# Questions tagged [saturation]

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### Why isn't the saturation current of a photodiode the same as its short circuit current?

The formula I see everywhere is: $$I_{sat} = \frac{V_{bias}}{R_L}$$ But this seems incomplete for the following reason: The larger the resistance is the smaller the saturation current, it stands ...
2answers
2k views

### What is the difference between “Collector-Emitter” and “Base-Emitter” Saturation Voltage?

As you can see on the datasheet below for the 2n2222a NPN transistor, the "Collector-Emitter Saturation Voltage" and "Base-Emitter Saturation Voltage" are defined respectively as 0.3 to 1.0 and 1.2 to ...
1answer
38 views

### Using MOSFET to prevent Op Amp saturation

How N-channel Q1B MOSFET prevent Op-Amp U1B from saturation.Terminal 5 of U1B and Q1B are connected to output voltage of a DAC. At 4 of Q1B and Q2B is the same signal multiplexed to control LED.
2answers
51 views

### What happens when transistor operates in saturation region for constant current source

I am learning about the constant current sources and I found this video What I dont understand is that, when the forward voltage of the LED is increased from 1.7V to 3.3V, and our Emitter voltage is ...
4answers
292 views

### What are these transistors doing and how are they working in this VU Meter?

I was thinking of making KITT's voice box from Knight Rider, which is essentially a VU meter. I did some researching and found an appropriate IC, LM3916, http://www.mouser.com/ds/2/405/lm3915-443929....
1answer
57 views

### How can I estimate the minimum beta for this driver to work in hard saturation?

Imagine I build the below LED driver circuit where I know all the component parameters such as 2V LED forward drop and resistors and Vcc and Vbb as in the following diagram: And if I only dont know ...
3answers
66 views

### Why does a rise in ambient temperature cause a base-voltage-biased grounded emitter stage to saturate?

This is actually exercise 2.9 in Horrowitz and Hill 2nd Ed. which is posed as: Verify that an $8 ^\circ C$ rise in ambient temperature will cause a base-voltage-biased grounded emitter stage to ...
2answers
3k views

### A confusion about the formula for transistor Vbe Ic characterisitcs

Below is NPN BJT transistor Vbe Ic characteristics and the formula: Many texts approximate this equation as: Ic = Is*e^(Vbe/Ut) and following this they say when Vbe=0, Ic becomes equal to Is. ...
1answer
288 views

### Cannot find “reverse saturation current” of base-emitter junction in the data-sheet

Regarding the reverse saturation current $I_{ES}$ aka $I_{EO}$ of an NPN transistor, according to Ebers–Moll Model: $I_E = I_{ES} (e^{V_{BE}/V_T} -1) -\alpha_RI_{CS}(e^{V_{BC}/V_T}-1)$ ...
2answers
242 views

### Where would Iceo flow through and would it cause thermal runaway?

I was reading this page about thermal run away. And it mentions: Due to increase in the temperature of collector junction, Ico will increase, Vbe will decrease. But for Ico to increase Ic and ...
1answer
107 views

### Channel shape of NMOS in saturation

According to the Sedra/Smith Microelectronic Circuits textbook, 6/7 eds., increasing $v_{DS}$ beyond $v_{OV}$ has no effect on the channel shape and charge. Why is that? It seems as if (...
3answers
89 views

### Transistor Analysis

Here is a problem I saw as an example of transistor analysis: (hFE is 50) simulate this circuit – Schematic created using CircuitLab The process is simple, the guy assumed that the transistor ...
0answers
45 views

### op amp saturation

I have this circuit which is acting with negative resistance. However when increasing the voltage well above saturation it produces a weird distortion on the output as seen below. can anyone explain.
1answer
103 views

### Inverting op amp design saturates at a fraction of power supply

I have built a simple inverting op amp. I am applying a 1 Vpp sinusoid at 10 Hz to a design with ~4.7x gain. The resistors I am using are 47kOhm and 10 kOhm. The op amp chip is the LT1222, and I am ...
2answers
5k views

