a constant baseemitter voltage. The easiest way to switch a higher power load than a microcontroller can handle is to use an npn transistor as explained in part 7. 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. Gain familiarity with with bjt transistor circuit calculations. Ensure the transistor can handle the voltage and current required by the load. Simple emitter follower transistor relay drive circuit. A relay switch circuit can be designed using npn transistor. This relay also works with the raspberry pi, with a driver transistor. The pnp transistor, like almost all transistors, is a 3lead device. Figure 82 shows a circuit using a pnp transistor as a high side switch.

A power supply source is also required to operate the relay. Bc558 is a pnp transistor hence the collector and emitter will be closed forward biased when the base pin is held at ground and will be opened reverse biased when a signal is provided to base pin. Diodes incorporated relay driver bipolar transistors bjt are available at mouser electronics. On this page we will look at transistor driver circuits using both bipolar transistors and power mosfets and will use them as electrical switches. Usually, an npn transistor in a common emitter configuration used as a switch drives the relay. Relays are electromechanical devices that has an electromagnet to operate a pair of movable contacts from an open condition to a closed condition. In some circumstances higher levels of current gain may be required. Trouble turning on relay using pnp transistor electrical. Pnp and npn darlington pair transistor amplifier circuits. This ic belongs to the family of uln200x ics and various types of this family interface to various logic families. Pnp transistor switch for relay electrical engineering. Working of transistor as a switch npn and pnp transistors. The schematic diagram of relay driver using pnp transistor.

How to wire a relay to a transistor explained through. Dec 19, 2016 the pnp transistor is a mystery to many. Using pnp transistors is essentially the same as npn transistors, except the polarities are reversed. Gain experience in interpreting manufacturers datasheet. Pnp medium power transistor features high current low saturation voltage complement to 2sd882 applications voltage regulation relay driver generic switch audio power amplifier dcdc converter description the device is a pnp transistor manufactured by using planar technology resulting in rugged high performance devices.

You may recall the tlc555 relay driver circuit that i recently posted, it too is a low side driver. Relay driver using pnp transistor in the circuit an pnp transistor bc547 is used to drive the relay from any active low output. 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. I can use a darlington as well using two 2n2222as if need be or whatever else works. How to wire a relay to a transistor explained through formulas.

Learn how to test bjt transistor using a multimeter. The maximum amount of current that could flow through the collector pin is 7a, hence we cannot connect loads that consume more than 7a using this transistor. Using a diode plus resistor, zener in series with a diode, or zener across the transistor tvs may take the place of a zener diode can allow the relay coil voltage to rise higher, hastening the collapse of the magnetic field but harder on the transistor. The gate will be closed when the relay is fed with one polarity and it opens when the polarity is reversed. 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. How to make simple electronic circuits using transistor bc547. A very useful transistor latch circuit module could be built using just a couple of. This is where a pnp transistor differs from a npn transistor. In this type of circuit, the purpose of the transistor is to behave as a switch to energise the relay coil. In the above image, two npn transistors created a npn darlington configuration. This is usually higher power bipolar transistors or power mosfets.

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. The pair of bipolar transistors provides a very high current gain as compared with single standard transistor as mentioned above. Using pnp transistors to switch higher voltage loads. High side toggle switch driver, low side toggle switch driver, bipolar npn transistor driver, darlington transistor driver, nchannel mosfet driver, and uln2003 driver.

So we can define the cutoff region when using a bipolar transistor as a switch as being, bother the junctions of npn transistors are reverse biased, vb transistor as relay driver, which better, pnp or npn. 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. It needs a constant current source because the excess base current at 12 volts is the problem. However, when using a transistor to turn on a relay coil, it is very important to. In preparation for some of the more advanced relay drivers i will be posting in the future, i have listed a few basic relay drivers for your reference. Npn and pnp transistors each have three leads, a collector, a base, and an emitter, as shown in figure 9.

May 08, 2019 2n3906 relay driver for this to happen we need to know the maximum load current for the device to be turned on and the minimum hfe of the transistor. Automotive applications for example usually require driving a grounded load with 12v. In circuit diagrams, the emitter always appears as an arrow. We will use the most widely used pnp transistor for our circuit, the 2n3906. Transistor switches are commonly used to turn on transmitter circuits, leds, cooling fans and even relays. Driving it in either cutoff or saturation mode, the transistor can create the binary.