Integrated circuit simplifies the process of designing printed circuit boards for relays

Relay

A relay is an electronic control device. It has a control system (also called an input circuit) and a controlled system (also called an output circuit). When the input quantity changes to meet the specified requirements, the controlled quantity occurs in the electrical output circuit. An electrical appliance with a predetermined step change.

Today, we will introduce you in detail how the relay works and the drive circuit.

The input signal x of the relay is continuously increased from zero to the action value xx when the armature starts to pick up. The output signal of the relay immediately jumps from y=0 to y=ym, that is, the normally open contact is disconnected to open. Once the contact is closed, the input x continues to increase and the output signal y will no longer change. When the input quantity x drops from a value greater than xx to xf, the relay begins to release and the normally open contact opens. We call this characteristic of the relay a relay characteristic, also called the input-output characteristic of the relay.

Electromagnetic relays are generally composed of a core, a coil, an armature, a contact spring, and the like. As long as a certain voltage is applied to both ends of the coil, a certain current flows in the coil, thereby generating an electromagnetic effect, and the armature will absorb the pulling force of the return spring against the iron core under the action of the electromagnetic force attraction, thereby driving the armature. The moving contact is in contact with the stationary contact (normally open contact). When the coil is de-energized, the electromagnetic suction force also disappears, and the armature returns to the original position in the reaction force of the spring, so that the movable contact and the original static contact (normally closed contact) are released. In this way, the suction and release are achieved, thereby achieving the purpose of turning on and off in the circuit.

For the "normally open, normally closed" contacts of the relay, this can be distinguished as follows:

A static contact that is in an open state when the relay coil is not energized, and is called a "normally open contact";

A stationary contact that is in an on state is referred to as a "normally closed contact."

Circuit principle

A relay is a kind of small-capacity control loop that turns on or off the AC/DC when the input quantity changes to a certain value.

The permanent magnet keeps the release state, and after the working voltage is applied, the electromagnetic induction causes the armature and the permanent magnet to generate suction and repulsive moments, generates downward movement, and finally reaches the suction state.

Transistor drive circuit

When a transistor is used to drive a relay, an NPN transistor is recommended. The specific circuit is as follows:

When the input level is high, the transistor T1 is saturated and the relay coil is energized, and the contacts are attracted.

When the input is low, the transistor T1 is turned off, the relay coil is turned off, and the contact is turned off.

The role of each component in the circuit:

The transistor T1 is a control switch;

The resistor R1 mainly acts as a current limiting device to reduce the power consumption of the transistor T1;

Resistor R2 causes transistor T1 to be reliably turned off;

Diode D1 reverses the freewheeling flow, providing a bleed path for the triode to turn off the relay coil and turn its voltage across +12V.

Integrated circuit driver circuit

Integrated circuits integrated with multiple drive transistors have been used, and the use of such integrated circuits simplifies the design process of printed boards that drive multiple relays.

Relay series RC circuit: This form is mainly used in circuits where the rated operating voltage of the relay is lower than the supply voltage. When the circuit is closed, the self-inductance of the relay coil will cause the electromotive force to hinder the increase of the current in the coil, thereby prolonging the pull-in time. After the RC circuit is connected in series, the pull-in time can be shortened. The principle is that at the moment when the circuit is closed, the voltage at the voltage across the capacitor C cannot be abruptly changed as a short circuit, so that a power supply voltage higher than the rated working voltage of the relay coil is applied to the coil, thereby accelerating the speed of the current increase in the coil, so that the relay Quickly pull in. Capacitor C does not work after the power supply is stable, and resistor R acts as a current limiter.

Relay from Fujitsu

Fujitsu is committed to developing quality products. By adhering to strict quality process standards, state-of-the-art technology and outstanding customer service support, we offer our customers a wide range of high-quality relay products that support a wide range of green applications, from PV to smart grid .

For example, the FTR-E1 series for PV energy DC charging, the FTR-K1 series for AC power converters, and the FTR-F4G series for micro inverters.

From TaiNangyang power supply systems to smart grids, electric vehicles to UPS, HVC systems, Fujitsu relays can meet the requirements of emerging and existing applications.