# Passive Sign Convention for Power

No doubt that most student will got confused on when to put positive sign or negative sign for average power.

In general, the positive sign is for element that absorb power from the circuit and negative sign for element that supply power to the circuit.

The image is one student ask me about how and when to use negative or positive. So my solution to her question is:

# MOSFET

A single MOSFET has two states: ON and OFF.

ON: current can flow both directions

OFF: current can flow one direction (source-drain, due to the body diode) and not the other direction (drain-source, because the FET is off)

A single MOSFET in series with a diode:

also has two states, ON and OFF.

ON: current flows one direction (drain-source, through the FET and the second diode), but not the other direction (source-drain, because the second diode is pointing the wrong way)

OFF: current won’t flow either way, because whichever way you look there’s a diode opposing the flow of current.

Two MOSFETs in series, pointing opposite directions:

have four possible states. ON-ON, ON-OFF, OFF-ON, and OFF-OFF. For this example, I’ll describe current flow with directions as seen in the picture above.

ON-ON: current can flow both directions through the circuit.

ON-OFF: current can flow from left to right (through the left FET and the right diode) but not from right to left (because of the right diode)

OFF-ON: current can flow from right to left (through the right FET and the left diode) but not from left to right (because of the left diode)

OFF-OFF: current can not flow in either direction, because with both FETs off all you have is two diodes blocking current flow in either direction.

So the third topology has the option of either blocking currents in both directions, or allowing current flow in either direction, depending on how it’s gated.

# Bidirectional Switch

Bidirectional switch allow both current directions. Applications can be found in converters in motor drives or systems that require the capabilities of two current directions

# Three-phase system-revisited

Lama tak jenguk-jenguk syllabus 3-phase system ni. Dah berkarat jugak..tapi cuba juga buat latihan sendiri. Kepada yang berminat boleh rujuk example ni

# Kisah RMS rectifier circuit

Untuk litar penerus (atau rectifier) with load resistor, the value of RMS current for load and source is equal

# Terbang UTM

Hari ni kita pi panas panaskan drone dji saya ni..dah beberapa bulan duduk dalam beg…takut bateri rosak pulak…bateri lithium ni kena selalu pakai..kalau tak nanti dia akan rosak…

So man main lah kejap dalam UTM tu..langit pun agak baik walaupun aak mendung sedikit. DJI Mavic Mini tak berapa bagsu sikit sensor. lagipun field of view agak terhad..tak macam GoPro Karma saya yang dulu.. memang ultra wide lens dia.

Saya harap, pada masa akan datang DJI dapat datangkan kamera yang mempunyai ultra wide angle lens