This can significantly reduce the life of the reed relay because the inrush current can exceed the rated maximum current by many times. Even comparatively small capacitors can use current spikes on many amps and this can significantly reduce the lifetime of the relay contacts, especially those of reed relays.
The fact can be reduced by balancing the amount of decoupling and selecting the minimum value consistent with applying good decoupling on the voltage rails or lines that are switched.
It is also possible to use small series resistors to reduce the surge. Here the voltage drop across the series resistor needs to be calculated and if any current is carried, this needs to be retained within he acceptable limits. There are many different circuits that can be used with relays. The actual relay circuit that is best will depend upon many factors and will often arise from the surrounding circuits add the general requirements. The relay circuit considerations can be split into two main areas: the driver circuits, and the switched circuits Applying the correct components and protection to both can make a significant difference to the circuit operation and also the reliability of the relay.
Relay control circuits The relay circuits used for controlling relays often use semiconductor devices. Simple common emitter transistor relay drive circuit To suppress this back EMF a diode is typically placed across the coil.
Simple emitter follower transistor relay drive circuit Like the common emitter circuit, this one too can use a PNP transistor, but with the diode polarity and supply reversed. Relay switched circuits Whilst it is important to design the circuits to drive the relays correctly, there are also points to note about the circuits that are being switched by the relays as well.
Shopping on Electronics Notes Electronics Notes offers a host of products are very good prices from our shopping pages in association with Amazon. Note: Electronics Notes receives a small commission on sales at no cost to you. Selected Video What is a Spectrum Analyzer? When they are used to drive relay coils the reed relay does not need a built in diode since no back EMF spike is generated.
Because the drive is connected to either ground or supply in turn with no back EMF the release time for the relay may be longer than when driven by an LED driver or an open collector drive. Pickering Electronics Reed Relays designed for 3.
Designing the relays around 3V ensure good operation even when driven by 3. For more indepth information about the wonders that are reed relays please see our Reed RelayMate page. All rights reserved.
Use of different wire gauges for the coil and number of turns creates relays with different drive voltage requirements and different coil powers. The resistance of the wire coil controls the amount of steady state current flowing through the coil and therefore the power the coil consumes when the contacts are closed.
Whenever fine wires are used in Pickering relays, the termination leads from the coils are skeined with several strands of wire twisted together to increase their physical strength.
Larger coils can be used to reduce power consumption, but that increases the size of the relay. Part Two will continue to explain the wonders that are reed relays, including information on changeover reed switches and two pole relays. From high voltage reed relay options to surface mount relays, find out more about our reed relays here. All rights reserved. Reed Relay Basics Part 1 Introduction. The reed switch explained: The reed switch has two shaped metal blades made of a ferromagnetic material roughly nickel iron and a glass envelope that serves to both hold the metal blades in place and to provide a hermetic seal that prevents any contaminants entering the critical contact areas inside the glass envelope.
Here is the simple NPN Transistor circuit to drive the relay. We can use less power to drive the relay. We have to make sure that base gets enough current to turn on the transistor. If the transistor gets enough base current then the transistor conducts and relay energizes. When there is no base voltage, the transistor is in open thus blocking the current through coil of the relay. Here the diode 1n or 1n is connected across the relay, used to protect the transistor from damage due to the back emf generated in the relay coils when transistor is in off.
Base resistor is used to set current to the base of the transistor. Now let us see how to choose the value of R1. Say relay needs 50mA current to the coil to pull the armature and assume coil has resistance of ohm. To turn on the transistor the base current should be greater than the collector current divided by current gain hfe.
In practice it is better to double the value, say 1mA of base current. If the input voltage Vin is switching between 0V and 12V. So it is better to use 10k resistor. Your email address will not be published. Electronics Tutorials.
0コメント