I was wondering if I can substitute the relay in the car head lighting system with some other device like mosfets or triacs. If it is possible what is the best way to use it?
N channel MOSFETs ground a circuit. If the relay grounds the lights to operate, go for it. Just find one that will accept battery voltage as input. Use a pull down resistor on the input to keep it turned off when it should be off.
ST do high side MOSFETs suitable for use in cars. They even have feedback controls to show any issues such as shorts or overheats and can be driven by a logic signal. They aren't cheap but are pretty well protected against most nasties in the automotive environment.
Have a look here - some interesting high side switches
ST do high side MOSFETs suitable for use in cars. They even have feedback controls to show any issues such as shorts or overheats and can be driven by a logic signal. They aren't cheap but are pretty well protected against most nasties in the automotive environment.
Have a look here - some interesting high side switches
Nice but most of these are low current devices that can not drive a headlight.
I did not look at all the data sheets but thay seem more geared towards powering the engine control systems.
I must say it took me a few minutes to find the current capacities on that page but they are well worth looking at if you need an automotive high side driver. For a low side switch, a decent low rds on will do fine
I was wondering if I can substitute the relay in the car head lighting system with some other device like mosfets or triacs. If it is possible what is the best way to use it?
If the IRF4905 is a real, high power P channel FET, why don't they say so?
I'm not an engineer so when I see Vdss = -55V and ID= -74A, I go away disappointed.
If the IRF4905 is a real, high power P channel FET, why don't they say so?
I'm not an engineer so when I see Vdss = -55V and ID= -74A, I go away disappointed.
Do yourself a favour though and have some way of bypassing it if it does fail - maybe a couple of terminals on the board you can jumper over with crocodile clips or an emergency switch arrangement.
Losing your headlights in the middle of nowhere may be unlikely but it's good to have a "plan b"
If the IRF4905 is a real, high power P channel FET, why don't they say so?
I'm not an engineer so when I see Vdss = -55V and ID= -74A, I go away disappointed.
Hi Crutschow
I never work with negative voltages and don't intend to for any of my projects. So when I see negative voltages on the data sheet, I assume that won't work for me.
Yes, I know about the word ass u me. My brain does well with logic but it doesn't go negative.
Why aren't we using that IRF4905 instead of bootstrap circuits for driving the high side on stepper motors?
The negative sign is just a notation to illustrate that those parts are the inverse of N-channel/NPN transistors. It has nothing to do with "negative voltages" as you put it. It's more about current flow perspective and proper engineering etiquette.