Relay driver circuit using pnp transistor

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. In the circuit below is most transistor relay driver circuit. 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. I agree with gene and doug, to drive an inductive load generally a mosfet is better than a transistor. The relay will be actuated when the input of the circuit goes high. The theory of operation and the calculations are exactly as the previous circuit.

I want to use raspberry pi gpio pins to control a few relays. Further the pin 8 is 2n906 to relay with pnp transistor 2n and a diode with some resistor as in the image. Application of high voltage at the base of bc548 causes turning on of the transistor and the relay coil to energize. Automotive applications for example usually require driving a grounded load with 12v. Usually, an npn transistor in a common emitter configuration used as a switch drives the relay. This is because the classic single transistor source produces a constant current in the collector circuit not the emitter using a constant baseemitter voltage. When using transistors to switch inductive loads such as relays and solenoids. So you need a helper, use a transistor to switch high current to drive the coil instead.

If you go with a darlington pair configuration using a couple of transistors, the hfe of one multiplies the hfe of the 2nd transistor. Analyzing a transistor relay driver electrical engineering stack. It is used to switch high loads or loads that needs ac current to operate. Basic transistor relay driver, actuated on low input pnp this circuit will actuate the relay when the input goes to logic low. Npn transistor based dc relay drive make triggering.

High side toggle switch driver, low side toggle switch driver, bipolar npn transistor driver, darlington transistor driver, nchannel mosfet driver, and uln2003 driver. Notice that the emitter is connected to the positive voltage. Collector of the transistor is connected to the supply ground. If its a pnp transistor, the base is coupled at the collector of the photo transistor, alternatively, if a npn transistor is used in the relay driver, the trigger is received from the emitter of the photo transistor. Uln2003a darlington transistor array with circuit examples. Driving 2n3055mj2955 power transistors with darlington transistors. Figure 82 shows a circuit using a pnp transistor as a high side switch. In some circumstances higher levels of current gain may be required. It is similar to others i have seen, though it appears to have two extra parts that others do. When the transistor switches off, the current flowing through the relay coil. Then consider using a latching relay and explore using a pchannel or an nchannel mosfet. Relay driver circuit using ic uln2003 and its working. The switching contacts of a relay are completely isolated from the coil, and hence from the arduino.

When you apply voltage to the base of a pnp transistor, by contrast. 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. The pnp transistor circuit works in opposite to the npn relay switching circuit. In this circuit microcontroller port pin p0 turns npn transistor q1 on and off. The relay is turned off by writing logic 0 on the port pin. Part 8 showed how to use a pnp transistor allowing the load to be at ground potential, as is sometimes necessary. 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. 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. Protect the transistor with a snubbing diode if the load is a relay, solenoid, motor or otherwise. The transistor is driven into saturation turned on when a logic 1 is written on the port pin thus turning on the relay. This is where a pnp transistor differs from a npn transistor. Transistor relay driver circuit with formula and calculations.

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. Interfacing relay to microcontroller dna technology. Optoisolated transistor drivers for microcontrollers. If the circuit uses the bipolar transistor as a switch, then the biasing of the. Trouble turning on relay using pnp transistor electrical. A generalpurpose bipolar junction transistor bjt works fine for small relay loads, however, for larger relays a twotransistor darlington circuit provides better performance. How to wire a relay to a transistor explained through. In case of npn transistor as shown in fig when v1 is 0v or turn off then base current ib will not flow. Pnptransistor based dc relay drive make triggering source.

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. Going from a back view, the first lead is the emitter, the second lead is the base, and the third lead is the collector. Using npn transistors, your output can be amplified by the hfe of the transistor and you can sink the load of the relays coil. 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. You need a better transistor and you have damaged the one you. How to connect a relay through an optocoupler homemade. 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. The most commonly used transistor switch is the pnp variety shown in figure 1.

Basic transistor driver circuits for microcontrollers. I was planning to use a 3904 npn transistor with a 330 ohm resistor on the base of the 3904. As you can see an npn transistor bc547 is being used to control the relay. Using pnp transistors is essentially the same as npn transistors, except the polarities are reversed. The pnp transistor, like almost all transistors, is a 3lead device. 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. You may recall the tlc555 relay driver circuit that i recently posted, it too is a low side driver. A relay switch circuit can be designed using npn transistor. 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 schematic diagram of relay driver using pnp transistor. Here is a simple circuit that uses a bipolar junction transistor bjt to drive a small 5 v relay coil. Bc557 is a pnp silicon planar epitaxial transistor. Simple emitter follower transistor relay drive circuit.

Using pnp transistors to switch higher voltage loads. You also need an emitter resistor to define the constant. Working of transistor as a switch npn and pnp transistors. 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. Relay driver ic circuit in order to drive the relay, we use transistor and only less power can be possibly used to get the relay driven. These transistors are mostly used in driver stages of audio amplifiers, low noise input stages of tape recorders, hifi amplifiers, and signal processing circuits of television receivers. 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. Here the ground refers to the negative line for an npn and the positive line for a pnp bjt.

We will use the most widely used pnp transistor for our circuit, the 2n3906. Design a sustainable relay driving circuit using bjt. We have a negative battery ground tied to digital ground. This page covers just about all the options for driving a relay with transistors. The majority of this page focuses on npn transistors. As shown in the following circuit diagram, the relay driver may consist a npn transistor or a pnp transistor. Q1 is not a constant current source your current will vary with input voltage. Circuitsphotoconductive relay circuitsphotodiode relay circuitsphotodiode amplifiersrelay driven directly by a photo diode section 9 controls 100 transistor detection sensor scr proportional control relay driverrelay circuitfullwave reversing drivemagneticamplifier circuit for an scrscr motor controlservo drivehalf.

Relay driver circuit using ic uln2003 with applications. These notes explain relays and transistors as theyre used for this purpose. 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. The arrow in the emitter of a pnp transistor points in the opposite direction than in an npn transistor. Lab iii voltage comparator and relay drivers by using bjts. 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. It consists of a npn bipolar transistor controlling a highpower light emitting diode connected to a 12volt battery. A cheap generalpurpose transistor such as the bc548 is capable of controlling a small relay with a. Transistor switches are commonly used to turn on transmitter circuits, leds, cooling fans and even relays. Tutorial using tip120 and tip125 power darlington transistors.

The base lead is the lead which controls the flow of current from emitter to collector. Since, transistor is an amplifier so the base lead receives sufficient current to make more current flow from emitter of transistor to collector. In case of npn transistor as shown in fig when v1 is 0v or turn off then base current ib will not flow due to which transistor remain in cutoff region and hence ic will not flow and relay coil remain deenergized but when base current ib is provided sufficiently the maximum amount of collector current starts flowing which. In the circuit an pnp transistor bc547 is used to drive the relay from any active low output. The ic uln2003a is a darlington transistor array which deals with highvoltage and highcurrent.

This video pnp transistor based 12v dc relay control drive simple make it, this type transistor is a semiconductor device used to switch. Like the common emitter circuit, this one too can use a pnp transistor, but with the diode polarity and supply reversed. Pnp transistor switch for relay electrical engineering. Using the output pulse from a microcontroller or digital gate ics. The basic circuit for using a transistor to control a highcurrent load is simple. This issue can be solved using a darlington transistor. Note a digital high is 5 volts and a digital low is zero volts. A relay driver circuit is a circuit which can drive, or operate, a relay so that it can function appropriately in a circuit. 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. It is also possible to control the relay operation using a transistor. Illustrated above is the most common transistor driver circuit.