Please help transistor amplifier

[michael1978]

Let me ask you this michael: How did you select the resistors in the schematic that you posted in post #42?

i think first voltage divider and after rc and re

 

[Averagesupernova]

i think first voltage divider and after rc and re

You went about it backwards. R1 and R2 are of course significant in order to get the proper base voltage but they are also important to determine input impedance. So their values need to be kept in mind for this. A low output impedance will reflect way back to a lower input impedance. The amplifier Jony posted has a Zin of about 1000 ohms. Can you tell why a single stage amplifier with the gain and Zout that you want cannot have a Zin of 50K?

 

[michael1978]

You went about it backwards. R1 and R2 are of course significant in order to get the proper base voltage but they are also important to determine input impedance. So their values need to be kept in mind for this. A low output impedance will reflect way back to a lower input impedance. The amplifier Jony posted has a Zin of about 1000 ohms. Can you tell why a single stage amplifier with the gain and Zout that you want cannot have a Zin of 50K?

ooo man i don't know how to deterimine zin and zout ;-) how do you select zin and zout, i am just a begginer, is zin R1 and R2 and zout rc and rl, if is yes, how you determine how you select calculate

 

[Averagesupernova]

Collector resistor is Zout.
Zin is R1||R2||(beta*Re). In the schematic that Jony posted Re becomes Re1||Re2.

 

[Jony130]

so this is the steps if i need to build an amplifier thnx
gain rc//rl/re, but i see there in resistor in serie with capacitor
how come now gain RC//RL/RE2+RE1 am i correct, if not can you tell me
i don't get gain of 50

Simply voltage gain of a CE amplifier is always equal to

Av = ( resistance seen from collector toward the output) / (re + (resistance seen from emitter to gnd)

So we have

Av = (Rc||RL)/ ( re + Re1||Re2) = 909Ω/( 6.5Ω + 220Ω||12Ω ) ≈ 909/18.5Ω = 49.13[V/V]

Zin = R1||R2||( Hfe+1 *(re+Re1||Re2) ) = 25KΩ||( 421 * 18.5Ω) = 25K||7.8KΩ = 5.9KΩ
And
Zout ≈ Rc ≈ 1KΩ

 

[michael1978]

Simply voltage gain of a CE amplifier is always equal to

Av = ( resistance seen from collector toward the output) / (re + (resistance seen from emitter to gnd)

So we have

Av = (Rc||RL)/ ( re + Re1||Re2) = 909Ω/( 6.5Ω + 220Ω||12Ω ) ≈ 909/18.5Ω = 49.13[V/V]

Zin = R1||R2||( Hfe+1 *(re+Re1||Re2) ) = 25KΩ||( 421 * 18.5Ω) = 25K||7.8KΩ = 5.9KΩ
And
Zout ≈ Rc ≈ 1KΩ

thank you,
you show me a good example
but i have one more question, if somebody want to desigin a amplifier, they do it like your example, of another design, i mean for ce claas a amplifier
one more time thnx for good example

 

[michael1978]

Collector resistor is Zout.
Zin is R1||R2||(beta*Re). In the schematic that Jony posted Re becomes Re1||Re2.

yes he show me a good example, but is so much important zin and zout in amplifier,
did you show jony example, this steps i have to take all time if i design an amplifier
thnx for answer

 

[michael1978]

so this is the steps if i need to build an amplifier thnx
gain rc//rl/re, but i see there in resistor in serie with capacitor
how come now gain RC//RL/RE2+RE1 am i correct, if not can you tell me
i don't get gain of 50

jony i start to look at you amplifier,
but i don't understand this ( re + (re1||re2) ) = (rc|| rl) / 70 = 909Ω/50 = 18Ω

where did you take 70? 909?50? can you explain me please...

 

[Jony130]

jony i start to look at you amplifier,
but i don't understand this ( re + (re1||re2) ) = (rc|| rl) / 70 = 909Ω/50 = 18Ω

where did you take 70? 909?50? can you explain me please...

