transistor selection question

Thread Starter

Alez87

Joined Sep 12, 2019
7
Hi,

I have a standard 2N4401 transistor.

a low voltage input on the Base pin.
Emitter pin to ground.
and a 15~20V input on the Collector pin with a load.

I have a 500mA draw from this circuit.

upon removing the transistor and applying the 15~20V directly to the load, I have 2A draw.

I want as much current as possible to my load. What kind of transistor can I use?
I need a transistor that can take high voltage input
(up to 100-200V and let up to 5A pass)
 

danadak

Joined Mar 10, 2018
3,578
2N4401 is only rated for 600 mA for starters.

What is the V and I available to drive the transistor ?


Regards, Dana.
 

Thread Starter

Alez87

Joined Sep 12, 2019
7
Im using this for a over-voltage protection circuit I am making. I have a generator giving me 0-100V DC (depending how fast you pedal) and Im using a transistor to auto-shut off when the voltage exceed a certain voltage (5V-15V depending on what i will be powering atm)
but my issue is using the current transistor my load (an LED atm) is barely on, yet when my power supply gives my circuit voltage directly its light up nicely.
So i figured its my transistor the issue.

I need input 0-100V and output will be shut off (using zener diodes etc) at certain voltage but current needs to draw ndecent amounts!
 

Thread Starter

Alez87

Joined Sep 12, 2019
7
2N4401 is only rated for 600 mA for starters.

What is the V and I available to drive the transistor ?


Regards, Dana.
how can I tell that the 2N4401 is 600mA? Im looking over the data sheet and im a bit confused:

Transistor Type NPN
Voltage - Collector Emitter Breakdown (Max) 40V
Vce Saturation (Max) @ Ib, Ic 750mV @ 50mA, 500mA
Current - Collector Cutoff (Max) -
DC Current Gain (hFE) (Min) @ Ic, Vce 100 @ 150mA, 1V
Power - Max 600mW

where is the max current? is it the Vce saturation??
 

Thread Starter

Alez87

Joined Sep 12, 2019
7
Sounds like something that would work better if you used a universal input variable output SMPS on the output of the generator.
im trying to build a over voltage protection circuit that shuts off automatically during sudden spikes to protect just such a board...
 

Wolframore

Joined Jan 21, 2019
1,280
Sounds like you need a regulator. When you say you’re generating 100-200V is this from an alternator? If so is it being rectified?
 

Thread Starter

Alez87

Joined Sep 12, 2019
7
ive tried with a MOSFET but it didnt work for what I need...

the higher the mosfet input voltage, the higher the current... at 22Vdc input I have about 500mA current.
at 12Vdc I have like 250mA...

I need something that will give me 4-5A current, take in 200Vdc and switch on-off when I control it (voltage at base).

I thought of using a relay switch but they cost way too much for a 200Vdc relay switch...
 
Your circuit looks ok, I can only think you need a bigger transistor.

If using a MOSFET you should use one with a very low gate threshold.

Be sure Q2 has a low enough drop across the EC junction to ensure turning off Q1.
 

DickCappels

Joined Aug 21, 2008
5,897
You are going to need a pretty high current gain for that transistor to pass 5 amps when the input voltage is only 15.7 volts with that 6.8k resistor in the base. If you used a MOSFET instead the 6.8k would be fine. Are you starting to sense that a MOSFET would be a good choice?
 

Thread Starter

Alez87

Joined Sep 12, 2019
7
ignore the resistor values. In fact for my tests I only used 1 of the transistors, connected to my load and switched the base manually on/off.
I even tried removing the zener diode and playing with different voltages.

Every time, the current was low. I tried a few transistors I had laying around... Im thinking of using a MOSFET kuz with higher voltages the current rises.

but Im not sure which one? anyone can send me some part numbers of transistors with high current gain that kud take ~200Vdc?
or a MOSFET part number that at low voltages (15-20Vdc) can already let at least 2A in??
 
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