Hi,

I am going to assist a member of this forum building a can crusher (Electronic projects Designs/Ideas/Reviews --> "Need help with auto starting a motor".

No matter if a can is crushed mechanically or pneumatically, the pressure on it has to be about 70lbs which is also sufficient to completely crush a hand.

To minimize the risk of injuries I want to make a receptacle fitted with a sliding door and driven by a small DC motor with reduction gear.

To activate the crusher an object has to be sensed and the door must be closed.

The door will slide open if an object is brought into sensing range, wait 1 to 2 seconds and then close. This again burries the risk of squeezing fingers in the door, which can be solved for by using an H-bridge IC with current sensing input(s), reversing the motor immediately if something goes wrong.

I have found a lot of H-bridges at ST and National, but not the right thing. They are either half bridges, dual bridges or high power (high voltage) bridges.

Maybe one of you knows a chip which will suit the requirements: single full H-bridge, motor supply voltage 12VDC, continuous motor current 1A, current sensing and several flag outputs (not desperately required) for malfunction tracking.

Remark: Half bridges require power MosFets at the outputs, which is not desireable because of the extra wiring and resulting board size.

Thanks

Hans

 

A 12V MOSFET half-bridge is nothing...just use power MOSFETs that can tolerate a gate voltage of 12V or more then use pull-up resistors+pull-down transistors to drive the high-side FETs (and maybe the low-side FETs too).

But if you want small...Digikey has lots.

Like this one:
http://www.infineon.com/dgdl/tle5206...12b438215b6a4b

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Tanaka Sensei (avatar) says: Please spell it "ridiculous" correctly! Not "rediculous". ^^

 

Why not just put two button switches in series on either side? Both have to be pressed to activate the crusher. Sorta like missile launches in movies.

 

That comes pretty close to the fully manual muscle operation: Use a timber to crush!

 

Yes dear,

this is it!

Makes a simple and small board, except for the overcurrent detection, which I will do using a shunt resistor.

And please, stop lying! (or lieing, I don't know exactly)

How do you like my desert fridge? It's me in front of the camel.

Hans

 

*SERIOUS TYPO*

THe transistors gates have to be able to tolerate a voltage of 12V or more. To use pull-down method on the high-side gates so you don't need floating gate drives means that the gates have to be able to tolerate the main supply voltage across the source-drain, or else they will burn out the gates when you try to pull the voltage low to turn them off (for NMOS) or turn them on (for PMOS). Any supply voltage greater than the maximum gate voltage will require floating gate drives for the high-side (even if it's a PMOS).

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Tanaka Sensei (avatar) says: Please spell it "ridiculous" correctly! Not "rediculous". ^^

 

Thanks for the advise.

I will just use TTL compatible logic (5V) for the gates, so the chip won't be a problem to use.

No input will be floating just because active braking is required for both, normal operation and emergency reversing, which applies in any case if the inputs have the same polarity voltage. (L-L = H-H)

If it had an adjustable overcurrent circuit it would be perfect.

Hans


What does serious typo mean?

 

Typo = typing mistake
Serious = big

Serious + type = big typing mistake.

Floating does not mean a disconnected input in this case. It means sections of the circuit that do not use ground as a reference, but instead use the voltage at another point as the reference, and the voltage at this point is not fixed and can change.

If you use an NMOS on the high-side, that means the source voltage of the NMOS is floating. It is not fixed and changes with operation. BUt the gate-source voltage is what controls the NMOS. So the gate drive circuit usually can't be referred to ground or any fixed voltage and instead must use the source voltage as it's the reference. THis means it's "floating" since the source voltage is not fixed.

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Tanaka Sensei (avatar) says: Please spell it "ridiculous" correctly! Not "rediculous". ^^

 

Hi dknguyen,

I didn't quite understand what should be floating in a circuit with common ground. The reference voltages will be ground and +VS (+12V).

I made a small schematic omitting most of the decoupling measures. Please be so kind as to explain what could be floating in that circuit.

Is the 'SERIOUS TYPO' referred to "lying", "lieing" or to the fact that the picture of yours isn't yours?

If it refers to the words listed, why didn't you post the correct version? You should know that I'm a non-English English. (German)

Hans

Attached Thumbnails

 

 

THe high-side transistor will not turn on and stay on properly. It cannot provide a voltage difference between the gate and source that is high enough. It is the voltage across the gate-source that matters, not the voltage between gate-ground (unless the source is connected to ground like it is in the low-side MOSFET).

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Tanaka Sensei (avatar) says: Please spell it "ridiculous" correctly! Not "rediculous". ^^

 

I'm not worried about that. It applies to every H-bridge though. The chip design should have taken care of that already. Otherwise the chip can be considered to be junk.

 

Oh that chip is an H-bridge. NEvermind. I thought it was just a gate driver.

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Tanaka Sensei (avatar) says: Please spell it "ridiculous" correctly! Not "rediculous". ^^

 

Already forgot it? It was you suggesting the chip.

Free tip: drink more milk!

Regards

Hans

 

Maybe I'm a step behind on this, but your cct is just powered by 12V and 1A, is that right? If so, how can you generate 70lbs of force?

Cool idea btw.

 

circuit diagram nga po ng h-bridge