### Prevent high-side BJT saturation

I am building high-speed (10-20ns on BC847-class transistors) digital "buffer"/"inverter" out of BJTs. Scheme is attached. While I can prevent saturation of low-side BJT by adding Schottky diode, it'...
2answers
38 views

### On interpreting this set of curves (Transistor in Saturation mode and decrease of $h_{FE}$)

The following figure was excerpted from Horowitz's The Art of Electronics, Appendix G: Transistor Saturation (page 1089 for the 2nd edition), It represents the current gain $\beta$ of an npn ...
1answer
237 views

### Questions regarding BJT saturation for a circuit

I have the following circuit which converts weak sine signal to pulses: I have tried it on breadboard and it seems it works fine. In my application freq. is between 1Hz to 30Hz or max 100Hz. And the ...
1answer
78 views

### Rectified current transformer output is asymmetric

I'm using a current transformer (CS4200V-01L) to measure the current in a half-bridge. I'm facing an issue where the signal out of the current transformer is asymmetric, almost as if the current ...
1answer
49 views

### How can U_CE be smaller than U_BE in this circuit?

Recently I was wondering why UCE can be smaller than UBE. I've drawn a small diagram with the typical values of the BC547 NPN transistor. This amazes me all the more as UBE shares its PN-regions with ...
2answers
21k views

### What is saturation in an inductor

I have heard a lot of the time that "the core is not large enough to handle the current, and will reach saturation". What is saturation and why is it a bad thing to reach saturation?
1answer
573 views

### Problem with output swing in LM358

simulate this circuit – Schematic created using CircuitLab I am working on a battery charger with indicator. I am using a LM358 to compare the voltage of my battery with a reference voltage of ...
1answer
231 views

### How to Calculate Saturation Current of a Transformer?

Is this Method applicable to calculate? My confusion is mainly regarding with Load current. My knowledge is, that load current is nothing to do with saturation of transformer.
0answers
82 views

### Can an inductor lose its characteristics permanently after short saturation?

I was testing a SMPS (boost) where I had an overcurrent due to overload for a few seconds. The inductor saturation current is 2A. Although I could not measure the current, I am quite sure that the ...
0answers
30 views

### Understanding PMOS's and NMOS's

The problem says solve assuming VI = 0, +2.5V, and -2.5V. I know that if VI = -2.5V the MOSFET's are in cutoff and that VDS = 0. and IDP and IDN will = 0, but would V0 also = 0? If VI = 0 the ...
1answer
75 views

### Instrumentation Amplifier Saturation to Rails

I am working with a TI INA821 Instrumentation Amplifier to try to amplifier a 0-5mV (delta) analog signal off a strain gauge. To reiterate, every DC analog value between the delta of 5mV represents a ...
2answers
41 views

### Magnitude of $I_{CBO}$ in a typical transistor

I read in a book that $I_{CBO}$ doubles for every 10 degree rise in temperature and hence contributes to thermal runaway. However I am confused since essentially it is the reverse saturation current ...
1answer
161 views

### Saturation Cascade MOSFETS (Need Help from EE Experts)

this is a very straightforward question. I'm running a Harmonic simulation on ADS where I need to design a cascode amplifier of two NMOS and one PMOS, that have a gain higher than Av > -100. The ...
0answers
47 views

### Usuing P_channel mosfet to make o normally closed switch

Hi, I am trying to implement a normally closed switch. In the shown circuit: Vcc = 16..60V (Vcc>>Vz) The characteristics of the P-mos are: Vth = -1V Rdson = 0,055ohm The circuit works correctly: in ...
3answers
69 views

### Saturation current on chip inductors

Inductors are really not my strong point, and I have been getting a bit confused on the rated current vs saturation current. I know the rated current is how much current the inductor can handle ...
1answer
72 views

### Magnetic material demagnetization through Curie temperature

It is known that some materials lose their permanent magnetic properties when they are heated above certain temperature known as Curie temperature or Curie point. As those materials are cooled down to ...
1answer
121 views

### Do BJT (Darlington) transistors have a minimum collector current?

I am using a TIP122 Darlington transistor. From the graph provided in the datasheet, I can see that the saturation voltage decreases as the collector current decreases. Since the load I am driving ...
1answer
269 views

