5V to 12V High Current Switch

[spec]

spec,
Check pin 8.
Also the required switching voltage levels for the 555 Trig pin #2
E

Hy Eric,
Nothing has been checked- it's just a concept which I did in a rush.
You didn't like my innovative use of pin 8
Thx for info anyway.

spec

 

[spec]

Hy AM,

Here is a practical design:
As you are in the United States, component availability will not be a problem: Mouser, Digikey, etc

NOTES
(1) R15 is selected for the desired LED current.
(2) R16 speeds the LED turn off
(3) All non polarized capacitors are ceramic 25V or more, with X7R dielectric. Small cased ceramic capacitors are not suitable.
(4) The LM555 timer chip is simply used as a gate driver
(5) R17 is a gate stopper to reduce the chance of the MOSFET oscillating at a high frequencies. R17 should be soldered directly to the PMOSFER gate pin. R17 plays no role in the fundamental function of the circit.
(6) All capacitors play no part in the fundamental functioning of the circuit. Instead the capcitors are decouplers to ensure that the circuit operates as intended.
(7) The NMOSFET is a low gate drive type which allows it to be turned on by low voltages (see data sheet)
(8) The NMOSFET is housed in a TO220 thru hole case for easy handling.

DATA SHEETS & SOURCES
(1) NXP PSMN017-30PL
**broken link removed**
(2) LM555
https://www.ti.com/lit/ds/symlink/lm555.pdf

 

[ericgibbs]

spec,
I see you have changed the 55r power to 5v, so what is the purpose of the 555.?
E

 

[spec]

Hy Eric

I see you deleted your post- you had me worried.

Feel like running your eye over the circuit for me and check for any errors- I normally include a few.

There is still scope for speeding the gate turn off with another resistor and capacitor, but I don't think it will be necessary as the NMOSFET has a fairly low gate charge.

spec

 

[ericgibbs]

hi spec.
I deleted my first post as I had missed the 12V to 5V change in 12V to 5V.
If the OP is using a MCU as the signal source at say 5V, it would be more practical to use the MCU output pin to drive the MOSFET.
or
just use the 555 as an Astable to drive the MOSFET.

E

 

[spec]

hi spec.
I deleted my first post as I had missed the 12V to 5V change in 12V to 5V.
If the OP is using a MCU as the signal source at say 5V, it would be more practical to use the MCU output pin to drive the MOSFET.
or
just use the 555 as an Astable to drive the MOSFET.

E

Hy Eric,
I did consider an MCU output pin directly driving the NMOSFET, but decided it didn't have enough clout. It is worth tying though. Also I don't like exposing the MCU pins to any fire and brimstone. The gate of an NMOSFET switching 5A at 12V fairly fast, is a pretty nasty place with the huge parasitic capacitors all over the place in the can.

Is that all the OP wants to do- flash the LED. If so using the 555 as a multivibrator would be ideal. Perhaps he would let us know.

Thx for the analysis.

spec

 

[spec]

spec,
I see you have changed the 55r power to 5v, so what is the purpose of the 555.?
E

Eric

It is simply to sharpen up the edges and to supply the current to fill and empty the NMOSFET gate charge in a hurry. That is good for lowering the NMOSFET dissipation and also to hopefully meet the OP's speed requirements.

spec

 

[ericgibbs]

spec,
A MCU pin set as an Output can easily actively source/sink the nC charge on the N MOSFET Gate.
An advantage is that the Gate drive could be PWM, enabling brightness control, if required.
E

 

[spec]

spec,
A MCU pin set as an Output can easily actively source/sink the nC charge on the N MOSFET Gate.
An advantage is that the Gate drive could be PWM, enabling brightness control, if required.
E

Hy Eric,

Hmm, I haven't found the out put of MCUs to be that powerful.

This is one of the problems of a paper design- you can't try things out.

The MCU does control the gate of the NMOSFET via the LM555, so PWM brightness could still be used..

spec

 

[spec]

Eric

The older 5V supply line MSP 430C3 MCUs, which the OP is using, don't have too much output capability which is a shame. The newer 3.6V supply line parts have much more clout, but not enough voltage swing to hit the NMOSFET gate hard.

spec

'The modern MSP430s, such as the members of
the MSP430x1xx family and the MSP430x4xx
family, are available for the supply voltage range from 1.8 V to 3.6 V only. This is due to the
manufacturing process used, and has the advantage of drawing even less current than with the
5-V supply used by the MSP430C3xx family.'
TI application report about interfacing to the 3.6V supply line parts
**broken link removed**

5V supply line MSP430 data sheet
**broken link removed**
3.6V supply line MSP430 data sheet
https://www.mouser.com/ds/2/405/msp430f2013-453371.pdf