The loads connected to the output pin can be maximum of 50C and mA each. However you can run higher current loads buy combining two or more output pins to gather. The COM pin is connected to ground through a switch, this connection is optional. It can be used a test switch, meaning when this pin is grounded all the output pins will be grounded. We will never spam you. We can use seven relays with relay driver circuit using ULN and the relay driver circuit using ULN enables to use eight relays.
The clamp diodes are built in these relays driver ICs and which eliminates the usage of freewheeling diodes. The program that can be used for turning the relays ON and OFF is given below with delay time of one second.
Based on the signals received from the microcontroller the relay driver circuit drives the relay or relays ON and OFF, such that controlling the operation of loads connected to these relays.
This is an innovative electrical engineering project that eliminates the power supply interruptions by auto power supply from integrating and controlling the four different electric power sources such as solar power, mains power supply, generator, and inverter. This project utilizes microcontroller of family which is interfaced with four switches these switches or selection keys are assumed to be four different power sources mentioned above. Transistor is used as a switch in this circuit.
The microcontroller provides High or low input signals to NPN transistors. NPN transistor provides high driving current to electromechanical relay through the volt external power supply.
Following components are used in relay driver circuit using transistor:. ULN is a very famous relay driver integrated circuit. Its contains seven Darlington pair of a transistor which have high voltage and high current carrying capability. Its mean ULN can drive up to seven relays at a time.
A diode is used with each pair of NPN Darlington transistor. Diode makes it easily useable with inductive loads. There are many applications of a relay driver circuit using uln, but some of the famous applications are given below:. The relay driver circuit using uln is given below. In this circuit diagram, the pic microcontroller is providing a signal to 4 relays through relay driver IC uln Single ULN can be easily used int this circuit to drive up to five relays.
Microcontrollers can easily provide a high or low signal to relays through its output port D. Simple programming instructions tells the microcontroller to provide either high or low signal to relays.
I have posted a project on the greenhouse system in which the relay driver circuit using uln is used to drive four relays. Four relays are connected with four different relays. Check the following link to know more about the practical use of relay driver circuit:. Intelligent green house control system. This could help the user to install the IC with any circuit without taking too much space as a transistors circuit.
The output power source could apply separately to all the outputs but the input will be the same as all microcontrollers and microprocessors. The voltage range for any load is 50V but the current range is mA which could be increased by combining the multiple output pins. ULN comes with internal safety protection from back emf. It has an internal flyback protection system which gives protection to the device.
To use this IC there are some rules which we need to follow to make it work perfectly. Then Attach the one end of the load with the output pin. Attach the other end of the load with the Power source of 0 — 50V. There is a pin as COM Pin 9. Attach this pin with the ground through a button. This button could be used to bypass all the pins and could produce the output. The power source of each motor could be different, but the ground should remain common. We could handle multiple devices with this single device.
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