calculating voltages made easy

[walters]

When looking at schematics of bias resistors of transistor stages how do u find out the voltages for each "node"?

Whats the easiest way to find out the voltages for each NODE in any stage or section of a circuit or schematic?

Most Schematics don't tell what the voltages are at each stage/section or node/point of a circuit

What would do the easiest way to find out or get these voltages?

What shortcut formulas or tech experience to find out "voltage drops" for bias resistors of transistor stages?


RULES:

1.) The collector bias resistor voltage should be "HALF" of the power supply voltage?
2.) The Base bias resistor voltage should be a 3/4 of the power supply voltage?
3.) The emitter bias resistor voltage should be 1/4 of the power supply voltage?

 

[penoy_balut]

Ohm's law helps,
VBE voltage of silicon transistors is about 0.7, based on this you can find BE current to be multiplied by HFE to find collector current

 

[walters]

1.) How do u use Ohms law to find the voltages for each node for these circuit?

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Added after 5 minutes:

1.) How do u use Ohms law to find the voltages for each node for these circuit?

https://www.drtube.com/schematics/fender/bassman-5f6-a-schematic.gif

https://lib.store.yahoo.net/lib/thetubestore/harvard6g10.gif

https://lib.store.yahoo.net/lib/thetubestore/twin5f8-a.gif

 

[nguyennam]

No, you cannot use Ohm's law in a circuit with p-n junction.

 

[walters]

((No, you cannot use Ohm's law in a circuit with p-n junction.))

1.) Why can't i use ohms law with a P-N junction?

 

[penoy_balut]

i thought those junctions are treated as a black box then Ohm's Law apply:|:|

 

[walters]

thats what i thought too but i guess u can't use ohm's law with transitors

 

[VSMVDD]

ohms law is a measure of resistance to the flow of current at a given voltage
transistors are gain devices and are very different from just one resistor

so you need to use many calculations and there compression forms of them to extract the data and its not a matter of resistance over current
except to the dc transistors supply points...
when its not amplifying as usual {ie no input}

bias is a matter also of gain and comes under the first set of rules
unless its dc bias your talking about
it which case its the voltage differance between gates that matters

but dc bias is also caused and used by rf/af rectification across a gate
so dc is formed leeding to bias....class c and this is the other statements

so gain is split into classes as per how its dirived

 

[e_eja]

depend, if you try to analize transistor as amplifier you should model it then aply KCL and KVL
if you would analize transistor as switch then you may aplly ohm's law