I have a device that controls a silicone rubber heater, which is an active load and whose resistance does not change a lot when heating.
250W heater for 110V has about 50 Ohm cold resistance, which is about 2A which is about what it is at 120V at full power.
I control it with a G3NE-205T-US DC5 SSR, which is a 240V AC capable 5A AC triac switch with opto input.
The SSR is control from a digital circuit that puts 5V across the input, a MOSFET Low Side switch (pull to GND).
The SSR is zero-crossing, and is beings switched for at least 10 seconds ON and then 30 seconds OFF. So, no switching noise due to firing angle control, no such nonsense.
I have conducted emissions when the relay is ON. When it is off I am way down under the CLASS B FCC. When it is on, I am way over, about 5dB or so. Or 5dB under CLASS A.
So why I think it is the SSR? The last test I did was, while the SSR was energized and the board was thinking it was controlling it by applying the ON voltage, I shorted the relay's output. And the noise immediately went away, with the load being connected to power and the input being controlled as usual.
I do not get it what could be causing this. Yes I could put am RC snubber and all other stuff, but I would like to understand, where the noise is from?
(Oh......the noise is ... 150kHz. Which is nothing I have in mhy controls, and the DCDC power supply that makes 5V is 100kHz.)
Ideas, anyone?
250W heater for 110V has about 50 Ohm cold resistance, which is about 2A which is about what it is at 120V at full power.
I control it with a G3NE-205T-US DC5 SSR, which is a 240V AC capable 5A AC triac switch with opto input.
The SSR is control from a digital circuit that puts 5V across the input, a MOSFET Low Side switch (pull to GND).
The SSR is zero-crossing, and is beings switched for at least 10 seconds ON and then 30 seconds OFF. So, no switching noise due to firing angle control, no such nonsense.
I have conducted emissions when the relay is ON. When it is off I am way down under the CLASS B FCC. When it is on, I am way over, about 5dB or so. Or 5dB under CLASS A.
So why I think it is the SSR? The last test I did was, while the SSR was energized and the board was thinking it was controlling it by applying the ON voltage, I shorted the relay's output. And the noise immediately went away, with the load being connected to power and the input being controlled as usual.
I do not get it what could be causing this. Yes I could put am RC snubber and all other stuff, but I would like to understand, where the noise is from?
(Oh......the noise is ... 150kHz. Which is nothing I have in mhy controls, and the DCDC power supply that makes 5V is 100kHz.)
Ideas, anyone?