All Questions
Tagged with switch-mode-power-supply mosfet
161 questions
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
12
votes
2
answers
5k
views
What is the purpose of using MOSFET instead of free-wheeling diode in Buck topology?
(Source)
I usually see Buck circuit models in which a MOSFET is used instead of a free-wheeling diode. What I understand from the Buck topology is, when the upper MOSFET is off, it doesn't matter ...
- 14.2k
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
10
votes
1
answer
2k
views
Do AC inverter H bridges ever get driven this way?
There's a google competition going on at the moment called the little box challenge. It's to design a very efficient AC inverter. Basically the inverter is fed a DC voltage of a few hundred volts and ...
- 473k
10
votes
2
answers
3k
views
Why do my push-pull driver drains ring so much?
I have read What is killing my MOSFETs which seems to present a similar circuit to mine (my secondary is center tapped as well and has 2 high-speed diodes rectifying into a 10R / 400uF load)
The ...
- 2,524
10
votes
3
answers
1k
views
What causes this knee in my MOSFET drain voltage drop?
FINAL UPDATE: Understand a previously mysterious power MOSFET switching waveform wiggle! @Mario uncovered the root cause here below, distinctive to so-called VDMOS devices, typical of many power ...
- 7,152
9
votes
4
answers
1k
views
Full bridge driver capacitor ringing problem
This is my first time designing a full bridge driver. I am experiencing problems with ringing on the output. I have made a pcb for it. This is a picture of the top side of the board.
Backside
Input ...
- 99
7
votes
2
answers
7k
views
How does power dissipation for surface mount components work?
I know that with usual through hole components we can attach heatsinks etc. But how does it work with surface mount components? Is having a copper plate around the component the way to go? How do we ...
- 1,831
7
votes
1
answer
3k
views
Boost SMPS getting very hot. Why?
I tried to experiment with boost SMPS with multiple supply rails and I almost burned myself when touching parts when running.
Here is the circuit and the part getting hot:
simulate this circuit &...
- 2,883
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
6
votes
1
answer
9k
views
Driving a MOSFET with Negative Off- State Gate Voltage
I know in practice Mosfet switches are driven by 0V to any Positive gate voltage (e.g. 0V - 15V). I am using a Mosfet pair (PMOS and NMOS) to switch 10A currents in pulses and the datasheet of MOSFET ...
6
votes
1
answer
4k
views
Transistor PWM Generator (No ICs) for practical application
I want to produce a good quality PWM signal with transistors(BJTs, FETS, etc..). I do not want to use an IC at all(learning to use transistors properly). I'm currently using a BJT Astable Mutivibrator
...
- 235
5
votes
2
answers
1k
views
What is the purpose of this sense pin in dual MOSFET package? [duplicate]
No info available in datasheet
http://www.aosmd.com/res/data_sheets/AONP36336.pdf
After going through the answers I got some additional doubts:
Why is the sense pin only there for high side MOSFET?
...
- 3,156
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
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
5
votes
1
answer
4k
views
IRF44n and push pull regulator topology
I'm studying the typical circuit implementations of push pull regulator topology.
I have a question about it's off cycle. When the secondary get exited on the off cycle
there is a back EMF also exited ...
- 1,705
4
votes
5
answers
8k
views
Why is the MOSFET driver in this circuit dying?
This circuit kills the driver (an IR2104s) when under normal conditions.
Bat+ goes to a 12V lead acid battery.
In+ goes to a 20V laptop power supply, though it is intended to be a solar panel instead....
- 276
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
4
votes
6
answers
2k
views
Buck converter MOSFET (IRF4905) heating up
I tried to build a buck converter without any ICs, just transistors, a diode and passive components. Its purpose is to convert 12V to 5V at 2 Amps. It works, but the switching MOSFET (IRF4905) heats ...
- 81
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
4
votes
2
answers
801
views
5V 5A rail controlled by 3.3v microcontroller - dual switching or power mosfet?
I think this is a common situation so hopefully an answer helps more than just me. I have a 3.3v low power MCU which will be controlling a 5v 5A run of LEDs. When the LEDs are off the system will go ...
- 41
4
votes
1
answer
6k
views
Current spikes when MOSFET turns on and voltage spikes when MOSFET turns off
I studying for my Power Electronics course and have come across something which I can't seem to wrap my head around.
In a lab, we built a buck converter with an inductive load and measured various ...
- 43
4
votes
1
answer
2k
views
Push-pull switch mode power supply using an attiny84
simulate this circuit – Schematic created using CircuitLab
I'm trying to build a "push-pull" switch mode power supply. I'm not entirely sure if that is the right term, but it consists of ...
- 1,259
4
votes
1
answer
677
views
Synchronous DC-DC converter and fast diodes
I'm a bit at a loss when trying to optimize a DC-DC converter (Half Bridge) and selecting my MOSFETs.
Up to 200V I get good results (MOSFET switching times are fast ~ 20ns and the anti-parallel diode ...
- 860
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 ...
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
3
votes
2
answers
542
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
3
votes
5
answers
5k
views
MOSFET is not turning off when the gate terminal is grounded
This figure shows a small portion of my circuit:
The maximum Vgs of the MOSFET is 20V. The MOSFET is initially turned on and now I want to turn it off. For that I am grounding the terminal A to ...
