JOB: Convert schematic to eagle+gerber

[fuper]

Well my only guess is that one of the ICs are bad. I'm gonna have to run to the store and grab some more ICs. The outputs are all high. I've got a microcontroller stepping and the outputs never change. Its the only thing I can think of because the board looks good and I double checked the solder joints etc. I'll post a pic when I get back.

 

[fuper]

Ya bad IC - I fried the 4027. Works fine!

 

[Boncuk]

Hi Alain,

I guess it's good practice to use extra caps near the power transistors to compensate for power surges the moment when a stepper coil is activated.

470µF is a good value for a coil current of 500mA. I could have used four of 220µF and each connected close to its switching transistor, but I guess that would be overkill.

Boncuk

 

[fuper]

Hey Boncuk - the boards are great! I'll post some pics soon! Thanks again!

 

[fuper]

Latest update

Just thought I would share with everyone my experience with this circuit - The PCB layout was excellent, no fault there.

Well I got the stepper driver boards built. They run hot, way hot. The TIP131 transistors I mean.

I asked around and come to find out the current output from the 4027 isn't enough to fully turn on the TIP131 so it runs hot. I measured it with a cheap infrared thing I got at radio shack, and it said over 150 degrees. I clamped a heat sink or two on them for testing but it's not shown in the pictures.

Anyway - after much fiddling I got the stepper to work correctly. I'm using an arduino to send a step signal for testing purposes. The sample blink program comes in handy!

Well turns out this may not be a great design going forward due to the heat issue and I still need fat resistors in order to drive the stepper at a higher voltage. I'm only running it at 5 volts which is pretty low.

Anyway with the voltage and current i'm dealing with here, I think these drivers will not suffice.

I suppose I could redesign and get the TIPs to fully turn on, using regular transistors I guess, or a quad opamp, but I don't know enough about electronics to know if this would work or not.

Here are the pics:

**broken link removed**

**broken link removed**

More info at the blog of my Millbox project

 

[dougy83]

Do do want an easy fix? Replace the TIP31 transistors with some MOSFETs and reduce the 1k base resistors to maybe 10 ohms. An N-channel mosfet usually has a pinout compatible with the TIP31 (G-D-S vs. B-C-E), so it'll be a drop-in replacement. Just make sure the one you choose has a low RDSon at the logic supply voltage & appropriate ratings.

 

[fuper]

Hi Dougy83! Thanks for the feedback. Do you know of any common part # for a mosfet that can do the 3 amps like the TIP31 ?

Thanks!

 

[dougy83]

Hi, I'm not sure of what suppliers you use. Have a look at their mosfets in TO220 packages and post the ones you think might do. You want one with a threshold voltage (VGS) << than your logic supply voltage, an RDSon of maybe <0.1 ohms, VDS > your motor supply current.

One that are readily available for me is https://au.element14.com/international-rectifier/irliz24npbf/mosfet-n-55v-14a-to-220fp/dp/8651175, but there may be something more available to you.

 

[Boncuk]

Hi fuper,

bipolar power transistors (also darlington power transistors) require a pretty high base current for switching.

You might overcome the problem using BUZ11 MosFet transistors. Replace the former base resistors with gate resistors of 100Ω.

If fast switching (high rpm of the stepper motor) is required connect a 10K gate discharge resistor to the output of the driving CMOS chip to ground. Connect the gate resistor on the junction of the discharge resistor to the gate as shown in the attachment.

The BUZ11 will fully conduct at a gate voltage ≥ 10V at a low RDS(ON).

I recommend to replace the TIP31 with BUZ11 first and add the discharging resistors if they are really required.

There is no changeover of pins and package.

Regards

Boncuk

 

[fuper]

Hi fuper,

bipolar power transistors (also darlington power transistors) require a pretty high base current for switching.

You might overcome the problem using BUZ11 MosFet transistors. Replace the former base resistors with gate resistors of 100Ω.

If fast switching (high rpm of the stepper motor) is required connect a 10K gate discharge resistor to the output of the driving CMOS chip to ground. Connect the gate resistor on the junction of the discharge resistor to the gate as shown in the attachment.

The BUZ11 will fully conduct at a gate voltage ≥ 10V at a low RDS(ON).

I recommend to replace the TIP31 with BUZ11 first and add the discharging resistors if they are really required.

There is no changeover of pins and package.

Regards

Boncuk

Hey Boncuk and dougy83 - Thanks for the feedback. I have access to both the mosfets you recommended. I live in the Silicon Valley, here in California, so I can get pretty much anything! However I'm lazy, and jameco is 20 miles away, can I substitute an IRF510 mosfet instead? It has a rds(on) of 0.54 ohm if I'm reading the data sheet correctly.

Am I understanding correctly the 10k resistor is to discharge the small capacitance on the gate?
Also I thought mosfets work by applying a voltage to the gate not a current like transistors. What is the purpose of the resistor and how are you all deriving the value?

THANKS!

*EDIT*

Okay - Logic level Mosfet - fully turn on at 5 volts instead of 10-12 volts normally. Interesting. I'm not sure what voltage I'll end up using and I like the idea of being able to use a lower voltage if necessary, so a logic level mosfet it is then. The IRF510 is not a logic level so I just answered my question.

