All Questions
Tagged with switch-mode-power-supply mosfet
161 questions
2
votes
0
answers
84
views
MOSFET gate charge, rise and fall time
The gate charge is selected from the datasheet of the MOSFET given in the application note of Texas instrument for phase shift full bridge converter.
I don't have any question regarding the charge ...
- 730
1
vote
0
answers
112
views
Why does this push-pull converter fail?
Consider the following circuit of a push-pull converter. I would be interested to learn why you think it fails (MOSFET and controller).
The controller is a UCC28084. The MOSFETs are SSM3K361R (i.e. ...
- 23.4k
2
votes
2
answers
214
views
Calculating junction-to-ambient temperature rise for switching MOSFET
So I'm looking at datasheet's since I'm looking for a N-Channel MOSFET for a DC-DC Buck Converter that will be switching at 1.2MHz. Since the MOSFET will be used as a switch for the Buck Converter, I ...
- 275
0
votes
1
answer
98
views
Do all SMPS ICs have an internal dead-time for the MOSFETs, specifically the LTC7878?
I am trying to improve myself in power electronics and currently trying to build a Buck-Boost converter. I chose LTC7878 for this purpose since it meets my requirements.
My issue is that while I am ...
3
votes
2
answers
1k
views
Best way to drive multiple LED strips at distinct times with one LED driver
Application:
6 LED strips: each strip has LEDs connected in series
Driver is TPS92691 (CC LED driver)
The source is a battery
The LED strips will be flashed in a carefully controlled cycle, starting ...
- 417
0
votes
1
answer
42
views
Analysis for the peaks in FFT
Suppose I have 2 cases:
1st MOSFET switches with rise times and fall times of around 10ns (Vds).
2nd MOSFET switches with rise times and fall times of around 50ns (Vds).
Both of them have a switching ...
- 295
0
votes
1
answer
80
views
FET selection and quantity for buck-boost converter design
I am working on designing a buck-boost converter where the input voltage is 24 V regulated, and the output voltage ranges from 12 to 48 V with a current rating of 5 A. The design should also allow for ...
- 534
1
vote
2
answers
146
views
DCM vs CCM Noise Spectrum
Will the noise spectrum (at the LISN) due to switching of a Synchronous Buck DC-DC converter be different (peaks) if the converter is operating in DCM (Inductor current) compared to CCM keeping the ...
- 295
0
votes
0
answers
67
views
Pspice simulation not working
I am simulating the evaluation board LM5145EVM-HD-20A on Pspice.
(https://www.ti.com/tool/LM5145EVM-HD-20A)
LM5145 already has the Pspice model for the same but the switches used are not Pspice models ...
- 295
0
votes
2
answers
98
views
Minimum on-time does not depend on MOSFET
I would like to better understand this topic: Minimum ON time for a buck converter
One of the answers seems to say that the minimum on-time depends on the selected MOSFET. According to the datasheet ...
- 2,610
0
votes
0
answers
39
views
Switching Freq. and Output voltage error
Attached is the datasheet for the Synchronous Buck Controller: https://www.ti.com/lit/ds/snvsb32b/snvsb32b.pdf?ts=1711536038118&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FLM5145EVM-HD-20A
...
- 295
4
votes
2
answers
161
views
MOSFET SOA relevant for switching power supply design?
I am picking the low and high side MOSFET switches for a 2 amp output buck converter, simplified schematic shown here. Vin = 20 V and Vout = 15 V.
The IC manufacturer has a spreadsheet for ...
0
votes
0
answers
134
views
What's causing this ringing? GaN SEPIC Converter Gate Ringing
I'm designing a SEPIC converter using a HEMT GaN from EPC (EPC2204) and a dedicated GaN driver IC (1EDN71x6U). I've been in this loop (mind the pun) trying to mitigate gate ringing, and I'm having a ...
- 325
0
votes
1
answer
67
views
Double Pulse Schematic
I had a doubt in the schematic of the gate driver part of the following double pulse test circuit.
Do I need to connect the source pin of Q2 to VDDB? What will be the path of the current during ON and ...
- 295
0
votes
2
answers
58
views
Acoustic Noise on SMPS
I'm developing an RGB LED driver and noticed some acoustic noise from the power supply.
The power supply is a cheap brandless 12V 20A, output voltage ripple is under 800mV @4A @50% duty. I have no ...
0
votes
1
answer
75
views
Simulation time for Full bridge
This is a full bridge circuit which I am trying to simulate in Ltspice with a snubber. When I use ideal switches instead of MOSFETS, the simulation works fine. But when I use the real mosfet models, ...
- 295
0
votes
0
answers
195
views
Why do we need a small external gate to source capacitor for a MOSFET drive circuit?
