# Tag Info

0

Yes, there's several ways to do this. Use a buck-boost converter This kind of device adapts based on the ratio between input and output voltage. They have three modes: Buck, LDO and Boost. Since your max LiPo voltage is 4.2V or so, the converter would be in LDO mode, then Boost mode as the battery drains. Use a boost followed by LDO Before there were ...

0

It is a switch mode regulator. It first turns on to allow current to flow into the coil, and when it turns off, current must keep flowing to output to release the energy to output, so the diode allows it. The less voltage drop over diode, the more efficient the buck converter is.

5

Figure 1. Buck converter. Inductors don't like you to change the current suddenly. When you try large voltages are induced. In the on-state current flows through the inductor to the load and the filter capacitor. In the off state there is no current supplied by the PSU. The inductor tries to keep the current flowing and since the right side of the inductor ...

2

D1 is not best described as a 'catch' diode. That's a better description of the diode across a relay coil, which 'catches' the high voltage transient when its driver turns off. In a buck converter, best to call it a 'freewheel' diode. During the on phase of the IC, the output is taken up to the input voltage. Current flows from left to right in L1, ...

4

I have a 12 V DC input that I am stepping down to 2 V with 610 ohm resistor. When power is removed the light is staying on for a period of time and slowly dims. I suspect that you mean when you switch off the mains power that the LED fades out. simulate this circuit – Schematic created using CircuitLab Figure 1. An old-fashioned power supply driving ...

0

What I would like to make clear is what exactly do we mean by input/output impedance, what the above Z_out,Z_in are supposed to represent $Z_o$ is the external impedance connected to the buck converter's output. $Z_i$ is the impedance presented by the buck converts input to the power source. how can I achieve impedance matching with the source, ...

0

It may not be enough, depending on what you are doing on the tablet. It may try to pull more current than just 1.5A. And the tablet may need the battery sensor connection, as its not just power and ground. Some devices are finicky about that (for example, a Mifi 7700 hotspot). You can certainly try it to see if it will run or not.

1

The way I would think of this is that the 25uF capacitor and associated 1N4148 diode form an analog of the output voltage on the mains side of the transformer. I think there's something wrong with where the zener diode and/or 3.9K resistor goes- it should inhibit the base drive of the BJT to regulate the voltage. Edit:- The red LED effectively goes on ...

0

Just commenting on Janka's idea that a 5:1 ratio is the practical limit to boost converter design. These kinds of limits only apply for continuos mode boost converters. In discontinuous mode, there are no such limits at all, I've built converters of this type with a 50:1 upconverting ratio, while maintaining reasonably high efficiencies. Since control ...

0

Why do we need a diode there? You need a snubbed to catch excess stored energy that isn't delivered to the secondary circuit. You need a diode to prevent the snubbed taking current when switch S1 activates and ruining efficiency. The snubbed should only take current when the back emf from the primary rises above the bus voltage, Vin.

0

This is a snubber circuit. Together with R3 and C3 the diode catches some or most of the ringing on the primary side and burns the excess energy in R3. D2, D3 and D9 are part of it as well and clamp the maximum voltage. More about it here: Wikipedia snubber

0

The FAN6754 will shut down when the supply drops below 9 volts and not restart until that voltage rises above 16.5 volts. Given that it can work at a peak supply voltage that is closer to 30 volts, it seems that more turns on your auxiliary winding might be the route to go.

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 ...

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/...

0

This answer is just to summarise up the John D's explanations. The "primary coil" (which is connected directly to IC) must reserve enough energy for the "secondary coil". Since the inductor current is discontinious, it is possible only when the load consuming enough current is applied. Without it the circuit will not work correctly - in my case the output ...

0

The fast low drop diode should have fixed things but it did not .If you are far enough down the design path and therefore feel that you must persist with the chip then try a diode in series with the input .This series will waste some voltage but it will stop the chip blowing up .

2

Trace at point A carries high di/dt current so it should have low inductance to the decoupling capacitor to minimize voltage spikes. $e = L \frac{di}{dt}$ and in dc-dc converters di/dt is pretty high so you want to minimize L. A few amps switched in a few ns with a few nH inductance = VIN drops a lot when it switches. I've had a case where this trace ...

5

Wider traces exhibit less resistance, but more significantly less inductance. The lower resistance and inductance helps a little bit with efficiency, and a little more with ripple, but the larger gains are in EMC. A lower inductance trace radiates less, particularly in conjunction with a solid ground plane.

3

Picking a topology for a DC-DC converter starts with defining the requirements. Personally, I'd first check the necessity of isolation. If it is not necessary then, depending on the relationship between VOUT and the range of VIN (e.g. check if output voltage will be lower than input voltage for the whole input range, as in your case) I'd go for buck (output ...

4

I recommend picking a topology, and running down the design path enough to get a feel for if you can meet your requirements. If you can't, and can't see a way to easily fix it, move on to the next topology and repeat. If you run out of topologies, edit your question to reflect the work you've done, where you're having trouble meeting the requirement, and ...

0

Linear regulators are good at load-dependent filtering of low-frequency noise (say under 1000 hz), but useless for filtering the lion's share of high-frequency switching noise in switch mode power supplies and boost converters. It depends on your power needs, but a good solution is to run the output of your boost converter into a well designed capacitance ...

0

So I figured out the problem was due to the fact that the capacitor (C10) was located physically too far from the MT3608. Hopefully someone can learn from my mistake :)

0

Even with a bit of unknown in your system spec requirements, here are my thoughts. You mentioned 2 ways to control the load power rail: On-off switch upstream the DC-DC converter (switching Vin) On-off switch downstream the DC-DC converter (switching Vout) I would add one more: Controlling the DC-DC converter on-off state through a built-in Enable or ...

Top 50 recent answers are included