MP240D4 OPTO 22, MP240D4 Datasheet - Page 17

• Manufacturer Part Number: MP240D4
• Description: Solid State Relay
• Manufacturer: OPTO 22

Specifications of MP240D4

• Control Voltage Type: DC
• Input Voltage: 3VDC To 24VDC
• Load Current: 4A
• Load Voltage Range: 24VAC To 280VAC
• Switching Mode: Zero Cross
• Relay Terminals: Through Hole
• Load Voltage Max: 280VAC
• Load Voltage Min: 24VAC
• Capacitance: 8 pF (Max.) Coupling (Input-Output)
• Current, Surge, Non-repetitive Peak: 85 Apeak @ 1 Cycle
• Dimensions: 1.70 in. L x 0.40 in. W x 0.98 in. D
• Control Voltage Max: 32V
• Control Voltage Min: 3V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

DATA SHEET
FAQ: SSR Applications
Q : What is a solid-state relay?
A : A solid-state relay (SSR) is a semiconductor device that can be
used in place of a mechanical relay to switch electricity to a load in
many applications. Solid-state relays are purely electronic, normally
composed of a low current “control” side (equivalent to the coil on
an electromechanical relay) and a high-current load side (equivalent
to the contact on a conventional relay). SSRs typically also feature
electrical isolation to several thousand volts between the control
and load sides. Because of this isolation, the load side of the relay is
actually powered by the switched line; both line voltage and a load
(not to mention a control signal) must be present for the relay to
operate.
Q : What are the advantages of using an SSR over a
mechanical relay?
A : There are many applications that require a moderate amount of
power (W to kW) to be switched on and off fairly rapidly. A good
example of this would be the operation of a heater element in a con-
trolled-temperature system. Typically, the amount of heat put into
the system will be regulated using pulse-width modulation turning a
fixed-power heating element on and off for time periods ranging
from seconds to minutes. Mechanical relays have a finite cycle life,
as their components tend to wear out over thousands to millions of
cycles. SSRs do not have this problem; in the proper application,
they could be operated almost infinitely.
Q : What are the limitations of using an SSR?
A : SSRs have a few limitations when compared to the capabilities
of their mechanical counterparts. First, because the relay is semi-
conductor-based, it will never turn all the way on, nor off. This
means that in the “on” state, the relay still has some internal resis-
tance to the flow of electricity, causing it to get hot. When in the
“off” state, the relay will exhibit a small amount of leakage current,
typically a few mA. This leakage can conspire to keep some loads,
especially ones with a high impedance, from turning off! Addition-
ally, SSRs are more sensitive to voltage transients; while Opto 22
relays are very well transient-protected, if a relay gets hit hard
enough a sufficient number of times, it will die or degrade. This
makes SSRs less ideal for driving highly inductive electromechanical
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loads, such as some solenoids or motors. SSRs should also never be
used for applications such as safety power disconnects because
even in the off state, leakage current is present. Leakage current
through an SSR also implies the presence of a potentially high volt-
age. Even though the relay is not conducting a large amount of cur-
rent, the switched terminal will still be “hot,” and thus dangerous.
Q : Do you make multi-pole or multi-throw SSRs?
A : Opto 22 manufactures only single-pole, single-throw SSRs. If
multi-phase operation is required, just use a relay on each phase.
Because of the limitations on semiconductor devices of the type
used in SSRs, it is not practical to build single-device multi-throw
SSRs. However, an alternative to multi-throw operation may be
accomplished with multiple relays.
Q : Can I hook up SSRs in parallel to achieve a higher
current rating?
A : No. There is no way to guarantee that two or more relays will
turn on simultaneously when operated in parallel. Each relay
requires a minimum voltage across the output terminals to function;
because of the optical isolation feature, the “contact” part of the
SSR is actually powered by the line it switches. One relay turning on
before the other will cause the second relay to lose its turn-on volt-
age, and it won’t ever turn on, or at least not until the first relay fails
from carrying too much current.
SOLID-STATE RELAYS
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