I have a project where I need to cycle the power on a 2.5=94 HDD, The power cycle is controlled by a micro. The drive need to be on during startup and switched off when the port pin on the micro is high. The micro does some initialization during startup for 5 secs (erasing SRAM, loading data) so it can=92t just switch the drive ON straight away. I was thinking of using a micro to a BJT to a FET but am not sure of the circuitry needed, again it needs to be on straight away and then switches off when the micro pin goes high, any idea guys?
what's the voltage input of HDD, what's the current rating? what's the control voltage of micro, and how much current it can drive?
you can use P-type FET (bigger, more Rdson). you can use the micro to drive the gate, or if the current output from micro is too small, use it to control the BJT and drive the gate from main rail.
or, you can use N-type on the low side (controls the ground path of the HDD). do this only if there's only one ground path for HDD. this is because the gate voltage have to be higher than the drain voltage of the N-FET to turn it on and keep it on fully.
the third choice is to use charge pump IC to drive the N-FET on the high side (controls the input path). there might be better parts but this is the one i know will work:
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.html just leave the timer pin float, short the Vcc and Sense pin, then you'll have a charge pump IC controlled by the voltage at the ON pin. seems like you have a logical reverse (your micro high means cut off the rail, but ON pin high means turn on the switch). what you can do is add a pull up resistor to the ON pin, and use a BJT from ON pin to ground, use your micro to control that BJT.
what's the voltage input of HDD, what's the current rating? what's the control voltage of micro, and how much current it can drive?
you can use P-type FET (bigger, more Rdson). you can use the micro to drive the gate, or if the current output from micro is too small, use it to control the BJT and drive the gate from main rail.
or, you can use N-type on the low side (controls the ground path of the HDD). do this only if there's only one ground path for HDD. this is because the gate voltage have to be higher than the drain voltage of the N-FET to turn it on and keep it on fully.
the third choice is to use charge pump IC to drive the N-FET on the high side (controls the input path). there might be better parts but this is the one i know will work:
formatting link
just leave the timer pin float, short the Vcc and Sense pin, then you'll have a charge pump IC controlled by the voltage at the ON pin. seems like you have a logical reverse (your micro high means cut off the rail, but ON pin high means turn on the switch). what you can do is add a pull up resistor to the ON pin, and use a BJT from ON pin to ground, use your micro to control that BJT.
does this makes sense to you?hope it helps.
==> Interesting.... I didn't know the AD manager could driver a N channel.
Check your suppliers as the AD part may have a large minimum order qty, if you are lucking one of the catalogue supppliers may have them in stock.
it's designed for Hot swap control, but can be used as FET control as it has integrated charge pump. for your own test, you can order 2 samples shipped to you for free.
Switching the power on a HDD is a bad idea and looking for trouble.=20 Especially as the IDE command set includes the commands to put the HDD=20 into various sleep modes.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
What are your local power supplies? Maybe you can use a regulator with enable function. However, if you cut the power to the drive but your processor is connected to the IDE lines, this will get interesting. Anyways I suppose it's a parallel ATA drive.
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