[SOLVED] Transformerless power supply

[anishkgt]

hi All,

Is a transformerless power supply a good idea for microcontrollers like in the circuit attached ? i was thinking of replacing the transformer to cut down cost with a schematic like this http://www.electroschematics.com/5678/capacitor-power-supply/


Thanks in advance.

[ataradov]

If you actually plan to use that FTDI while device is plugged into mains, then it is a horrible idea. You will end up killing USB ports, or yourself in the worst case.

[anishkgt]

Thanks alex.

The reason would be because the power supply is grounded and......what else

[ataradov]

You will have potentially live voltage with minimal to no isolation exposed on the USB connector. It is just a bad idea all around.

You can use switching power supply, and small transformers are pretty cheap. You can probably even find complete sub-assembly at a decent price.

Your other option would be to power all low-voltage part from USB +5V, if device is constantly plugged in.

Or power FTDI from USB and use optocouplers to decouple it from the high-voltage part. Although this one also depends on what else on that board is accessible by the user. You don't want to have mains on encoder knobs either.

[anishkgt]

you will have potentially live voltage with minimal to no isolation exposed on the USB connector. It is just a bad idea all around.

yea, i will just stick to the existing.

[M4trix]

@anishkgt,

regarding the TRIAC driving. From where you got that schematic ? What was the main purpose or what was the main load ?

[anishkgt]

The load is an MOT. The TRIAC driver schematic is in the data sheet of the driver itself. It's a dual SCR back to back.


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