2n3904 relay driver circuit

Relay driver circuit using ic uln2003 with applications. Oct 07, 2019 in the circuit below is most transistor relay driver circuit. The maximum rating for the 2n3904 is 625mw, so no surprise that the transistor gets hot fast. The transistor 2n3904 comes under the category of npn small signal, low power, general purpose transistor, mainly applicable for switching and for signal amplification. In general, while designing electronics projects the loads are controlled switched on or off using microcontroller block. The 2n3904 is an extremely popular npn transistor that is used as a simple electronic switch or amplifier that can handle 200 ma absolute maximum and frequencies as high as 100 mhz when used as an amplifier figure 1. All about 2n2222 transistor and its circuit diagrams. In this project, we will design a preamplifier circuit for a condenser microphone using a single 2n3904 transistor. The base is connected with a 330ohm resistor or a 10k resistor ive tried.

This is often done with a lowside mosfet switch and current recirculation diode fig. I tried using a 2n3904 transistor to amplify it doesnt seem to work. One set of relay contacts is used to control the load, while the other is used to provide feedback to keep the relay activated or deactivated. When the switch of the circuit is open, no current flows to the base of the transistor. Blog entry using transistor as a switch december 23, 2008 by rwb, under electronics most of microcontrollers work within 5 volt environment and the io port can only. Hi, i want to use the output of a lm339 comparator to drive a 5v ohm relay. You will need the following parts to make this project. The beta or current gain drops off drastically at that current, in this case, the gain is only 17. If you drop a tip41c into the circuit you should still be able to measure a signal at the amplifier. Usually, the signal from a microcontroller, or logic gate, does not possess sufficient drive current to. The 2n3904 is an extremely popular npn transistor that is used as a simple electronic switch or amplifier that can handle 200 ma absolute maximum and frequencies as high as 100 mhz when used as an amplifier. If your circuit is the standard pnp switching circuit and the voltage you are switching is 3. And, the input current at output of a normal digital circuit is about 2 ma.

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 make simple electronic circuits using transistor. The capacitor and resistor in series acts as the transient voltage suppressor to suppress voltage spikes. It is a high gain but low power output and inverts signal output. Switch using 2n 3906 transistor all about circuits. This article brings out the working of uln2803 ic and how to use it in a circuit. The relay in the npn driver circuit in figure 3 can be activated via a. When i showed bob pease one of the many solenoid driver circuits available on the web, he scoffed. Heres a poweron time delay relay circuit that takes advantage of the emitterbase breakdown voltage of an ordinary bipolar transistor. The schematic of the led driver circuit we will build is shown below. The 2n3904 will need to drive some kind of 12v relay that requires less than 200ma otherwise youll need some other kind of transistor.

An illustration of the pin out of a standard to92 package for digikey part number 2n3904fsnd. One 2n2222 transistor code lock system is a simplest electronic code lock system. So, my guess is the relay needs a current of 563 79ma. This is a simple audio preamplifier with single transistor 2n3904. It is used to switch high loads or loads that needs ac current to operate. Microphone preamplifier circuit using 2n3904 transistor. B weve added ammeters to measure the base and collector currents as well as voltmeters to. In this circuit with bjts, vcc higher voltage supply than the logic. How to build a relay driver circuit learning about electronics. The relay driver circuit based on the q2 transistor is required since the output pin current rating of the launchpad is limited to 6ma and not capable to drive the relay coil. The circuit has only one transistor with a relay as load at its collector. Uln2803 relay driver working operation embetronicx. Transistor relay driver demo the basic transistor relay driver circuit is shown in fig. Getting the 2n3904 to take 100 ma is really pushing it.

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. I am thinking that i have enabled a breakdown of the 2n3904 although i am not sure. We will use the most widely used pnp transistor for our circuit, the 2n3906. An led driver is an electronic circuit that utilises a transistor to switch power to an led. In the circuit below is most transistor relay driver circuit. The circuit is simple but really efficient and works the best. Nov 17, 20 one more thing one can do with an npn transistor is use it as a relay.

The 2n3904 shown below is a small discrete bjt transistor is used for a driver circuit that required less than 200ma. Often a need arise to interface output of the microcontroller with an electromagnetic relay emr. The circuit in figure 1 can easily pull a relay to full. The transistor is typically and solely employed for operating the. The circuit shown in figure 1 will drive the relay through optocoupler in same circuit with same power supply. The ac relay driver circuit we will build is shown below. The uln2803 ic consists of eight npn darlington pair which provides the proper current amplification required by the loads. I have a 12v relay that has a dc coil resistance measuring 392r, so at 12 0. The relay can switch up to 220vac at 20a using a logic signal for control, but the small pcb layout and screw terminals likely limit it to lower voltage and current levels to at least half of these ratings. We all know that the transistors are used to amplify the current but here darlington transistor pairs are used inside the ic to make the required amplification. Blog entry using transistor as a switch december 23, 2008 by rwb, under electronics most of microcontrollers work within 5 volt environment and the io port can only handle current up to 20ma. Its contains seven darlington pair of a transistor which have high voltage and high current carrying capability.

