Inexpensive High side solenoid driver that can handle 6A without getting hot?
eagletalontim
Posts: 1,399
As the title says, I am on the hunt for a mosfet / profet / transistor that can fit in a 1/2" square and can handle 6A minimum. I just found out that 2 solenoids that my product may be connected to are 3ohm which at 16V is 5.3A. 16V is worst case. Average voltage should be 12 to 14.3. One of the solenoids will have to handle a 45hz pulse to the solenoid. Does anyone have a recommended component that would connect directly to the prop (with or without a current limiting resistor) and work for my application? I am browsing Digikey now, but most are pretty expensive or too big. The entire circuit including resistors, and flyback diodes must fit in 5/8" x 1/2" square at tops! To save some space, I am using all 1206 resistors.
Comments
There are plenty of P-ch MOSFETs in small packages that will handle this easily and since the operation is slow-speed you can just drive it with a 2222 using 10K across the gate-source. So that's a full 12V drive to the MOSFET so it should be fully on.
How do you go about selecting a suitable MOSFET? Well I just went for a TO-252 and sorted according to price and picked the next to cheapest at 75 cents 1 off which handles 17A up to 30V.
-Phil
1. This started out as a small low side relay driver with a 12V power supply.
2. Then a higher current high side relay driver using automotive relays but still a 12V power supply.
3. Now it's a much higher current high side solenoid driver in a full blown Automotive application.
Now come on, tell us what you want in the first place. There are lots of guys here who have vast experience in designing stuff.
A full automotive application is pretty severe. In cold weather it is easy to get the charger/alternator to deliver 18V.
Worse yet, lets say the battery is dead and you get a jump from a wrecker and it's 30C below zero. So he jumps the car at double voltage. It's pretty easy to see 30V or more on the power buss/battery.
Designing to a clean 16V just won't cut it.
If you want to drive a 3 ohm solenoid at 30V the driver must use MOSFETs with at least 10A, probably 30A, and at least 60V ratings. I would use a full high side N-Chanel MOSFET driver such as:
IRS21853S
IRS21962S
These things are rugged and very reliable.
I have used many thousands of a different part in the same family. I'v seen no failures due to the part.
I doubt you can cram 2 of the driver chips and 4 power MOSFETs in 1/2" square.
Duane J
-Phil
What I am still confused on is the Gate capacitance. Is this the "charge" that holds the gate on? Not draining it fast enough could cause the MOSFET to turn off too slowly generating more heat? Since I will be pulsing the "high side" of the solenoid at 45hz, I need to discharge the gate quickly enough to prevent it from staying on between pulses. Sorry for all the questions! I am just trying to learn
Quite unfortunate that you picked the IR510 as that is very unsuitable not just for the Prop but just about anything else, what with a Rdson of 0.6 ohms and that's at 10V gate drive. The "thing" won't hardly turn on at 3.3V if at all as the graphs don't even bother showing anything below 4V gate drive but at that voltage it is unusable.
The gate capacitance is something you have to deal with because it's a MOSFET, it would be really really nice if they could produce a MOSFET without any gate capacitance at all but that's not possible. When the Prop output tries to turn a MOSFET on it has to charge that capacitance first but it's like trying to fill a bucket (gate capacitance) with a hose (Prop output), the more pressure (voltage), the bigger the hose (current capacity), then the faster it will fill. When it's full then in this case the MOSFET is as fully turned on (low resistance) as it is going to get in this application. So always see the Prop output as a finite resistance, probably in the 50 ohms or there abouts region and it can't fill that bucket fast enough, relatively speaking.
If the MOSFET only gets turned on for a while then off later it doesn't matter too much as the time it spent in this "not fully switched" region where it is a very poor conductor but great heat generator! is insignificant. Now when you are trying to turn the MOSFET on and off very quickly then it will get hotter and hotter unless you can switch it "hard", that is use a gate driver that can charge/discharge that gate capacitance very quickly so that the MOSFET is mostly either fully on or fully off, not in between (heat). A suitable mechanical switch won't get hot even if it's switching many amps because it has very low on resistance. That is why we refer to devices as switching devices because they should ideally behave like this. BTW, 45Hz is fairly slow so with a good MOSFET you can drive it directly from the Prop.
It will probably not be the one I go with due to the size. If I could find a TO-220 that will work, I will probably go with that. The one above is just so I can learn a bit more about these nice components
A 9V battery's negative terminal is -9V when "referenced" from the positive terminal. When the source of a Pch is tied to positive guess what the reference is?
What's wrong with the TO252 pack? You can also get through-hole TO251 packs that you can mount vertically.
BTW, people say that Australia is "down under" and why is it that in all the SciFi movies the alien ships conform to the "upright globe" (north pole at the top) and the bottom of the ship towards the earth as well? Maybe that says a lot about how people think, 3D space mapped into 2D minds.
Most IGBTs are characterized with a 15 V gate drive. If there is a logic level IGBT, I haven't encountered it (but would like to!).
BTW, a half-bridge gate driver IC (like the 8-pin IRS2106) will handle practically any gate drive voltage your transistors may require. The only problem is that the bootstrap capacitor approach to generating the high-side gate voltage requires frequent switching to stay charged.
But you simply cannot drive a high-side pMOSFET directly from a Prop pin. If you tried, it would be on all the time. To do so, you will need to go through either an NPN transistor, such as a 2N3904, or a small nMOSFET, such as a 2N7000, either one with a pullup to the 12V supply.
The other alternative would be to use a driver chip, such as the MIC5060 that can drive the gate of an nMOSFET well above the 12V power rail to turn it on.
But to ditto what others have said with even more emphasis, throw those IRF510s in the trash! Jusdt get rid of them! Seriously. I don't know why RadioShack keeps selling those ancient dogs. They're worthless.
-Phil
I uploaded a design and was wondering if I have this correct. For some reason, I think I have this backwards.
-Phil
Here is an updated version. Q1 is a surface mount 2N3906. Now I need to figure out the values for each of the resistors.
I am thinking these values :
R1 = 4.7k (Per suggested value previously posted)
R2 = 10K (To prevent the gate from "floating". May need to move to gate side instead of PNP collector side)
R3 = 1K (Should be enough to drive the base of the transistor correctly from a prop pin.)
D1 = Maybe I could use these : http://www.digikey.com/product-detail/en/SMAJ18A-E3%2F61/SMAJ18A-E3%2F61GICT-ND/1091631 I am already using this on the power supply.
BTW, the MOSFETs shown in your schematics are pMOSFETs and are the correct choice for high-side switching. The IRF510 is an nMOSFET and will not work there.
-Phil
-Phil
It wouldn't hurt you to get a good book or download a pdf about basic electronic theory. A random scattershot approach to design tends not to be very productive. This is my recommendation:
It's expensive and worth every penny.
-Phil
On Ebay I got a cheap bunch of those: BTS441T
but there are other similar ones here ...
http://www.digikey.com/product-search/en?vendor=0&keywords=bts44
These are real automotive parts, not quite so cheap, but with some protection designed in.
and they work with input levels of 2.2V - so great for Prop, no additionals Parts needed besides DIODE.
In any event, you really need to test your circuit before committing to a PCB. And why not do a proto run with the PCBs (i.e. no soldermask or silkscreen -- fast and very cheap) since you seem to be rather uncertain about the design? There's nothing that we are willing to commit to here that will guarantee your success.
-Phil