# transistor current time-base generator

#### jafal

Joined Jul 4, 2017
14
hi

what is the difference if we replace r 2.2 kohms by 1nf cap and r 100 ohm with 1 kiloohm resistance

#### crutschow

Joined Mar 14, 2008
27,737
what is the difference if we replace r 2.2 kohms by 1nf cap and r 100 ohm with 1 kiloohm resistance
The circuit will operate differently, or perhaps not at all.

What is the purpose of the circuit besides "time-base generator"?

#### jafal

Joined Jul 4, 2017
14
The circuit will operate differently, or perhaps not at all.

What is the purpose of the circuit besides "time-base generator"?
hi
thanks for response

i do have smiller circuit in a laser range finder l1 warped around the beam it self and i dont know how the circuit works but i think its kind of chopping or sort of timing

#### Audioguru again

Joined Oct 21, 2019
3,541
1) The base of the transistor is missing a series resistor to reduce the 200mA or more from the output of the 555. Then the transistor will be destroyed.
2) The collector of the transistor has no +DC voltage so it will do nothing.
EDIT: 3) The 555 might be destroyed trying to drive unlimited current into the base of the transistor.

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#### jafal

Joined Jul 4, 2017
14
1) The base of the transistor is missing a series resistor to reduce the 200mA or more from the output of the 555. Then the transistor will be destroyed.
2) The collector of the transistor has no +DC voltage so it will do nothing.
EDIT: 3) The 555 might be destroyed trying to drive unlimited current into the base of the transistor.
hi

the base has resistor in series not shown with 555 tiner and the collector has 5 volts dc

#### Audioguru again

Joined Oct 21, 2019
3,541
You asked, "What would happen if (the circuit is like this):"

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#### jafal

Joined Jul 4, 2017
14
You asked, "What would happen if (the circuit is like this):"
hi

this is the signal of collector

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#### jafal

Joined Jul 4, 2017
14
You asked, "What would happen if (the circuit is like this):"

this is the same circuit but the resistance r 2.2k replaced with 1 nf cap

#### Audioguru again

Joined Oct 21, 2019
3,541
Your collector signal is so small that it is almost nothing. It suddenly goes to only -0.05V then it slowly rises to +0.05V, over and over at 12.5Hz. If the collector of the transistor has a load then the signal level will be much less.

Your 'scope is AC-coupled but it is supposed to be DC-coupled to show the DC levels. Maybe the AC-coupling on your 'scope does not work at a frequency as low as 12.5Hz.

Post the 'scope photo when it is DC-coupled, and slow-down the 'scope timebase to show a few cycles.

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