# Questions tagged [buck]

A non-isolated DC-DC converter topology which outputs voltage less than or equal to the input voltage

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103 views

### Buck Converter PCB Planes

I have a question about PCB copper planes with buck converters. For reference, I'm using the LM2673/LM2679. The parts are identical in layout, utilizing the DDPAK/TO-263-7 with the PCB tab being ...
25 views

### Startup current for buck converter controller

In this Reference Design, a buck converter was designed using the UCC28881 controller. According to the datasheet, the HVIN pin is a current source, with an internal supply current of 58 uA typically....
104 views

### Laptop adapter + DC buck/boost converter or buck convereter only?

I have an old laptop adapter, with 19 V - 4.74 A DC output ratings. Suppose I need to draw 3 A @ 11.1 V for one of my circuits. I have been doing some research about dc-dc converters and have some ...
41 views

### Minimum Input Voltage of Buck Converter

How do I determine the minimum voltage for a buck converter to work? For example, in this Reference Design the minimum voltage is 166VAC. But what if I want to operate it at 100 VAC? What do I need to ...
119 views

### I can't get the desired output voltage

This is a simulation of a buck boost converter. I want to get -12V as the output voltage , but I get -1.148V. I checked the PWM and the duty cycle and it is right. I think that my problem in ...
65 views

### Buck-Boost Transformer with Three Phase Wiring

I live in a residence with 120v / 208v electrical service. (Measured as leg1: 124v, leg2: 125v, 215v across legs) I am nearly certain that the service is the result of two legs of three phase power. ...
110 views

### why are non isolated buck converters a safety risk with 120V DC?

So i've come to understand that buck converters CAN be used for 120V to 5V BUT they are not becuase they are often a safety risk. I also understand that they can be used if they are away from a ...
144 views

### 36x LED 5730 in series: diodes burnt when LED driver (based on BP9833A or MT7854BD) powered up

Background: I have 18W, 36 LED lamp fixture which I cannot change. Originally it has 2x parallel 18off 5730 LEDs and 300mA driver. It works for some time, but diodes starts burning. I thought that ...
48 views

### How to split high current low voltage? Voltage regulators , current regulators(?)

I am using a 20v dc laptop charger that supplies 4 amps. I need 5v dc 4 amps. When I use a linear voltage regulator itās too much current to pass through safely.. 15 amps change and 4 amps, so I use a ...
93 views

### Which buck converter can be used for 120 V AC to 5 V AC rated at 5 amps?

I have used buck converters that can move from 30 V DC to 5 V DC, their maximum current is set at 400 mA, I need 3.5 amps. I am looking to move from 120 V AC to 5 V AC. I'm then going to change it to ...
184 views

### Why does my comparator not compare?

I have designed a buck converter and I am baffled with its comparator's functionality. The op-amp comparator does not give a PWM, instead it gives an amplified ramp. What am I doing wrong?
75 views

### Distributing the output capacitance of a buck regulator

Buck regulators often specify the value and placement of the output capacitor. Typically 10ĀµF placed very close to the buck regulator. However, what would the effect be of replacing the 10ĀµF output ...
184 views

### Current Sensing on positive and negative voltage rails

I'm working on a design that uses two separate buck regulators to generate a positive and negative voltage, and I'm trying to implement current limiting with a current sensor. However, I am running ...
117 views

### Why Gate voltage must be higher than source voltage in N-MOSFET as High side switch?

In many circuit, like buck converters, MOSFET used in high side for switching, I've came across the term that Gate voltage with respect to ground must be greater than source voltage by +8V. For ...
79 views

### Buck converter output instability

First post here, mechanical engineer with not too much experience in designing circuits. I'm trying to control a DC motor torque via a buck; the motor is driven, so it's acting as a brake, and I'm ...
68 views

