Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Do you think of "linear" control or just On/Off?
And, how big is the load (voltage/current)?
Here is an example of 10A switch:
h**p://www.phoenixcon.com/products/interface/db/datasheets/DEK-OV-10A.pdf
Regards,
IanP
Let say, i got 1 logic to control it then the A1 i put it High and the A2 control by logic signal. Then what i need to connect at A and +? What's mosfet number i need to choose?
Hi,
1) Is it you meant that, if i got 1 DC-Motor for 24Vdc then i need to supply the 24Volt at A then my motor get the supply from + and 0, is it that? If i use 12Volt dc motor and i connected to + and 0 is it will damage my motor?
2) Let say, if my motor only use 2-3Amp then i need to use bellow circuit is it?
3) Between the A1 to optocouple is it the LED and between the 14 and 13+ is what componet, what shuld i choose it?
Attached is a diagram of optocoupler and PMosfet with required resistors.
If you want to drive optocoupler directly fro a µC pin then better option will be to connect A1 to +5V supply and A2 to microcontroller PIN.
Component between 13 and 14 is a transient vltage surpressor to protect transistor against voltage surges ..
To drive 3A you will need external transistor to boost the current.
Optocouplers can deliver only mAs ..
Ya i decide to use uC to control. So, the DC output current draw is depent our P type MOSFET support is it? Why we dont use normal transistor... to drive it, what the advantage for MOSFET and what the disadvatage for transistor?
* i need to comfirm again, we are using N or P type because your drawing is N-type?
Drawing mistake: for PMOSFET arrow should be in the opposite direction ..
You can use normal power transistor (PNP to replace PMOSFET, or if you reverse the circuit you can use NPN power tansistor).
And in most cases you will be using darlington transistors, and the reason will be transistor's gain factor: β .
Be aware the the collector current Ic=β * Ib, where Ib is the base current.
So, for example, if β of a transistor is 50, and you want Ic=3A the Ib=3A/50≈60mA
If, on the other hand, you use a darlington transistor its base current will be much smaller as darligton transistors have β>500, quit often several thousands ..
So as you can see to control BJT transistors you need to "pump" some power to the base to achieve desired Ic.
In case of MOSFETs you need some power for a very short period of time during fast trasnition of voltage at mosfets gate (charging/discharging gate's capacitance). After that moment you just need to maintain voltage at mosfets gate and the gate's current is negligible ..
Regards,
IanP
Ya i decide to use uC to control. So, the DC output current draw is depent our P type MOSFET support is it? Why we dont use normal transistor... to drive it, what the advantage for MOSFET and what the disadvatage for transistor?
* i need to comfirm again, we are using N or P type because your drawing is N-type?
If you really need to have electrical isolation and using separate power rails (say 5V on one side, 25V on another side) between your microcontroller and the high-power load such as a 25V motor, use an opto-coupler, but the opto-coupler might (not always, depending on the opto-coupler you use) need another transistor or darlington pair to drive your load.
If you do not need to have any electrical isolation and sharing the same rail voltage (5V on the same PCB), just driving a 5V, 1A DC motor, the methods (below) would do.
Power BJT and Power MOSFET are different in limitations and applications.
Differences only appear between BJT and MOS when used in the area in of RF, Analog, Digital and High Power Electronics. For low power and low speed electronics, not much difference.
For your application, no difference between to use BJT or MOS. In fact the probably difference is perhaps cost and additional component, some circuit calculation to find the values of components to use.
BJT
In the case of NPN, you use a small base current Ib and forward current gain β to yield the large collector current Ic, then Ib+Ic = emitter current Ie that drives the power hungry load at the emitter.
You need to use a microcontroller output port pin TTL/CMOS to drive a output logic high or '1' to source a small current, typically 50µA, then via a base limiting resistor of about 220Ω to the base. This BJT is a low-power or most commonly called signal BJT, with β about 100 to 200 at most, thus driving load current of 1A at most.
In the case of PNP, your microcontroller has its port pin set to serve as input to sink current from the base of PNP via a limiting resistor. The load current is Ic=Ie-Ib It is just opposite of the NPN.
Most people uses NPN because of Ie=Ib+Ic instead of PNP's Ic=Ie-Ib. Another reason is because it discouraged to sink current through a microcontroller's input port pin. It's not so much about danger since your limiting resistor is there to protect your microcontroller port pin, it's just a preferred way of doing things.
BTW, it is confusing to say normal transistor. In engineering practices, we either call it signal or low-power BJT (less than 1A) or Power BJT (more than 1A).
Since the signal BJT has low load current driving capability, you can replace it with either:
1. Darlington Pair or Superbeta (super β) BJT, with β above 800, yet using low voltage and yielding large load current.
2. Power BJT, with larger load current (not using Darlington Pair. It is a transistor designed to handle high current and high voltage)
If your design doesn't handle more than 5V or 9V, I don't advise you to use Power BJT.
MOSFET
No β needed to calculate. No gate resistor needed.
You only need to use a microcontroller to have it's output port pin to switch logic high '1' or low '0' above or below the MOSFET's threshold voltage Vth to turn it on or off respectively.
If the MOSFET is turned on, it will pass current from the supply rail down to the load.
You can use a PMOS or NMOS, -ve Vth (-1V) and +Vth (+1V) respectively, in many MOSFETs sold in the market. Some comes with Vth above 5V or even 20V but those are high power Power MOSFETs.
All MOSFETs work the same way. Use an input voltage Vgs switching > or < Vth to turn the MOSFET on or off.
WARNING!
Always check if you need to place heatsink, protection diode and limiting resistor specified in the datasheets.
All datasheets usually come with recommended application reference. Read them carefully if you are not sure.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
