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26 votes

Difference between latch and flip-flop?

A flip flop is built from two back to back latches with opposite polarity clocks, which form a master slave topology. The type of latch is irrelevant (JK, SR, D, T) to this constraint, but it is ...
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19 votes
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How does an SR Latch get started

It is true that the latch will "wake up" in an unknown state. In the real world, given a little time, the latch will have a valid state with either Q=0 or Q=1. You make the latch "get started" by ...
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16 votes
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What is the difference between the circuits?

Instead of just poking at random values and asking what difference they make, stop and actually think about the circuit. Once you understand what each part does, you'll be able to find acceptable ...
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14 votes
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Why do all transistor latch circuits (that ive seen) use two transistors?

The base to emitter voltage is pretty stable at 0.6V, you are not adding any feedback with the resistor. You actually built a emitter follower or common collector. The main property of this circuit ...
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13 votes
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Where does the power supply go in an SR Latch?

Of course there's an external power supply. Take a look at a NOR gate chip (say, 74HC02) and you'll see it there clear as day: Logic symbols purely show the logic flow of a circuit, not the power ...
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13 votes
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Identification of a circuit element

Try this for size: - Image from here. Here's a truth table and picture: - Image from here.
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12 votes

Can we declare Schmitt triggers to have memory? Can we call their output levels states?

Yes, "memory" in the sense of "this system is not memoryless" is any difference in behaviour that depends on previous internal or external state. Since the exact idea of a Schmitt ...
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11 votes
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What is a flip flop?

I have been thinking about this definition a lot today. As others pointed out, the exact meanings will vary. On top of that, you will probably see more people get this wrong, even on this site, ...
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11 votes
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JK latch, possible Ben Eater error?

Ugh. This again. tl, dr: The gated JK latch is a junk circuit and should not be used in a modern design. It's useless, except as a lesson of how not to design a latch. Let's start with the The Ben ...
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10 votes
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What is the difference between registers, flip flops and latches?

Flip-flops are single bit devices with two stable states. The outputs are typically Q and \$\mathsf{\small \overline{\text{Q}}} \$. There are several kinds, here are probably the most common: SR ...
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10 votes

Why do all transistor latch circuits (that ive seen) use two transistors?

The analog-focused answers are correct, but there's also a digital way to look at it. The circuit you linked to is basically two inverters connected in a loop, not unlike an SRAM cell. Here's a ...
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10 votes

How does an SR Latch get started

When you power on a bi-stable element like a NOR SR latch (with inputs at 0) it will start at to some state. That is not necessaraiy a 'binary' state, the the outputs can for instance be halfway ...
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10 votes

The difference between these two D latch circuits

They are more-or-less equivalent but the timing is not identical, especially for data stable and runt pulses on E in the second circuit. There may be other differences you can find.
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9 votes

Where does the power supply go in an SR Latch?

Of course there is an external power supply (as you suspected). Here's a quad nor gate: - Notice pin 7 and pin 14 The same sort of thing is done with op-amps - they don't necessarily show the power ...
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8 votes
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Flip-flop vs latch: Do flip-flops have an edge detector integrated?

Each digital circuit can only work with a given amount of capacitance load which is given by the logical effort and its fan-out. If you connect too many blocks (latches in your case) at the output of ...
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7 votes
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A simple clarification on latches and flip-flops

The two are different because the first doesn't show the internal structure of the SR latch, and it is hooked up in reverse of the second example. The first example is concerned entirely with the ...
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7 votes

Can we declare Schmitt triggers to have memory? Can we call their output levels states?

A latch is like the simplest form of memory. If you configure a Schmitt trigger as a latch, it is not a stretch to call it one bit of memory. But any buffer can be set up as a latch. I guess I am ...
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6 votes

Where does the power supply go in an SR Latch?

The other answers have addressed part of the question, but it may also be worth noting that the power supply connections are often omitted from schematics (especially conceptual rather than practical ...
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6 votes
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How is a latch different from Schmitt Trigger?

They differ in the level of the signal that is required to change their state. In a Schmidt trigger, a relatively small, well-controlled change of signal level is needed. The input is designed to ...
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  • 143k
6 votes

Looking for better design

What you actually need: Why? The Attiny13 can power itself down, and wake up on any of the input pins changing. In power down mode, it uses practically no current, see Table 18-1, p. 118 of the ...
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6 votes

Doubt regarding SR latch

You're getting misled by the very simple Boolean logic model of the actual complicated digital logic circuit and power supply operating at a temperature. Digital logic is just 'convenient analogue'. ...
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  • 18.5k
5 votes

Why do all transistor latch circuits (that ive seen) use two transistors?

In order for a circuit to behave as a DC-stable latch, it is necessary that there be a feedback loop with a positive gain at DC which is greater than one. While bipolar junction transistors and field ...
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5 votes
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Do registers have a multiplexer?

shift registers are divided into serial to parallel and parallel to serial shift registers. This is serial to parallel: I think your teacher was teaching parallel to serials. The seria to parallel ...
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  • 1,221
5 votes

What's wrong with this power latch design?

It's bad design. You press the button and this initially activates the mosfet. That mosfet then turns the bjt on and before you have thought about removing your finger the voltage that was turning the ...
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5 votes
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Why are two transmission used gates to make a D Latch?

This is the simplified view of the transistor level implementation of a positive latch, you have in the figure. When CLK is high, TG1 is ON, TG2 is OFF. So you will get at output Q, whatever input ...
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5 votes
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How do I avoid a race condition in SR latch?

Attaching LEDs like that to a little CD4001 is drawing too much current from the output when powered from only 6V. You are pulling ~8mA and the device is only rated for closer to ~2mA. What will ...
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5 votes

What is the difference between the circuits?

The circuit basically consists of 3 sections: Q1 + Q2 + R2 - R5 forming the latch Q3 + SW1 + SW2 to set the latch in a certain state Q4 to drive the load Changing R2, R3 will make the latch work or ...
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