Fully integrated H-bridge motor driver vs externals FETs

Thread Starter

learnfromfailures

Joined Jun 14, 2021
10
I'm designing a new motor driver for a DC motor which has starting peak current of 30A and 28Volts power supply. Previous engineer used an integrated motor driver IC solution (VNH3SP30-E) that has a MOSFET (Full H-bridge) inside an IC. There are so many customer complaints that it is blowing up in the field. When I look at the IC there is not good separation and everything things runs off the high power line. I dont know what is the advantage of using a integrated driver solution over original MOSFET/IGBT approach. I personally think having external FETs would be a safer approach. Has any one used the integrated solutions before ? if yes, is it better than original power electronics. I'm trying to see which is a better approach.
 

LowQCab

Joined Nov 6, 2012
1,308
The usual problem is adequate HEAT-Dissipation.
It's quite often easier to get adequate Heat-Dissipation using discrete components.

SMD Devices are especially challenging in this regard.

Usually, when you dig into the Spec-Sheet,
the manufacturer will provide all the necessary information required to provide adequate Heat-Sinking,
but some people think they know better.

Unless you're trying to shave-pennies off of the production-cost,
its a good idea to Double the, Voltage, Current, and Heat-Dissipation-Ratings,
so that the device is more likely to be able to withstand an unusual situation.
In known harsh environments, you should go for 3X, or more, on these ratings.

A simple small Fan can quite often Quadruple the Heat-Dissipation capacity of a Heat-Sink.
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Thread Starter

learnfromfailures

Joined Jun 14, 2021
10
The IC VNH3SP30 has a linear current limiter which will avoid it from damaging in case current reaching its max value of 30A. Then I don't think increasing the current ratings to 3x on a new device, will improve the system or remove blowing issues.

I still feel the original power electronics has a win over the integrated IC solution with FETs inside. May be they have better heat dissipation than integrating all the FETs inside an ASIC to small space.
 

LowQCab

Joined Nov 6, 2012
1,308
When you put the same amount of Heat into a larger structure with more mass,
the Peak-Temperatures will virtually always be less.

Adding excessive Current-Rating value probably won't improve performance much,
but that's not the reason for doing it.
The reason for doing it is to reduce the "stress" on the parts.

Concentrated Peak-Temperature stresses are usually the cause of smoking parts.

Anything that you do to help keep the temps under control will improve reliability.

"" There are so many customer complaints that it is blowing up in the field.""
Unless this is caused by an Over-Voltage problem, it is definitely related to too much Heat.
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Thread Starter

learnfromfailures

Joined Jun 14, 2021
10
I'm trying to sum up all the ingredients for motor control power electronics:

High Inrush current circuit – The short circuit and starting current rating of the DC motor is 7 times higher than the steady state operating state.

Current Sensing circuit - Active current control/feedback is needed as torque (~current) is the only right control parameter.

Current limiting circuit

Protection circuit from transient/spike from power supply

Overheating protection/Thermal shutdown

Overvoltage Clamping

Overvoltage and undervoltage shutdown

Better heat dissipation IC & Board layout



Back EMF protection circuit

Reverse current protection
– Charge builds up can cause damage back to the circuit by a reverse current surge when switch is closed. The electrical energy stored in the windings that have inductance in the DC motor. Flyback diode is a solution that dissipate the stored charge.

PWM Interface - Use a PWM, measure current, feedback the PWM with a PI controller from the current measurement

I have covered it all, unless I've missed anything.
 

LowQCab

Joined Nov 6, 2012
1,308
Give us a complete and accurate description of exactly what the Motor is powering and
the nature of the desired User-Controls, and/or, Automatic-Controls for the Motor or Machine.
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Thread Starter

learnfromfailures

Joined Jun 14, 2021
10
The brushed DC motor is moving a valve Up/Down with starting current of 30Amps on 28volts supply. The starting torque is 650lb-in. The valve is to stop the water from flowing freely.

The user control is simple push button to open the value, so when button is pressed the it opens or closes fully.

I'm looking into controlling the torque thus, current. The inrush current is 30Amps during start of the motor when connected to load. I'm thinking about the current sensing and PI controller. The feedback system will measure active current flowing to the DC motor then compare it with the desired current and generates an error. This error is amplified to generate correct voltage then modulated, PWM, use the correct voltage and feed it to the motor. I don't know if it will work. Usually, PID is to control the speed of the motor. I never heard or used in controlling the current.
 

LowQCab

Joined Nov 6, 2012
1,308
As far as I'm aware, there's no "Controller-on-a-Chip" that can deal with ~840+Watts DC.

I assume that this is a "commercial production" item because you referred to "Customer Complaints",
so this requires a different approach than the more usual "Custom-One-Off" design philosophy.

