[H-bridge circuit] If you apply force in the opposite direction of the motor, the MOSFET and diode will die

[myksj]

[H-bridge circuit] If you apply force in the opposite direction of the motor, the MOSFET and diode will die.

Hello. Nice to meet you.

1. H-bridge circuit (refer to the circuit image)

• IRF5210(P) IRF3710(N)
• Diode : SS36
• MOTOR : 24V, 400W

2. Problem

• If you apply force in the opposite direction of the motor, the MOSFET and diode will die.
  (If you apply force in the opposite direction of the motor with an external force, the diode and MOSFET will die.)
• For example,

1. Command the motor to move in the forward direction
2. Turn the motor in the opposite direction 'by applying force externally'
3. The MOSFET and diode will die

3. Questions

• Is there a circuit that can prevent reverse voltage and reverse current?
• And, I don't know the exact reason why the MOSFET and diode die.
• If implemented with MOSFET, is 'Diode' not necessary?

[kolaha]

H-bridge is used to drive motor in both directions, so it have no opposite direction.
If the circuit is destroyed in use, it is only possible if it was designed incorrectly.

[jremington]

@myksj

if you apply force in the opposite direction of the motor

If you mean force the motor shaft to turn in the opposite direction of its normal rotation, then it is possible to destroy the MOSFETs, as the current flowing through the motor is much higher than the stall current. You might even damage the motor power supply.

The same thing can happen if you command the H-bridge to "instantly" reverse the direction of a rapidly spinning motor. Always make sure that the motor is stopped before changing direction of rotation.

[JCA34F]

What voltages are you applying to the MOSFET gates?

[myksj]

@kolaha
@jremington
@JCA34F

• JCA34F : Gage voltage : 12VDC

1. 12VDC, photocoupler circuit
2. It works fine if you just drive it electrically.
3. If you manually apply force to the motor, it seems to generate power. This seems to cause damage.

• kolaha :

1. Electrically forward
2. Physically reverse (by external force)
3. Diode and MOSFET die after a few seconds
   (They don't die when applied only electrically.)

• jremington :

1. 'If you mean force the motor shaft to turn in the opposite direction of its normal rotation,'
   That's right.
2. Is there a way to solve it in terms of circuitry?

[JCA34F]

How much current is the motor drawing when you stall it and force it backwards? You need to limit current to 150% of full load current. 400W / 24V = 16.7A, so current limit = 25A.

[gilshultz]

Complete your schematic and include the gate drives.

[jremington]

@myksj

it seems to generate power.

That is a very fundamental feature of motors. Back EMF

Is there a way to solve it in terms of circuitry?

Proper H-bridge choice or design. For reliable operation, the H-bridge must be designed to support much more than the maximum expected current flow. Twice the motor stall current is a reasonable design goal.

[westfw]

@jremington

That is a very fundamental feature of motors. Back EMF

But we're suspecting here that the circuit is dying just because it's being asked to provide more current than it was designed for (ie continuous "stall current"), and NOT a back-emf effect, right?

[jremington]

@westfw

NOT a back-emf effect, right?

Same effect, but the "back EMF" voltage is reversed and effectively adds to the battery voltage, instead of subtracting, so the current flow through the windings is driven by a much higher voltage than during normal operation.

[myksj]

First of all, thank you so much for your sincere answer.
@JCA34F

• It has a 0% failure rate when driven electrically. It has not failed in 4 years. However, if a person intentionally applies force to the mechanism while it is in operation or at rest, the board will die. For example, electrically it is at a standstill. However, if a motor is turned mechanically, the PCB components will burn out.

@gilshultz

• I'll attach the photos. Please review them.
• MR1 : 0.01R/1%
• R1,R2,R3,R4 10K / CN34_2 10K
• CN34_1 240R

@jremington
@westfw

• It has a 0% failure rate when driven electrically. It has not failed in 4 years.
• 'so the current flow through the windings is driven by a much higher voltage than during normal operation.'
• I haven't checked it in real time with an oscilloscope or a digital multimeter, but the current problem seems to be what 'jremington' said.
  The cause seems to be correct, but what I'm curious about is how to solve it.

[myksj]

I'm trying to install a DC relay so that it turns ON only when it's running.

Is this a way to avoid 'Back EMF'?

What do you think?

[jim-p]

@myksj
I see several design flaws that may contribute to your problem:

1. G1 and G3 are left floating when the optocoupler is off. Need to be connected to source with low resistance.
2. The gate voltage at Q1 and Q3 is only 6V, should be at least 10V.

[Grumpy_Mike]

@myksj

What do you think?

Designing a H-Bridge from scratch is quite a difficult task. The design has to be much more complex than the very simplistic designs you are posting here.

There are many problems you have to overcome, one of which is the problem of shoot through. That is when, for a small instant of time, both FETs are conducting and thus preventing a dead short which takes a lot of current. This is your number 1 problem.

I would advise you not to try to design your own, but go for a ready built H-Bridge. One that uses FETs and not bipolar transistors.

I use a SN754410 Quad Half H-bridge for these sorts of applications. See the example circuits in the data sheet for example circuits.

[myksj]

@jim-p
@Grumpy_Mike

Thank you for your interest. Thanks for your reply.

@jim-p

1. The circuit label is a bit complicated.
2. Gate voltage: 12V
3. Input voltage: 24V
4. G1, G3 are not 'floating'. They are connected to the array resistors.

@Grumpy_Mike

1. It is not a problem with the 'H-Bridge' circuit. The electric motor can be driven very well through that circuit. It works well.
2. However, there are two cases where problems occur.

• When the motor is electrically stopped, if you turn the motor with an external force, the 'MOSFET' and 'diode' will die due to the counter electromotive force.
• When the motor is rotating in the forward direction, if you turn it in the reverse direction with an external force, the 'MOSFET' and 'diode' will die.

[jim-p]

@myksj

The circuit label is a bit complicated.

If you don't post the actual schematic that we can follow, then how do you expect us to help you debug your problem

G1, G3 are not 'floating'. They are connected to the array resistors.

and the resistors are floating. When the optocoupler is OFF the gate is neither connected to ground or any voltage.

[myksj]

@jim-p
Thank you so much for your interest.

I posted the actual schematic in 'post #11'.

1. Photo-C OFF : BAT(+) -- CN34_2 -- G1
   G1(Voltage) : BAT(+)

2. Photo-C ON : BAT(+) -- CN34_2 -- G1 -- E1
   G1(Voltage) : 0.5 * BAT(+)

When the photocoupler is off, G1 has the BAT(+) voltage, i.e. 24VDC.

Am I wrong in what I'm saying?

[jim-p]

@myksj

Am I wrong in what I'm saying?

No, you are right, my mistake.

[myksj]

@jim-p

I truly respect and appreciate you.

What I'm curious about now is

1. It's not an electrical drive problem of the H-bridge. It works fine with electrical drive.
2. The problem is that the 'FET' and 'DIODE' die due to 'Back EMF'.
3. I'm asking because I'm curious if there's a way to solve the 'Back EMF'.
4. It works very well electrically.
5. And, if you force the motor to turn with an external force, the 'FET' and 'DIODE' will be damaged.

[jim-p]

@myksj
The only way you could create a back emf great enough to cause current flow is if you rotated it so fast that it generated more than 24V.
Simpling spinning it by hand should not generate such a large voltage.
Something else must be happening.
Is this a geared motor?
Is this actually powered by a battery or a power supply?