 

[fuper]

Okay I decided to order: IRLIZ24NPBF

They have insulated tabs, learned something new. I want to be able to clamp a single heat sink on all 4 mosfets but that will create a short with the current circuit. I didn't know you could get these parts insulated so its a nice discovery and it's something I know to look for in the future.

Thanks for everyone's help! I'll report back on my findings.

 

[AlainB]

@Boncuk : Thanks for your reply!

@fuper:

As stated in your post, I think that ou are using TIP131, not TIP31 (or are you??). TIP131 is a Darlington transistor and, as far as I know, is very easy to turn on. I may be wrong but I think your problem is not there.

This simple driver provide a full step sequence, that is there is always 2 transistors on at the same time even when the motor is stopped. That is probably when the transistors are heating up, when the motor is stopped.

I have many drivers using TIP121 and they are equiped with small heatsinks. I also use a fan but just for peace of mind. It is not really required. The TIP121 is rated at 5 Amp. I use them with motors rated at 1.5 Amp.

One thing about the TIPXXX transistor is that they are very rugged compare to MOSFETS. The mosfets don't forgive mistakes.

Alain

 

[fuper]

Hi AlainB

I am using TIP31C.

The IRLIZ24NPBF came in and I soldered them in place. They don't work, I think I got the wrong part, and the pins aren't compatible. Really disappointing for me.

I tried reading the datasheet for the IRLIZ24NPBF but I couldn't infer the pin arrangement.

Shane

 

[fuper]

@Boncuk : Thanks for your reply!

@fuper:

As stated in your post, I think that ou are using TIP131, not TIP31 (or are you??). TIP131 is a Darlington transistor and, as far as I know, is very easy to turn on. I may be wrong but I think your problem is not there.

This simple driver provide a full step sequence, that is there is always 2 transistors on at the same time even when the motor is stopped. That is probably when the transistors are heating up, when the motor is stopped.

I have many drivers using TIP121 and they are equiped with small heatsinks. I also use a fan but just for peace of mind. It is not really required. The TIP121 is rated at 5 Amp. I use them with motors rated at 1.5 Amp.

One thing about the TIPXXX transistor is that they are very rugged compare to MOSFETS. The mosfets don't forgive mistakes.

Alain

Do you have a schematic for this circuit? I couldn't read the IC markings.

Thanks!

 

[AlainB]

I dont have a schematic for my circuit. I just drew it on a piece of paper before drawing the PCB using FreePCB software. It is a circuit even easier to make than yours. The chip is a L297 that can be used to provide half or full step sequence to an unipolar (like my board) or bipolar stepper motor. But for your boards, I would simply change the TIP31 with TIP121 or TIP131. For the heatsink, there is some special mica parts that are used to isolate each transistor before fixing them to a commun heatsink.

As I said, this is a simple circuit and, providing the proper voltage to the motors, you can expect something like 300 RPM, this is with a good usable torque. Not very fast but still you can do a lot of things with that.

Here is one of my machines in action:

https://www.youtube.com/watch?v=OwjynFhSbWk

This machine is running with the same drivers as the one in the picture upthere.

 

[fuper]

Ah L297 - ya i looked at that chip but its $10.00 in single quantities. ALthough it appears that LSI has a new pin compatible replacement chip that they claim to be cheaper but I haven't seen single quantity pricing:

LS8397
https://www.lsicsi.com/StepperDrivers.htm

 

[fuper]

Hi AlainB

I am using TIP31C.

The IRLIZ24NPBF came in and I soldered them in place. They don't work, I think I got the wrong part, and the pins aren't compatible. Really disappointing for me.

I tried reading the datasheet for the IRLIZ24NPBF but I couldn't infer the pin arrangement.

Shane

So I'm a little confused on the IRLIZ24NPBF -

As I said earlier, I swapped these in place of the TIP31C I was using. When I hook everything up I get what appears to be a short, as my Arduino power light goes out. When I unplug the stepper motor the arduino starts flashing again [I'm using it as my "pulse"]

So what I am thinking is that the pins are not compatible. I've never used Mosfets before but from the data sheet I gather

Pin 1 is the Gate
Pin 2 is the Drain
Pin 3 is the source

Whereas for the TIP31

Pin 1 is the Base
Pin 2 is the Collector
Pin 3 is the Emitter

I thought these should be pin compatible but I suppose they are not. Can anyone shed additional light?

THanks!

Shane

 

[AlainB]

I saw the L297 as low as $2.40, free shipping on EBay, 10 pieces for $16.00 again free shipping. I bought many things on EBay, electronics and also parts for my old 1972 Honda Cup (C70 moped), and I am yet to be disapointed.

Here is a picture of 2 testers that I made to help understand what is going on when working on these kind of circuits. You should build some too if you don't have something similar. This is a tool that I use quite often.

You should check that the logic is working properly before testing the power stage. Be sure that the arduino is sending the good sequence, some highs and some lows, no floating. Then the logic sequence. It should be:

XX00
0XX0
00XX
X00X

The leds tester is very handy to visualize that.

Then you can start to work on the power stage. I don't thing that the pin compatibility is your problem.

I am not an electronic expert. I just know a little bit. My personnal experience is this: When you are not an expert, when you play with mosfets, they are begging you to kill them and if possible kill the whole board too.