post #21 of 72
3/17/09 at 6:25pm
The circuit you soldered with the mosfets, isn't that actually some sort of solid state relay?
"A solid-state relay may include a driver circuit and a field-effect transistor (FET) providing the output signal and having a control terminal or gate connected to the driver circuit. The driver circuit receives the control signal and operates or drives the output FET based upon the control signal."
The only difference I can find at first sight:
"A typical solid state relay consists of a light-emitting diode (LED) optically coupled across an electrically isolating gap to a photovoltaic array. The photodiode array is electrically connected to an output device such as a field effect transistor (FET)."
So you control the mosfets directly with the control signal, while in a solid state relay the control voltage is "optically coupled" to the mosfets so that there's isolation between the control circuit and the switched circuit.
So I'm just wondering, wouldn't an SSR be just as good as a solution, or even better because of the isolation of the control and switched circuit? Since the SSR is also consists of mosfets. And an SSR switches silently, so there shouldn't be any noise.
While we're at it...
In your post you sketched a problem with a voltage drop with 2 circuits.
You mentioned that the second one resolved all your problems, may I ask how? Is there such a big difference in the placement of the TEC in your circuits above?
20 milliseconds to turn on and off is pretty slow for a SSR
Where are the Mosfet is 140 ns
i couldn't see the SSR working. anyway i see no reason to use the SSR anyway