There is a error instead-of 70 it should be 50. The voltage gain we want is equal to 50[V/V].
OE amplifier voltage gain is equal to
Av = Rc/re so to find desired re value I use this equation:

re = Rc/Av

And in my example the gain I want is equal to 50[V/V] and Rc = 1K; RL = 10K
So form this

Rc||RL = 909Ω

re = Rc||RL/Av = (1K||10K)/50 = 909Ω/50 = 18Ω

It is clear now ?

 

[michael1978]

There is a error instead-of 70 it should be 50. The voltage gain we want is equal to 50[V/V].
OE amplifier voltage gain is equal to
Av = Rc/re so to find desired re value I use this equation:

re = Rc/Av

And in my example the gain I want is equal to 50[V/V] and Rc = 1K; RL = 10K
So form this

Rc||RL = 909Ω

re = Rc||RL/Av = (1K||10K)/50 = 909Ω/50 = 18Ω

It is clear now ?

yes thank you

 

[michael1978]

Collector resistor is Zout.
Zin is R1||R2||(beta*Re). In the schematic that Jony posted Re becomes Re1||Re2.

is so important to know resitance zin and zout, i am a begginer, how do you select zin zout is easy zout=RC but zin? you select, but zin how do you select

 

[michael1978]

yes thank you

oo joney sorry i have to ask you this
is this correct re2 = ( 220 * 11.5 ) / (220 - 12.5) = 12.1 = 12Ω.
of this one re2 = ( 220 * 11.5 ) / (220 - 11.5) = 12.1 = 12Ω.

 

[Averagesupernova]

Michael, are you asking why Zin and Zout are important to know?

 

[Jony130]

of this one re2 = ( 220 * 11.5 ) / (220 - 11.5) = 12.1 = 12Ω.

This one is correct of course.

 

[michael1978]

This one is correct of course.

jony can i ask you something, is possible for you to make one another amplifier but without Re2, with gain av 50, i know you maket very good the one, i understand all, but how to make without re2, you can select self the value but desired voltage to be 50, can you do it the same as in first example , if you want thank you PLEASE

 

[Jony130]

OK
Av = Rc/re = gm*Rc = Ic/26mV*Rc = (Ic*Rc)/26mV

50[V/V] = (Ic*Rc)/26mV

from this

(Ic*Rc) = 1.3

I choose Rc = 1K

So

Ic = 1.3/1K = 1.3mA

But as you can see this approach is not very good because give as low voltage swing.

We need to use Re1 or use a different type of a circuit. But lest as add Re1 resistor.
Now Av = Rc/(re+Re1)

And for Rc = 1K we can use this

Ic = 0.5Vcc/Rc = 5V/1K = 5mA

So re = 26mV/5mA = 5.2Ω

And

Re1 = Rc/Av - re = 1K/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

This circuit is also not very good because low Re1 means that Hfe spread and temperature change will have significant impact on bias point stability. This is why I use Ve = 1V and add Re2 to reduce the voltage gain to 50[V/V]

 

[michael1978]

ok
av = rc/re = gm*rc = ic/26mv*rc = (ic*rc)/26mv

50[v/v] = (ic*rc)/26mv

from this

(ic*rc) = 1.3

i choose rc = 1k

so

ic = 1.3/1k = 1.3ma

but as you can see this approach is not very good because give as low voltage swing.

We need to use re1 or use a different type of a circuit. But lest as add re1 resistor.
Now av = rc/(re+re1)

and for rc = 1k we can use this

ic = 0.5vcc/rc = 5v/1k = 5ma

so re = 26mv/5ma = 5.2Ω

and

re1 = rc/av - re = 1k/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

this circuit is also not very good because low re1 means that hfe spread and temperature change will have significant impact on bias point stability. This is why i use ve = 1v and add re2 to reduce the voltage gain to 50[v/v]

thank you very much

 

[Jony130]

Also we can split Re resistor with a capacitor. And use Re1 = 14Ω and Re2 = Ve/Ic - re1 = 1V/5mA - 14Ω ≈ 180Ω

And now we can select R1 and R2

Vb = Ve + Vbe = Ic*(Re1+Re2)+ Vbe = 5mA* (180 + 14) + 0.65V = 1.62V

If we assume Hfe = 150

Ib = Ic/hfe = 5mA/150 = 34μA

R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R2 = Vb/(10*Ib) = 4.7KΩ

 

[michael1978]

OK
Av = Rc/re = gm*Rc = Ic/26mV*Rc = (Ic*Rc)/26mV

50[V/V] = (Ic*Rc)/26mV

from this

(Ic*Rc) = 1.3

I choose Rc = 1K

So

Ic = 1.3/1K = 1.3mA

But as you can see this approach is not very good because give as low voltage swing.

