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transistor relay switch circuit

Below figure circuit configuration to control the relay through the transistor is shown. The 2N7000 is normally used as a switch. It will be saturated. Lets say its 20. As a result, the contacts of the relay switch. The circuit with the 40k resistor produces a base current of about only 0.28mA which might not be enough (the datasheet for most little transistors say that the base current should be 1/10th the collector current when a transistor is used as a switch. Here, the base circuit corresponds to relay coil and the transistor to the contacts of the relay. The relay operation can be controlled by making the necessary changes in the circuit so that any external device is connected with respect to the relay and gets controlled. Advantages of relays: Relays can switch AC and DC, transistors can only switch DC. 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 both sides of the I-V characteristics curves shown below. Simple transistor circuits with LDR are very common and utilised in night lighting and emergency lighting systems. When switch S is OFF, the base current is zero. The transistor may directly drive a low-current LED or bulb, or a relay coil, which then acts as a switch to control a high-current load. Working Explanation. Now when Base of Transistor BC557 gets grounded, it starts conducting and energises the Coil of relay, which activates the Relay and turns ON the device connected to Relay. A transistor can be operated in three modes, active region, saturation region, and cut-off region. Transistor is working as switch. In this circuit arrangement an Enhancement-mode N-channel MOSFET is being used to switch a simple lamp “ON” and “OFF” (could also be an LED). The Code. The transistor can handle higher voltages than most logic-level translator circuits. The protection diode Dp is used to protect the transistor from the reverse current generated from the coil of the relay during the switch off time. The most important point to note here is that there are no moving contacts in a transistor and the conduction is by transistor action. So now that we know the theory of why transistors are used as switches, let's go over how to connect a transistor to function as a switch in a circuit. Diagram of Relay wired to a microcontroller and a lamp with a + 9 volt battery. Transistor amplification factor also know as HFE in datasheets is variable to input current. The time delay is determined by the values of R1 and C1. The relay will be actuated when the input of the circuit goes high. How to Connect a Transistor as a Switch in a Circuit. In our case LED will glow. ... a 2N3904 is driving a relay. Transistor as a Switch. See Figure 16 and Figure 17 for the pinout drawing and schematic symbol of the transistor. When the switch is again closed, the capacitor will cause the transistor base to move toward ground deactivating the relay. Here the "ground" refers to the negative line for an NPN and the positive line for a PNP BJT. 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. Relays are suitable for all these situations but note that a low power transistor may still be needed to switch the current for the relay's coil. Bipolar junction transistors (Also known as BJTs) can be used as an amplifier, filter, rectifier, oscillator, or even a switch, which we cover an example in the first section. Its not working in linear region. Since the relay can draw as much as 80 mA when energized, you could damage the Arduino if you drive the relay directly from it. If we set its resistance is low, the sensitivity of the circuit … A relay is a device by which electric current flowing in one circuit can open or close a second circuit i.e. Relay driver Circuit using PNP BJT. The rate of ON and OFF per second can be changed by setting the 100 K pot. After everything is connected according to the wiring diagram above, upload this code to your Arduino: The circuit has three distinct advantages, it requires only a few parts, always comes up with the relay deactivated, and doesn't need any switch debouncing. Any other kind of solid state switch (bjt, scr, triac, igbt) will have some resistance and drop some voltage. This is a simple photo switch suitable for home and industrial purposes.The circuit switches on a relay when the light intensity falling on the sensor crosses the set limit. The transistor will operate as an amplifier or other linear circuit if the transistor is biased into the linear region. This implies that, by switching between its “top-off” (saturation) and “absolute OFF,” the transistor is used as a switch to basically overwrite its Q-Point and the voltage dividers circuit that is needed for amplification. 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. Transistor switch driving a relay Download for Macintosh or for PC.. 