The pnp transistor, like almost all transistors, is a 3lead device. Illustrated above is the most common transistor driver circuit. C2 is a 104 capacitor which is practically a short at rf. The transistor is typically and solely employed for operating the relay in response to the commands received from the preceding control stage. The 2n3904 has a spec of peak 200ma current capacity, which i translate to be 2. The beta or current gain drops off drastically at that current, in this case, the gain is. So, in this project, we are going to design a simple timer circuit using 3 2n3904 npn transistors. An illustration of the pin out of a standard to92 package for digikey.

Vbe of 2n3904 in led driver circuit electronics forums. Applications include stepper motor, relay drivers, hammer drivers, lamp drivers, display drivers led and gas. 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 circuit below requires a double pole, double throw relay in conjunction with a single transistor to allow toggling the relay with a momentary push button. What im getting at is that this is a very poor choice for a relay driver transistor, and you couldnt use it in the circuit in that url above. The 2n3904 has a beta hfe of 300 max, so the minimum ib i need for saturation is 29ma 300, or 96ua, though it should be higher to be reliable.

It is very simple amplifier circuit using transistor 2n3904 only. Relay driver circuit using uln2003 and its applications. Ive used a 2n2222 transistor, an arduino uno, a 12 volt power supply, a 12 volt relay and a multimeter. These simple optocoupler relay driver circuits can be used in variety of electronic projects. The relay boards driver circuit is built using a bjt as seen in the schematic below. Relays are devices which allow low power circuits to switch a relatively high current andor. Transistor relay driver circuit with formula and calculations.

Referring to the above circuit diagram we see that the configuration only. We, again, feed the ac relay the ac voltage it is rated for. Vbe increases with base current, decreases with temperature, and increases with collector current. If we use a relay with a rated voltage of 110vac, we must feed it 110v from an ac power source. The circuit shown in figure 1 will drive the relay through. Very simple amplifier circuit using transistor 2n3904. Analyzing a transistor relay driver electrical engineering. Electro tech is an online community with over 170,000 members who enjoy talking about and building electronic circuits, projects and gadgets. How to make simple electronic circuits using transistor bc547. Its dynamic range may include a current handling capability of more than 100ma for switching applications and a 100mhz frequency handling capacity fits with amplification purposes. We have a negative battery ground tied to digital ground.

It consists of a npn bipolar transistor controlling a highpower light emitting diode connected to a 12volt battery. I am using a 2n3904 transistor to bring neutral to the other side of the coil to make it fire. May 31, 2018 the simplest way to drive a solenoid is to switch the current on and off. The reverse connected emitterbase junction of a 2n3904 transistor is used as an 8 volt zener diode which creates a higher turnon voltage for the darlington connected transistor pair.

Relay driver circuit using ic uln2003 and its working. Jul 12, 2008 hi, i want to use the output of a lm339 comparator to drive a 5v ohm relay. Note a digital high is 5 volts and a digital low is zero volts. Dec 21, 2015 when the software detects the double clap, it toggles the p1. This easy circuit provides good gain to weak audio signals. On the figure, c represents the collector side of the transistor and e represents the emitter side, r represents the 12 volt relay and m represents the multimeter. It consists of a relay, a transistor and some passive devices like resistors, capacitors and switches. Do have a look at the uln2803a which is a darlington highcurrent driver whose outputs can be paralleled for currents up to about 2a with 4 in parallel. You can calculate a limiting resistorsr from the input voltage and current. Hence, the improved signal from a preamplifier is usually sent to a power amplifier where the current is amplified. Pic 16f54 needs to drive a 5v relay i am using a pic 16f54 and need to trigger a 5v relay. Complete technical details can be found at the 2n3904 datasheet given at the end of this page.

This page covers just about all the options for driving a relay with transistors. In this circuit with bjts, vcc higher voltage supply than the logic power supply and 6 or 12v dc is required for motors or relays. If this is the case, you will need a level shifter. Relay driver ic uln2003 is high voltage and high current integrated ic which used darlington array. A relay driver is nothing but an additional transistor stage attached with the relay which needs to be operated. One very useful inductordriving circuit is the relay driver, and a number of examples of this are shown in figures 3 to 7. The ic uln2003a is a darlington transistor array which deals with highvoltage and highcurrent. On the figure, c represents the collector side of the transistor and e. Can someone draw a small circuit showing me the transistor the resistors required. Transistor 2n3904 pinout and specifications homemade. Jun 15, 2019 the transistor 2n3904 comes under the category of npn small signal, low power, general purpose transistor, mainly applicable for switching and for signal amplification. In this type of circuit, the purpose of the transistor is to behave as a switch to energise the relay coil.