This PWM slot car motor controller with adjustable brake works well at low frequency (apx 470 hz) using an Op amp with its push pull output. But I want to up the frequency to 20khz and learn how to use the 339 comparator. The attached diagram is my testing set up. The 339 is running at 28khz for now.

I am having trouble figuring out a gate drive circuit.

I have been experimenting with the MCP14A0453/4/5 ( https://www.mouser.com/datasheet/2/268/20005985A-1365832.pdf) I have the inverting version and I have inverted my set up.

It works but the chip blows for reasons I don't understand.

I am pulling the 339 output up to the Supply rail less 2 diode drops. And I am seeing a good volt negative on the wave form at the driver chip inputs. the data sheet says the inputs can be rail to rail and .3v beyond. I thought I might be exceeding that so I reduced the pull up by a simple means.

(The diagram doesn't show the 2 diodes)

The reason I am pulling the 339 so high is that it has to exceed the brake control voltage which is the top of the tri wave. Perhaps I should reduce that pull up voltage further there is still room to go down and still be above the max brake control voltage.

I'm strictly a hack trying to learn something. So I cannot necessarily give better information here. I am hoping someone can point me in the right direction based on the diagram. Like a better gate driver chip. Or help me understand the ins and outs of the MCP1405.

Also like should there be a pull up on the P Gate and a Pull down on the Ngate. currently I am experimenting with those in place.

The PFET total gate charge is 240nC
the NFET has total gate charge is 65nC

Most gate drivers I am finding are for boosting the high side gate and using NFETS for both high and low.

I have tried those too with no luck so I just want to find simple gate driver that will do this.
All comments and suggestions are welcome.

 

The Frequency of the PWM Controller is not a "performance" factor, only a "noise" factor.
It's easier to work with lower Frequencies.
DC is best.

How does your Hand-Controller work ......,
1) Connections,

2) Resistance measurements, and

3) Your personally expected or desired behavior, as it regards Motor Power/Braking application.

4) How does your Hand-Control transition from "Coast-Mode" to "Braking-Mode" ???
Or is Braking simply removing Finger pressure from the Trigger ??
Do you even have a "Coast-Mode" or would that be an advantage ?

5) Do you supply your own Low-Voltage Power-Supply, or is Power supplied by the Local-Track ??

6) If Power is supplied by the Track, how do you interface with it, (wiring Schematic),
what is the Voltage, and is the Voltage purposefully Current-Limited ?

7) You need a Diode and a Capacitor on the Motor inside your Car, do you have them ??

8) How much Maximum-Current (in Amps) does your Motor consume at Maximum Voltage ?

9) "Traction-Control" is entirely feasible, are you interested in it, or are spinning Tires more fun ?

The power that you need delivered to your Car is really well filtered, pure, variable, DC, not PWM.
A more detailed Schematic would be great, laying out the entire Motor-Control and Power-Scheme.
(your present Schematic doesn't make a lot of sense)

 

Here is an awesome article that explains a common source of failure, and some tips in selection:
https://www.power-and-beyond.com/mosfet-driver-a-common-cause-of-failure-a-883520/

 

Thanks Click, I did get some insight from that.

Attached is the full schematic of my low freq op amp based unit. I only posted a diagram of my test set up as that interface, from 339 to gates, is my focus at the moment. I have added a pull down R on the NFET gate. I should have updated the schematic.

I understand that the frequency of such a motor controller has no obvious relation to performance. As I read on that topic there seems to be some consensus to make it just above the audible range around 20hkz so, that is my target. This is mostly to learn about the gate drive circuitry.

By the rules of slot car racing (it still exists and is big in Europe. There national and international races every year) the controller can have no power other than the track power. No batteries etc. So the gate driver, the power fets and the load are all on the same supply.

The unit is very basic but seems to work well. Although I did experience a burnt motor brush last time I raced with it. That is partly why I want to build one with a significantly higher frequency. So I can compare them in real time.

Some of the motors are high current 10-30 amps peak is not uncommon. The tracks pride themselves on big supplies and hugely redundant wiring. None run higher than 14 volts.

