PWM controllers... shopping

snip

I am driving a thermoelectric cooler with an H-bridge configuration (induct or in series with the TEC). So I need to drive 4 switches, but really only need one PWM signal and its inverse.

Since there are only so many PWM controllers with 4 outputs (and 2 of them for driving high-side switches), I will likely need an external gate driver IC. Also, I need to be able to drive the reference pin with the temperatu re setpoint, and the majority of PWM controllers don't allow for external r eference. This is what led me down the path of "you know what I'll just fi nd the simplest possible PWM block and do the rest myself"

Also, yeah I have used the UCx84x family a bit too. I might end up using o ne of those at the end of the day.

This is for work, so it could end up in production for many years.

Thanks for that link, Tim. Nothing warms my heart like seeing a meme about an IC. Also I hadn't realized the MC34063 is hysteretic. I'll make sure I check out the chips you mention in that blog post.

You would generate a timer in the FPGA (digital version of the ramp waveform), and compare it to the digitized input from your error amp.

This might be the bare-bones solution I was looking for. I'll give it a whirl.

ime looking for the ideal PWM controller.

to handle just the PWM function, and I provide my own error amp, gate driv er, and reference externally. The ideal part would look like this: oscilla tor set by resistor, comparator non-inverting input, and pulse out. Plus V dd and ground equals 5 pins only! Does anything like this exist?

never used them. Does anyone here have horror stories from these parts th at I can't infer from the datasheets?

I'm looking for. Vdd=6V max for example, kind of sucks. I do like how t hey use a 50uA current source as the reference pin, so you set Vref with a resistor or drive from low-impedance source, nice.

using an FPGA. ICE5LP1K-SG48ITR50, under $3.00 qty 100.

tally these days.

Cool part. Vdd up to 45V. Integrated bootstrap diodes, nice.

nverter

for a one-of you can get a a ~$30 dev board

Sounds very anecdotal...

QFN using an FPGA. ICE5LP1K-SG48ITR50, under $3.00 qty 100.

the board, then you could get this PWM block for free.

pretty much all of them.

orm), and compare it to the digitized input from your error amp.

I thought you were saying if there were an ADC on the board you wouldn't ne ed the FPGA. The only real shining star of using the FPGA is that it allow s virtually any algorithm to be implemented. Analog has a lot of restricti ons in that department and you are left with little room for customization once the board is designed.

From the way people are describing this I don't think an FPGA is needed. A simple CPLD could be used I'm sure, but then you would need a separate ADC . You can get a lot of capability in a $3 part.

n QFN using an FPGA. ICE5LP1K-SG48ITR50, under $3.00 qty 100.

n the board, then you could get this PWM block for free.

s pretty much all of them.

eform), and compare it to the digitized input from your error amp.

need the FPGA. The only real shining star of using the FPGA is that it all ows virtually any algorithm to be implemented. Analog has a lot of restric tions in that department and you are left with little room for customizatio n once the board is designed.

A simple CPLD could be used I'm sure, but then you would need a separate A DC. You can get a lot of capability in a $3 part.

if the performance isn't too critical and there's a comparator available, l ike an LVDS input, you can make simple delta-sigma ADC

pin QFN using an FPGA. ICE5LP1K-SG48ITR50, under $3.00 qty 100.

on the board, then you could get this PWM block for free.

is pretty much all of them.

aveform), and compare it to the digitized input from your error amp.

t need the FPGA. The only real shining star of using the FPGA is that it a llows virtually any algorithm to be implemented. Analog has a lot of restr ictions in that department and you are left with little room for customizat ion once the board is designed.

. A simple CPLD could be used I'm sure, but then you would need a separate ADC. You can get a lot of capability in a $3 part.

like an LVDS input, you can make simple delta-sigma ADC

Yes, I mentioned that nearly all FPGAs have differential inputs. But most CPLDs do not, at least not any I know of. But then I don't look at CPLDs s o hard. They are typically below my radar. They get very complicated and expensive as the size gets up even slightly. They also are typically desig ned for simple functions with many outputs. FPGAs are weighted for more in ternal logic per output and more recently there are some available with an adequate amount of logic in lower pin count packages. By "more recently" I mean the last decade or so.

I cannot see me "retiring" from electronics. Only freeing my time up to do things I want to do. I don't think I will be around by 2050, or at least be able to hold on to a soldering iron.

Maybe, if I am successful at "retirement", I can hire a couple of technicians to help me build circuits that I have always wanted to build ! Dream products !

boB

AHA !!! Great !

You'll certainly need a PWM controller. But you will also need dead time control.

For full bridge, I am useing external FET drivers but depending on the gate drive constraints and frequency and all that, that is secondary to the PWM unless the dead time is included in the driver.

