DC-DC Buck Converter Design for 5V 5A laser control.

[dunkelheit_phoenix_2008]

This is a DC-DC stepdown circuit for laser control (better option than a LM311), at engineering level, it's based on texas instrument documentation, for testing proves I used three 9W 1Ohm resistors in parallel, the elementrical characteristics prove to work well with the laser load. There you have the electrical circuit:



You'll find more information on:
Mechatronic Strike wordpress.
Hope this information was usefull, have a nice day.

 

[Giannis_TDM]

This is a DC-DC stepdown circuit for laser control (better option than a LM311), at engineering level, it's based on texas instrument documentation, for testing proves I used three 9W 1Ohm resistors in parallel, the elementrical characteristics prove to work well with the laser load. There you have the electrical circuit:
View attachment 70756


You'll find more information on:
Mechatronic Strike wordpress.
Hope this information was usefull, have a nice day.

Ehm... Where's the feedback loop? You can't just give things 40khz PWM and expect everything to run smoothly or even at all. Without a feedback loop, this is an unregulated supply both on voltage and current and would annihilate any diodes. Also, it running a few resistors doesn't mean jack. It's like saying that TATP ignites so I can use it as fuel for my car.

 

[dunkelheit_phoenix_2008]

That's a good question, actually if you visite the blog you'll find that's not necessary a feedback loop for the laser control, that's optional, this is a basic circuit, but yes you are right, the 40KHz signal reduce the size of the inductor that you need, at the same time, using power simulator you can prove the results, at testing scale this works perfectly.
The load is defined by P=V*I, V=I*R, then you have P= I*I*R, having in consideration that for an NUMB44-V2 you need 25w (5V,5A) for an average of 7w laser output, that meas R=P/(I*I), R=1Ohm. This is less expensive than a real NUMB44-V2, perfectly for testing, actually, I'll be posting the results with this laser. Hope this answer your question Giannis_TDM.

 

[dunkelheit_phoenix_2008]

That's the signal at 60% of dutty cicle, provide from the microcontroller (in this case a STM32), the dutty cicle limits the voltage provide to the diode. I'm using a HANTEK, sorry for the resolution.

 

[Giannis_TDM]

That's a good question, actually if you visite the blog you'll find that's not necessary a feedback loop for the laser control, that's optional, this is a basic circuit, but yes you are right, the 40KHz signal reduce the size of the inductor that you need, at the same time, using power simulator you can prove the results, at testing scale this works perfectly.
The load is defined by P=V*I, V=I*R, then you have P= I*I*R, having in consideration that for an NUMB44-V2 you need 25w (5V,5A) for an average of 7w laser output, that meas R=P/(I*I), R=1Ohm. This is less expensive than a real NUMB44-V2, perfectly for testing, actually, I'll be posting the results with this laser. Hope this answer your question Giannis_TDM.

Ehm a feedback loop is absolutely not optional. That is if you want the diode to survive... Diodes are not perfect resistive loads with no deviations.. Their vf and internal resistance lowers with temperature so it will just run away without a feedback loop controlling the current. Also, what is the p-p there? 1.6ish v? Please do not hock up any diodes to that...

 

[Cyparagon]

You need a current sense feature, dunkelheit. Thermal runaway is a real concern. Also, any variation in your supply voltage translates to a variation in your output. This is not acceptable for driving sensitive devices like laser diodes.

A PWM signal from a microcontroller is lazy, expensive, and inefficient. Your component count is high, compared with both a lm317 circuit, and a proper switchmode constant current source.

Where exactly are your probe points?

I don't have a problem with you saying something along the lines of "this was a fun experiment", but I DO have a problem with you saying this is somehow a better alternative than current laser driving options. That's just nonsense and you should be ashamed for making claims like this on a subject you clearly haven't researched.

 

[Giannis_TDM]

You need a current sense feature, dunkelheit. Thermal runaway is a real concern. Any variation in your supply voltage translates to a variation in your output. This is not acceptable for driving sensitive devices like laser diodes.

A PWM signal from a microcontroller is lazy, expensive, and inefficient. Your component count is high, compared with both a lm317 circuit, and a proper switchmode constant current source.

Where exactly are your probe points?

From what I can gather based on the waveforms and the voltages it seems like channel 1 is probing the microcontroller PWM output and channel 2 the output of the "converter" after the output cap.

 

[dunkelheit_phoenix_2008]

That's the point, an step down circuit can establish a limit voltage (without taking in consideration the losses in the circuit), a laser diode is that, A DIODE, and diodes works depending the voltage that is provide for the source, in the case of the graphic you are providen 5V to the diode, the current will be demanded depending the laser diode model. But if you set your dutty cycle, at 10% there's a diferent voltage provided,

You'll supplied 1.51V at D=10%, the diode will not consume more current than that, I mean, it's impossible supply more voltage 'cause the inductor and the capacitor settles this, and with an acceptable peak on the first milisecond, you can control perfectly you circuit.
This is important, I'M NOT SAYING THAT A PID CONTROLLER ON DISCONTINUOS CONDUCTION MODE IT'S NOT NECESSARY, acutally PID it's better for mechanis, for electronics a P loop it's better this is a BASIC SOLUTION, compare this with an LM311, that you're turning on and off the diode, YOU'RE KILLING THE DIODE, this step down gives you a CONTINUOUS SIGNAL.