### Solar DC circuit: Preventing Buck Converter from Dropping out Due to Motor switching on/off (in Parallel)

I have an off-grid orchard which has a well pump running directly off of a 24v PV array. (27-32v when at full power) Parallel to this direct circuit, I have a buck converter to power a Raspberry pi (...
278 views

### PCB Layout advice for high current buck converter

I am building a dual high current buck driver for driving two fiber coupled laser diode arrays. This is my second attempt at a board -- my first attempt had excessive ringing due to the board layout (...
58 views

### How to model / control a FCCM buck (variable frequency)

I am trying to control the voltage of a buck in FCCM mode (where the half bridge grounds the inductor until the inductor current goes negative by X mA, and then turns it on again), but I am suffering ...
80 views

### Zener diode at the output of High-Side Buck Converter

I'm designing a buck converter based on UCC28881 and this Reference Design. The datasheet for the UCC28881 states that: 9.2.1.2.5 Pre-Load Resistor (RL) The pre-load resistor connected at the ...
55 views

### Input capacitor in buck converter

I've chosen this Reference Design as starting point. Here the schematic. I'm using full wave rectifier instead. I'm designing a buck converter with these requirements: Input voltage: 120-690Vrms AC ...
38 views

### Reverse voltage in LED buck converter circuit [closed]

The circuit simulate this circuit – Schematic created using CircuitLab Everything is fine except when the switch is open, I measure ~-3.5V on the points marked. Why is that and is it ...
48 views

### Limiting the current with the LM2679

I'm building a power supply, and I'm trying to see if the LM2679 will fit my needs. I like how it's similar to the LM2596 as well as the fact that it has a pin to limit the switch current. However, I ...
76 views

### Buck Converter with RLE Load

I am trying to calculate the duty cycle of the buck converter as in the figure for discontinuous conduction mode of operation. I have worked to the math and have got the following graph as in the ...
118 views

### Limiting input voltage for buck converter

I want to power some micro controllers and a couple of leds on my electric bike, counting up towards 5 Amps. Power supply is a 36V battery, with a range of about 42V to 33V. This voltage is to be ...
53 views

I'm having a hard time explaining to myself why the output voltage of a buck regulator drops at the load when the load pulls more current than the max limit of the buck regulator. Can someone help ...
32 views

### Buck converter simulation issues

I am trying to use a buck converter to step down a 48v to 33v. The confusing part is that I am trying to simulate it using LTspice and I canāt figure what how to control the nmos with pulse width ...
46 views

### Buck converter ringing on rising and falling edges before failure

I have recently designed a PCB with a buck converter based on the LM3671 buck converter IC from TI to step down 5V to 3.3V. However, there is ringing on the rising and falling edges, and after a short ...
534 views

### Is it better to have a higher Vgs than Vds on a MOSFET (n-channel)?

I've been studying MOSFET switching applications recently, and have been playing with the Circuit Simulator Applet here. In my diagram below, I have Vds usually set to either 12 or 14, as I am trying ...
85 views

### Buck Converter Capacitor and Inductor Characteristics

I'm trying to make a buck converter with this mickey-mouse MC34063A chip that will step-down +5V to +3V3 up to 500 milliamps. I've gone through the calculations by hand and validated them with an ...
574 views

### How does LTSpice model reverse recovery time?

Hello everyone, I am working on the prediction of the reverse recovery losses in a Buck converter. I have the following schematic: You can see below a zoom on the turning-off time of the diode: I ...
64 views

### Load impedance simulation of buck converter

I would like to design a buck converter that will feed a printed circuit board that contains an inductive load like a DC motor and a relay, and some capacitive circuits like RLC filter. I have started ...
76 views

### Why capacitor value should be greater than gate capacitance of gate of NMOS in Bootstrap topology?

In case of buck converter when NMOS is used as high side driver then bootstrap circuit is used to keep gate voltages higher. While designing that bootstrap circuit, the value of capacitor is ...
82 views

### How to charge an android device with a buck converter

I've got a male micro USB connector like this one I'm feeding the output of a buck converter set at 5V to pin 1 positive and pin 5 negative. Remaining pins are not connected. When I plug the ...
87 views

### In a buck boost inverting converter is there any difference exchanging the position of the diode from the positive to the negative rail?

