New Industry Products

Littelfuse’s Optically-Isolated Gate Driver Needs No External Power Supply

September 19, 2021 by Gary Elinoff

Designed to partner with external MOSFETs, the high-voltage device provides load turn-on speeds measured in tens of microseconds.

The CPC1596 converts a tiny portion of the switched load’s power supply down to 12.2 volts for its own use. The gate driver combined with appropriate MOSFETs can switch loads of up to 570 volts.

The CPC1596 from IXYS, now part of Littelfuse. Image courtesy of Littelfuse


Opto-isolated photovoltaic (PV) gate drivers can be used to directly drive MOSFETs to effect a solid-state relay (SSR) as depicted below:


Image courtesy of Littelfuse Video

High-power, high-voltage loads need to be switched by large MOSFETs, and the output of the PV device, only in the µA range, is swamped by the high input capacitances of these power semiconductors.  The time it takes to “charge” that “capacitor” to a voltage level sufficient to turn on the MOSFET can be unacceptably long for many use cases.


Load Biasing

The CPC1596 exploits its onboard load biasing circuitry to achieve fast switching. Referring to the article’s first illustration, the regulating semiconductor works from load rails of up to 570V, supplying 12.2 to charge the external capacitor, CST, to 12.2V. This enables constant voltage control for properly driving the MOSFETs.

Load biasing serves to boost MOSFET start-up speed, and as illustrated, does so without the need for a separate power supply. The technique, as implemented in the CPC1596, allows for devices like MPUs to directly affect the switching of high-power AC or DC loads.

In addition to load biasing for fast turn-on, the gate driver also features a gate clamping section to enable fast turn-off.


A Critical Market Need

As described by Steve Andrezyk, Senior Product Marketing Manager at Littelfuse, "The CPC1596 570V Load-Biased Opto-Gate Driver addresses a critical market need.” He goes on to state that, “Universal AC power line applications now have a custom, higher power optically isolated solid-state relay (SSR) solution without the cost of an auxiliary power supply or additional discrete devices to meet fast start-up speed requirements."



Because the CPC1596 is designed to use external components for over-voltage protection and load switching and design requirements, engineers are afforded a range of design flexibility. This allows designers to choose from a divergent range of MOSFETs for use in a wide variety of applications. However, the designer does need to know the candidate MOSFET’s total gate charge (QG), in order to choose the appropriate external capacitor (CST). The capacitance of this storage capacitor must be ≥  QG/0.5V.


Other Specifications

  • Maximum turn-on time is 80µs
  • Maximum turn-off time is 600µs
  • Typical off-state leakage current at the full 570V load is 14.5µA
  • Typical input to output capacitance is 3pF



The CPC1596 is aimed at a wide range of 110V to 230-volt loads, including

  • Industrial controls
  • Automatic test equipment
  • HVAC controls
  • Medical equipment
  • The internet of things (IoT)


Physical Considerations

  • The CPC1596 operates over a temperature of -40 to 110°C
  • It is available in 8-pin DIP or surface mounted packages



  • Isolation voltage is 3750 VRMS
  • ESD rating is 1kV, human body model 
  • Basic Insulation is 490 VRMS
  • Reinforced insulation is 245 VRMS


Regulatory and Environmental Considerations

  • UL Recognized Component: File E76270
  • CSA Certified Component: Certificate 70196286
  • RoHS compliant