# Tag Info

7

Usually when we measure the output current to evaluate a DC power supply we are primarily interested in the DC component, and some mV or tens of mV of ripple on top (either from the power supply or because the load current has an AC component) on top of volts are not important at all. If you want to turn things around and actually measure the ripple ...

7

I'm going to call the lower input voltage range but less efficiency circuit, circuit A. I'm going to call the more efficient configuration, circuit B. Note that both circuits are actually the same, only some component values are different: The inductor L1: 0.33 uH (circuit A) vs 6.8 uH (circuit B) The RC network connected to the Vc pin These two changes ...

6

LTspice solves nonlinear differential equations numerically. It's not an AI system that can figure out intelligently whether a diode is conducting or not, and thus solve your homework questions or whatever. In general I think that models that are not "smooth" will cause convergence problems. So a perfect resistor is fine, but a perfect diode would have ...

4

Quasi-square-wave quasi-resonant converters also called QR converters are popular structures in ac-dc chargers for notebooks and portable electronics. They are popular because: they operate permanently in discontinuous conduction mode (DCM). they remain a first-order system easy to stabilize despite a right-half-plane zero located in high frequency (versus ...

3

What is the unit of inrush current? Ampere. It's a current. Typically, you'd look at peak current. As you can see from that, it's not really a meaningful thing to give on its own. How can we identify (thus test) the inrush current provision of a power supply? Short circuit the output. Observe the current through the short with a fast measurement ...

3

For the case of a periodic signal with period $T_p$ you can use a different formula for the rms, and not worry about the integration limits going to infinity. $$f_{RMS} = \sqrt{\frac{1}{T_p}\int_0^{T_p} f^2(t) dt}$$ With this definition, you should be able to simply calculate the RMS value of your periodic signal directly from the formula.

2

If you are controlling the pulse width but not using a DC restore circuit, it will mean that at a high value of duty cycle, the peak voltage from the transformer will not be enough to properly turn on the MOSFET. Fact: the output of a transformer must have an average value of 0 volts and if the original pulse shape is 10 volts for 90% of the time, it will ...

2

This is quite difficult to achieve and in some sense still a topic of research, there is not a surefire way to stack MOSFETs in series and assure the voltage will be divided evenly at all times during operation. You gotta think about it like this, whoever has the highest impedance will have the most voltage, if it is too high it will break and then the next ...

2

In a sense all components in LTSpice are ideal, but generally networks of them are used to simulate imperfect real components, with greater or lesser fidelity. Sometimes the defaults give you imperfect components, but you can always override that by choice. It often helps to use perfect components in a first cut proof of principle circuit, before turning up ...

2

Idea My current approach is as follows: Here when the current exceeds the limit set by the variable resistor (the one between Vref2 and GND), the output of OPAMP will clamp to ground, so the led will illuminate which in turn will decrease the Vout, thus the output current. Solution I've successfully implemented the following solution: ...

2

If one was to design at the output a low-pass PI filter with a cutoff frequency of 10kHz for example (purely hypothetic), how would one proceed? You would proceed by going backwards and recognizing that you already have capacitance on the output of your current circuit so, all you actually might require is an LC low pass filter to tack on to the output. ...

2

What is your technical definition of a PWM controller? – Andy aka @Andyaka A circuit that changes the duty cycle of a constant frequency pulse wave outputs in response to analog inputs OK, just like an LTC6992 then. Does anyone knows if it is a useful practice to build a PWM controller from discrete components or not and why? I'd say it's not ...

2

Why is it driven with rectified mains which equals to 375 VDC? It isn't, the rectified mains is alternately switched onto the primary of the flyback transformer (in order to store energy) then it is disconnected thus allowing most of that stored energy to be transferred to the secondary winding. U1 does that switching: - the duty cycle does in fact, like ...

2

Standard computer ATX power supplies are not isolated contrary to your understanding. The mains plug earth/ground is internally connected to black ground wire of the output side. Therefore, if you connect two ATX computer power supplies to earthed mains sockets, the black ground wires are already referenced to same potential as they are connected together ...