I have a question regarding a MOSFET half bridge driver circuit. We always connect a small capcitor between the gate and source of both the high side and the low side switch, typically in picofarads. ...
- 357
0
votes
1
answer
161
views
PCB trace width and high current with MOSFETs
Having designed the PCB for my double pulse test circuit I'm facing problems with the trace widths. Operating current is 30A and I checked on the trace width calculation sites and they are coming up ...
- 295
4
votes
1
answer
122
views
What is meant by Switching charge ( under Gate charge characteristics) in the given MOSFET datasheet?
What is switching charge in this MOSFET datasheet?
The switching actually takes place during Miller region. Hence I belive Qgd should be called as switching charge. But looks like the remianing gate ...
- 3,156
0
votes
1
answer
219
views
Why is an LLC converter designed to operate in the ZVS region? how does the Resonance in the LLC circuit contribute to low "MOSFET losses"?
For the first question I understand that operating in the ZCS region can result in shoot through but why does that happen?
I understand that an LLC converter uses the leakage inductance of the ...
0
votes
1
answer
47
views
Why is my simulation not loading when V2 has no current?
I'm trying to make a two power source circuit that regulates 9V6 to 5V. The supply is not gonna be connected all time, but I want to make sure that when it is connected, just uses the voltage supply, ...
0
votes
0
answers
53
views
Microcontroller mosfet switch
There are three different processors in my circuit. These are STM32F401RCT6, ATmega328P and ESP32. I want to turn these processors on and off with the switch whenever I want. The circuit I created for ...
0
votes
0
answers
94
views
How to decide the number of layers? [duplicate]
I am new to PCB design and I want to understand how exactly we should select the number of layers. I just know more layers helps us with making the routing easy but I don't understand what is power ...
- 295
3
votes
2
answers
541
views
Which is the more important switching parameter in MOSFET datasheet? Turn on/off/delay times or Input/Output/Reverse capacitances?
I see both capacitance and timing details mentioned in the MOSFET datasheets.(Ref:)
Which one should be considered for comparing the MOSFET switching performance between 2 MOSFET part numbers?
Note: ...
- 3,156
0
votes
2
answers
189
views
Why do my MOSFET keep blowing up saying the gate-drain voltage exceeds its rating?
I'm working on a switched mode power supply that outputs 9 V in a simulation using a NE555 timer connected to the gate of my MOSFET and switching at 96 kHz frequency. Other components works just fine ...
- 1
5
votes
3
answers
940
views
Does turn-on and turn-off delay cause MOSFET switching loss?
I know during rise time and fall time, there are MOSFET switching losses.
Is same the case with turn on and turn off delay?
I don't see any relevant pics in internet with the IDS waveform included. ...
- 3,156
0
votes
1
answer
80
views
Quad-Channel Smart High-Side Switch Schematic Review
I am using TPS4H000BQPWPRQ1 in my design. Below is my design. Can you please review my design especially current sense (PIN No 8) and current limit (PIN No 9) design?
In the datasheet page no 27 you ...
- 3,061
1
vote
1
answer
97
views
ZVS driver not oscillating - powersupply
I'm using a ZVS driver to create a spark for a plasma speaker. The circuit above is the one I'm using for my project however I have run into some issues whihc I do not understand. First of all the ...
1
vote
2
answers
158
views
MOSFET SOA: Why is the max current limit lower for DC case? [duplicate]
Shown above is the academic definition of MOSFET SOA. Rdson limit is not considered as a real limit in most academic texts - that's ok- understandable.
But why is the max drain current limit different ...
- 3,156
1
vote
1
answer
38
views
Why does this multi-phase buck controller have one phase to be driven by external driver?
https://www.renesas.com/in/en/document/dst/isl62883-isl62883b-datasheet
"The ISL62883 uses two integrated gate drivers and an external gate driver to provide a complete solution"
Why would ...
- 3,156
2
votes
1
answer
159
views
Multiple Source Terminals of SiC MOSFET
I want to know that most of the semiconductor top side cooled package have more than one power source terminal. I can understand by doing so you can minimze the loop inductance of gate driver loop ...
- 357
1
vote
1
answer
879
views
Influence of gate resistors and capacitors on driving gate of mosfet
Good Day,
I wannted to ask in a typical gate driving circut of a Mosfet, we always have Rgoff, Rgon,RGS and CGS as shown in below screenschot. What is the purpose of these components in driving the ...
- 357
0
votes
1
answer
150
views
One of the parallel SiC MOSFET is getting hot quick
I need your help here. One of the SiC MOSFETs (SCTH70N120G2V-7) on top is getting hot as I increase the voltage for boost testing with a 50% duty cycle circuit. I cannot understand why my MOSFET is ...