We need to use Re1 or use a different type of a circuit. But lest as add Re1 resistor.
Now Av = Rc/(re+Re1)

And for Rc = 1K we can use this

Ic = 0.5Vcc/Rc = 5V/1K = 5mA

So re = 26mV/5mA = 5.2Ω

And

Re1 = Rc/Av - re = 1K/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

This circuit is also not very good because low Re1 means that Hfe spread and temperature change will have significant impact on bias point stability. This is why I use Ve = 1V and add Re2 to reduce the voltage gain to 50[V/V]

AND value of r1 and r2 is r1=22k, and r2=4.7K and power supply 10V

 

[Jony130]

AND value of r1 and r2 is r1=22k, and r2=4.7K and power supply 10V

Yes for Vcc = 10V and hfe = 150

 

[michael1978]

Yes for Vcc = 10V and hfe = 150

THIS is the same example without re2, but you add in serie re2
i mean this laste circuit, and the first example without R2 has the same value value of r1 and r2 is r1=22k, and r2=4.7K and power supply 10V ,
and this is correct R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

of this R1 = (Vcc - Vb)/( 10*Ib) = 22KΩ


---
OK
Av = Rc/re = gm*Rc = Ic/26mV*Rc = (Ic*Rc)/26mV

50[V/V] = (Ic*Rc)/26mV

from this

(Ic*Rc) = 1.3

I choose Rc = 1K

So

Ic = 1.3/1K = 1.3mA

But as you can see this approach is not very good because give as low voltage swing.

We need to use Re1 or use a different type of a circuit. But lest as add Re1 resistor.
Now Av = Rc/(re+Re1)

And for Rc = 1K we can use this

Ic = 0.5Vcc/Rc = 5V/1K = 5mA

So re = 26mV/5mA = 5.2Ω

And

Re1 = Rc/Av - re = 1K/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

This circuit is also not very good because low Re1 means that Hfe spread and temperature change will have significant impact on bias point stability. This is why I use Ve = 1V and add Re2 to reduce the voltage gain to 50[V/V]

thnx

 

[Jony130]

I don't understand the question?

 

[michael1978]

I don't understand the question?

you show me first this example
-----


---
OK
Av = Rc/re = gm*Rc = Ic/26mV*Rc = (Ic*Rc)/26mV

50[V/V] = (Ic*Rc)/26mV

from this

(Ic*Rc) = 1.3

I choose Rc = 1K

So

Ic = 1.3/1K = 1.3mA

But as you can see this approach is not very good because give as low voltage swing.

We need to use Re1 or use a different type of a circuit. But lest as add Re1 resistor.
Now Av = Rc/(re+Re1)

And for Rc = 1K we can use this

Ic = 0.5Vcc/Rc = 5V/1K = 5mA

So re = 26mV/5mA = 5.2Ω

And

Re1 = Rc/Av - re = 1K/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

This circuit is also not very good because low Re1 means that Hfe spread and temperature change will have significant impact on bias point stability. This is why I use Ve = 1V and add Re2 to reduce the voltage gain to 50[V/V]
----------------------

after you show the second example
Also we can split Re resistor with a capacitor. And use Re1 = 14Ω and Re2 = Ve/Ic - re1 = 1V/5mA - 14Ω ≈ 180Ω



And now we can select R1 and R2

Vb = Ve + Vbe = Ic*(Re1+Re2)+ Vbe = 5mA* (180 + 14) + 0.65V = 1.62V

If we assume Hfe = 150

Ib = Ic/hfe = 5mA/150 = 34μA

R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R2 = Vb/(10*Ib) = 4.7KΩ

-----
is this the same like in example 1 and example 2

i mean this second example, and the first example without R2 has the same value value of r1 and r2 is r1=22k, and r2=4.7K and power supply 10V ,
and is this correct R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

of this R1 = (Vcc - Vb)/( 10*Ib) = 22KΩ

do you understand you show 1 example in 2 party, first without re2 second with re2, so this one example, do you understand