Just to clarify you about the application of loop controllers, it's a design criteria that a signal for a DC-DC converter should be higher than 20KHz (DW Hart, Power Electronics, 2011), if you're considerating a variation higher than 0.01V (than means less than 5% of the signal), you must use PID controller on accurate, 'cause an peak of at leats 2 times your inital voltage is created, that why you need a PID in that application that can be for example in PCB's solding created with lasers.

I'M SHOWING A BETTER ALTERNATIVE, most of the time people just buy a driver laser, instead of created one, this is a good point start.

 

[dunkelheit_phoenix_2008]

Cyparagon, an LM311 turns on and off your diode, leading your dutty cycle, that affects the quality and the life of your product (laser diode), an stepdown provide a non discontinuous signal, that's the main difference, using the totem pole you have a better fall of you PWM, STM32 resolution is awesome, you should try it.

 

[dunkelheit_phoenix_2008]

Yes CH-1 is the PWM signal, CH2 is the signal of the laser. In the following picture, CH-2 is the totem pole signal.

The feed back helps to compensate that 4% lost 'cause the amplification of the BJT.

 

[Giannis_TDM]

That's the point, an step down circuit can establish a limit voltage (without taking in consideration the losses in the circuit), a laser diode is that, A DIODE, and diodes works depending the voltage that is provide for the source, in the case of the graphic you are providen 5V to the diode, the current will be demanded depending the laser diode model. But if you set your dutty cycle, at 10% there's a diferent voltage provided,
View attachment 70758
You'll supplied 1.51V at D=10%, the diode will not consume more current than that, I mean, it's impossible supply more voltage 'cause the inductor and the capacitor settles this, and with an acceptable peak on the first milisecond, you can control perfectly you circuit.
This is important, I'M NOT SAYING THAT A PID CONTROLLER ON DISCONTINUOS CONDUCTION MODE IT'S NOT NECESSARY, acutally PID it's better for mechanis, for electronics a P loop it's better this is a BASIC SOLUTION, compare this with an LM311, that you're turning on and off the diode, YOU'RE KILLING THE DIODE, this step down gives you a CONTINUOUS SIGNAL.

Just to clarify you about the application of loop controllers, it's a design criteria that a signal for a DC-DC converter should be higher than 20KHz (DW Hart, Power Electronics, 2011), if you're considerating a variation higher than 0.01V (than means less than 5% of the signal), you must use PID controller on accurate, 'cause an peak of at leats 2 times your inital voltage is created, that why you need a PID in that application that can be for example in PCB's solding created with lasers.

I'M SHOWING A BETTER ALTERNATIVE, most of the time people just buy a driver laser, instead of created one, this is a good point start.

Ehm Ill keep this short:
You got all the fundamentals about laser diodes wrong.
That is a beyond shitty design that would kill ANY laser diode with that short of ripple together with it being CV instead of CC
Nobody ever uses an lm311, We use 317s and essentially "hack" their feedback loops into CC regulators.
This circuit is more expensive and performs way way way worse than a conventional driver coupled with the fact that it is essentially unregulated.
I appreciate your effort but just no mate... Building this would be a waste of an STM32.

 

[dunkelheit_phoenix_2008]

Giannis-TDM, you're right quality and complex things are more expensive than single modules, I assume that it's better for most of the people just buy things, and don't design; as I said to you, I'll be posting images of the laser results, base on the NUMB44-V2, so we can compare reality and math with your position.

 

[dunkelheit_phoenix_2008]

Giannis_TDM, LM311 also turn on and off the diode, as I said, you're killing the diode.

 

[Cyparagon]

Okay, I thought you just typo'd the lm317. The LM311 makes even less sense in this context because it's a comparator. No one uses a comparator for current feedback. You're demonizing an idea that no one here utilizes, proving once again you don't know what's going on.

Driving a diode with a voltage rather than a current is not safe because of the risk of thermal runaway, and because the IV curve is very steep. Diodes are current-driven devices.

I could go on about a half-dozen other flaws with your idea, but the lack of current feedback is a deal breaker. "I got this pile of shit to run" is a far cry from "everyone should use this pile of shit" and you're consistently confusing the two.

 

[Giannis_TDM]

Giannis-TDM, you're right quality and complex things are more expensive than single modules, I assume that it's better for most of the people just buy things, and don't design; as I said to you, I'll be posting images of the laser results, base on the NUMB44-V2, so we can compare reality and math with your position.

All I can say is that I already consider the diode that you will buy dead. Also, you don't need to compare anything, I have designed multiple actual drivers and there is so much that you have gotten wrong about everything that is not even funny anymore... But first I want to point out: you said that "LM311 turns on and off your diode" So I say look at your waveform:

I have marked the dead zones where the voltage of your converter drops to the 0 mark which is essentially turning off and on the diode. Then 40khz Is way way way too low, You will need a lot more output caps and also learn how to use a scope, To measure the ripple and get a proper waveform out of an SMPS converter you need to select AC coupling for your channel.... And finally, NOBODY HERE USES 311s FOR POWERING DIODES!

 

[dunkelheit_phoenix_2008]

Cyparagon, actually, LM317's output signal is an PWM signal, not an non sine signal, and I'm using a certified power supply, buy don't worry I'll be posting the results with NUMB44-V2, so we can debate with the reallity, your points.