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Solid State Relay High Side DC Switch
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petersanch:
Hi All,
The internal circuit of the SSR im using has 2 N channel MOSFETs.
Is it possible to make a high side switch with this? Can I connect the load in either configuration as in the pictures and expect the same results?

Cheers
Zero999:
Yes, that will work.

Does the polarity of the power supply to the load never change? If it's DC and is never reversed, then only one MOSFET is needed or the two MOSFETS in the package can be connected in parallel. For DC operation, pins 4 and 6 could be connected together and to the positive side, with the load on pin 5.
petersanch:
Thanks. The polarity is always the same.
So I understand fully, is the reason for connecting the positive side to pin 4 or 6because of the body diode in the MOSFET?

If it is the body diode, does that mean for configuration B in the picture, the power supply ground connects to pin5 and the load can connect to 4 and 6?
Zero999:

--- Quote from: petersanch on January 06, 2019, 09:17:06 am ---Thanks. The polarity is always the same.
So I understand fully, is the reason for connecting the positive side to pin 4 or 6because of the body diode in the MOSFET?

If it is the body diode, does that mean for configuration B in the picture, the power supply ground connects to pin5 and the load can connect to 4 and 6?

--- End quote ---
The MOSFETs are connected back-to-back so they block current in both directions, when they're off. If the current is only ever applied in one direction, then only one MOSFET is required, although they're are two in this IC, so you might as well connect them in parallel to give a much lower on resistance.

To use the two MOSFETs in parallel, connect pins  4 and 6 together. The load can then be either connected between pin5 and 0V, with pins 4 and 6 at +V or between pins 4 and 6 and +V, with pin 5 to 0V.
petersanch:
Thanks for explaining
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