8
PR308T21ESZ
■ Design Considerations
In order for the SSR to turn off, the triggering current (l
F
) must be 0.1mA or less.
When the input current (I
F
) is below 0.1mA, the output Triac will be in the open circuit mode. However, if the
voltage across the Triac, V
D
, increases faster than rated dV/dt, the Triac may turn on. To avoid this situation,
please incorporate a snubber circuit. Due to the many different types of load that can be driven, we can
merely recommend some circuit vales to start with : Cs=0.022µF and Rs=47Ω. The operation of the SSR
and snubber circuit should be tested and if unintentional switching occurs, please adjust the snubber circuit
component values accordingly.
When making the transition from On to Off state, a snubber circuit should be used ensure that sudden drops
in current are not accompanied by large instantaneous changes in voltage across the Triac.
This fast change in voltage is brought about by the phase difference between current and voltage.
Primarily, this is experienced in driving loads which are inductive such as motors and solenoids.
Following the procedure outlined above should provide sufficient results.
For over voltage protection, a Varistor may be used.
Any snubber or Varistor used for the above mentioned scenarios should be located as close to the main out-
put triac as possible.
Particular attention needs to be paid when utilizing SSRs that incorporate zero crossing circuitry.
If the phase difference between the voltage and the current at the output pins is large enough, zero crossing
type SSRs cannot be used. The result, if zero crossing SSRs are used under this condition, is that the SSR
may not turn on and off irregardless of the input current. In this case, only a non zero cross type SSR should
be used in combination with the above mentioned snubber circuit selection process.
The load current should be within the bounds of derating curve. (Refer to Fig.2)
Also, please use the optional heat sink when necessary.
In case the optional heat sink is used and the isolation voltage between the device and the optional heat sink
is needed, please locate the insulation sheet between the device and the heat sink.
When the optional heat sink is equipped, please set up the M3 screw-fastening torque at 0.3 to 0.5N•m.
In order to dissipate the heat generated from the inside of device effectively, please follow the below sugges-
tions.
● Design guide
Sheet No.: D4-A02001EN
● Recommended Operating Conditions
Parameter Symbol Unit
Input
Output
Input signal current at ON state
Input signal current at OFF state
Load supply voltage
Load supply current
Frequency
Operating temperature
I
F
(ON)
I
F
(OFF)
V
OUT
(rms)
I
OUT
(rms)
f
T
opr
mA
mA
V
mA
Hz
˚C
−
−
−
Locate snubber circuit between output terminals
(Cs=0.022µF, Rs=47Ω)
−
−
Conditions
(
∗
) See Fig.2 about derating curve (I
T
(rms) vs. ambient temperature).
20
0
80
0.1
47
−20
30
0.1
240
I
T
(rms)
×80%(
∗
)
63
80
MIN. MAX.
