Can a Diode Protect a Transistor from High Voltage?

In summary, if the transistor is saturated, it is unlikely to have a high voltage across it. To protect it from high voltage, you would use a Zener diode.
  • #1
manshuk89
7
0
i want to protect my transistor(working in saturation) from high incoming voltage...
can a diode be used to protect it from the high voltage?
 
Engineering news on Phys.org
  • #2
manshuk89 said:
i want to protect my transistor(working in saturation) from high incoming voltage...
can a diode be used to protect it from the high voltage?

It would help to have more information. Normally you would use a Zener diode (reverse biased) as a uni-directional transient supressor, but there are other options available as well.
 
  • #3
Yes - a circuit would help.If a transistor is saturated, it is unlikely to have a high voltage across it! You'd expect less than 1V.
 
  • #4
Well, if it's really always saturated why not be done with and replace it with a wire? Seriously though, as others have said we need more information. What is the circuit, what does it do?

If you are actually referring to protecting the device when it is OFF, or in the process of turning off, that's another matter. Properly chosen protection devices (TVSs etc.) can often safely absorb more energy from such things as switching transients. Note however that these things are no substitute for transistors with adequate voltage ratings.

In fact, it may be necessary to use a higher voltage transistor than might otherwise seem to be necessary, in order to be sure that the protector absorbs the energy without the transistor avalanching. Some otherwise excellent protection devices have (in my opinion) surprisingly vague voltage ratings.
 
  • #5
further information:-
the transistor is being used to control an electronic lock.the device switches between cut off and saturated region.
the collector is connected to a lock which is further connected to 12 volt dc.
when there is no current on base the transistor is in cut off- infinite impedence.
it can be said that the lock is being used as a relay. wen the microcontroller provides 5 volt at the base , the transistor goes into saturation and conducts.
the lock requires 12vdc and 3A CURRENT to operate.
how to protect the transistors against such ratings?
 
  • #6
So you want to protect against transients when yo try to turn off an inductive load.
One way to do it is to put the diode across the load (in parallel with the lock) but 'upside down', so it is reverse biased, normally and will take no current. When the transistor 'tries' to turn off (reducing the current) a voltage spike will occur, due to the inductance, which would take the collector volts way above Vcc (positive). The diode will stop this happening by shorting out the inductance when its volts are above Vcc. As long as the transistor will survive Vcc, it will not be harmed.
 

1. What is the purpose of a diode in protecting a transistor?

A diode is used to protect a transistor by preventing reverse current flow. When a transistor is turned off, there is still a small amount of current that can flow in the reverse direction. This can damage the transistor, but a diode placed in the circuit will only allow current to flow in the forward direction, protecting the transistor from potential damage.

2. How does a diode protect a transistor from reverse current flow?

A diode is a semiconductor device that only allows current to flow in one direction. When placed in series with a transistor, the diode will only allow current to flow from the anode to the cathode, preventing any reverse current from reaching the transistor.

3. Can any type of diode be used to protect a transistor?

Yes, any type of diode can be used to protect a transistor as long as it is connected in the correct orientation. However, Schottky diodes are often preferred due to their low forward voltage drop and fast switching times.

4. Where should a diode be placed in a circuit to protect a transistor?

A diode should be placed in series with the transistor, with the anode connected to the collector or drain of the transistor and the cathode connected to the positive voltage supply. This placement ensures that any reverse current is blocked from reaching the transistor.

5. Can a diode protect a transistor from all types of damage?

No, a diode can only protect a transistor from reverse current flow. Other forms of damage, such as overvoltage or overcurrent, may require additional protection measures. It is important to analyze the specific circuit and potential hazards to determine the most effective protection methods.

Similar threads

Replies
68
Views
3K
Replies
10
Views
1K
Replies
6
Views
812
Replies
11
Views
2K
Replies
10
Views
939
  • Electrical Engineering
Replies
13
Views
3K
  • Electrical Engineering
Replies
7
Views
915
  • Electrical Engineering
Replies
3
Views
755
Replies
5
Views
2K
Replies
42
Views
2K
Back
Top