I usually use a Building-Block approach when designing a complex Controller,
but before I attempt something like that, more info is needed,
because this whole thing may be just stupid-simple.

Is this Valve-Actuator designed to be compatible with some sort of "Industry-Standard" ?

Is there any reason why 28VDC was chosen as a Power-Source ? ( possibly Personnel-Safety )
What is Your source of Power ? .........................
Self-Contained-Batteries, (with some sort of Charging-Circuitry), ?
Remote located Batteries ?
Is this Valve-Actuator for possible use on a large Ship ? ( special-Standards, special-Voltages ) ?
Does it have a Self-Contained-Mains-Powered-Step-Down-Transformer-Supply ?
Must this unit be compatible with a "Single-Phase" Mains-Power-Circuit ?

In other words, is it practical to Power this setup with 3-Phase-Mains-Power instead of 28VDC ?
( 3-Phase Power is standard in virtually all Commercial/Industrial environments )

3-Phase-Power, (120V to Ground, 15-Amps),
could simplify things tremendously,
and reduce Production Costs,
and reduce any required Maintenance, and associated Maintenance-Costs,
and increase Reliability,
all at the same time.
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Thread Starter

learnfromfailures

Joined Jun 14, 2021
10
Is this Valve-Actuator designed to be compatible with some sort of "Industry-Standard" ?
Not really, this a DC motor connecting the valve simply opening and closing it.
Is there any reason why 28VDC was chosen as a Power-Source ? ( possibly Personnel-Safety )
This is given can't change it.
What is Your source of Power ? .........................
DC power supply - which is simple rectification of AC source sitting close to 100m away powering off entire system.

Is this Valve-Actuator for possible use on a large Ship ? ( special-Standards, special-Voltages ) ?
No, this is on a small water container.

In other words, is it practical to Power this setup with 3-Phase-Mains-Power instead of 28VDC ?
This is not an option, we only can use 28VDC.

The power source is AC generator and DC is supplied after rectification. There is like hood of having a transient.
 

LowQCab

Joined Nov 6, 2012
1,308
Got it, 28VDC.

What is the size of the Control-Box, ( inches or mm ) ?

Is the Control-Box Plastic or Metal ?

Is the Valve-Actuator and Control-Box outside in the Sun, or
protected from the Sun with a roof ?
In other words, is it expected to work reliably at 150F+ Temperatures ?
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When the devices have failed, have you sent them for failure analysis? Decaping, curve tracing, SEM imaging?

Even if the analysis comes back as EOS, the most likely response, mapping the area or pins which have failed will give you hints at probable causes.
 

Thread Starter

learnfromfailures

Joined Jun 14, 2021
10
What is the size of the Control-Box, ( inches or mm ) ?
It roughly 7cm.
Is the Control-Box Plastic or Metal ?
It is metal

Is the Valve-Actuator and Control-Box outside in the Sun, or
protected from the Sun with a roof ?
Yes, it covered with partial shade sometimes. But, it goes out in field and sometimes the weather is super hot and sunny.

In other words, is it expected to work reliably at 150F+ Temperatures ?
Yes, temperatue rating is close to 176F
 

LowQCab

Joined Nov 6, 2012
1,308
There is no "sometimes",
if it will ever be in the direct Sun it must be rated for at least 150F continuous operation.

When you say "" Yes, temperature rating is close to 176F ""
this sounds more like the maximum operating temperature of the Chip You are now using,
not the rated "ambient" operating temperature.

This is the reason You are experiencing failures in the field.
The difference between the temperature of the Semi-Conductors, and their environment,
is what determines how fast Heat can be transferred away from the Chip.

You need the biggest Heat-Sink that you can stuff into your Control-Box.

7cm is ~2.75-inches, ( I'm assuming that's a cube 7 X 7 X 7 ),
that's a small Wiring Junction-Box,
with barely enough room for the 10-gauge-Wires that need to be powering this Motor,
and that just isn't enough room for a Heat-Sink large enough
to dissipate any significant amount of Heat from the Electronics.

Careful design considerations must be made to insure as little Heat generation as possible.

You need to simply replace all the Electronics with
a Heavy-Duty-DPDT-Center-Off-Spring-Loaded-Switch.
There seems to be no reason to have the Electronic-Controls in the first place.

Just install this ~$26.oo Switch and all your problems will go away.
https://www.grainger.com/product/HONEYWELL-Toggle-Switch-24D410
24D402_AS01.jpg
It has an "IP68" rating, so it won't be affected by the Weather.

If you really just have to have fancy Electronic-Controls,
You will have to use a much larger Junction-Box.
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