How to properly use a TIP47G transistor as a switch for larger currents?

[David lopez]

has anybody used a tip47g transistor? i can't get it to act as switch for a larger current. i have tried reading the datasheet. the datasheet won't work.

 

[phinds]

has anybody used a tip47g transistor? i can't get it to act as switch for a larger current. i have tried reading the datasheet. the datasheet won't work.

What does "the datasheet won't work" mean? Is it on strike? They usually just lay there and let you look at them.

The point of my sarcasm is that you really need to be a bit more specific.

 

[Baluncore]

The middle pin is electrically connected to the heatsink, so you may need an insulated mounting on the heatsink or chassis.

Drag and drop the circuit diagram you are using onto your next post.

 

[David lopez]

pin 1 is the gate according to the datasheet. current is suppose to flow into pin 3 and out pin 2. but i have been
unable to get current to flow into pin 3 and out pin 2. current flow into pin 2 or pin 3 and out pin 1, but then the
transistor won't act as a switch. there is no signal turning the transistor on or off.

 

[DaveE]

Trust me, the data sheet does work for this sort of device. It is basically telling you what sort of stresses the device will tolerate plus very basic performance metrics in specific test circuits. This is a very typical bipolar junction power transistor (BJT), so you can look at web sources for BJT applications and apply it to this device (within reason, of course).

Your comment that "pin 1 is the gate" leads me to suspect that you aren't familiar with the differences between FETs and BJTs. My apologies if I am reading too much into this comment, but experienced EEs rarely interchange "base" and "gate". They act very differently in practice. If true you just need to study the different types of transistor a bit more.

The most likely issues here are:
1) You haven't actually built the circuit you intended, something is wrong with you implementation.
2) You don't really understand BJTs and/or the circuit design necessary to implement you desired function.
3) Your specific device is broken.

Note, in my experience it is hardly ever the last one (3), but that is what people always try to fix first. Then if it is a bad part, it is probably your circuit that broke it, and it will also break the replacement.

Perhaps you should try building a very simple test circuit, which will allow you to either test parts or learn more about how BJTs work. Perhaps start by learning how to test a BJT with an DMM (or two). When you are confused by a circuit, step 1 is to simplify the problem.

 

[David lopez]

so how to create a circuit, where base receives input from arduino uno, and then turns on allowing a larger
voltage or current to flow through? i have 8 tip47G transistors. i have tried using a different tip47G. that didn't
work. so what would be the right implementation?

 

[davenn]

so how to create a circuit, where base receives input from arduino uno, and then turns on allowing a larger
voltage or current to flow through?

You were asked, several posts ago, to provide your circuit diagram
and as with most of your threads you don't do as asked...
If you want good help, you need to show us what you are doing to we all can figure out if you have made a mistake

Please post your circuit

 

[Baluncore]

so what would be the right implementation?

The TIP47 is an NPN bipolar transistor with a base, not a MOSFET transistor with a gate.
The circuit you need to use will depend on the load the tip47 is driving.
You have not yet identified the load or the supply voltage.

 

[David lopez]

if i use this circuit the diode won't light up.

if i use this circuit the diode will light up.

is this normal? i don't know if this is normal.

i am using a led as a load and the battery voltage is 3.7 to 4.1 volts.

 

[berkeman]

Try this:

https://i.stack.imgur.com/70rGQ.png

 

[phyzguy]

if i use this circuit the diode won't light up.

if i use this circuit the diode will light up.is this normal? i don't know if this is normal.

i am using a led as a load and the battery voltage is 3.7 to 4.1 volts.

Very normal. In your first circuit you are trying to flow current backwards through the LED. No current flows, so it doesn't light up.

 

[David lopez]

in my first circuit i connected the positive lead to the positive terminal and connected the negative terminal to
the transistor's collector. is this still normal?

 

[dlgoff]

in my first circuit i connected the positive lead to the positive terminal and connected the negative terminal to
the transistor's collector. is this still normal?

No. As @phyzguy said:

In your first circuit you are trying to flow current backwards through the LED.

 

[David lopez]

so my first circuit cannot work?

 

[phyzguy]

so my first circuit cannot work?

That is correct. Just look at the arrows. In the top circuit, the current through the transistor is flowing from bottom to top, in the direction of the arrow on the emitter. So it will attempt to drive current from right to left through the LED, which it can't do.

 

[David lopez]

actually i connect the positive lead of the led to the positive terminal and the negative lead of the led to the
transistor's collector. i didn't know the rear of the arrow symbot was the positive terminal and the front of the arrow
was the negative terminal. but my first circuit still won't work?

 

[berkeman]

actually i connect the positive lead of the led to the positive terminal and the negative lead of the led to the
transistor's collector. i didn't know the rear of the arrow symbot was the positive terminal and the front of the arrow
was the negative terminal. but my first circuit still won't work?

We generally don't use the words "positive terminal" and "negative terminal" when talking about LEDs or other diodes. We use "Anode" and "Cathode" to be less ambiguous. For LEDs, current flows from Anode to Cathode.

https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/diode-diode12.gif

 

[David lopez]

when i try the first circuit, the anode of the led is connected to positive terminal and the cathode of led is connected to the transistor's collector. the led still won't light up. the led cannot light up?

 

[phyzguy]

when i try the first circuit, the anode of the led is connected to positive terminal and the cathode of led is connected to the transistor's collector. the led still won't light up. the led cannot light up?

Show us a diagram of your new configuration.

 

[David lopez]

this is the configuration i am using.

the led won't light up if i use this configuration.

 

[phyzguy]

I would expect it to light up in this configuration. You may have fried the BJT. You really should have a resistor in place to limit the base current, like @berkeman showed in post #10. You could try measuring the current flowing in each leg of the circuit.

 

[davenn]

the led won't light up if i use this configuration.

I would expect it to light up in this configuration. You may have fried the BJT. You really should have a resistor in place to limit the base current,

agreed, but without that base resistor as @phyzguy said, the transistor may have been damaged
due to the excessive current flow through the base to emitter
What is the transistor "model/type" ?

 

[NTL2009]

agreed, but without that base resistor as @phyzguy said, the transistor may have been damaged
due to the excessive current flow through the base to emitter
What is the transistor "model/type" ?

Even if it is not damaged, the base-emitter junction would clamp the battery voltage below the voltage required to turn on the LED. It needs a base resistor as shown/discussed above.