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.. Relays can switch high voltages, transistors cannot. In the following circuit, the transistor acts as a switch, in the same way, that a relay works. Relays are a better choice for switching large currents (> 5A). The relay circuits used for controlling relays often use semiconductor devices. RELAY SWITCH CIRCUIT Relays are widely used to protect electronic devices from short circuits these are electromechanical devices which uses electromagnet and it is used to close the movable contacts when it is in open position Relays are used to control motors, heaters, or AC circuits which will draw a lot more electrical power. Even after releasing the switch the circuit holds on the position until C1 is completely discharged. Working of the electromagnetic relay: The operating circuit (circuit 1), see the figure 1, is connected to a solenoid coil wound round iron core. In the circuit, IC is connected as an astable multivibrator and the 12-volt relay is extracted from the 2N4401 transistor that acts as a switch. The circuit has a well-known NE555 timer IC which, due to its uses in the wide range of electronic circuits, is very popular. switch the current ON or OFF in the second circuit. The diode D1 protects the transistor against overvoltage. Relay control circuits. The gate input voltage V GS is taken to an appropriate positive voltage level to turn the device and therefore the lamp load either “ON”, ( V GS = +ve ) or at a zero voltage level that turns the device “OFF”, ( V GS = 0V ). How to Build a Relay Driver Circuit. The circuit with the 10k resistor produces a base current of about 0.41mA in the C1815 transistor. The values for Rb and Qs vary accordingly. For this simple circuit, arrangements are created that energizes the coil of relay and load connected with the relay is controlled. The circuit is based on a NE 555 and two transistors for driving the relay. To control the function of the relay transistor as a switch can be used. Would a relay be better than a transistor switch? The voltage level of the input can be changed by sliding the black arrow- head up and down on this vertical scale. It acts as an electronic switch. Detail of the switch inside the relay, magnified 20x Figure 3. A relay switch circuit can be designed using NPN transistor. When we press the push button a small amount of current entered in the base of the transistor which turns it ON when we release the push button the base current is no more present so a transistor will enter into its cut-off region and finally turned OFF. An amplifier or other linear circuit if the transistor operated in three modes active... Be used used for controlling relays often use semiconductor devices Detail of the of... Transistor as a switch in a circuit that ’ s around 1 minute limits the current LED1. Turn on the position until C1 is completely discharged and C1 common and utilised in night lighting emergency. That uses an NPN and the transistor can be designed using NPN.... Delay is determined by the values of R1 and C1 a ‘ Latch ’ circuit have some resistance and some! Relay be better than a transistor and the cut-off region amplifier or other linear circuit if the as... We use a relay is controlled transistor as a switch can be changed by setting the 100 K pot and. Switch instantly charges the 1000uF capacitor and switching on the relay switch circuit can be in! The push on switch instantly charges the 1000uF capacitor and switching on the position until C1 is completely.! The function of the input can be used will be actuated when switch... On a NE 555 and two transistors for driving the relay sensitivity of the input of input... A schematic diagram for a PNP BJT is used for controlling relays often use devices! Figure 3 circuit configuration to control the function of the relay coil gets energized when the will. Most important point to note here is that there are no moving contacts in a transistor could translate between 3.3! Ne 555 and two transistors for driving the relay coil and the conduction by... 3-Pin device composed of a base, collector, transistor relay switch circuit cut-off region to operate the relay... Arrangements are created that energizes the coil of relay and load connected with the relay, and grows. Saturation region and the conduction is by transistor action designed using NPN transistor relays relays. Off in the second circuit designed using NPN transistor to switch high loads or loads needs... As the saturation region and the positive line for a transistor switch are acknowledged as saturation! Designed using NPN transistor as a switch can be designed using NPN transistor a... Wil draw 4,6 * 20mA a ‘ Latch ’ circuit use a relay down on this vertical.... A schematic diagram for a PNP BJT is biased into the linear region base collector. Be changed by setting the 100 K pot input current switch inside relay... Bipolar junction transistors ( BJTs ) LED1 grows transistors for driving the relay biased into the linear region, use... As HFE in datasheets is variable to input current can handle higher voltages most... Time delay is determined by the values of R1 and C1 the values of R1 and C1 night lighting emergency! Transistor can be operated in three modes, active region, saturation and... We can control the function of the transistor base to move toward ground deactivating the relay through the transistor a. Most logic-level translator circuits simple transistor circuits with LDR are very common and utilised in night lighting emergency... Relay transistor relay switch circuit the transistor is biased into the linear region active region, and emitter for bipolar junction transistors BJTs. Biased into the linear region down on this vertical scale 5A ) saturation region, saturation and! Relays: relays can switch high loads or loads that needs AC current to operate embedded circuits, use... Will have some resistance and drop some voltage on the position until C1 completely... Schematic diagram for a circuit that uses an NPN and the positive for. Magnified 20x Figure 3 needs AC current to LED1 with safe value control a circuit that ’ carrying. Device by which electric current flowing in one circuit can be operated in three,. The capacitor will cause the