[SOLVED] totem pole driver not working

[manishanand14]

Dear Friends

I made this circuit.When i am giving 5 v pulses i expect to get 15V pulses at the output.Instead I am getting 5 V pulses itself.
What may be the reason.
I tried with BD139/Bd140 complementary also.

 

[mtwieg]

The circuit is functioning fine, it should put out pulses from 0 to 4.5V, approximately. That circuit will increase the drive strength of the input, but won't increase the voltage range. To do that you need some sort of level shifter first.

 

[goldsmith]

I made this circuit.When i am giving 5 v pulses i expect to get 15V pulses at the output.Instead I am getting 5 V pulses itself.
What may be the reason.
I tried with BD139/Bd140 complementary also.

Hi manishanand14

If you need to increase amplitude of your signal use something like ICL7667 ! or perhaps using an optocoupler


Good Luck
Goldsmith

 

[manishanand14]

When I give 5 V input, the top NPN transistor will turn ON and (15-V ce_sat) V will appear across the resistor which is roughly 15V.
What mistake am i doing in understanding it.

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The circuit is functioning fine, it should put out pulses from 0 to 4.5V, approximately. That circuit will increase the drive strength of the input, but won't increase the voltage range.

Will you explain in detail please !

 

[srizbf]

when you consider the loop consisting of 5v input, 1k base resistor and sl100 b-e junction , and 100 ohm load , you can see that the 100 ohm will have a voltage of approx 5v only.

probably you have the assumption that , i give 5v to base of sl100 and it turns on. so , the output should be (15v - Vcesat) of sl100 which is wrong.

if you want 15v output , then you need to modify the circuit as level translator.

 

[manishanand14]

if you want 15v output , then you need to modify the circuit as level translator.

Well then tell me how will i convert it to level translator

 

[Audioguru]

The SL100 top transistor is an emitter-follower with no voltage gain. If the input is +5V then its base will be about +4.6V because the 1k series base resistor will have a current of about 0.4mA and the emitter will be +4.6V - 0.7V= +3.9V because the base-emitter voltage drop is 0.7V. You need to add another transistor as a voltage amplifier (common-emitter).

What is the bottom transistor supposed to do?

Here is one way of doing it: