Capacitive-Coupled Isolated Relays Vs Optically-Isolated Relays

January 22, 2016
By Mamitha Mathew

Low power consumption and long lifetime are two main tenets of modern electronic design. To perpetuate development, design engineers continuously search for new technologies that both add functionality and improve reliability.

A popular choice for among engineers is to use solid-state relays which use semiconductors to switch their output circuits rather than traditional electromechanical relays. With no moving parts, optically-isolated solid-state relays such as Panasonic PhotoMOS relays offer low capacitance, low on-resistance, physical isolation and high linearity that often correlates with reliability and performance.

PhotoMOS relays use a light emitting diode (LED) on their input side, MOSFETs on the output side and an array of photo sensors in between. In operation, current flows through the LED, which then emits light. The photosensor array detects the emitted light, triggering a voltage drop that drives the MOSFETs. The MOSFETs finally switch the load circuit.

Recently, Panasonic has introduced a new technology that uses a voltage-driven method, with capacitive-coupled isolation as opposed to current-driven, optically-isolated relays.

The Figure below shows the structural comparison of PhotoMOS and PhotoMOS CC type.

PhotoMOS vs. PhotoMOS CC

The PhotoMOS CC Type relays offer distinct benefits for certain markets including Test & Measurement, Safety & Security, and Industrial. These advantages include:

• Low Current Consumption (input current Max 0.2mA)
• High-Temperature Performance Guaranteed (Max 105◦C or 221◦F)
• Voltage Driven (3V to 5V)
• Low Output Capacitance and Low On Resistance 
• Energy Savings and Increased Drivability (No LEDs on input side)

Since PhotoMOS CC relays are voltage driven, there is no need for an external resistor on the design. This feature tremendously eases design work by eliminating the need to analyze and calculate an accurate resistor value. The super miniature TSON package (1.8 x 1.95x0.8mm) is approximately 46% less than previous SON package contributes to space savings and high-density mounting.

PhotoMOS Size Comparison


The operation of Capacitive Coupled-Isolated relays is mentioned below during turn on and turn off. 

PhotoMOS CC Operation

To keep up with small electronic devices, it is crucial to select super miniature, high reliability, high-temperature relay components to control loads. All these features can be achieved by using voltage driven Capacitive Coupled relays. The demand for this new product is increasing tremendously. 

Get more information on Panasonic Solid-State Relays or contact us today to learn more.