Hi,

What is the purpose of the resistance (1MOhm) between the primary and the secondary of a transformer. Is this for better knowing the isolation between the primary and the secondary ? It is also common to see capacitance between them.




Thank you and have a nice day,

 

Are you referring to a physical resistor wired in or just the apparent resistance between the two winding's?
Max.

 

I m talking about a physical resistor wired.

 

Never seen that, and cannot quite see any purpose.
A capacitor from a common to a earth ground is generally for HF decoupling.
Max.

 

Sometimes it is done to limit the DC difference between the primary and secondary of a power supply, particularly where the primary side is grounded and the secondary side is not known to be grounded. Otherwise large voltage differences can develop that can result in strange effects such as cyclic static charge build-up on one side followed by arcing or other discharge means which can be undesirable, particularly in audio systems. A large value resistor is used to minimize the chance of ground loops.

 

What you probably saw in a schematic diagram is not a resistor between the primary and secondary windings of the transformer but a large value resistor between the secondary winding (signal common) and the chassis ground (earth connection).

 

Ja saw it at Samsung HVAC.

I'm affraid that those resistors R105 and R107 of 12M violates isolation form main current.

Is it dangerous to touch GND on DC side?

 

Hi,

What is the purpose of the resistance (1MOhm) between the primary and the secondary of a transformer. Is this for better knowing the isolation between the primary and the secondary ? It is also common to see capacitance between them.

View attachment 180134


Thank you and have a nice day,

Resistor? Your diagram shows a capacitor.
I can tell you what the capacitor does - it shunts induced currents from the transformer back to the primary. It's essential for EMC control.
If there were a resistor in that position it would have to withstand a 4kV flash test.

 

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