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Topic: 12VDC (0.35A) Motor with 1N4001 Diode? (Read 8441 times) previous topic - next topic

beingobserver

Dec 14, 2015, 07:55 pm Last Edit: Dec 14, 2015, 07:58 pm by beingobserver
Hi people.

I have 12VDC motor which draws 0.35A which is controlled by an Arduino.

Can I use 1N4001 diode to block voltage spikes?


Thanks in advance.

Wawa

Yes.
The diode goes across the motor. Cathode to +supply.
What sort of transistor do you use to switch the motor.
And what is the value of the base resistor.
Leo..

MarkT

You need to find out the maximum current draw (stall current), not just the
nominal full-load current, since the transistor will have to survive these peaks too.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

raschemmel

Quote
Can I use 1N4001 diode to block voltage spikes?
I think you mean flyback diodes to block inductive BACK EMF. (not voltage spikes)

Archibald

I think you mean flyback diodes to block inductive BACK EMF. (not voltage spikes)
See "voltage spike" in the first sentence of this Wikipedia article.

However I believe "flyback diode" is derived from a diode used in some television line output circuits.  Flyback is not a sudden voltage spike in my view.

yendis

I assume you are using PWM (and driving the motor via a transistor) and talking about the inductive kick when the motor is switch off.  If you place a diode between motor +/-  as suggested by wawa, this will prevent the voltage greatly exceeding the supply voltage.  A 1N4001 should work OK but it is not the best for the job. 
Chris

Wawa

A 1N4001 should work OK but it is not the best for the job. 
Please explain.
Leo..

raschemmel

Quote
A 1N4001 should work OK but it is not the best for the job. 
Please explain.
Flyback diode is a SCHOTTKY DIODE application

larryd

Quote
A 1N4001 should work OK but it is not the best for the job.
From: motors, contactors , relays or solenoids I have never had any problems using a 1N4000 series diode in a fly-back application.
No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

raschemmel

Quote
From: motors, contactors , relays or solenoids I have never had any problems using a 1N4000 series diode in a fly-back application. 
Just for the record, neither have I.

Wawa

#10
Dec 16, 2015, 11:36 pm Last Edit: Dec 16, 2015, 11:36 pm by Wawa
Flyback diode is a SCHOTTKY DIODE application
Please explain.

Don't say: "becasue a schottky diode is faster".
Because it isn't.
At least not the "turn-on" time.
Leo..

MarkT

A schottky diode is not always the best, since the low on-voltage will slow down the current decay
to perhaps twice as slow as a pn-junction diode, which might be too long for some applications.

For fast decay you can use a back-to-back zener+diode so that the voltage can be set for more
rapid current decay.  dI/dt = V/L

For a large electromagnet you might do the zener thing to make the thing let go quicker at turn-off

The speed of turn on isn't in the least bit critical so long as the device can prevent the forward
voltage rising to the breakdown voltage of the switching device, not hard to achieve in practice.

Typical slow diodes can have a sluggish turn on, but you rarely see the transient Vf rising above
a few volts even so, which is nothing for a free-wheel diode/snubber.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

raschemmel

#12
Dec 17, 2015, 03:11 am Last Edit: Dec 17, 2015, 03:16 am by raschemmel
I can't find any switching time specifications for this schottky diode so I don't know how to compare it to a 1N4001 but when I tried to research it I found this article which supports your recommendation of the 1n4001. In the absence of any data to support my claim I am forced to retract my statement that a schottky diode is better for a flyback application. If I knew how to compare the two in a side by side test I would do so.
If anyone wants to suggest a test I could obtain a schottky diode and give it go. I wouldn't know what frequency to use but I am fairly certain the standard switching test is a simple step pulse.
Another specification is the inductance of the test inductor. The arduino should be adequate to use as a pulse generator. The ball's in your court.

Wawa

#13
Dec 17, 2015, 03:41 am Last Edit: Dec 17, 2015, 05:17 am by Wawa
Typical slow diodes can have a sluggish turn on, ...
Not true.
They only have slower turn-off.

http://www.cliftonlaboratories.com/diode_turn-on_time.htm#Release_Time_Change

Turn-off times might be important for higher PWM frequencies though.
But I doubt it will make a difference for the default ~500hz of an Arduino.
Leo..

raschemmel

#14
Dec 17, 2015, 04:14 am Last Edit: Dec 17, 2015, 05:01 am by raschemmel
SCHOTTKY DIODE

Quote
When forward current flows through a solid-state diode, there is a small voltage drop across its terminals. A silicon diode has a typical voltage drop of 0.6-0.7 V, while a Schottky diode has a voltage drop of 0.15-0.45 V. This lower voltage drop can be used to give higher switching speeds and better system efficiency.

The Schottky diode is often used as a voltage limiter (aka clamp or bypass diode), in reverse bias. This is because the reverse bias voltage, the voltage at which it meaningful reverse leakage occurs, can be made quite low relative to other diode types, and in fact stable and specific.
Schottky diodes for this use are sold by their reverse bias voltage spec. The impedance is quite low as with any diode in conducting mode. In effect it becomes a conductor at that voltage, and can be considered to be a switch.. "If reverse bias voltage >= X, then switch on ,otherwise remain OFF". This should not be relied on for high frequencies due to stability issues but the diodes are simply made stable for DC use ( perhaps to PWM frequencies ). The reverse bias voltage will not climb as any increase in current or voltage will simply bypass the protected circuit by easily passing through the diode, and yet if the applied voltage is not high enough, its not conducting.. The voltage is limited to be relatively close to the specified voltage.  
FYI,
After rereading the schottky diode datasheet I found this:
Quote
*Pulse test: Pulse width 300 msec, Duty cycle 2%

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