12V input for SRK FET drivers

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cherkess_jan
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12V input for SRK FET drivers

Hello folks.

The driver that i’m intended to use is this BLF SRK FET V2 – 46mm by RMM posted here

My use case would not be including cell batteries but a 12V input from a computer PSU. In the circuit, there is an LDO voltage regulator section (for 2S+ input) which i don’t know what to put there. Maybe LDO is not necessary at all, since FET’s Drain to Source Voltage would be around 30V, so i can directly fed 12V to T+ and T- on the circuit……can’t i?

If LDO is needed, what type of it is required for my voltage source?

Edited by: cherkess_jan on 03/17/2017 - 01:57
Mike C
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I can’t say what type of LDO is used as they all have different pin configurations, but it looks like it’s a SOT-23-5 package with same pin configuration as the LT1761. Someone else can chime in with exactly what LDO was intended for this board.

The reason for the LDO is to prevent the high voltage from frying the MCU. At 12V the MCU will die.

cherkess_jan
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Mike C wrote:
The reason for the LDO is to prevent the high voltage from frying the MCU. At 12V the MCU will die.

Thanks for the info. So LDO may be there just for powering the MCU. Then LT1761 seems fine as it’s max input is 20V.

DavidEF
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cherkess_jan wrote:
Mike C wrote:
The reason for the LDO is to prevent the high voltage from frying the MCU. At 12V the MCU will die.

Thanks for the info. So LDO may be there just for powering the MCU. Then LT1761 seems fine as it’s max input is 20V.


You still need to check the pinout. IIRC, Texas_Ace messed up a driver a while back, because he wrongly assumed all LDO’s of the same size/shape had the same pinout. I think his drivers use a different LDO than Richard’s drivers. If you want to know what Richard uses, look at what he sells in his Components category at Mountain Electronics.

Edit: Well, I just looked, and couldn’t find an LDO listed for sale at Mountain, although he does sell them with the SRK V2 driver kit, and he also sells LDO add-on with the full driver, for a small fee.

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Mike C
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cherkess_jan wrote:
Thanks for the info. So LDO may be there just for powering the MCU.

Yes, the LDO’s only function is to lower the voltage so the MCU doesn’t burn.

cherkess_jan wrote:
Then LT1761 seems fine as it’s max input is 20V.

As DavidEF wrote, pin configuration of the LDO must be checked. I use LT1761 LDOs myself, I like them, and to me that board looks like it could use a LT1761, but I think it’s best to ask RMM what LDO he has used. Then you know it’s tried and tested, and you don’t need to take a chance based on a random dude’s guess.

Welcome to BLF by the way. I noticed this thread is your first post.

cherkess_jan
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Mike C wrote:

cherkess_jan wrote:
Then LT1761 seems fine as it’s max input is 20V.

As DavidEF wrote, pin configuration of the LDO must be checked. I use LT1761 LDOs myself, I like them, and to me that board looks like it could use a LT1761, but I think it’s best to ask RMM what LDO he has used. Then you know it’s tried and tested, and you don’t need to take a chance based on a random dude’s guess.

Welcome to BLF by the way. I noticed this thread is your first post.

It would fit and i guess the pinout could be figured by following the traces, which i’m doing right now.

And thanks for your welcoming Smile

HarleyQuin
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Hello cherkess_jan, welcome to BLF.

I have built one BLF SRK FET V2 and it’s a great board.

It was TomE who had noticed the hard way that there are different LDO-pinouts although they share the same footprint (SOT-23-5). I responded to him here, commenting about the LDOs and linking to the 4 types wight had dug out which are pin compatible. The same LDO layout is used on the V2 board.

.

cherkess_jan wrote:
so i can directly fed 12V to T+ and T- on the circuit……can’t i?
No. This won’t work and instantly destroy the MCU (AttinyXXX)
The T+ pad sits behind the LDO (LDO-output, the same signal as MCU+(pin8)). Feeding 12V there will destroy the MCU – and the small wire to T+ might not support your intended current.

T+ is the voltage supply for a temperature sensor, meant for regulated output and small current.

V+ on this driver is usually fed in via the large round pad on the other side of the board. You can also use on of the 5 LED+ pads instead, it’s the same signal. V- is fed with the GND ring.

This driver is usually meant for single cell input (1S), the LDO was meant for 2 cells in series (2S). I haven’t heard of more with this driver, yet, so you might be off to new ground. Perhaps you want to tell us what you intend to do, which input, which LED’s.

The driver itself is a usual FET/direct-drive driver, so it does not buck or boost the output to the LED. The LDO only regulates the voltage to the MCU and a possible temperature sensor.

Hope that helps.

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cherkess_jan
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Thank you HarleyQuin.

I want to light up a 12V XHP70. Power source is a computer PSU. I’ve read here that this LED could draw 5.5A, though it’s datasheet says 2.4A max, anyway, so i also wonder if this driver is capable of such loads.