Fluctuating voltage from a bad transistor

[danny davis]

Since U114 is a comparator with hysteresis, it is logical to assume that the Q119 is a switch that transmits the reference voltage of the comparator to an other part of the scheme.

How is Q119 Turns ON and what turns Q119 OFF?

What would happen if Q119 wasn't even in the circuit, would it make that much of a difference? if we just bypassed it with jumpers

Why would Q119 need to switch the reference voltage of the comparator? what does that do

What does hysteresis really do for a circuit? it just makes the switching from a slow input to a fast output, but it also does what else?

I have heard that hysteresis fixes and interfaces with other components values, hysteresis biases the transistor better and works with other components better, is this true?

When using a FET as a switch, a FETS input capacitance needs to be discharged?

 

[D.A.(Tony)Stewart]

Danny are you going to ask about every single part of this design?

Q19 is simply an open collector driver for the LM211 comparator. the 2N2907 is PNP so the output is pullup or "high side drive"

Looking at the the quality of the schematic, the design appears to be have done by an amateur.

 

[danny davis]

why is the output pulled high? Any reason why not pulled low? Why not have used a npn transistor?:

 

[D.A.(Tony)Stewart]

high side driver is used for low side loads.

 

[danny davis]

high side driver is used for low side loads.

What does this mean, high side driver? and low side loads? what

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Level Shifter PIC#2

Take a look at these transistors , they look like they are transistors in series to do level shifting? but how do they work?

 

[D.A.(Tony)Stewart]

if you want to switch V+ to a grounded load, you pull the load up to the V+ using a PNP or similar high side switch.

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if you want to switch V+ to a grounded load, you pull the load up to the V+ using a PNP or similar high side switch.