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Structure and operational principle of Photrelays

Product line up

A PhotoRelays is a semiconductor relay with an LED as an input and MOSFET as an output.
It is used in various fields to improve device reliability and reduce size.






  • img01.jpg


  • (1)LED (light emitting diode)

  • (2)Photodiode dome array (PDA)

  • (3)MOS FET





、img02.jpg



  • (1)The LED lights when the current is connected at the input side.

  • (2)The light sent by the LED will be converted into voltage again when it is received by the photodiode .

  • (3)This voltage will be a gate voltage to drive MOS FET via control circuit.



Advantages of PhotoRelays


Obviously the PhotoRelays differ from the conventional electro-mechanical relays.
PhotoRelays are classified to semiconductor relays that have no moving contact, therefore they are superior to conventional electro-mechanical relays in life-expectance and reliability of contacts, operation speed, and their sizes.

But they also distinguish themselves from other switching solutions that utilize photo-couplers, photo-transistors etc.. PhotoRelays have MOSFET for output, therefore they are the most suitable devices for small analog signal switching.


Compared with Electro-Mechanical Relays
have moving contact:		Compared with SSR (Solid State Relays)
have phototriac for output:
●Longer lifetime (No limit on mechanical and electrical lifetime)
●Higher-speed and high-frequency switching
●Higher sensitivity (less power consumption)
●Smaller size
●Less contact problems such as arcs, bounce, and noise
●More resistant to vibration and impact
●No limitation for the mounting direction		●Able to control miniature analog signal
●Applicable to both AC/DC
●More sensibility
●Less leakage current
●Lower offset voltage
●Various contact structures such as 2a, 4a, 1b, 2b, and 1a1b in addition to 1a


PhotoRelays Technical Terminology


            1．Technical Terminology   

            2．Reliability tests   


            Here is PDF of this page.   

1. Technical Terminology


Term
Symbol
Description

Input
LED forward current
IF
Current that flows between the input terminals when the input diode is forward biased.

LED reverse voltage
VR
Reverse breakdown voltage between the input terminals.

Peak forward current
IFP
Maximum instantaneous value of the forward current.

LED operate current
IFon
Current when the output switches on (by increasing the LED current) with a designated supply voltage and load connected between the output terminals.

LED turn off current
IFoff
Current when the output switches off (by decreasing the LED current) after operating the device with a designated supply voltage and load connected between the output terminals.

LED dropout voltage
VF
Dropout voltage between the input terminals due to forward current.

Power dissipation
Pin
Allowable power dissipation between the input terminals.
Output
Load voltage
VL
Supply voltage range at the output used to normally operate the PhotoRelays.    Represents the peak value for AC voltages.

Continuous load current
IL
Maximum current value that flows continuously between the output terminals of the PhotoRelays under designated ambient temperature conditions. Represents the peak value for AC current.

On resistance
Ron
Obtained using the equation below from dropout voltage VDS
(on) between the output terminals (when a designated LED current is made to flow through the input terminals and the designated load current through the output terminals.)
    Ron
＝ VDS
(on)/IL

Off state leakage current
ILeak
Current flowing to the output when a designated supply voltage is applied between the output terminals with no LED current flow.

Power dissipation
Pout
Allowable power dissipation between the output terminals.

Open-circuit output voltage
Voc
Voltage required for driving a MOSFET

Short-circuit current
Isc
Current that is output from the driver when the input is turned on
Electrical    characteristics
Turn on time
Ton
Delay time until the output switches on after a designated LED current is made to flow through the input terminals.

Turn off time
Toff
Delay time until the output switches off after the designated LED current flowing through the input terminals is cut off.

I/O capacitance
Ciso
Capacitance between the input and output terminals.

Output capacitance
Cout
Capacitance between output terminals when LED current does not flow.

I/O isolation resistance
Riso
Resistance between terminals (input and output) when a specified voltage is applied between the input and output terminals.

Total power dissipation
PT
Allowable power dissipation in the entire circuit between the input and output terminals.

I/O isolation voltage
Viso
Critical value before dielectric breakdown occurs, when a high voltage is applied for 1 minute between the same terminals where the I/O isolation resistance is measured.
Ambient    temperature
Operating
Topr
Ambient temperature range in which the PhotoRelays can operate normally with a designated load current conditions.

Storage
Tstg
Ambient temperature range in which the PhotoRelays can be stored without applying voltage.
Max. operating frequency
—

Max. operating frequency at which a PhotoRelays can operate normally when applying the specified pulse input to the input terminal



2. Reliability tests


Classification
Item
Condition
Purpose
Life tests
High temperature storage test
Tstg
(Max.)
Determines resistance to long term storage at high temperature.

Low temperature storage test
Tstg
(Min.)
Determines resistance to long term storage at low temperature.

High temperature and high humidity storage test
85°C
185°F, 85%R.H.
Determines resistance to long term storage at high temperature and high humidity.

Continuous operation life test
VL
= Max., IL
= Max.,    IF
= Recommended LED forward current
Determines resistance to electrical stress (voltage and current).
Thermal    environment    tests
Temperature cycling test
Low storage temperature (Tstg
Min.)
    High storage temperature (TstgMax.)
Determines resistance to exposure to both low temperatures and high temperatures.

Thermal shock test
Low temperature (0°C)
(32°F),    High temperature (100°C)
(212°F)
Determines resistance to exposure to sudden changes in temperature.

Solder burning resistance
260±5°C
500±41°F, 10 s
Determines resistance to thermal stress occurring while soldering.
Mechanical    environment    tests
Vibration test
196 m/s2
{20 G}, 100 to 2,000 Hz*1
Determines the resistance to vibration sustained during shipment or operation.

Shock test
9,800 m/s2
{1,000 G} 0.5 ms*2;    4,900 m/s2
{500 G} 1 ms
Determines the mechanical and structural resistance to shock.

Terminal strength test
Determined from terminal shape and cross section
Determines the resistance to external force on the terminals of the PhotoRelays mounted on the PC board while wiring or operating.

Solderability
245°C
473°F
3 s (with soldering flux)
Evaluates the solderability of the terminals.


*1 10 to 55 Hz at double amplitude of 3 mm for Power PhotoRelays.    *2 4,900 m/s2, 1 ms for Power PhotoRelays.



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