2

When in doubt, read the datasheet, apply some circuit design knowledge, and maybe go dig up some applications notes. The SG3525 has become a standard part, so there may even be books written around it. If you look in the datasheet, you'll see that the error amplifier gain is stated as a transconductance, with a range of $1.1\mathrm{mS} < G_m < 1.5\... 1 The reason I'd like to know the inductance at the secondary is to calculate some RLC filter with it (to match the output filtering to my desire), You are misunderstanding how this forward converter works; it appears you might be thinking it operates like a flyback converter, which it doesn’t. The inductance that can be used in the secondary in terms of ... 1 A typical flyback design From my understanding, if we go above the primary peak power, the transformer will saturate. How this CCM mode overcome that? It's better to talk about reaching a peak in primary current rather than a peak in primary power because it's an excess of current that creates core saturation. So, if you define$I_{MAX}\\$ as the ...

1

the electrical representation of leakage flux is leakage inductance. Leakage flux : It is that flux which is doesn't link primary and secondary. Useful flux is that which links primary and secondary.

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I would like to know why leakage inductance is function of the air gap transformer. How does it influence the leakage flux ? What is the relation between them ? With a transformer core of high effective magnetic permeability, you could say that the flux produced by one winding 99.9% couples to the other winding. The closer the coupling is to 100%, the ...

1

I thought input capacitors are used only for providing a constant DC supply during power interruptions to the downstream circuit. In the first image, it is writter as "Add cap for filtering high peak currents". I dont understand how a capacitor can filter high peak currents. Please explain with an analogy. Capacitors can't provide DC current when the power ...

1

SMPS switch at high frequencies to reduce the magnetics. Because of this switching, the current in some traces are discontinuous; i.e. the current switches from some very high value to zero at high frequencies. These currents need to be delivered by your source which can be at some distance. The distance (pcb trace, cable etc) translates itself into ...

1

I dont understand how a capacitor can filter high peak currents The input capacitor provides an unambiguous source of energy during the switching cycle. The level of energy required by the switching circuit can be high over a short period of time and, this can collapse the external input power supply if a capacitor is not used. When that "instantaneous" ...

1

You can control the noise pickup by using the usual copper-foil of planes, to be magnetic shields. And the planes are of course fine electric-field shields, as long as you tie the E_field collection regions to the larger Ground system to prevent radical upsets of the pieces of metal by "displacement currents". I suggest you design your discrete analog sense/...

1

If you use a depletion mode PMOS, you must apply a voltage on the gate higher than what's on the source (or drain) in order to stop it from conducting. Since the source (or drain) is often connected to the highest potential in the circuit, that would be inconvenient. In this case, the drain is connected to VBAT, so you'd need a control voltage at least ...

1

I don't know how the minimum current specification of the SSR will affect the operation of the power supply. This should be OK. The SSR leakage current spec of 3.0mA max at any rated voltage, which implies for 240Vac a power leakage worst case of 720 mVA. This may charge up the input caps to some voltage and may be unsafe to touch the input voltage but is ...

1

Your waveform is poorly labeled. See this example And we have: $$I_{AV} = \frac{I_{max}+ I_{min}}{2}$$ $$I_{RMS} = \sqrt{I_{AV}^2 +\frac{(I_{max}-I_{min})^2}{12}} \approx I_{AV}$$ Now you can try to figure it out yourself.

1

As you correctly pointed out, a quasi-square-wave resonant converter colloquially called a quasi-resonant converter (QR) is a self-relaxing converter: there is no clock in the controller except for clamping purposes. The switching frequency varies with operating conditions. It is low at low line and high power, it is high at high line and low power. QR ...

1

That switch could do anything. More often than not, especially on Chinesium power supplies, having a switch like that indicates a lack of a PFC stage. 1) That switch most likely switches which taps on their transformer are used. Say their supply needs 60V on the secondary, for 120 you need a 2:1 ratio, for 240 you need a 4:1 ratio. They may have 2 2:1 ...

1

When an inductor is not saturating, the inductance is constant because magnetic permeability is constant. This applies when applying an AC waveform or applying a moderate AC waveform superimposed on some moderate level of DC current. If the core is not saturating the inductance measured (or predicted) is constant. If the core is saturating then there are ...

1

As I said in the comments, before attempting to stabilize a converter of any type, you need its control-to-output transfer function. The problem here is that the data-sheet of this Alpha & Omega chip is eloquently empty so difficult to figure out what its internals are. Anyway, I have captured a schematic using Elements, the SIMPLIS free demo version in ...

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