 

[michael1978]

Michael, are you asking why Zin and Zout are important to know?

yes i ask you, i want to know

 

[Jony130]

This two equation holds only if Ve > 0.6V
R1 = (Vcc - Vb)/( 11*Ib)
R2 = Vb/(10*Ib)

 

[michael1978]

This two equation holds only if Ve > 0.6V
R1 = (Vcc - Vb)/( 11*Ib)
R2 = Vb/(10*Ib)

i ask you for gain av 50 without re, and you show me example
---
OK
Av = Rc/re = gm*Rc = Ic/26mV*Rc = (Ic*Rc)/26mV

50[V/V] = (Ic*Rc)/26mV

from this

(Ic*Rc) = 1.3

I choose Rc = 1K

So

Ic = 1.3/1K = 1.3mA

But as you can see this approach is not very good because give as low voltage swing.

We need to use Re1 or use a different type of a circuit. But lest as add Re1 resistor.
Now Av = Rc/(re+Re1)

And for Rc = 1K we can use this

Ic = 0.5Vcc/Rc = 5V/1K = 5mA

So re = 26mV/5mA = 5.2Ω

And

Re1 = Rc/Av - re = 1K/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

This circuit is also not very good because low Re1 means that Hfe spread and temperature change will have significant impact on bias point stability. This is why I use Ve = 1V and add Re2 to reduce the voltage gain to 50[V/V]
----------------------

Also we can split Re resistor with a capacitor. And use Re1 = 14Ω and Re2 = Ve/Ic - re1 = 1V/5mA - 14Ω ≈ 180Ω



And now we can select R1 and R2

Vb = Ve + Vbe = Ic*(Re1+Re2)+ Vbe = 5mA* (180 + 14) + 0.65V = 1.62V

If we assume Hfe = 150

Ib = Ic/hfe = 5mA/150 = 34μA

R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R2 = Vb/(10*Ib) = 4.7KΩ

-----
ah joney i make you tired, is possibe to write me in one party not separate all this here, like in first example with re2, you explain me very good, but this is not in one party , i can understand better PLEASE

 

[Jony130]

OK

For this diagram the voltage gain is equal to

Av ≈ Rc/(re+Re1)

Rc = 0.1*RL = 0.1*10K = 1K

And for Rc = 1K we can use this

Ic = 0.5Vcc/Rc = 5V/1K = 5mA

So re = 26mV/5mA = 5.2Ω

And

Re1 = Rc/Av - re = 1K/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

This circuit is not very good because low Re1 means that Hfe spread and temperature change will have significant impact on the bias point stability. This is why I use Ve = 1V for good bias stability.
To overcome this problem of a low value for Re1 = 14Ω and Ve = 70mV (Ve = Re1 *Ic = 5mA*14Ω = 70mV).
I add anther Re resistor in series with Re1.
Now we have

Ve = Ic * Re1+Re2 and we want Ve = 1V so

Re2 = Ve/Ic - Re1 = 1V/5mA - 14Ω ≈ 180Ω

And now we can select R1 and R2

Vb = Ve + Vbe = Ic*(Re1+Re2)+ Vbe = 5mA* (180 + 14) + 0.65V = 1.62V

If we assume Hfe = 150

Ib = Ic/hfe = 5mA/150 = 34μA

R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R2 = Vb/(10*Ib) = 4.7KΩ

And I use C2 capacitor to "remove" Re2 from gain equation for AC signal.

