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Mechanical relay Replacement(e-Book)

Toshiba Photorelay

General information

Mechanical relay 


Evaluation board
 present campaign


Name Outline Date of issue
Describes what are Photorelays and how they compare to Mechanical relays for around 70 pages. Also shows application examples. 9/2018

What are photorelays?

Relays are electrically operated switches and can be broadly classified into contact (mechanical) and contactless (semiconductor) types. Photorelays are semiconductor relays made up of an LED optically coupled to a MOSFET, used mainly as signal relay replacements. Having no movable contacts, photorelays are known to have better long-term reliability over mechanical relays.

Group Sub-group Notes
(Mechanical Relay)
Signal Relay
  • low current switching mechanical relays, often below 2A, for applications such as signal, circuit, high frequency control etc.
  • includes high frequency relays
Power Relay
  • high current switching mechanical relays, above 2A
  • includes general purpose relays for control panel, high DC current control power relays etc.
(Semiconductor Relay)
(MOSFET output)
  • uses MOSFET as the output device
  • mainly used as signal relay replacement
  • able to handle both AC and DC loads
  • products with ION>1A are referred to as high capacity (current) photorelays
(Solid State Relay)
  • uses semiconductor photo traic, photo transistor or photo thyristor as the output device
  • photo traic, photo thyristor output devices are limited to AC loads

How does photorelays compare to mechanical relays?

Below is a general comparison based on size, reliability, power consumption, and switching capabilities of photorelays compared to mechanical relays. Further details are available in the relevant application note.


How does photorelays compare to mechanical relays?
Characteristic Photorelays Mechanical Relays
Size Generally smaller than mechanical relays Package size increases with higher power products
Reliability Long lifetime Limited lifetime due to movable contacts
Input power consumption Low. Battery operation possible High. Also requires additional components in the circuit for operation
  • High speed
  • Low noise
  • Quiet
  • Low speed
  • Spikes at on and off with contact bounce
  • Audible mechanical clicking sound
Hot switch capability Good Reduction in lifetime due to stresses from instantaneous current flow at contact and arcing at contact off.

Terminology – Photorelays vs mechanical relays

In this section, terminologies used in mechanical relays are mapped to that of photorelays.

Terminology – Photorelays vs mechanical relays
Mechanical Relay Characteristic Explanation Photorelay Characteristic Equivalent
Rated Coil Voltage and (Coil) Nominal Operating Current Voltage, intended by design, applied to the coil for operation and the resulting value of current flow in the coil Input Current (IF) , Input Voltage (VF) Recommended Input Current (IF)
Contact Form
Contact mechanism and the number of contacts in the circuit
Eg:Normally Open × 1 Contact (1a)
Normally Close × 1 Contact (1b)
Change-over contacts × 1 Contact (1c)

Contact Form
Eg:Normally ON × 1 Contact (1a)
Normally OFF × 1 Contact (1b)
Contact Resistance Total resistance when the contacts meet ON Resistance (RON)
Contact Capacity Voltage and current that the part can handle in the ON state OFF-State Output Terminal Voltage (VOFF), ON-State Current (ION , IONP)
Maximum Allowable Contact Power Upper limit of power within which the part can be turned on and off properly Output power dissipation (PO)
Maximum Allowable Contact Voltage Maximum open circuit voltage
Requires derating according to operation load and current
OFF-State Output Terminal Voltage (VOFF)
Maximum Allowable Contact Current Maximum current that the contacts can handle
Requires derating according to operation load and voltage
ON-State Current (ION , IONP)
Operation Time Time from which power is applied to the coil until the closure of the contact. (Bounce time not included) Turn ON Time (tON)
Release Time Time from which power is removed from the coil until the return of the contact to it’s initial position. (Bounce time not included) Turn OFF Time (tOFF)
Lifetime Mechanical Life Minimum number of operation cycles the relay can be undergo with no load on the contacts. LED Lifetime Data
Electrical Life Minimum number of operation cycles the relay can be undergo with a specified load on the contacts. LED Lifetime Data
Operating Temperature Ambient temperature of the environment at which the relay is operated at. Operating Temperature (Topr)

Photorelay Selection Guide and Design Considerations

Not sure how to go about choosing the right fit photorelay for your mechanical relay replacement? We take you through some main points to note when selecting photorelays in this section.

Contact Form

  • Check required contact form (Form a (1a), Form b  (1b) etc.)
  • Toshiba currently provides photorelays in the contact forms 1a, 2a, 1b, 2b, 1a1b.

Package and Isolation

  • Strapped for space or have insulation voltage requirements? Choose from the industry's smallest S-VSON4 package to the conventional DIP packages.











BVS:500V 500V BVS: 1500V (Some with 3750V) BVS: 2500V
(Some with 5000V)

Operation Conditions

  • Confirm VOFF(V) and ION(A) requirements.
    • VOFF: For safe operation, design with margin in mind
    • ION: Derating should be considered according to the operation environment.
      For example, Photorelay ION required = Mechanical relay ION ÷ 0.7@Ta:60℃

Electrical Conditions

  • While mechanical relays generally have low ON resistance, photorelays have a range of high to low RON products. High capacitance photorelays with lower RON than that of mechanical relays also exist.
  • Unlike mechanical relays, in photorelays, leakage current flows when voltage is applied on the output side. For applications where leakage is a concern, please consider Toshiba’s low leakage (pA range) products.

Switching Characteristics

  • Mechanical relays typically takes a few milliseconds for signal relay switching and contact bounce time also needs to be taken into consideration.
    Toshiba has photorelays with typical switching times less than 1ms and also high speed photorelays with that of 0.01ms.  No bounce!


  • For further details on photorelay selection and design considerations, please refer to the relevant application notes.

High Current Photorelay Line-up

Below is a list of Toshiba’s high current photorelays in various packages and OFF-State terminal voltage (VOFF). For the full line up of photorelays, please refer to the main photorelay webpage here.

A parametric search function is also available here.

High Current Photorelay Line-up
Part PKG VOFF (V) ION (A) Status
TLP3543 DIP6 20 4 In mass production
TLP3553 DIP4 3 In mass production
TLP3100 SOP6 2.5 In mass production
TLP3403 VSON4 1 In mass production
TLP3106 SOP6 30 4 In mass production
TLP3406S S-VSON4 1.5 In mass production
TLP3544 DIP6 40 3.5 In mass production
TLP3102 SOP6 2.5 In mass production
TLP3554 DIP4 2.5 In mass production
TLP241A DIP4 2 In mass production
TLP241AF DIP4 2 In mass production
TLP3123 SOP4 1 In mass production
TLP3547 DIP8 60 5 In mass production
TLP3107 SOP6 3.3 In mass production
TLP3545 DIP6 3 In mass production
TLP3542 DIP6 2.5 In mass production
TLP3103 SOP6 2.3 In mass production
TLP3555 DIP4 2 In mass production
TLP3127 SOP4 1.7 In mass production
TLP3122 SOP4 1 In mass production
TLP3823 DIP8 100 3 In mass production
TLP3109 SOP6 2 In mass production
TLP3546 DIP6 2 In mass production
TLP3105 SOP6 1.4 In mass production
TLP3556 DIP4 1 In mass production
TLP3825 DIP8 200 1.5 In mass production
TLP3548 DIP8 400 0.4 In mass production
TLP3549 DIP8 600 0.6 In mass production

Note: ES: Engineering Sample, MP: Mass production
         Specification for products currently under development is subjected to change.

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·Before creating and producing designs and using, customers must also refer to and comply with the latest versions of all relevant TOSHIBA information and the instructions for the application that Product will be used with or for.