In a buck boost inverting converter is there any difference exchanging the position of the diode from the positive to the negative rail keeping the same current rotational direction ?
24 views

### What modifications can I do in my simulation so Vg must not exceed 20V?

I have implemented gate driver of Buck Converter. But when input voltage exceeds 20V then Vg also exceeds 20V wich is threshold value of transistor. What modifications should I do so that my gate ...
52 views

### Low profile buck converter [closed]

This is a follow up to my previous question regarding USB-C power delivery as a power source. There's been a fair about of development since when that question was asked and since STM have released a ...
97 views

### In Buck Converter, when the ESR and EPR of Inductor increases then what is the its effect on output voltages and why?

I have done LTSpice simulation. I have seen that by increasing ESR of inductor, the output voltages decreases and by increasing EPR of inductor the output voltages and ripple in output current and ...
34 views

### Buck converter output power definition

I'm designing a buck converter to feed the following loads: A control circuit 3.3V/100mA A 80V solenoid which has a DC resistance of 300 ohms. This means a current of ~270 mA. My plan is to ...
256 views

### Slope compensation in current mode control

There is something a little bit confusing to me between papers dealing with the theory of external slope compensation in current mode control of SMPS and application notes dealing with implementation (...
54 views

### Add isolation to a switching power supply

Actually I'm using a simply switching buck regulator that perform a 24v to 12v convention. I'd like to add isolation between power source and regulator. I've checked already all-in-one isolating DC-DC ...
443 views

### What will happen if you supply a higher voltage to a buck converter? [duplicate]

The title says enough, but letās give a real life example too. Take one of those LM2596 35V boards. What will happen to it if it gets 50V on the input? Most likely it will burn, but will this voltage ...
31 views

### Current mode buck modeling

I am following this document Loop response consideration in PCM. Here I am implementing fig 5 schematic in page 9. From equation 1 to 22 got me some of the hidden values of the schematic which I have ...
418 views

### Optimizations for LM2596, Positive and Negative Voltage

I'm working with the LM2596 to get a positive and negative voltage using two separate IC for each. I'm having trouble optimizing them for a 1 A load. I followed along with TI's WEBBENCH designer to ...
52 views

### DC current at input and ouput capacitance of buck

I'm working on this website http://www.onmyphd.com/?p=voltage.regulators.buck.step.down.converter Could someone help me to understand those two statements: 1) "since the DC current of the inductor ...
62 views

### Rectifier to Step Down Buck Regulator

I'm trying to simulate an AC to DC voltage regulator. I'm trying to go from 115 Vrms to 5 V DC at 1 amp max, though 0.5 amps nominally. I initially thought of using the LM317 at first, but after ...
5k views

### How to reduce MOSFET heating in Buck Converter

I have designed this Buck Converter which convert 60VDC to 12VDC at 10A. Switching Freq 100KHz. Facing MOSFET too much heating issue. MOSFET ON time and OFF time is decided by a UC3845B based circuit. ...
2k views

### High current buck converter has excessive ringing and poor regulation

I am designing a power supply to power two fiber-coupled diode arrays for a solid state laser. The diode arrays need a current controlled source of about 50 A and will have a voltage drop of < 2.2 ...
43 views

### PCM CCM Converter using SIMetrix/SIMPLIS

I have built the attached file which is a peak current mode buck converter on SIMetrix/SIMPLIS software but I cannot simulate due to some errors that I could not troubleshoot. Please can anyone ...
48 views

### SIMtrix/Simplis Simulator

I'd like to use SIMtrix/Simplis Simulator for simulation of SMPS design, and I'm about to start building a peak current mode buck converter like the one shown below from richtek.com: but ...