Av = Rc||RL/(re + Re1)

 

[michael1978]

OK

For this diagram the voltage gain is equal to

Av ≈ Rc/(re+Re1)

Rc = 0.1*RL = 0.1*10K = 1K

And for Rc = 1K we can use this

Ic = 0.5Vcc/Rc = 5V/1K = 5mA

So re = 26mV/5mA = 5.2Ω

And

Re1 = Rc/Av - re = 1K/50 - 5.2Ω = 20 - 5.2Ω = 14Ω

This circuit is not very good because low Re1 means that Hfe spread and temperature change will have significant impact on the bias point stability. This is why I use Ve = 1V for good bias stability.
To overcome this problem of a low value for Re1 = 14Ω and Ve = 70mV (Ve = Re1 *Ic = 5mA*14Ω = 70mV).
I add anther Re resistor in series with Re1.
Now we have

Ve = Ic * Re1+Re2 and we want Ve = 1V so

Re2 = Ve/Ic - Re1 = 1V/5mA - 14Ω ≈ 180Ω

And now we can select R1 and R2

Vb = Ve + Vbe = Ic*(Re1+Re2)+ Vbe = 5mA* (180 + 14) + 0.65V = 1.62V

If we assume Hfe = 150

Ib = Ic/hfe = 5mA/150 = 34μA

R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R2 = Vb/(10*Ib) = 4.7KΩ

And I use C2 capacitor to "remove" Re2 from gain equation for AC signal.

Av = Rc||RL/(re + Re1)

JONEY THANK YOU, i understand everything, just this one no

R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ, where come 11, how come this 11 can you explain me thnx

 

[Jony130]

First think first.
The one of the methods to become independent of hfe changes is to select voltage divider resistor (R1 and R2) in such a way that base current don't load our voltage divider to much. The maximum base current is equal to Ib_max = Ic/Hfe_min where Hfe_min is a minimum value for Hfe in data sheet.
And we select voltage divider current so that I_divader > Ib_max
In our example voltage divider current is I2 current .

But as you can see the current that flows through R1 resistor is equal to divider current plus base current.
Additional if we assume that divider current is ten times greater than base current.

I2 = 10 * Ib

the R1 resistor current I1 becomes

I1 = I2 + Ib = 10*Ib + Ib = 11*Ib

And this is why
R1 = (Vcc - Vb) / (10*Ib + Ib) = (Vcc - Vb)/(11*IB)
and
R2 = Vb/(10*Ib)

 

[michael1978]

First think first.
The one of the methods to become independent of hfe changes is to select voltage divider resistor (R1 and R2) in such a way that base current don't load our voltage divider to much. The maximum base current is equal to Ib_max = Ic/Hfe_min where Hfe_min is a minimum value for Hfe in data sheet.
And we select voltage divider current so that I_divader > Ib_max
In our example voltage divider current is I2 current .

But as you can see the current that flows through R1 resistor is equal to divider current plus base current.
Additional if we assume that divider current is ten times greater than base current.

I2 = 10 * Ib

the R1 resistor current I1 becomes

I1 = I2 + Ib = 10*Ib + Ib = 11*Ib

And this is why
R1 = (Vcc - Vb) / (10*Ib + Ib) = (Vcc - Vb)/(11*IB)
and
R2 = Vb/(10*Ib)

this is a bit difficult to me, and how much is ib to your example, can you explain in similary way because i find difficult, sorry joney i try to understand but is difficult, ah value of ib is 1 is correct

 

[michael1978]

this is a bit difficult to me, and how much is ib to your example, can you explain in similary way because i find difficult, sorry joney i try to understand but is difficult, ah value of ib is 1 is correct

joney please can you explain this, i know you explain to me but i don't understond, this 11 and the value of ib HOW YOU CALCULATE 11AND IB PLEASE joney you help a lot to design amplifier. i am simple an beginner

------------------
ib is 0,034
johy this i know R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R1 = (Vcc - Vb) / (10*Ib + Ib) = (Vcc - Vb)/(11*IB)

(10*Ib + Ib) IS (10*IB(0.034)+0.034)=(0.34*IB)

but 11 i don't know can you explain me please CAN YOU ANSWER ME

 

[michael1978]

joney please can you explain this, i know you explain to me but i don't understond, this 11 and the value of ib HOW YOU CALCULATE 11AND IB PLEASE joney you help a lot to design amplifier. i am simple an beginner

------------------
ib is 0,034
johy this i know R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R1 = (Vcc - Vb) / (10*Ib + Ib) = (Vcc - Vb)/(11*IB)

(10*Ib + Ib) IS (10*IB(0.034)+0.034)=(0.34*IB)

but 11 i don't know can you explain me, can you show me another example of ths 11 please CAN YOU ANSWER ME

?

