The specifications for solid state relays are necessarily complex due to some parameters that must be defined and understood to avert misapplication. Each style of relay generally has a set of specifications categorized by model number. The specs are variations of load current, voltage and input conditions. SSR output configurations are considered to be 'single pole, normally open' unless otherwise stated.

This next section is meant to be a guide to understanding the technical specs as listed on the spec sheet pages on our Web site.

• Input Parameters
• Output Parameters
• General Characteristics

Input Parameters:

Impedance:
Minimum impedance at a given voltage which defines input power requirements, as an alternative to, or in addition to, input current.

Turn On Voltage (Max):
The voltage applied to the input at or above which the output is guaranteed to be in the on-state. Also known as 'must operate' or 'pickup' in EMR parlance.

Turn Off Voltage (Min):
The voltage applied to the input at or below which the output is guaranteed to be in the off-state. Also known as 'must release' or 'dropout' and considered to be the SSR 'noise immunity' level.

Note:
In the band between the turn-on and the turn-off voltages (typically 2 Volts), the SSR can be in either state. For an SSR defined as being 'normally closed' the on-off conditions would be reversed.

Reverse Protection:
In a DC input SSR, if the polarity is accidentally reversed and the voltage does not exceed the value stated, the relay will not be damaged.

Output Parameters:

I_OUT (Continuous)...A_RMS-- Maximum Load Current:
The maximum steady-state load current capability of an SSR, which may be further restricted by the thermal dictates of heat sink and ambient temperature conditions.

Voltage Drop @ I_OUT...VAC -- Maximum On-State Voltage Drop:
The maximum (peak) voltage that appears across the SSR output terminals at full rated load current. Not to be confused with 'zero voltage turn-on' or 'peak repetitive turn-on'. Used to calculate power dissipation.

I_SURGE - 1 Cycle (60 Hz)...A_PEAK -- Maximum Surge Current (nonrepetitive):
The maximum allowable momentary current flow for a specific time duration, typically one line cycle (16.6 milliseconds) for AC, specified as a peak value. Relay control may be lost during and immediately following the surge.

I_SURGE - 1 Second...A_PEAK -- Maximum Overcurrent (Nonrepetitive):
Similar to the above, but expressed as an RMS value for a one second duration.

Note:
The duty cycle is not generally specified for either of the above 'nonrepetitive' values, but is considered to be in the order of several seconds and related to the cooling time of the output semiconductor junction.

V_OUT...VAC -- Voltage Range:
The range of voltages which, when applied across the input terminals, will maintain an 'on' condition across the output terminal. This parameter is also used to define the absolute limits of input voltage that the SSR can withstand without damage.

Over Voltage Rating:
The maximum allowable excursion of the applied voltage that an SSR can withstand without damage or malfunction while maintaining its off state.

Frequency Range:
For AC output units this is typically 50-60 Hz.

Maximum Leakage @ V_OUT...mA:
The maximum off-state leakage current conducted through output terminals, with no turn-on control signal applied.

Turn On (Max @ 60 Hz)...(mS) -- Turn on time:
The maximum time between the application of a turn-on control signal and the transition of the output device to its fully conducting (on) state

Turn Off (Max @ 60 Hz)...(mS) -- Turn off time:
The maximum time between the removal of the turn-on control signal and the transition of the output device to its blocking (off) state.

Holding Current (min) ... mA -- Minimum Load Current:
The minimum load current required by the SSR to perform as specified

DV/DT @ V_OUT (Max) ... V/mS -- Minimum Off-State dv/dt (static):
The rate of rise of applied voltage across the output terminals that the SSR (AC) can withstand without turning on in the absence of a turn-on control signal. Expressed as a minimum value at maximum rated voltage in terms of 'volts per microsecond' (V/ms).

Commutating dv/dt - Snubbed for Power Factor @ I_OUT ... P.F.:
Refers to the proportion of triac withstand capability to the rate of rise of reapplied voltage immediately after conduction. In other words, it is the device's ability to regain blocking. When the triac turns off at zero current, the voltage which has advanced into the next half cycle instantly appears across the triac. It is this rate of rise of voltage that must be limited below the stated value or retriggering may occur, causing the triac to lock on. Dual SCRs do not have the commutating dv/dt problem that triacs do since each SCR has a full half cycle to turn off. However, they are susceptible to static dv/dt. In addition to protecting the output devices from voltage spikes, a snubber also suppresses dv/dt across the SCR.

I²T Fusing (8.3 ms) ... A²S:
The maximum nonrepetitive pulse-current capability of the SSR used for fuse selection. Expressed as 'ampere squared seconds' with a stated pulse width (8.3 ms). See other sections in this handbook : 'Surge Ratings/Fusing' and 'Protective Measures - Fuses'

R_0JC (TJ=115^oC) ...^oC/W -- Thermal Resistance:
Expressed as 'degrees celsius per watt' (^oC/W), this value defines the temperature gradient between the output semiconductor junction (T_J) and the SSR base (T_C) for any given power dissipation. R_0JC is necessary for calculating heat sink values and allowable current and temperature limits.

General Characteristics:

Dielectric Strength (Min) (Input-Output-Base) ... V_RMS:
Also referred to as 'isolation voltage'. Expressed as a voltage (RMS) at 50/60 hertz, that the SSR can withstand without breakdown. Considered as a minimum value.

Capacitance Input to Output pf:
Maximum value of capacitive coupling between control and power output terminals.

Ambient Temperature Range (Operating) ... ^oC:
The surrounding air temperature limits. The maximum operating temperature may be further restricted by the thermal dictates of heat sink and dissipation considerations.