Why the resistor across the positive to collector?

[Bluepoint SEO]

Hi can someone explain why you often have a resistor across the collector of a transistor? What does it do? I'm thinking power out then because there's a resistor there the power takes the easy route and goes to the main load? Currently I'm blogging about all the stuff I'm learning so your answers will be much appreciated and quoted/referenced. Thank you.

 

[Minder]

I believe you mean a resistor from positive to collector, If a NPN this will connect the transistor to positive and provide a load for the collector in order for the E-C to conduct.
Often a 'pull up' resistor is needed where the load the transistor is connected to cannot provide this current sufficient for the transistor to conduct..IOW a high impedance load.
M.

 

[Bluepoint SEO]

Okay it's starting to settle in my mind thank you.

 

[Minder]

Another example, Many transducers are supplied with open collector output, and if they are connected to something such as a μprocessor that has high impedance input, then a pull up resistor is required.
M.

 

[Bluepoint SEO]

I have heard of these pull ups in other posts - also with ICs isn't it a need to put diodes after outputs? Also, what is a transducer? Trans means across ducer is something that makes orange juice :-D

 

[Minder]

Transducer: a device for converting a physical entity into an electrical signal, i.e. thermocouple, hall sensor, Light dependant resistor, etc.
Your ear buds or head phones are transducers in reverse of these.
The diode on output is across any inductive device in order to supress the BEMF that occurs when the device turns off.
M.

 

[Bluepoint SEO]

Mr. Minder BEMF? Back Energy Mine Field?

 

[Minder]

If in doubt Google, Google, Google.!! Back Electro Motive Force.
An inductance when powered creates a magnetic field, when the voltage goes to zero, the field collapses and induces an high voltage in the opposite polarity to the one applied.
Think coil on your car. How does it get 20kv from 12v.?
M.

 

[Bluepoint SEO]

If in doubt Google, Google, Google.!! Back Electro Motive Force.
An inductance when powered creates a magnetic field, when the voltage goes to zero, the field collapses and induces an high voltage in the opposite polarity to the one applied.
Think coil on your car. How does it get 20kv from 12v.?
M.

Hehe I don't drive I failed my test twice however I know from tank circuits about the voltage swapping polarity between a capacitor and an induction coil. I do love Google and even spoke to Matt Cutts once on Twitter but the truth is there's no real engagement like speaking to a human being! just tell me to sod off ha

 

[Minder]

Would I do that to a Welshman?
M.