- 1,635
3
votes
1
answer
1k
views
Why turn-on speed of a MOSFET is linked to diode reverse recovery time
Here is a quote from section 3.4 "Speed-Enhancement Circuits" in "Fundamentals of MOSFET and IGBT Gate Drive Circuits" written by Texas Instruments:
When speed enhancement circuits are mentioned, ...
- 2,610
3
votes
3
answers
10k
views
Choosing the correct Gate Driver for a MOSFET in a DC-to-DC Converter
I am building my first simple buck converter, stepping down 12 V to 5 V and driving a small load of 5 Ω - 10 Ω. Something like the following:
or:
The above images both show an N-channel MOSFET. I am ...
- 1,191
3
votes
1
answer
2k
views
10kV high voltage switch using mosfet stack
I need to make a pulse generator for a 10kV power supply, few mA.
Surprisingly, I could not find any standard design of HV switch using mosfet (Sic or not) stacks.
Could someone give me some ...
- 31
3
votes
1
answer
3k
views
MC34063 Current Mode
I'm trying to build a LED driver using an MC34063 dc-dc converter in step up mode. Since LEDs need current mode operation to run stably, I elected to use a 51mOhm current sense resistor combined with ...
- 567
3
votes
0
answers
882
views
Large negative current spike in N-Channel MOSFET source when turn-off
I am working on repairing a power supply board of a LCD TV (200W power), more specifically, the PFC section (active power factor correction). See schematic (adapted from here):
I've replaced some ...
- 159
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
2
votes
2
answers
397
views
pulse width modulation versus amplification
If I want to make a sine-wave inverter where the output AC voltage is lower than the input DC input voltage, how can I see that using pulse-width modulation will be more efficient that just using a ...
2
votes
3
answers
4k
views
Switching 60V with 3.3V microcontroller at 50kHz - 1MHz
I'm playing around with some switching mode power supply things. For this reason, I'd like to switch the input voltage with a microcontroller, from the PWM output or other output pins.
The specifics:
...
- 444
2
votes
3
answers
814
views
Can GaN FETs be driven directly by logic level signals?
I've gotten interested in using GaN FETs for their combination of fast switching speed and very low on-state resistance. Most of the eval boards (for example by EPC) use GaN driver chips such as ...
- 3,541
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
2
votes
1
answer
4k
views
High side N-Channel IGBT/Mosfet drive methods
According to this paper http://www.fairchildsemi.com/an/AN/AN-9742.pdf
"However, a transformer may cause half bridge crossconduction due to the offset voltage of
gatepulse deadtime stage."
...
- 1,022
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
2
votes
1
answer
1k
views
Why is an Enhancement P-Channel MOSFET Used?
I'm trying to design the power circuit for my project. I wanted to implement both USB and a LiPo battery to power it. I came across this circuit online but I'm struggling to understand how it works.
...
- 428
2
votes
2
answers
1k
views
Optocouplers driving MOSFETs in an inverter
For many hours I was trying to simulate in LTspice XVII an optocoupler driver for MOSFETs in an inverter. My project is to build a SMPS with linear voltage stabilizer (I didnt put it on the schematic ...
- 25
2
votes
1
answer
992
views
How does the PWM from MCU get translated into a output voltage as in Power Electronics [closed]
Background: I am preparing for a full-time employment starting in May. I am coming from a computer engineering background so I only have some working knowledge regarding EE. The job duty is Firmware ...
- 23
2
votes
1
answer
1k
views
Calculating the switching loss IRF44n
I'm trying to get rid of this heat problem , I know that I have to use heat sinks according
to it's specification , but the problem here is there's no space for that heat sink.
So I do have to need a ...
- 1,705
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
2
votes
1
answer
124
views
Balancing the short trace requirement with the thermal ones
I'm designing a substantial (200W) buck converter with the LT3840 (datasheet) controller (but the question is not really part specific). As usual with these parts the datasheet says:
Minimize the ...
- 8,744
2
votes
1
answer
3k
views
SMPS test circuit PWM controller not switching the MOSFET
Trying my fingers on a very old SMPS circuit (15+ years) section.
The open loop test circuit generates 25 kHz pulse train (12 V - 0 V) with 50% duty cycle as designed in the actual SMPS circuit. ...
- 175
2
votes
1
answer
812
views
How much power IRFP460 can proccess?
I decided to use IRFP460 in a two-switch forward converter. This Mosfet can dissipate 280 watts. Can I get 1000 Watt from my converter?
As a general rule how much power a Mosfet can transfer with ...
- 47
2
votes
2
answers
2k
views
High side Driver Issues
I am currently developing a small low power (high switching) Buck converter and have run into a strange issue that I have never seen before and was looking for some insight into the issue. I am also ...
- 21
2
votes
1
answer
1k
views
How to adjust this circuit to use N-Mosfet instead of P-Mosfet
Background information
(You can skip this part if you just want to answer the question by heading straight to the "The Question" paragraph)
I'm a hobbyist in electronics and a professional ...
- 541