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11 votes

Can ULN2003 be a poor-man’s matched diode array?

I've measured thermal tracking on SOT23-6 dual matched transistors like DMMT3904, by sending a current pulse in one transistor and measuring the Vbe of both. Thermal coupling is very poor. They're two ...
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9 votes
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What are the purpose of the extra diodes in this peak detector circuit (LM1815)?

The actual (but probably still a bit simplified) circuit has no diodes, but a Darlington-ish pair Q23 and Q24 and the other lone "diode" is Q20, Q21 and dual collector transistor Q22. The ...
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7 votes

Can ULN2003 be a poor-man’s matched diode array?

I think the answer is a qualified yes, at least at DC. I haven’t checked anything at AC just yet. Results so far: I’ve picked 5 ULN2003 from the junk bin - all different lots, and from at least 2 ...
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6 votes

Can ULN2003 be a poor-man’s matched diode array?

While the datasheets don't specify any of these diode characteristics, at low currents (say < 10 mA), where the resistance of the metal interconnect won't come into play, they will likely match ...
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5 votes

Can ULN2003 be a poor-man’s matched diode array?

It should work. You might have to connect the GND pin to a negative bias point to keep sneak paths from conducting. They're diodes so they don't respond in as ideal a fashion as diode-connected ...
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5 votes
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Determining LO drive voltage for 13dBm mini-circuits mixer

My question is how can I determine the required LO input voltage. Do I assume that the input impedance looking into the LO port is 50 ohms and calculate from there? Yes you do. The clue is the VSWR ...
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4 votes

Op-amps in series – why does this op-amp subtractor not subtract?

Here is a way to do it. As you can see, it subtracts 5.00V from the 6.5V-biased 1.0V signal. I would not use 100K resistors with the AD8031- the bias current is quite heavy, as much as 2uA, and it's ...
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4 votes

Determining LO drive voltage for 13dBm mini-circuits mixer

If the output impedance of your generator is also 50 Ohm (like the input impedance of your mixer) and if your transmission line on your PCB is also matched to 50 Ohm you can simply calculate the ...
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4 votes

Can ULN2003 be a poor-man’s matched diode array?

The CA3046 transistor array can be used to provide a minimum of 4 B-E diodes. This is a monolithic die which guarantees the diode matching to 5mV, and the thermal matching should be excellent.
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3 votes

Op-amps in series – why does this op-amp subtractor not subtract?

With your difference amplifier as it is, you are adding 5V, not subtracting. You can easily tell which one is being subtracted; it's the signal feeding the op-amp's inverting ('−') input. That also ...
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3 votes
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Op-amp wrong output

For finding the open-loop curve, you should use "special" feedback. For reference, Example with a "classic" op-amp. For closed-loop, with one resistor your feedback is ok. ...
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3 votes

ADC parameters confusion

For example, if ADC sampling rate is 100Hz does that mean it outputs 100 digital values/sec? Yes, because 'sample' === 'digital value'. However, a 100 Hz sampling ADC is unlikely to require an input ...
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3 votes

What are the purpose of the extra diodes in this peak detector circuit (LM1815)?

You’re looking at a block diagram: it is a somewhat abstract depiction of what is going on. The diodes on the block diagram are not literal components. They are blocks, just as the rest of the ...
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2 votes

DC signal to Integrated signal for analog filter circuit

Just so we are clear... you will need a rectifier, otherwise an integrator will yield the average of the signal and you will get zero. Use a precision full wave rectifier. Source: https://...
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2 votes
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Self biased transistor current limiter

First of all, you are operating the BJT outside its limits. The BJT you are simulating has a maximum collector current of 50 mA. Why transistor in self bias arrangement never goes into saturation for ...
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2 votes
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Analog circuit for battery discharge protection

M1/IC1 form the latching 'thyristor type' power switch. It draws no power when off, and little when on. The TLV431 (not the right symbol, this was close) is designed as a 3 terminal shunt regulator, ...
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1 vote
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Raspberry Pi: current sensor ACS724 noisy output

The RaspIO Analog Zero seems to be reporting otherwise accurate and stable voltages. I tested this with a simple voltage divider circuit on the 5 V rail of the Raspberry Pi, and it reported 2.5 V with ...
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1 vote
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How do I know what each pin represents in a Spice model of an op-amp in OrCAD?

The link you provide shows .subckt code which (mostly) matches the accompanying image of the opamp's internal schematic. I'll duplicate both for clarity and ...
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1 vote

Protecting only part of a circuit from reverse polarity?

That should be OK, but it looks like the analog circuitry in the schematic shown has a relay that connects 12 VDC to an external fan. The fan connector has one pin connected to ground. The relay is ...
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1 vote

74121 one-shot trigger on inputs A and B - can B be held low continuously?

Think of it like this: You can wire the '121 to be triggered from a rising edge, or from a falling edge. If you want a rising-edge trigger, you trigger the B input, and hard-wire one or both of the A'...
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