0.05R resistance in emitter of a darlington transistor?

[steve_rb]

darlington emitter design

I have a bridge circuit and it has 4 legs having a darlington (MJ10016) transistor connected with a 2N6079 and MJE210 in each leg. There is also one 0.05 ohm resistor connected to the emitter of each darlington transistors. My questions are:

1. What is the purpose of such a low ohm resistor in the darlington emitter?

2. If the darlington and the other two transistors in the leg burn due to overload (for example darlington explodes and a hole opens on the darlington's colector), what will happen to this 0.05 ohm resistor? Will it be shorted (zero resistance) or disconnected (infinite resistance) or it may not damage at all?

Regards

 

[A.Anand Srinivasan]

please post the circuit diagram... also give the supply and other constraints....

most resistors of such low values come with a power rating and it would be better if you can specify that....

 

[John Miles KE5FX]

If this were a linear circuit, I'd say the resistor helps to guard against thermal imbalance (current hogging). As the transistor gets hot and its beta increases, its C-E current will increase accordingly, resulting in more voltage drop across the emitter resistor in that leg of the bridge. The change in the transistor's bias point would tend to counteract the increase in beta.

However, since this is a (presumably) on-off bridge where the transistors won't be running in their linear regions anyway, I'm not sure what the resistors would be there for.

Resistors fail by opening the circuit, so the resistors may just be a simple fusing scheme.

 

[necolei]

I have a bridge circuit and it has 4 legs having a darlington (MJ10016) transistor connected with a 2N6079 and MJE210 in each leg. There is also one 0.05 ohm resistor connected to the emitter of each darlington transistors. My questions are:

1. What is the purpose of such a low ohm resistor in the darlington emitter?

2. If the darlington and the other two transistors in the leg burn due to overload (for example darlington explodes and a hole opens on the darlington's colector), what will happen to this 0.05 ohm resistor? Will it be shorted (zero resistance) or disconnected (infinite resistance) or it may not damage at all?

Regards

resistors are there to limit and supply current for trnsistor. searching the net for H bridge circuit, I got an idea of building my own H bridge using a ULN2003 IC. It has three H bridge circuits and can drive three DC motor simultaneously, bi-directional. If you want the schematic just e-mail me. necoleis@yahoo.com