Traction control would interest me but first I must get the gate drive working reliably. Thanks lowQ for your interest.

 

For the PWM have a look at

Have a look at how the dc is created

This is one of my favourite channels, so many great circuit tutorials

 

I am subscribed on his you tube channel as well...he has a great teaching style. I had not seen that one! There are many good details that apply to this motor controller. I understand how it all works but none of it exactly. I will take notes and watch it multiple times before I approach "exactly".

I have built this controller with a few different op amps including the LMC 6484 he speaks of. It doesn't like my wide differential input voltage yet it still works just fine. Using a low frequency (a few hundred hz) prevents a lot of problems. And needs no additional gate driver.

I will pursue 20khz and a gate driver set up...it seems a reasonable quest.

Thanks, click, for that video point out

 

It's hard to figure out your schematic.
More Labeling would be good,
especially the Track connections.

It would appear that you have a Ground, a 13.8V Hot, and
a controlled, returning Hot-Wire to feed power to your Lane of the Track.
Does that sound correct ???

Your Speed Control looks a little funky too.
"Stop" has a Ground-Contact, plus an additional Contact, what is the purpose of these ?

What does "Choke" and "Attack" mean ???

 

Thanks for the interest LowQ

The only odd thing about my schematic is how I represent the power fets (upper right): as a broken line for Source / Drain with the Gate shown down a bit as a circle G.

The track power positive 13.8, through the fuse, hits the Source pin of the power PFET (SUP90P06). The motor, upper right, is grounded as the track is wired negative common. So the PFET simply connects that top rail, via its Drain, to the top of the motor as its gate is pulsed toward ground.

The other power fet (upper right), is an NFET with its Source at ground. It grounds the flyback voltage from the motor, for brake effect, when its Gate is pulsed high.

The control is a quad op amp. First 2 sections are a typical free running tri wave generator. The bottom sections serve as PWM comparators with their push pull outputs to the power fet gates. Those P/P outputs are fully adequate at low frequency.

The trigger, (wiper pot) far left side, is shown in the Off / Brake mode. The trigger stop grounds gate of the small switch PFET connecting vcc through the resistor dividers to the controlling input of the Brake comparator. The trimmers allow adjustment of that control voltage so the duty cycle can be at max / min precisely at the ends of the main control pot.

You probably just wanted to know if I understand it. Thanks for the opportunity to write it out.

There maybe no good reason raise the frequency, it's mostly a learning experience. I am not even trying to use an NFET for the high side for gods sake. I just want to learn how to do it with a comparator at 20khz and a gate driver for those two big fets.

Attached is an updated drawing showing the addition of a couple resistors. I have built it with several op amps the lowly 324 works well but currently I am using the TLV9154.

 

You caught me at the end of the day ..............
I'll get back to you with a Schematic showing how I would do it if it was mine.

 

This PWM slot car motor controller with adjustable brake works well at low frequency (apx 470 hz) using an Op amp with its push pull output. But I want to up the frequency to 20khz and learn how to use the 339 comparator. The attached diagram is my testing set up. The 339 is running at 28khz for now.

I am having trouble figuring out a gate drive circuit.

I have been experimenting with the MCP14A0453/4/5 ( https://www.mouser.com/datasheet/2/268/20005985A-1365832.pdf) I have the inverting version and I have inverted my set up.

It works but the chip blows for reasons I don't understand.

I am pulling the 339 output up to the Supply rail less 2 diode drops. And I am seeing a good volt negative on the wave form at the driver chip inputs. the data sheet says the inputs can be rail to rail and .3v beyond. I thought I might be exceeding that so I reduced the pull up by a simple means.

(The diagram doesn't show the 2 diodes)

The reason I am pulling the 339 so high is that it has to exceed the brake control voltage which is the top of the tri wave. Perhaps I should reduce that pull up voltage further there is still room to go down and still be above the max brake control voltage.

I'm strictly a hack trying to learn something. So I cannot necessarily give better information here. I am hoping someone can point me in the right direction based on the diagram. Like a better gate driver chip. Or help me understand the ins and outs of the MCP1405.

Also like should there be a pull up on the P Gate and a Pull down on the Ngate. currently I am experimenting with those in place.

