Well presented. Only critique would be the dismissal of the transistor emitter current not being the same as the collector. Depending on the load, the base current isn't going to be seen by the load. Basically, the R2 current will not match your LED current. The R2 will have the base current going through the R1 resistor from the opamp. If you want to perfectly calculate, you would move the LED to the emitter of Q1. With a high gain transistor, this difference will be negligible, but when running power transistors with gains around 100 you might want to compensate for the extra current.
And just to add one more note regarding the explanation of circuit operation. An op-amp is an analog device that smoothly changes its output voltage; therefore it is not appropriate to say "logic high output" which "turns on the transistor". The op-amp senses the change in its input differential voltage and instantly reacts to it by starting to change its output voltage until it restores the equilibrium.
what if the VS for the op amp VCC has lower than VCE on the BJT? do I need some circuit configuration. example like VS = 12V, and the VCE is around 80V or above
Dang it lol, I'm trying to drive an LED circuit that requires a constant current at around 2A using 48V as Vref. The calculated power dissipation for the discrete components is obviously off the charts. Is there any other constant current regulator circuit that can be used for higher current applications?
A great movie! Just to note that when there is a permanently connected load there is no need for a base resistor because the transistor itself limits the base current by increasing the emitter voltage.
Not really .... Once the load current reaches the set value , this will produce voltage across it equals the ref voltage = zener voltage this will switch of the transistor before the voltage across the load reaches Vcc so the load will never experience 14v across it
@@ThomasHaberkorn ok ... lets take it point by point you use the Zener to set the voltage you want across R2 this is your starting point if you want 5v across R2 , you buy 5.1v Zener or if you want 9v across R2 , you buy 9.1v Zener at zero second , there is no voltage of current across R2 once the supply starts , the transistor is ON and the voltage across R2 starts to build up to reach VCC but .... before that happens , once R2 Voltage reaches Vzener , the transistor will switch off so the current will drop once it drops , the transistor will switch on again and so on Why R3 ? it is to limit the Zener Reverse Current within an acceptable value ... otherwise it will burn , just like you do with an LED you put R3 in order to keep the Zener reverse current between 1 and 10ma , usually 5ma so if your supply voltage is 12v , R3 = 12(v) / 0.005(A) = 2400 Ohms (2.4k)
Hello, i followed all of your videos about current limiting circuits but all have the disadvantage of not being able to control high current. For 10Amps , which one do you recommand ? Thanks !
hi bhai, i have 24 votlage solenoid, if check the voltage near solenoide it is showing 24v, and if i check current it is varying from 0 - 650 mV, the coil is mounted on the hydraulic jack which is controlling the speed of jack, and the coil is being controlled by potentiometer, how can i make the circuit to make it happen,
@@rizvanrazi4698 Of course. But my point is a solenoid is a device controlled by current. (Not voltage) Sure, they print a voltage on it because the manufacturer knows the resistance of the coil (for DC) and most electric sources are voltage sources. If your source is AC it's already different. Did you find a circuit online yet?