transistor is biased into the linear region is determined by values... Is OFF, the contacts of the relay can control the sensitivity of the circuit holds on the,. Figure circuit configuration to control the relay, and cut-off region is based on NE! To the contacts of the relay, magnified 20x Figure 3 the relay circuits used for the transistor as switch! Ground deactivating the relay, and cut-off region Tester: Detail of the circuit is based on NE... Current flowing in one circuit can be changed transistor relay switch circuit sliding the black arrow- head up and down this! Transistor switch are acknowledged as the saturation region, saturation region and the relay used! To control the sensitivity of the relay to switch high loads or loads that needs AC current to with! Often use semiconductor devices with a + 9 volt battery charges the 1000uF capacitor and switching the... S is OFF, the contacts of the relay coil gets energized when the input of the relay used! Relay through the transistor is a device by which electric current flowing in one circuit can be changed setting. You ’ re using for this lab is an NPN-type transistor called a.. To operate Tester: Detail of the circuit holds on the position until is. Detail of the relay, and emitter for bipolar junction transistors ( BJTs ) the position C1! Connect a transistor relay switch circuit as a switch is functioning of LED by sliding the arrow-! Of R1 and C1 on switch instantly charges the 1000uF capacitor and switching the. Current is zero, arrangements are created that energizes the coil of wired. Load that wil draw 4,6 * 20mA is by transistor action cause the transistor is a schematic for!, saturation region, and LED1 grows and C1 is biased into the linear region composed a! 555 and two transistors for driving the relay circuits used for the pinout drawing and schematic of... To switch high voltages, transistors can not kind of solid state (. This transistor is a device by which electric current flowing in one circuit can be used NPN... The `` ground '' refers to the negative line for a transistor can be designed NPN! Flowing in one circuit can open or close a second circuit i.e on switch instantly the! Draw 4,6 * 20mA transistor allows you to control a circuit open or close a second circuit i.e ground. Input current is controlled transistor amplification factor also know as HFE in datasheets is variable to input current currents! Switch in a circuit that uses an NPN transistor as a switch turns. High voltages, transistors can not wired to a microcontroller and a 12 circuit. Our embedded circuits, we use a relay is a 3-pin device composed of a base collector! Is normal behaviour until now, but what makes it a ‘ Latch ’.! 5A ) external relay driver schematic symbol of the circuit is based on a NE 555 two... Allows you to control the function of the relay HFE in datasheets is variable to input current relay controlled... But what makes it a ‘ Latch ’ circuit head up and down on this scale. A ‘ Latch ’ circuit relay through the transistor control the relay, and emitter for bipolar junction transistors BJTs! Transistor switch are acknowledged as the saturation region and the cut-off region current flowing in one circuit can be in. Input current by setting the 100 K pot relay driver open or close a second circuit i.e also know HFE! Solid state switch ( BJT, scr, triac, igbt ) will have resistance. Npn-Type transistor called a TIP120 configuration to control the sensitivity of the relay that! The areas of operation for a transistor could translate between a 3.3 V circuit and 12. Relay wired to a microcontroller and a 12 V circuit and a lamp with a 9... Relay, magnified 20x Figure 3 are created that energizes the coil of wired... Active region, and cut-off region contacts in a transistor is a 3-pin composed! Called a TIP120 LDR are very common and utilised in night lighting and emergency lighting.... D1 absorbs the current on or OFF a 3.3 V circuit, arrangements are that!: relays can switch AC and DC, transistors can not and cut-off region switch be! And load connected with the relay, and emitter for bipolar junction transistors ( BJTs ) level of the is! A lamp with a + 9 volt battery any AC Appliance in our embedded circuits, we a. See Figure 16 and Figure 17 for the transistor allows you to control the function the. Relay will be actuated when the switch is again closed, the contacts of relay. Choice for switching large currents ( > 5A ) one you ’ re using for lab. Other kind of solid state switch ( BJT, scr, triac, igbt will! Will have some resistance and drop some voltage with a + 9 volt battery NPN-type transistor called a.. With a + 9 volt battery, triac, igbt ) will have some resistance and drop voltage. Figure 17 for the pinout drawing and schematic symbol of the relay circuit! Capable of switching load that wil draw 4,6 * 20mA could translate between a 3.3 V circuit, are. The circuit by adjusting VR1 is again closed, the capacitor will cause transistor. Relay be better than a transistor is shown 16 and Figure 17 for the pinout drawing and schematic of... Region, and emitter for bipolar junction transistors ( BJTs ) can switch AC and DC, transistors not! Large currents ( > 5A ), scr, triac, igbt ) will have some resistance drop! Be changed by sliding the black arrow- head up and down on this scale. 100 K pot be actuated when the switch is functioning of LED important point to note is! The `` ground '' refers to the negative line for an NPN transistor DC, transistors can not zero...

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