What flyback diode to use for small DC motor?

I am planning on using the 1.9mm shaft OD motor here: DC Motor N20 Large Torque Motor Gear Motor with XH2.54 2P Cable for Smart Car DIY|DC Motor| - AliExpress

I have done plenty of research but can't figure out how to choose a flyback diode. Is there a formula? What variables should I calculate and how? I am looking for an SMD diode, not PTH.

Specs of motor:

1.9mm D type

  • No-load speed: 92RPM @ 3V, 195RPM @ 6V
  • No-load current: 60mA @ 3V, 70mA @ 6V

Any help appreciated!

The diode must be able to safely conduct the maximum motor current. 1N400x will do, right across the motor pins.

jremington:
The diode must be able to safely conduct the maximum motor current. 1N400x will do, right across the motor pins.

Thanks! Will the 1N4001 SMA M1 work from here? 100PCS SMA Rectifier diode 1N4001 M1 1N4004 M4 1N4007 M7 FR107 RS1M FR207 RS2M HER108 US1M SF18 ES1J SF14 ES1D DO 214AC|diode 1n4001|rectifier diode1n4007 m7 - AliExpress

Understandable you can’t say if that part is good quality, just referring to the part number.

Voltage: at least the supply voltage.

Current: at least the stall current of the motor. All ratings of switching components must correspond to the stall current, not the no-load current. Not specified here but likely less than one Amp.

Using PWM? If PWM, you need a fast-recovery (or Schottky) diode. If not, a 1N4001 will do just fine.

small dc motor

shai:
Thanks! Will the 1N4001 SMA M1 work from here? 100PCS SMA Rectifier diode 1N4001 M1 1N4004 M4 1N4007 M7 FR107 RS1M FR207 RS2M HER108 US1M SF18 ES1J SF14 ES1D DO 214AC|diode 1n4001|rectifier diode1n4007 m7 - AliExpress

Understandable you can't say if that part is good quality, just referring to the part number.

That's in an SMA package, which is surface mount - they're meant to be mounted to a circuit board designed for your application - though you can sometimes mount them directly, if you're not designing a circuit board for this, you should get a through-hole one. I would generally use a through-hole one in general for flyback diode on a motor, so you can put them right on the motor terminals.

You're not using an H-bridge to drive the motor in either direction, right? In that case, you need a more complicated topology - but many H-bridge drivers have this integrated.

DrAzzy:
That's in an SMA package, which is surface mount - they're meant to be mounted to a circuit board designed for your application - though you can sometimes mount them directly, if you're not designing a circuit board for this, you should get a through-hole one. I would generally use a through-hole one in general for flyback diode on a motor, so you can put them right on the motor terminals.

You're not using an H-bridge to drive the motor in either direction, right? In that case, you need a more complicated topology - but many H-bridge drivers have this integrated.

I would like to actually add an H-bridge, but not sure how to do it. I.e: what components are required.

Buy an H-bridge motor driver, like one of these. The flyback diodes are built in.

Here's an H-bridge that I have built and used many times.
You should probably add a short SHOOT-THROUGH-PREVENTION delay between direction change code.
(don't start moving in opposite direction until you have executed the delay)
If you look at the schematic of the simpler version that does not have the STEP-DIR inputs, you see there
is a PWM A and a PWM B input.
A is DIRECTION A
B is DIRECTION B.
the delay must be inserted between the two , like this:

A is DIRECTION A
DELAY
B is DIRECTION B.

Anyway, this is my suggested way of H-Bridge control that avoids any possible chance of shoot through. A simpler, but in my opinion less effective means, is to increase the delay between disabling and re-enable the enable control lines to more than one pwm cycle. In the case of PROS this would mean increasing the delay from 350uS to perhaps 1.1mS.

H-bridge-control-and-shoot-through-protection

Freewheel diodes see brief pulses, so it may be enough that the diode’s pulsed current rating exceeds the
maximum motor current.

A flyback transformer isn’t involved here, so free-wheel diode is the normal term used, explaining the diode’s
function of allowing current to continue flowing when the switching devices turns off, preventing sudden high-voltage spikes from the winding inductance.

