<Application Guide> Switching High Power LEDs with MAXQ™ Solid State Relay
Updated: 4 days ago
The following information applies to MAXQ™ solid state relays only.
MAXQ™ SSR can be used to switch ON/OFF high power DC LEDs within μs. The guideline for selecting the minimum SSR voltage and current rating is as follows：
High power LEDs relying on constant current use many different types of drivers such as large buck-boost driver or smaller IC drivers. Depending on the type of driver used, when the LED circuit opens, the switching voltage could be 7x higher than the nominal voltage.
The actual switching voltage also depends on the type of DC power supply you are using. If you are using batteries, voltage spikes may not be a problem. However, in most cases, AC/DC converters are used to power LEDs, and they have output power ripples. Every time the LED driver senses a reduced power output from the AC/DC converter, it will ramp up the voltage to compensate. The magnitude of the voltage spikes depends on the type of your AC/DC converter can be 7x higher than the nominal voltage.
To resolve this issue, clamp the voltage with a zener diode across the power supply, then choose a SSR rated at least 3x the operating voltage. If you are unable to clamp the voltage, choose a SSR with rated voltage at least 7x higher than the operating voltage.
LEDs are expected to generate very high inrush current, 10x or more. The magnitude of the inrush current depends on the LED's internal driver. However most of the inrush current is short lived, only on the order of 10's of μs. Thus, it is usually sufficient to choose a current rating 5x the nominal current.
You may choose to measure the peak inrush current of your LED's, then divide this current by 2 for the recommended relay's rated current.