Threshold Hall Sensor converter

168

02:15:07

Some threshold Hall Effect sensors latch state  and maintain that state until an opposite field is detected.   these latching types are useful in brushless motors, but useless as solid state Reed switch replacements.

this circuit converts one of these latching type Hall Effect sensors into a conventional type, which will reset the output state once the magnetic field is removed.  this works by cutting power to the sensor, resetting it to its initial state.

in this circuit the magnet is represented by the logic source, 0 is no field, 1 is a southerly field. the hall effect sensor is represented by the npn/pnp latch.  

the left opamp starts a clock which switches the sensor on/off repeatedly.  the output of the sensor stays high.  bringing the magnet near the sensor turns it on and the output goes low.  but the clock resets the sensor, sending the output high again.  if the magnetic field is still present, the sensor turns back on, but switches on immediately, sending the output low again.  this output is filtered and read by the second opamp as a comparator, and while the sensor is switching, the voltage is reduced, so the comparator output is low.  if the field is removed, the next reset of the sensor leaves the output off, sending the comparator high.

the latch on the far right shows the behaviour of the latch type sensor if you move the magnet near and far; once the magnetic field is detected, it's latched on and won't turn off until an opposite field is detected.  

so if you're like me and have a pile of broken  brushless fans that you want to use the sensors from to do other things, this should help.

published 10 years ago

bilben08

10 years ago

Nice description sir

lenzrulz

10 years ago

Although the MOSFET is a four-terminal device with source (S), gate (G), drain (D), and body (B) terminals, the body (or substrate) of the MOSFET is often connected to the source terminal, making it a three-terminal device like other field-effect transistors. Because these two terminals are normally connected to each other (short-circuited) internally, only three terminals appear in electrical diagrams. The MOSFET is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common. The main advantage of a MOSFET over a regular transistor is that it requires very little current to turn on (less than 1mA), while delivering a much higher current to a load (10 to 50A or more). However, the MOSFET requires a higher gate voltage (3-4V) to turn on. In enhancement mode MOSFETs, a voltage drop across the oxide induces a conducting channel between the source and drain contacts via the field effect. The term "enhancement mode" refers to the increase of conductivity with increase in oxide field that adds carriers to the channel, also referred to as the inversion layer. The channel can contain electrons (called an nMOSFET or nMOS), or holes (called a pMOSFET or pMOS), opposite in type to the substrate, so nMOS is made with a p-type substrate, and pMOS with an n-type substrate (see article on semiconductor devices). In the less common depletion mode MOSFET, detailed later on, the channel consists of carriers in a surface impurity layer of opposite type to the substrate, and conductivity is decreased by application of a field that depletes carriers from this surface layer. this is what happens when we become bored, we post drivel on each other's circuits, faceblast started this trend and I'm continuing it...enjoy!

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