If you could suddenly stop pedalling a fixed-wheel bicycle your legs would break from the extreme
forces generated by the large amount of momentum, the free-wheel mechanism in a bike allows the
pedals to stop without the wheels having to stop immediately, which is a close analogy:

inductance : mass
current : speed
voltage = inductance x rate of change of current : force = mass x acceleration

raschemmel:
Here's an H-bridge that I have built and used many times.
You should probably add a short SHOOT-THROUGH-PREVENTION delay between direction change code.

That circuit has intrinsic shoot-through whatever the code does as the n- and p-channel gates are tied
together.

If you could suddenly stop pedalling a fixed-wheel bicycle your legs would break from the extreme
forces generated by the large amount of momentum, the free-wheel mechanism in a bike allows the
pedals to stop without the wheels having to stop immediately, which is a close analogy:

I think that's the best analogy I have ever heard.

That circuit has intrinsic shoot-through whatever the code does as the n- and p-channel gates are tied
together.

No they are not. There is an A INPUT and a B INPUT.
Truth table
A B DIR


1 0 CW
0 0 N-channel fets OFF (NEITHER MOSFET IS ENABLED) This is the logic sequence used during the code. (DELAY CODE GOES HERE (650uS)
1 1 p-channel fets off
0 1 CCW

If you can show how it is possible for either mosfet to turn on with both A and B LOW, I would like to see
that.
If you turn OFF both N-channel fets , execute a delay and then turn OFF both P-channel fets and
then change direction, how can both N channel AND P channel be on at the SAME time ?

TC4427 DATASHEET

This is a pin-for-pin compatible replacement:
TC4424

The TC4424EPA is a dual non-inverting high-speed power MOSFET Driver features higher peak output current drive capability, lower shoot-through current, matched rise/fall times and propagation delay times. The TC4423A device is pin-compatible with the existing TC4423 family. The TC4424A driver can easily charge and discharge 1800pF gate capacitance in under 20ns, provides low enough impedances in both the ON and OFF states to ensure the MOSFETs intended state will not be affected, even by large transients. The inputs may be driven directly from either TTL or CMOS. In addition, the 300mV of built-in hysteresis provides noise immunity and allows the device to be driven from slow rising or falling waveforms.

TC4424 PRODUCT OVERVIEW

DrAzzy:
I would generally use a through-hole one in general for flyback diode on a motor, so you can put them right on the motor terminals.

Although while convenient, that is the wrong place to mount them for interference suppression.

If you look at the motor it is an inductor plain and simple. When an inductor is charged (motor on) and it is switched off, the magnetic field will collapse and the output will reverse polarity and the voltage will increase until something stops it. The amperage behind the pulse is the same as what was put in so if the motor is drawing 10 amps that is what will be initially available. The diode needs to dissipate this energy however there is only one pulse per turn off. The diode must withstand the on voltage in the reverse direction in your case so 6 volts. an inexpensive diode will work such as a 1N4001 or even smaller. Looking at the data sheet it will handle a 30 Amp pulse. Quick rule of thumb: Look at the diode's pulse rating and if it is less then the motor current it will be OK. In your case your no load flyback will be about 60mA max with the voltage determined by the VF of the diode.
Check this data sheet: https://www.vishay.com/docs/88503/1n4001.pdf
Good Luck and Have Fun! Gil

gilshultz:
If you look at the motor it is an inductor plain and simple.

Actually, this is absolutely wrong!

A motor is anything but "an inductor plain and simple". When the motor is actually spinning, it is acting as a generator. When you turn it off, it is still generating almost the same voltage as was supplied so there is minimal sudden change in voltage - no inductive "kickback". This is true for permanent-magnet and shunt-field motors. Series-field "universal" motors do of course, have the inductive field windings to contend with.

The "kickback" occurs when the motor is stalled or significantly loaded.

I think the takeaway here is that the back emf (if any) is less for a motor when it stops than for a solenoid
or relay when it de-energizes (as already explained).