There are some 1/2 bridge drivers that take care of the dead time.

My latest full bridge PWM is being done with the advanced timers in an STM32F4xx processor. That takes care of the dead time and PWM and stuff from pins that just go o the FET drivers. In my case, individual gate optically coupled drivers.

You could use that Microchip part of course and invert the output and drive one of thse 1/2 bridge FET drivers using diode-cap charge pump for the high side drive. 18V or something like that.

This is fun stuff ! But you have lots of choices.

BTW, I think we pay around 35 cents fo the UCC3843 parts so they are definitely cheap, if that matters.

About the same price for the Greenpaks from Dialog or Silego... I use those in another circuit to generate dead time for the 4 corner gate drivers from 2 lines of PWM from a single peripheral to do phase shift PWM. The dead time control into the Greenpak is controlled from another PWM peripheral at a few MHz so it an be adjusted in software. The Silego does a bit more than that but is an inexpensive part that helps do a lot of stuff.

No, I don't expect I'll ever stop doing it, that aspect was unclear to me when I started fiddling with transistors in my early 20s but in my early 40s it's become clear I'll be doing this in some capacity as long as I can. But I'm even now, not as young and energetic as I used to be and how long I can do it for pay is a question.

Age-ism in the tech field is real (as it is in many fields) and even at

That most of my friends and family don't see the appeal or understand what it's all about doesn't bother me much it's not the kind of stuff you can post about on Facebook and expect dozens of "likes" like a woman in her underwear. Oh well.

I'm 65 (a boomer), but have not had the age-ism issue. Maybe cuz I've been in business for myself (and with partners) for that last 20+ years. I think that's the way to get around that problem especially if you have a wide and varied base of talents and can answer the technical questions or know where to look for the answer.

Me, I'm a master of none. And I'll never make it as an accountant !

:)

I went to art college I didn't really start taking STEM classes (adult-ed) until my late 20s/early 30s when I was looking to get out of the industry I was in. But like a lot of guys who are into electronics as adults I guess I'd been writing BASIC and Pascal programs and building little dioramas with working miniature streetlights for school projects and such since I was a child.

My father was 52 when I was born (I'm the youngest of four) and a WWII vet but had trouble finding well-paid work sometimes by that point also because didn't have a college degree in addition to his age. He wasn't particularly tech-literate then and never was but he decided our family should get a computer as soon as the PC became relatively affordable - "this computer-stuff is going to be really big, someday."

I wanted to be a rock star when I was a teenager. I did work in the music/recording/entertainment industry for a while after college. Long enough to learn I NEVER WANT TO BE A ROCK STAR

Also it would have been difficult for a 62 y/o to keep up with a 10 y/o on the ball field but father-son time at the computer was a way for him to stay engaged

time looking for the ideal PWM controller.

le to handle just the PWM function, and I provide my own error amp, gate dr iver, and reference externally. The ideal part would look like this: oscil lator set by resistor, comparator non-inverting input, and pulse out. Plus Vdd and ground equals 5 pins only! Does anything like this exist?

ve never used them. Does anyone here have horror stories from these parts that I can't infer from the datasheets?

t I'm looking for. Vdd=6V max for example, kind of sucks. I do like how they use a 50uA current source as the reference pin, so you set Vref with a resistor or drive from low-impedance source, nice.

N using an FPGA. ICE5LP1K-SG48ITR50, under $3.00 qty 100.

gitally these days.

erter

I once did a digital SMPS with what Lasse suggest here.

The error signal was fed into the ADC and DMA transferred the error voltage directly to the PWM timer (so not computation involved)

Around that was looped a peak current limit and soft start

In this can it only replaces the PWM part

You can do more by adding the loop, but then you get phase problems if you loop is not fast, wrt to the PWM frequency

Cheers

Klaus

ctor in series with the TEC). So I need to drive 4 switches, but really on ly need one PWM signal and its inverse.

m for driving high-side switches), I will likely need an external gate driv er IC. Also, I need to be able to drive the reference pin with the tempera ture setpoint, and the majority of PWM controllers don't allow for external reference. This is what led me down the path of "you know what I'll just find the simplest possible PWM block and do the rest myself"

one of those at the end of the day.

Sloman A.W., Buggs P., Molloy J., and Stewart D. ?A microcontroller

-based driver to stabilise the temperature of an optical stage to 1mK in th e range 4C to 38C, using a Peltier heat pump and a thermistor sensor? ? Measurement Science and Technology, 7 1653-64 (1996)

Describes an example of such a circuit. We got the the low frequency conten t of the PWM waveform down by playing around a small programmable logic dev ice. The device is long obsolete, but there are plenty of more modern equiv alents around.