- 43
5
votes
1
answer
516
views
Why are MOSFETs connected in reverse for synchronous rectification?
I'm trying to understand how synchronous rectification works.
Here is an example in boost topology:
The function of D1 is to allow current from left to right and ...
- 429
4
votes
3
answers
2k
views
What is the purpose of using more than one MOSFET for switching in a switch-mode power supply?
As shown in the model, two MOSFETs are employed for converting DC to AC to be fed into the transformer. Why would we need a second one when a single MOSFET could handle the entire voltage?
- 71
0
votes
2
answers
978
views
What is the mode of MOSFET or BJT in buck converter?
I want to implement buck converter with conventional design (not synchronous etc) like below.
And I want to implement the converter for two cases. One is to use BJT as switching device and another is ...
- 11
-1
votes
1
answer
468
views
Why don't inverters use BJTs to easily produce a pure sine wave?
This has been in my mind for a while now, I'm curious. Why not use a BJT H-bridge on the high voltage side, to convert the high voltage DC to AC. I saw a simple circuit that converts square waves to ...
- 146
-1
votes
2
answers
114
views
Are SMPS (inductor) current limits mostly thermal?
I'm building a boost converter that needs to boost 200A for 1 second and then shut down. The vast majority of reading I've done on SMPS and various PSU topologies assumes an RMS current and high duty ...
- 325
1
vote
1
answer
269
views
Switching losses in a power supply
Switching losses calculation in resistive load and inductive load are different. For a full-bridge DC-DC topology with a resistive load at the output, should I calculate my switching losses like I ...
- 319
11
votes
4
answers
2k
views
How does this PNP transistor improve the switching performance of MOSFET?
My guess is PNP transistor might ensure fast turn off by shunting the gate capacitance (ie, when diode is reverse biased and the PNP is on.)
Additional questions:
Why is the gate current limiting ...
- 3,156
0
votes
1
answer
171
views
Sensing current into a battery while charging
I want to sense the current into a 84 V battery while charging and disconnect it when fully charged using a MOSFET. Is it advisable to use lowside current sensing? I used a noninverting opamp ...
- 101
0
votes
2
answers
408
views
Power loss in gate driver independent of duty cycle?
Inside a generic switch mode power supply a MOSFET is used. The switching frequency is \$f_{sw} = 300\text{kHz}\$ and the duty cycle is \$D=0.45\$.
To drive the gate of a MOSFET, we use a gate driver ...
- 4,559
1
vote
1
answer
206
views
Power MOSFET gate driver: voltage and current levels
Following are the doubts on the gate driver section of a forward converter.
Peak drive voltage = 7.4 V (Shouldn't it be higher, say 10 V or so, usually for driving power MOSFETS?)
Peak MOSFET gate ...
- 3,156
7
votes
4
answers
1k
views
Why is increasing gate voltage beyond 'reasonable' limits not advantageous in power MOSFETs?
In a power MOSFETs datasheet I see Rds(on) specified at Vgs= +10V whereas +Vgs (absolute max) is +30V. Why do they (manufacturers) restrict to +10V while quoting Rds(on)? The manufacturer could have ...
- 3,156
2
votes
2
answers
218
views
MOSFET selection for buck regulator (SOA vs thermal dissipation)
I am trying to design a buck regulator with the following specification: Vin = 24V Vout = 5V I max = 8A Fsw=228k. The load is basically a long strip of RGB LED's. Which in certain cases would be all ...
- 757
1
vote
0
answers
177
views
Mosfet power dissipation in this example
I am trying to design a buck regulator with the following specification:
Vin = 24V
Vout = 5V
I max = 8A
Fsw=300k. The load is basically a long strip of RGB LED's. Which in certain cases would be all ...
- 757
0
votes
0
answers
128
views
Vin startup circuit for LM5021-1
I've recently got my PCB developed for a power supply unit using the LM5021-1. After testing i've concluded there's problems in the circuit for the Vcc pin. I've used the following circuit for this, ...
- 3
2
votes
3
answers
1k
views
How does junction to case thermal resistance depend on PCB?
Shouldn't the junction to case (top or bottom) thermal resistance depend only on package or IC internals? How do the PCB details play a role as mentioned in footnote 1?
- 3,156
1
vote
4
answers
597
views
Why is it bad to drive a MOSFET asymmetrically using BJTs?
And by that title, I Mean that the drive current to the gate of the MOSFET when the BJT is on differs from the drive current for when it is off. I know that it would cause a difference between Toff ...
- 633
14
votes
2
answers
6k
views
Suicidal ASUS power brick?
I was playing around disassembling an Asus laptop power brick (19V, 4.74A) and came across this strange arrangement in the circuit, where just after the bridge rectifier, there is a MOSFET (Q1, N ...
- 857