Protecting the LTC3780 (or other DC/DC converter)

The main problem when playing with LTC3780 (or other) is it can fry easily.
Especially when you are playing with the feedback loop.

How so ?

Easy, just disconnect the feedback pin, it will crank up the output voltage to the max and burn
As a bonus, it will also fry what's connected to it if they don't like higher voltage.

So here, we'll add a very simple protection circuit :

  • An enable pin that turns the LTC off by default, i.e. if the signal is not driven
  • A shutdown circuit if the output voltage exceeds ~ 28v

The right side is glued to the DC/DC converter
The left side is on the control board.

If the Enable pin is high (or floating), the STBY pin is pulled down and the DC/DC turns off
Similarly, if Vout exceeds ~ 26 V, STBY is pulled down, and the DC/DC turns off

Very primitive, but that should help when connecting/disconnecting stuff all the time

NB: If you use another N-FET (Q4), you'll have to change R9 to something else

Test setup with a very cheap boost/buck converter that i can afford to fry :


It is far from perfect as the output will still go to 27v when the feedback is not driven, but it's better than 60 V and death



Comments

Post a Comment

Popular posts from this blog

Component tester with STM32 : Part 1 ADC, Resistor

Image
I was always  fascinated by the so call "transistor testers" that identify and report pin out, features of pretty much whatever you throw at it. They are based on Atmel 328p chip, the same as arduino nano. So why not do the same thing with a STM32/Bluepill ? The STM32 is faster, has a better ADC accuracy, more memory, can do float etc... and is not more expensive. Warning : I'm doing this for fun & to learn, it might contain error & plain misunderstanding So, i watched a couple of video on the general principle on how they work. This is not a "port" but a rewrite from ~ scratch. When something is weird, i check what the original one does for comparison. Measuring resistance So first thing first :  Resistance & Capacitance. These 2 will unlock the other ones. So how do we measure resistance ? What we do is a resistor divider with a know resistance value: Measure = Vcc*(RtoTest/(RtoTest+Rknown)) As far as the ADC goes, it means ADC=...
Read more

Fixing the INA3221

Image
It 's not too complicated to change the board we have seen  previously . You 'll need to cut some tracks, i did it with a dremel and i'm not very handy, so you'll do better. Red =Cut tracks Blue = Add wire 1- You'll need to separate the bottom connector from the ground, cut the 3 connectors BOTH SIDES. 2- Remove the small red area below the middle resistor to isolate each channels from each other Last, connect right side of each connector to the now isolated pad. Mine looks like this after the operation (ugly i know): Be wary of the small track on the left connector that leads to the left side of channel3 resistor. I cut it while isolating the right pad. Now it works, we can go back to the charger.
Read more

INA3221, weird wiring

Image
Continuing my "smart" battery charger, i've finally received the INA3221 module. It is the purple one you can find on ebay for ~ 5 bucks I soldered a couple of pins to be able to connect it so that i could test it and something immediately caught my attention. It is supposed to be a high side current/voltage sensor, typically in a setup like that : So you can measure the voltage supplied to the load, and the current going through it. Now, let's have a look at the module, look at the top of the following pic, where the sense connectors are. CH3/GND/CH2/GND/CH1/GND ? Wait ? What ? Yes, all the IN- pins are connected to ground, so it is a bottom current only sensor. Additionally, the - side of the shunts are ALSO connected to the ground, no only the connectors. The actual layout is like that : That raises two problems :  The voltage is meaningless as we are only measuring Current x ShuntValue, not the supply volt...
Read more