# Pull Up Resistor Value for LM319 Transistor

Discussion in 'General Electronics Chat' started by tck1911, Nov 12, 2012.

1. ### tck1911 Thread Starter New Member

Nov 12, 2012
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0
Hi Guys,

I am currently designing a triangular wave generator and am using an LM319 operational amplifier. I am aware that a pull up resisitor needs to be used at the output of the amplifier, but I do not exactly know what value of resistor should be used in this case.

Also, I am expecting a 100 kHz output from the op amp. I am not sure wehther this will affect the value of the pull up resistor.

What I hope to understand is the value of the pull up resistor that should be used and what parameters affect this value?

I hope someone could help me out.

Thanks!

2. ### bertus Administrator

Apr 5, 2008
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3. ### tck1911 Thread Starter New Member

Nov 12, 2012
5
0
HI,

I'm afraid I do not have a schematic that could be uploaded.

However, the LM319 op amp is used as a comparator with a 5kΩ resistor connected to the non-inverting input. The inverting input is connected to the ground. Also, a 5kΩ resistor is connected betweent the non-inverting input and the output of the opamp.

I hope this helps.

Thanks.

4. ### MrChips Moderator

Oct 2, 2009
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3,361
LM319 is not an operational amplifier. It is an analog comparator with open collector outputs.

Any circuit with open collector outputs means that the output is uncommitted, i.e. not connected to any load, hence the need for an external load.

You calculate the pullup resistor based on the pullup voltage and the load current. For example, if the supply voltage is 12V and the load current is 10mA, R = V/I = 1.2kΩ

For 12V @ 25mA, R = 470Ω

Do not exceed 25mA for the LM319.

(This is an approximation since I have ignored the output saturation voltage, but the answers are close enough.)

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5. ### tck1911 Thread Starter New Member

Nov 12, 2012
5
0
Thank You. This sure will help me go ahead with the design.

I actually made the mistake of allowing a current greater than 25mA to flow through the LM319.

Also, I did not know the difference between an op-amp and a comparator with open collector outputs.

I am a bit new to designing circuits and still getting to know things. This really helps.

Thanks again.