The PFET total gate charge is 240nC
the NFET has total gate charge is 65nC

Most gate drivers I am finding are for boosting the high side gate and using NFETS for both high and low.

I have tried those too with no luck so I just want to find simple gate driver that will do this.View attachment 240204
All comments and suggestions are welcome.

what package is your ic? Pd is different for each package. If it's frying, it's because you're exceeding it's ability to dissipate power- period (which means you probably don't understand the datasheet).

 

The MCP14A0453 is surface mount soic 8. It blows when I am working around the bread board. perhaps i am causing an oscillation and it overheats before I realize what I have done.

When I say it's working I mean the motor runs and is controllable and the adjustable brake action works too. But then as I am probing around looking at the wave form at various places it will suddenly quit or one output quits.

Another question pertains to how do I know it's working well? How do I know it is charging and discharging the gate fully fast enough? are we looking for good wave forms at the gate?

I am also seeing a volt of negative over shoot on each pulse at the comparator output. Since there is no logic level stuff here I am pulling the comparator up all the way to vcc. I have tried pulling it less high but that doenst seem to help.

 

You are also dealing with long wiring runs which create a substantial amount of Inductance,
plus, a "Brushed" Motor which can put out a tremendous amount of RFI Hash,
with Voltage-Spikes potentially more than double the normal Supply Voltage,
and at frequencies so high that only expensive 'Scopes can detect them.
.
.
.

 

This may give you some ideas ...............
.
.
.

 

Thank you, Cab. That must have taken some time. Indeed it will give me some ideas.

Can you explain why it is better than my simple circuit. Besides that it's running at 15khz.

Are you saying it's better to run the circuitry at 5 volts?

Regarding the motor is that Brushless? If so, that's another topic. The motors we are dealing with are 3 pole high current brushed.

Why all the filter caps on board? The PS's at these tracks are generally quite good with a couple of Super Caps on them as well. Another design goal is keeping the size down. Everything fits in the handle. The only long lines are 10awg from the handle 3 feet down to the track connection. I would hate to think they need to be shielded. Maybe at at 20khz and up they should be.

And finally, where Is the Trigger? The spring loaded wiper pot around which the whole thing operates? Lower left? If so I don't understand how it switches to Brake Mode.

 

1)
I selected 5-Volts so that it could be regulated, and therefore extremely stable and repeatable.
I wouldn't trust the Track Power-Supply without building it myself,
and I do realize that you must "play with the cards you are dealt".
which blends right into #2 ............

2)
All those Capacitors .............
The Wiring almost has to be fairly long to the Power-Supply,
this introduces both Resistance, and Inductance, between You and the Power-Supply,
this will introduce at least some measurable Voltage-Drop,
as well as a substantial amount of "Electrical-Noise",
neither of which is conducive to getting the most out of it.

A Capacitor has an internal Resistance of some value.
Most Capacitors have a specific rating, in Amps, at a given Frequency,
at which they can reliably absorb Power, or dump Power into a Load.
When you use multiple, smaller sized, Capacitors,
the amount of Current that they can collectively absorb or dump is increased
substantially over that of a single, much larger Capacitor.
For instance, I provided the calculated Amperage that those 8 Capacitors can handle.
The Manufacturer provides Amperage Ratings at Frequencies of 120hz, and 10khz,
( 10khz is close to the PWM Frequency that I chose to use ).
At a Frequency of 10khz, these Capacitors can collectively handle around ~18-Amps.
With this particular PWM Controller,
the power turns completely "Off", and completely "On", 15,000 times per Second !!!
So, for best efficiency, lowest Heat generation, and longest Capacitor Life-Expectancy,
they have to be able to handle those rather extreme conditions without undue stress.
Plus, a bunch of smaller Capacitors take-up much less Real-Estate than a single large one,
and can be grouped into various different shapes.

