I have already posted a question about this topic at...
http://forum.allaboutcircuits.com/t...able-multi-vibrator.111778/page-3#post-865231
but I didn't want to resurrect an older thread.
This schematic is a BJT astable multivibrator with diodes in the feedback channel to decrease rise time. (I.E. get actual square waves.)
I think I have a handle on how it works, but let's make sure. (Assume Q1 turns on first.)
1) Q1 is ON, so all the current through R1 and R2 is diverted to Q1's collector and into ground. The left plate of C1 is at 0V.
2) C1 charges through R3, dictated by T = R3(C1). C2 is at rail voltage on both plates.
3) When the right plate of C1 achieves +.7V, Q2 turns on. C2's right plate suddenly becomes 0V, and the left side decreases from +5V to 0V turning Q1 off.
4) The process repeats in the opposite direction.
I've built this circuit, but unfortunately it's not working.
The 1k resistors limit the current to the collector of the transistors. According to the datasheet, 2N3904's are able to handle 200mA. At 5V and 1kΩ, using Ohm's Law the current shunt should only allow 5mA which is more than safe.
I tried my best to get the frequency of the output. What I came up with is...
RC = T
T5 = 5V
T = 1V
T/1V = X(.6V)
1/X = Ψ
In the same order substituting my values:
(3.3 * 10^2)(2.2 * 10^[-9]) = 7.26 * 10^[-7]
(7.26 * 10^[-7])/1 = X(.6)
X = 1.21 * 10^[-6]
1/(1.21* 10^[-6]) = 8.2644628099 * 10^5
If my process and math is correct, I should get a frequency of about 826446 Hz, or about 826kHz.
However, the output of my circuit is nothing. Not even a voltage. It just sits at 0V on my oscilloscope.
Is my explanation of the circuit correct? Is my process correct? Is my math correct? Is this component failure, or a circuit design flaw?
Thanks!
http://forum.allaboutcircuits.com/t...able-multi-vibrator.111778/page-3#post-865231
but I didn't want to resurrect an older thread.
This schematic is a BJT astable multivibrator with diodes in the feedback channel to decrease rise time. (I.E. get actual square waves.)
I think I have a handle on how it works, but let's make sure. (Assume Q1 turns on first.)
1) Q1 is ON, so all the current through R1 and R2 is diverted to Q1's collector and into ground. The left plate of C1 is at 0V.
2) C1 charges through R3, dictated by T = R3(C1). C2 is at rail voltage on both plates.
3) When the right plate of C1 achieves +.7V, Q2 turns on. C2's right plate suddenly becomes 0V, and the left side decreases from +5V to 0V turning Q1 off.
4) The process repeats in the opposite direction.
I've built this circuit, but unfortunately it's not working.
The 1k resistors limit the current to the collector of the transistors. According to the datasheet, 2N3904's are able to handle 200mA. At 5V and 1kΩ, using Ohm's Law the current shunt should only allow 5mA which is more than safe.
I tried my best to get the frequency of the output. What I came up with is...
RC = T
T5 = 5V
T = 1V
T/1V = X(.6V)
1/X = Ψ
In the same order substituting my values:
(3.3 * 10^2)(2.2 * 10^[-9]) = 7.26 * 10^[-7]
(7.26 * 10^[-7])/1 = X(.6)
X = 1.21 * 10^[-6]
1/(1.21* 10^[-6]) = 8.2644628099 * 10^5
If my process and math is correct, I should get a frequency of about 826446 Hz, or about 826kHz.
However, the output of my circuit is nothing. Not even a voltage. It just sits at 0V on my oscilloscope.
Is my explanation of the circuit correct? Is my process correct? Is my math correct? Is this component failure, or a circuit design flaw?
Thanks!