 

[Jony130]

Do you understand first kirchhoffs law ?
Do you know how loaded voltage divider work?

 

[michael1978]

Do you understand first kirchhoffs law ?
Do you know how loaded voltage divider work?

joney i know i think

and i do like i see in some book voltage divider like this

for example we need base current of 50MICRO
AND base voltage of 1.7V so now
for example if is 10vcc

r2 1.7v base/50micro is come 34ohm
r1 must have 8.3V/50MICRO is come 166ohm
so 10VCC/200=5MICRO
so the current in serie is the same, maybe i do somewhere mistake

i am curios to know your calculation how you get 10 and 11 in voltage divider, this is something new to me, but can you show another with example so i can understand, you show also the first example with gain of 50 do you rembember also there i see
R2 = Vb / ( 5 * Ib) = 30K

R1 = ( Vcc - Vb) / ( 6 * Ib) = 150KΩ

wher how you get 5 and 6, and second example r2 10 and r1 11, can you show me example just one the second i find self, i know you can do it, just with example in some easy way please joney i whait yesterday all day message from you, because i want to learn it, and i learn good how to select desired voltage and i am happy, but this no
R1 = (Vcc - Vb)/( 11*Ib) = 22KΩ

R2 = Vb/(10*Ib) = 4.7KΩ

valu of 11 and 10
joney plase show me example in easy way so i can understand thnx for reply...

 

[Jony130]

joney i know i think

and i do like i see in some book voltage divider like this

for example we need base current of 50MICRO
AND base voltage of 1.7V so now
for example if is 10vcc
r2 1.7v base/50micro is come 34ohm
r1 must have 8.3V/50MICRO is come 166ohm
so 10VCC/200=5MICRO
so the current in serie is the same, maybe i do somewhere mistake

Simply you forget about base current which loads the voltage divider in your calculations.

So to reduce this loading effect on output voltage we need increase the current that is flow through voltage divider or output current should be a small fraction of the voltage divider current.
So when we design voltage divider we assume that voltage divider current is larger then the load current.
Normally Divider current is 5 to 30 times larger then the load current.

So if we want 1.7V and load current is equal to 50μA and we choose voltage divider current 10 times larger then load current we have this

R2 = 1.7V/(10*Iload) = 1.7V/(10*50μ) = 1.5V/500μA = 3.4K

And from I Kirchhoff's Law we see that R1 resistor current is equal:

I_R1 = 10*Iload + Iload = 11*Iload = 550μA

So

R1 = (10V - 1.7V)/(550μ) = 15K

 

[michael1978]

Simply you forget about base current which loads the voltage divider in your calculations.

So to reduce this loading effect on output voltage we need increase the current that is flow through voltage divider or output current should be a small fraction of the voltage divider current.
So when we design voltage divider we assume that voltage divider current is larger then the load current.
Normally Divider current is 5 to 30 times larger then the load current.

So if we want 1.7V and load current is equal to 50μA and we choose voltage divider current 10 times larger then load current we have this

R2 = 1.7V/(10*Iload) = 1.7V/(10*50μ) = 1.5V/500μA = 3.4K

And from I Kirchhoff's Law we see that R1 resistor current is equal:

I_R1 = 10*Iload + Iload = 11*Iload = 550μA

So

R1 = (10V - 1.7V)/(550μ) = 15K

o sorry joney i make you tired, i understand now, so if load current is 50μ we chose voltage divider current 10 larger then the load current, and we have

R2 = 1.7V/(10*Iload) = 1.7V/((this is 10 time larger)10*50μ(base current)) = 1.5V/500μA = 3.4K this i understand

but this i don't understand
I_R1 = 10*Iload + Iload = 11*Iload = 550μA

10*Iload(50μA)+Iload(50μA)=11(how we get 11 now)*Iload(50μA)=550μA

i don't understand that 11 how we get? 10*Iload(50μA)+Iload(50μA)=0.55 not 11 sorry i don't know where i make mistake, where come this 11, i don't know how to calculate, i know 11*Iload is 550μA
thnx for answer

 

[Jony130]

Solve this pure math problem
B = 10A + A

Also from KCL we see that R1 must provide current for R2 resistor and also the current for the load.

