PWM IC

[ronv]

I'm in search of a really simple PWM IC, like the SG3625 except able to get a duty cycle close to 100%. It would be nice if it had a spice model - wish wish.
All I want to do is put a voltage level in and get PWM out - not a power supply or anything.

 

[alec_t]

Have a spice model of an ideal PWM source (can't remember its origins). Any use?

 

[audioguru]

Look at TL494.

 

[chemelec]

Look at TL494.

Or TL594 is the same.

 

[jpanhalt]

The TPIC 2101 is getting hard to source, but it has a lot of features, like softstart and 100% duty cycle (https://www.ti.com/lit/ds/symlink/tpic2101.pdf ). It requires a separate mosfet driver for anything big (output is only about 50 mA). All that begs the question of why not use a microcontroller, which may explain why devices like the TPIC 2101 are getting hard to source?

John

 

[ronsimpson]

All I want to do is put a voltage level in and get PWM out - not a power supply or anything.

So not a PWM power supply IC but a oscillator. Voltage in and duty cycle out.

 

[jpanhalt]

The TPIC 2101 does that (Figure 4). In fact, that is how I used it (i.e., a voltage divider). You do not need to enable the softstart, but I did, because I was controlling a large DC, 12-V motor.

John

 

[ronsimpson]

All I want to do is put a voltage level in and get PWM out - not a power supply or anything.

Here is a option. LTSpice model.
Watch out there are 4 different versions.
A resistor sets the frequency.
A voltage 0-1V sets the duty cycle.

 

[ronv]

Thanks guys.
I think the Tls only do 50%.
My mind turned to spaghetti looking at the TPIC 2101 block diagram.
The Linear part is what I am looking for. Wish it had a little more drive and a little higher voltage, but it is sure simple.
A lot of uses for a vanilla PWM, but not many chips. I wonder why. Anyway, way simpler than building a triangle and a comparator and not to expensive.

 

[KeepItSimpleStupid]

ronv:

Here https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_120539_-1 is a Velleman kit that supposedly does 0-100%. Check the datasheet on the page.

It also does slow-start because I used it to run of all things a solenoid that controlled a shutter that was next to a $1000 very thin piece of glass.

 

[ronv]

That uses SG3525. How do they get the duty cycle to 100%?

 

[KeepItSimpleStupid]

They OR'ed the two outputs together, so a typical 0-49% from the SG3525 datasheet becomes 98%. Who's gonna miss 2%?
So, all you might have to do is say set the range to 0-2.4 V and make 2.5V or whatever, and force the output on all the time.
Use a comparator on the input.

So, you would just have a slight discontinuous jump between 98% and 100%

Would that work for you?

I found this https://www.diyaudio.com/forums/power-supplies/167837-simple-ic-0-100-duty-cycle-pwm.html discussion too.

 

[ronv]

Ahh, I got it now. Like you say, what's a few % between friends.

 

[jpanhalt]

Here's another way to do it: https://www.beta-estore.com/download/rk/RK-10149_127.pdf

John

 

[shortbus=]

Here's another way to do it: https://www.beta-estore.com/download/rk/RK-10149_127.pdf

View attachment 88610

John

I've posted the original of that circuit several times, and have always been told it is no good. Although the original doesn't use the L298 (another part that everyone claims to stay away from). https://www.wzmicro.com/3525.htm

But I have used the wzmicro circuit several times and can't see a reason that it's so 'bad'.

 

[jpanhalt]

I've posted the original of that circuit several times, and have always been told it is no good. Although the original doesn't use the L298 (another part that everyone claims to stay away from). https://www.wzmicro.com/3525.htm

But I have used the wzmicro circuit several times and can't see a reason that it's so 'bad'.

What???? The circuit to which you link has the outputs OR'd (See KISS, #12). The circuit I linked to does not. Which circuit, in your opinion, is problematic?

John

 

[alec_t]

How about this ?

 

[ronv]

Hi Alec,
Thanks, I was looking for something with few parts and able to drive some good sized FETs. The SG part, I think, is about as simple as I will find.

 

[jpanhalt]

Are you looking for a single side driver, like some of the SG schematics provide, or a half ridge? When I was messing with these things >10 years ago, I went half bridge. The mosfets were cheaper than the comparable diodes. Besides, I liked the control a half bridge gave me. Are you doing a motor, power supply, or something else?

John

 

[shortbus=]

What???? The circuit to which you link has the outputs OR'd (See KISS, #12). The circuit I linked to does not. Which circuit, in your opinion, is problematic?

John

I don't think either is problematic myself. Though without the diode or'd outputs you will only get ~49% duty cycle, or no duty cycle if both outputs are used, due to the totem pole drivers on the output.

I'm just saying all the "experts" have said it is a bad PWM driver for motors. And one other thing about it is there is a slight "dead" spot in the PWM output above 49% duty cycle. As one output switches off and the other switches on. Which for motor driving doesn't make a difference. But if using it to drive logic circuits that are edge triggered it does.