3)
The Motor Symbol that I used only has 2-Wires, that usually indicates that it's a
standard "Brushed, Permanent-Magnet, DC-Motor".
Brushed Motors need a "Fast-Diode" across their Terminals to use the
inherent Induction of the Motor to keep the Motor "powering-its-self" during the
"Off" period contained in a PWM Supply.
The Diode must be over-rated to withstand the maximum Current that the Motor can draw,
it must also be rated for ~3 to ~4 times the maximum expected Power-Supply-Voltage
being supplied to the Motor because of continuous Voltage-Spikes that
normally are created by Brushed-Motors,
and it should have the highest recovery-speed that is practical because of the
extremely high Frequencies of the Noise and "Hash" generated by the Brushes.
This last problem is also the reason for the small Ceramic-Capacitor,
it is there to help smooth-out the super-high-Frequency RFI Hash from the Brushes.
( Radio-frequency-Interference )
The 2 Larger Electrolytic-Capacitors are for smoothing the Power-Delivery to the Motor.
The Connection between the Track-Rails, and the Car-Brushes, is in a constant state of
being "half-ass" connected, and Sparking during brief periods disconnection.
This "On-and Off" connection changes at extremely high Frequencies,
the Electrolytic-Capacitors smooth-out that Power-Delivery to the Motor.
This also reduces the sparking between the Brushes and the Track-Rails,
and will extend the Life of the Motor-Brushes, and of your Slot-Brushes.

4)
"" Another design goal is keeping the size down ""
What would you think about a small 3-Conductor Cable,
or something like a Coily-Microphone-Cable,
running from your Controller to a small Aluminum-Box, say about ~3" X ~6" X ~1",
with your 3 short-heavy-Wires coming out the other end ???

With this design, you can use ANY Controller that has a Pot inside,
( or virtually any type of variable Resistance Element not lower in Resistance than around ~200-Ohms,
lower Resistances than ~200-Ohms require only slight modifications to the Circuitry ).
Zero Electronics need to be inside the Controller, with only 3 very small Wires connected to it.
Nothing needs to be shielded.
Adjustments to Braking-Functions, or Lowest-Power, or Maximum-Power, adjustments can be
implemented with knobs on top of the Box, or left inside as semi-permanent Trim-Pot adjustments.

Also, currently your minimum and maximum adjustments may have some unwanted
interactions between them, ( when you adjust one, you have to re-adjust the other one ),
most of this type of interaction is eliminated in this design.
The only interaction is between Minimum-Power and the point where Braking is turned on.
Once Minimum-Power is set, then the point where Braking starts can be set.
These settings can be made on a Test-Bench, or,
they are simple, and non-critical enough, to be adjusted in the field to suit changing conditions,
that is, after you spend ~15-Minutes getting used to how and why it works.

5)
"" I don't understand how it switches to Brake Mode ""
Brake Mode is initiated by an adjustable "Voltage-Comparitor" which compares 2 Voltages,
and when Voltage A is higher than B, the Brakes are enabled, and the PWM Circuitry is turned Off,
and when Voltage B is higher than A, the Brakes are disabled, and the PWM Circuitry is turned On.
"Voltage A" is the Voltage coming from the Speed-Control-Slider,
"Voltage B" is set by a Pot to the desired "trip" Voltage.

When Brake-Mode is "On", the amount of Braking effect is adjustable via another Pot,
which can be either a Board-mounted Trim-Pot, or,
an external-Pot with a Knob, for convenient frequent adjustment.

6)
All of this may be very "cool", but in reality,
it will probably only add around ~5 to ~10% more power to your Car,
and may give you a nicer, smoother "feel" for controlling the Car in Corners.

7)
If You do nothing else ............
add the components recommended INSIDE the Car,
it's super easy, and most definitely worth the time.
The larger 2 Capacitors don't really have any critical values except for Voltage,
if you need smaller, or different-shaped Capacitors to be able to stuff them under your Body,
pick any Electrolytic-Capacitor with the same Voltage-Rating.
The physical dimensions are always listed.

8)
You could possibly stuff all these parts inside your controller, I have no idea of how big it is.
The last time I messed around with Slot-Cars was around ~53 years ago.
I'm just a stickler for keeping things as cool as possible, Heat destroys parts,
and even if they can "survive", their performance will suffer from too much Heat build-up.

9)
Let me know if I can help you to understand how all this Circuitry works.
.
.
.