So if Iload = 50μA and we pick voltage divider 10 times load current we have this:

I_R1 = Iload + 10 times load current = 11 times load current = 11*50μA = 550μA

 

[michael1978]

Solve this pure math problem
B = 10A + A

Also from KCL we see that R1 must provide current for R2 resistor and also the current for the load.

So if Iload = 50μA and we pick voltage divider 10 times load current we have this:

I_R1 = Iload + 10 times load current = 11 times load current = 11*50μA = 550μA

i am with calculator in my hand, i make mistake with my calculator but i don't understand i do it 0.050+10*0.050=0.55 how to do it ? CAN YOU TELL ME PLEASE HOW TO CALCULATE WITH CALCULATOR,

 

[michael1978]

Can you tell me how to calculate with calculator joney

 

[Jony130]

LoL
Use Google
https://www.google.pl/search?q=0.05...illa:pl:official&client=firefox-a&channel=rcs

 

[michael1978]

lol
use google
https://www.google.pl/search?q=0.05...illa:pl:official&client=firefox-a&channel=rcs

haha i rely don't find i find one like min 0.050+10*0.050=0.55, joney were i make now mistake, with my calculator pfff i am shame

JONEY can you tell me please how to calculate in my calculator please

 

[michael1978]

Joney i know you know how to do it with calculator, can you tell me because i have in my hand calculator, i can find nothing in google the same result please...

 

[Jony130]

Simply use your brain instead of a calculator.
And if you still don't know how you should quit EE and start learn math.

 

[michael1978]

Simply use your brain instead of a calculator.
And if you still don't know how you should quit EE and start learn math.

JONEY i use me brain, why you don't tell me to calculate with my calculator, you just help me, i thank you for help, just tell me a little bit, and i use a calculator, you help so much, help also this one

 

[Jony130]

But I don't understand what is your problem?
I_R1 = 50uA + 10*50uA = 50 + 500 = 550uA = 0.55mA = 0.00055A

 

[michael1978]

But I don't understand what is your problem?
I_R1 = 50uA + 10*50uA = 50 + 500 = 550uA = 0.55mA = 0.00055A

joney i know this from begin to calculate this is easy, but my problem was other you forget,
i ask you for this

-------------------------------
o sorry joney i make you tired, i understand now, so if load current is 50μ we chose voltage divider current 10 larger then the load current, and we have

R2 = 1.7V/(10*Iload) = 1.7V/((this is 10 time larger)10*50μ(base current)) = 1.5V/500μA = 3.4K this i understand

but this i don't understand
I_R1 = 10*Iload + Iload = 11*Iload = 550μA

10*Iload(50μA)+Iload(50μA)=11(how we get 11 now)*Iload(50μA)=550μA

i don't understand that 11 how we get? 10*Iload(50μA)+Iload(50μA)=0.55 not 11 sorry i don't know where i make mistake, where come this 11, i don't know how to calculate, i know 11*Iload is 550μA
thnx for answer
----------------------------------
joney this 11 is my problem

 

[Jony130]

OMG
Look here
We have this equation
B = 10*A + A = 11*A
The first part tell as that we have a ten apples and we need add one more apple.
So we end-up with eleven apples .

 

[michael1978]

OMG
Look here
We have this equation
B = 10*A + A = 11*A
The first part tell as that we have a ten apples and we need add one more apple.
So we end-up with eleven apples .

ah you mean so
10*0.0.5+0.0.5=
10+0.5+0.5=11

you mean like this

 

[michael1978]

ooh joney boy, i make again mistake of is right, ooo thank you try a lot to explain me

 

[Jony130]

In our cases we have 11 apples
B = 10*A + A

And apples are equal to 50uA of load current.
So we substitute for A = 50uA
B = 10*50uA + 50uA = 550uA
And this is equal to 11*A = 11*50 = 550uA
the 11 tell as that the R1 current is 11 times large the load current.