I am reading this material for understanding the switch mode push pull power supplies. Push Pull Switched Mode Power Supplies

I am unable to understand the working though. Can someone provide a simple explanation for the circuit in 3.4.2 and its waveforms?

And it is mentioned as R3 and C2 are the timings components which I dont understand also. How do the internal transistors and the external transistors function? Please explain. Thanks.

  • \$\begingroup\$ If you haven't already, strongly recommend reading modules 1-3.4.1 \$\endgroup\$ – K H Jan 16 '19 at 4:39

The working of the circuit is described here in this document which describes the functionality of PWM modulators.

RT and Ct are part of an oscillator circuit where

\$ f = \frac{1.18}{R_T C_T}\$

(Rt is in kΩ, Ct is in uF, f is in kHz)

Practical values of CT fall between 1 nF and 100 nF. Practical values of RT fall between 1.8 kW and 100 kW. This results in a frequency range typically from 120 Hz to 500 kHz.

Source: datasheet listed above

enter image description here

| improve this answer | |
  • \$\begingroup\$ Thanks. Can you provide a run through of the operation of the blocks during one on state and one off state? \$\endgroup\$ – Freshman Jan 16 '19 at 5:09
  • \$\begingroup\$ And sorry for the basic question, how does the capacitor charge and discharge through the resistor. From where the R and C get the charge and discharge? \$\endgroup\$ – Freshman Jan 16 '19 at 5:17
  • \$\begingroup\$ Is this homework? \$\endgroup\$ – Voltage Spike Jan 16 '19 at 5:55
  • \$\begingroup\$ No I am trying to understand the working of the circuit \$\endgroup\$ – Freshman Jan 16 '19 at 6:03
  • \$\begingroup\$ I am unable to understand how the RC section works. We will get a ramp waveform at the timing capacitor pin only when RC is connected in series, right? But here R and C are not in series. How is this ramp generated? \$\endgroup\$ – Freshman Jan 16 '19 at 6:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.