Yeah, it’s a good suggestion, and looks like Loneoeceans method is the same. I could actually fit a tiny charge pump I’ve used before to keep mosfet resistance low, so I squeezed it in for the mosfet gate.
I only use my own firmware, for me it’s the fun part of the hobby. My firmware is E-switch, clicky switch and dual switch compatible as it is so no need for different firmware files for different lights.
I hesitated to use a charge pump gate driver like mic5019 to get a very low resistance, but I thougt that there was already enough parts, so I chose a mosfet that have arround 2.5mΩ at 2.8V, a bit expensive but not more than mosfet+driver. Ah but I forgot, the LDO is also to keep the mosfet resistance constant, without it the charge pump should virtually eliminate that resistance variation.
Ok, without the charge pump the LDO is probably a good idea. It’s the MIC5019 I have used, it works well but if you use it, make sure to put a pull down resistor on the enable pin. At first I didn’t, and the datasheet states that it can be unpredictable if the pin is floating. The datasheet was right.
Which mosfet did you choose? When do you expect your parts? I’ll follow this project with interest.
Not sure, depends how much time it takes for shipping from Oshpark, also I haven’t made my order at Digikey yet, it’s the only place where I see the TPS61288 in stock, and it’ll have to go through customs unfortunately.
Ok, it’s the same mosfet that was in your schematics… I have ordered the same.
What’s the issue with Digikey? I ordered mine from Digikey.se, I got free shipping when buying over 50€ and UPS take care of all the customs. I only have to pay added 25% tax, but I have to do that when buying from Mouser too. The only difference is that Mouser add the 25% to the invoice that I pay. Digikey doesn’t add that, I get a separate tax bill from UPS with only taxes, no additional costs, end cost is the same. They don’t offer this service with Digikey.fr?
Hmm, I’ve never had a package with UPS coming outside of EU, but looking at other French feedbacks it is the same as DHL when the seller doesn’t take care of the VAT, they charge some customs clearance fees (like 20~25€) on top of the VAT, and it takes more time. Mouser is much better since they take care of everything, it’s like buying from the EU, initially I planned to wait until they receive the part, it was predicted for the end of March but got delayed to the end of the year
Same in Sweden, if the seller doesn’t take care of it there is additional fee regardless of courier.
But in my case the seller (Digikey.se) takes care of the VAT via UPS. Only difference from Mouser is it’s a separate bill for the VAT. So for me ordering from Digikey is as easy as Mouser. UPS send me the VAT bill which I pay with Swedish bank app for quick money transfer, very convenient. Check with digikey.fr, send them a mail and ask. I would be surprised if ordering from Digikey.fr is more of a hassle.
For a long time I avoided Digikey for that reason, my first order in 2014 was indeed a hassle. But since then Digikey.se was introduced and last year I wanted some stuff that only Digikey had so I decided to give it a go and was pleasantly surprised. Now I don’t care weather it’s Digikey or Mouser, I order where the parts are which is very convenient.
I think I ordered more 61288s than I need. If you want, send me a PM once your driver boards arrive from OSH Park and I can send you one or two. You can paypal me the cost once you receive it, no need for pre-payment.
I received the last parts Wednesday (at last), yesterday I made one board, first time reflowing anything else than an LED but it turned out well :
This morning I tested the driver, only the hardware by bypassing the MCU :
And it works! The output voltage/current is stable, here is a quick output voltage waveform with the scope I just bought :
The only issue is that I got less current than expected, with 44mV ref voltage and 9.2mΩ (7+mosfet resistance) I should get ~4.78A, but I only get ~3.7A. After a quick check the real ref is ~43mV and the mosfet resistance is ~4.4mΩ which explains the difference. Swapping the resistance with a 5mΩ one should do the trick, but I’m worried about the ON resistance variation of the mosfet between parts.
How does your driver regarding these characteristics? If behaves well regarding these qualities (from dtr’s laser shop), your driver could be a good choice for LEP driver swaps if more e-switch LEPs pop up in the future.
An ideal power supply for a laser diode has the following characteristics:
• Current source
• Transient suppression (also low noise)
• Independent clamping current limit
• Slow start / ramping the current signal during switch-on
• Output overvoltage protection
• Input undervoltage detection
• Output short-circuit / interruption detection
• Shorting output during driver off status for ESD protection
• No undershooting of the output voltage at switch-off of the laser, so that a negative voltage over the laser diode cannot occur.
I got a bit of a scare yesterday, I couldn’t read the device in microchip studio. Couldn’t sleep while trying to figure out what was wrong, then it clicked, I ordered the older programing key , despite that you told me you changed it, I completely forgot that, I must have had the older key already in my oshpark projects. Thankfully it didn’t fry the chip (5V on UDPI, UDPI on GND, GND on +).
For now I just tested your TCD sample code.
Aren’t laser diodes low voltage ? The present driver uses a boost converter for voltages higher than li-ion.
• Current source : yes.
• Transient suppression (also low noise) : switching converters are noisy, maybe a linear driver would be better suited for this.
• Independent clamping current limit : sometimes there is an adjustable switch limit but this isn’t the case with the TPS61288 (fixed limit).
• Slow start / ramping the current signal during switch-on : sure that’s possible, in hardware (it’s already the case, but can be increased) or software.
• Output overvoltage protection : yes.
• Input undervoltage detection : most switching ICs have an undervoltage lockout, sometimes adjustable, on the TPS61288 it’s 1.9V, can be done in software, anduril have a default LVP of 2.8V (or 2.7 ?).
• Output short-circuit / interruption detection : don’t know how to do that.
• Shorting output during driver off status for ESD protection : idem.
• No undershooting of the output voltage at switch-off of the laser, so that a negative voltage over the laser diode cannot occur. : not sure about this either.