How to understand this oscillating circuit made of two transistors and R C?
This is an oscillating circuit which is made of two transistors and some R C.
As below schematic shows, during the power on the capacitors, C1 and C2 are charged through R1 and R2.
After about 0.5s the C1 is fully charged to 24*(1/(1+0.2))V = 20V and after about 10s the C2 is charged to about 20V+0.34V=20.34V.
The voltage difference between E and B of Q1 makes the Q1 PNP transistor to work, the current flow through the R5 resistor then makes the Q2 NPN turn on. after then the current flow to the LED D2, then the D2 turns on and emit light.
But quickly as soon as almost 3-5ms the energy in C1 and C2 capacitors will be exhausted which then makes the process go back to the very beginning.
Then the capacitors C1 and C2 are recharged.
The above process is the basic description of the circuit. I simulate the circuit by using the Tina V9 software and the result is as the pic. shows.
My questions are:
- How to calculate the suitable value of the R and C which can make the oscillating time equal to 5s?
- How does the circuit work which very precisely makes the circuit to oscillating?
- What are the roles of the two transistors and how they work?