How these transistor circuits work?

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EDA_hg81

The purpose of this circuit is for shifting the voltage level from logic level to +1.5V and -3V.

When the base of NPN receives -7V: NPN is off and PNP is on, the output is around +7V.
But when the base of NPN receives -2V: NPN is on and PNP is off, the output is around +12V.

Where this +12V comes from?

Thanks you.

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Prototyp_V1.0

The battery V2 seems to be placed wrong way, and I can't se why V3 should be as huge as -15 volts. That may damage T2 (haven't read any specs, it may as well survive).

Exept from that, the circuit looks like some half bridge variant that have floating input as it's common state, and whnenever the input logic state changes, output will conduct to either positive or negative voltage.

Where do that circuit belong?

EDA_hg81

Points: 2

mr_anderson

Although I did not practice electronics since a while, but I think this circuit is an audio amplifier and one channel will amplify the positive part of the speech signal while the other will amplify the negative part of the speech signal.

EDA_hg81

Points: 2

EDA_hg81

The purpose of this circuit is for shifting the voltage level from logic level to +1.5V and -3V.

I have tested the circuit and it is not working, I have to find out the reason.

In my mind, V2 is in right way and V3 is for providing DC offset at the NPN input.

Thank you so much.

I have added one 50ohm resistor at the output then output voltage is between +5V and -1V.

this resistor gives the DC current loop for the PNP transistor.

Prototyp_V1.0

EDA_hg81 said:
The purpose of this circuit is for shifting the voltage level from logic level to +1.5V and -3V.
No. C1 and C2 would prevent output to stay at either high or low.

EDA_hg81

Points: 2

WYL

Junior Member level 2
Maybe you can use pspice to simulate it,
and you can see the result...

EDA_hg81

Points: 2

EDA_hg81

I am using TINA to simulate it.

I am confused, C1 and C2 are for taking off DC offsets and regenerate DC voltages.

FvM

Super Moderator
Staff member
I agree, that the result is surprizing at first sight. Unfortunately I didn't hear a plausible explanation yet.
To understand the detail behaviour, it would be good to see transistor switching states, particularly the currents.

To get concrete help, you may want to post the TINA project file (including non-standard libraries, if there are any).

vily

vily

Points: 2

ringo888

Member level 1
I have used TINA in the past with proven circuits and the simulator displays no output, so i'm very dubious to use TINA again, try using the 30day B2 Spice it seems more reliable and is frequently updated (I can't remember the last time TINA had an update)

EDA_hg81

They said they will let me know the answers soon.

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