I'm trying to analyze the circuit below and I understand that the transistor T201 is acting like an inverter . Am I wrong ? And also why are the two capacitors in parallel at the beginning of the circuit ? I know that there are many parameters to be considered to select a capacitor such as working temp, temp coeff,working voltage ,leakage current etc., but how do they matter for the circuit below? what does "3A" at the input pin mean ? and also what does "10E" and "11G" at the output pins mean ? Thank you


T201 is a dual transistor, there is a PNP and an NPN part. The T201(P) collector will float (so it will be pulled low by the T201(N) and T200 bases). When VDD5 goes low, T201(P) will turn on and the bases of the other two will go high which will in turn pull their collectors low. So I suppose you could say that T201 acts as an inverter, if that's what you meant.

The two caps in parallel are to provide better filtering of high frequency noise. There are lots of other questions on here that go into a lot more detail of why this is done. It's not a matter of temperature coefficients, working voltage, or leakage, it's about frequency response.

The labels you mentioned could be just references perhaps to other parts of the schematics. 10E and 11G don't mean much otherwise. 3A could indicate the expected current at that terminal, but perhaps not. I expect there is not enough information provided to answer that.

  • \$\begingroup\$ Can you please tell me what you mean when you say the "collector will float" ? and can you pls tell me what is the function of T200 ? \$\endgroup\$ – Nidhi Mar 13 '17 at 14:16
  • \$\begingroup\$ When the PNP part of T201 is off, it's collector will be allowed float to whatever voltage based on how the other connected devices influence it. In this case, the PNP transistors have pull-down resistors at the bases, so that collector will be pulled-low. The purpose of T200 is to pull down the voltage at P205, but beyond that I can't say what that does given only the portion of the schematic you provided. \$\endgroup\$ – AngeloQ Mar 13 '17 at 14:22
  • \$\begingroup\$ what parameters should I consider when choosing a capacitor ? And the diodes in series is for protection against what ?Thank you very much for your answers. \$\endgroup\$ – Nidhi Mar 13 '17 at 14:37
  • \$\begingroup\$ The capacitor factors you mentioned in your question are all relevant when selecting a cap, but in terms of why there are two and how it applies to this circuit, mainly it's voltage and value. The voltage of course needs to exceed the max expected voltage seen on the P200 signal. The value depends on what frequency cut-off they are expected to filter out. The diodes are there to prevent the voltage exceeding the P204 and GND levels by more than ~0.7V \$\endgroup\$ – AngeloQ Mar 13 '17 at 15:12
  • \$\begingroup\$ Thank you very much.And can I ask you one more thing, what formula should be used here to calculate the capacitance ? Please help. \$\endgroup\$ – Nidhi Mar 13 '17 at 15:40

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