|
{------SHAKE DEVICE TO POWER UP!------}
How it works!;
Resistor layout + names for better explanation:
- - -
/ / /
\ R1 = 1k \ R3 = 10k \ R4 = 10k
/ / /
- - -
- -
/ /
\ R2 = 10k \ R5 = 10k
/ /
- -
Transistors: From left to right:
Q1(PNP) - Q2(PNP) - Q3(NPN)
Charging:
The two resistors R1 & R2 provide a bias voltage on the base of Q1. About 300mV is applied across R3 causing approximately 300uA flowing out of the collector.
That current is being dropped into the 10nF capacitor giving us the linear voltage ramp (the charge).
Discharge:
The two almost back to back connected transistors, Q2 and Q3, make for a positive feedback circuit which, after turning on, stays on untill it is turned off.
The two resistors R4 & R5 form a voltage divider giving 4.5V on its output. This voltage will be placed on the base of the PNP Transistor Q2.
If Vc (capacitor voltage) has increased to a value at which it can turn on the base-emitter junction of Q2, it starts conducting. Its collector current becomes base current for the PNP Transistor Q3 causing it to conduct aswell.
What is expplained in the paragraph here above results in the following:
The collector current of Q3 now starts pulling current from the base of Q2 and out of the voltage divider network. Because current is drawn away from the base of Q1 it will start conducting harder. This basically reinforces Q2 and Q3 being turned on.
Now, the the collector of Q3 is being pulled low and Q3 saturates. Hence the current trough R5 gets pulled down low. Because of that, and because Q2's emitter is basically an emitter follower, the current trough the capacitor is also being pulled low thus causing it to discharge.
Then at that point the Q2-Q3 network shuts itself off because there isn't enough current available anymore to keep the structure conducting (looping). So then the process repeats itself.
I hope you learned something from this! I sure did and it was a lot of fun analysing this circuit!
Please feel free to leave suggestions, improvements and that sorts of good stuffs!
Have a nice day!
|