### DC Shunt Generation Ascending/Descending Terminal voltage Saturation Curve help?

In a DC Shunt Generator we increased Field Current from 0 to 2.0 and calculated the Terminal Voltage, we then decreased field current from 2.0 to 0 and collected our field current again. When plotting ...
1answer
73 views

### What part of Ebers-Moll equation shows the decrease of the collector current in saturation region

By looking at the Ebers-Moll equation for a BJT transistor: Is this formula explicitly showing why Ic starting to decrease towards zero in saturation region. Which part of the equation shows that?
1answer
102 views

### MOSFET goes into saturation mode much later

I am using IRLML6346 NMOS in LTSpice. Its threshold voltage is Vt = 0.95V. I plotted the graph of Vds(voltage between drain and source) vs Ids(Current from drain to source) for different values of Vgs(...
1answer
56 views

### BJT saturation question

For the following question, how do we find $I_B$ and $I_C$? Would it be $$I_C = \frac{V_{in}-V_{BE}}{80k}$$ and $$I_B = \frac{12-0.12}{5k}$$
1answer
390 views

### how does a Avalanche photo diode[APD] recovery time depend on TIA

in one my of low light pulse detection project i want to sense a very low light of 1mW/m2 so for this kind of scenario an APD is a device with its internal gain can give me abundant current to detect ...
1answer
375 views

### Collector voltage in saturation

I saw the following question online I knew that while Vbe was less than 0.6v, there would be no current and the collector voltage would be Vcc. At 0.6V, I knew that the transistor would turn on, and ...
1answer
658 views

### got a too low VCE on a Infrared Phototransistor

I used an Infrared Light Emitting Diode QED123(VF=1.7V) and an Infrared Phototransistor QSD123 in pair. I learnt from QSD123's datasheet that its VCE(SAT) under IC=0.5mA is 0.4V max. But the VCE I ...
1answer
152 views

### NMOS/PMOS Saturation

If I recall correctly, saturation occurs if $V_{GS}>V_{TH}$ and $V_{DS}>V_{Dsat}$ for NMOS. But is there an upper limit for the voltage? Like, when does a transistor not saturate after ...
1answer
142 views

### Double BJT circuit with one BJT off and one in saturation

In the circuit below, due to the base voltage, the circuit becomes a common-emitter setup. However, assuming a reasonable value for the base current the BJT should be in saturation. However the value ...
1answer
76 views

### How can a magnetic circuit with an airgap have a higher e.m.f in the secondary coil than the same circuit without the air gap?

I have a magnetic circuit with the same configuration as in the image, the primary coil has 203 turns and the secondary has 406 turns, how do I get a higher eletromotive force when there is an air gap ...
2answers
268 views

### Self-made Schottky transistor doesn't behave as I'd expect

For a project of mine I need to generate UART-like signals with higher voltage (up to 18V) and a baudrate of 115200 bps and later possibly 250000 bps. I tried a basic BJT level shifter which worked as ...
3answers
1k views

### Photodiode in photovoltaic mode, overcoming saturation

can anyone explain to me why moving to configuration (b) overcame the problems I was having with the photodiode saturating? Many thanks, John
2answers
1k views

2answers
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### OPAMP saturating when output is negative, simulation is OK

The schematics: It should convert 0-3.3V input from the DAC to -4.1 + 4.1V (roughly) The positive part works great, the negative output voltage saturates at -2.95V. Is it ok? The simulation looks ...
2answers
2k views

### How does a photodiode behave in saturation?

In my design, a photo diode is connected in reverse bias with 12V. The LDO (low-dropout) voltage regulator which is used for biasing can deliver a maximum current of 500mA My configuration: simulate ...
1answer
289 views

### Do we have a voltage drop across this ideal current source?

Additional info includes Vss=0V, Vdd=3V. Also assume saturation (since we have Vd=Vg) and λn=0. We also know the reference current but not the Resistor. I know Vgs and thus Vds but I am looking to ...
2answers
598 views

### Why collector current is small in value in saturation mode?

Why is the collector current smaller in value when a transistor is in saturation mode of operation? My guess is that although both the junctions are forward biased, the (forward) currents are '...