# Problems in 100W wireless power transfer project

#### myaeaindrathein1996

Joined Jun 11, 2021
16
I made an experiment for 100W wireless power transfer for my research. I used IR21844S for half bridge converter using IRFP360 MOSFETs. I designed the transmitter and receiver coils. I used full bridge rectifier using 1N4002 diodes and 2.2uF filter capacitor. I tested 10.5 ohms as a load by using an electronic load and measure voltage and current. I gave 24V dc supply for MOSFETs and 15V for gate driver. But the problem is that there is no current from the supply for MOSFETs and the power at the load is not even 0.1W. I planned to use schottky diodes in parallel with MOSFETs to reduce voltage spike and change schottky diodes in the rectifier of the receiver circuit. I used the frequency around 80kHz. I have no idea where I have the problems. I also simulated using LT spice and the simulation results are not that bad. Can someone help me or suggest any ideas?

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#### Deleted member 115935

Joined Dec 31, 1969
0
I made an experiment for 100W wireless power transfer for my research. I used IR21844S for half bridge converter using IRFP360 MOSFETs. I designed the transmitter and receiver coils. I used full bridge rectifier using 1N4002 diodes and 2.2uF filter capacitor. I tested 10.5 ohms as a load by using an electronic load and measure voltage and current. I gave 24V dc supply for MOSFETs and 15V for gate driver. But the problem is that there is no current from the supply for MOSFETs and the power at the load is not even 0.1W. I planned to use schottky diodes in parallel with MOSFETs to reduce voltage spike and change schottky diodes in the rectifier of the receiver circuit. I used the frequency around 80kHz. I have no idea where I have the problems. I also simulated using LT spice and the simulation results are not that bad. Can someone help me or suggest any ideas?

#### Martin_R

Joined Aug 28, 2019
103
Surely need ultrafasr rectifier diodes, UF4002 for example.

#### myaeaindrathein1996

Joined Jun 11, 2021
16
It says measure speed for current and voltage up to 50kHz so I don't think it can measure for around 80kHz. Instead of that one, which one should I use?

#### myaeaindrathein1996

Joined Jun 11, 2021
16
Surely need ultrafasr rectifier diodes, UF4002 for example.
I ordered schottky diodes 1N5819 and MBR1645tg. Can I use them?

#### Papabravo

Joined Feb 24, 2006
17,624
I ordered schottky diodes 1N5819 and MBR1645tg. Can I use them?
You will want to check the datsheets for any candidate diodes for the parameter named "Reverse Recovery Time", sometimes abbreviated:
$$t_{rr}$$
Diodes will not block current in the reverse direction during this time, when the bias switches from forward to reverse.
Also make sure they can handle the forward current and the Peak Inverse Voltage.

#### myaeaindrathein1996

Joined Jun 11, 2021
16
You will want to check the datsheets for any candidate diodes for the parameter named "Reverse Recovery Time", sometimes abbreviated:
$$t_{rr}$$
Diodes will not block current in the reverse direction during this time, when the bias switches from forward to reverse.
Also make sure they can handle the forward current and the Peak Inverse Voltage.
I cannot check from both diodes that I ordered. It says extremely fast switching and high frequency operation.

#### Papabravo

Joined Feb 24, 2006
17,624
I cannot check from both diodes that I ordered. It says extremely fast switching and high frequency operation.
I don't quite understand what you are saying. You can find a datasheet for anything you can order online and save a copy for printing or future reference.
Familiarizing yourself with a part's datasheet is a useful thing to do. This presumes that the manufacturer puts this information in the datasheet. I'll look for one that does.

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#### myaeaindrathein1996

Joined Jun 11, 2021
16
I don't quite understand what you are saying. You can find a datsheet for anything you can order online and save a copy for printing or future reference.
Low drop power Schottky rectifier (st.com)
MBR1635 - Switch-mode Power Rectifiers 16 A, 35 and 45 V (onsemi.com)
Familiarizing yourself with a part's datasheet is a useful thing to do.
Yes I already checked datasheets but they don't mention about the exact reverse recovery time. They mention that the diodes are extremely fast switching. I think it's enough for my work. Isn't it?

#### Papabravo

Joined Feb 24, 2006
17,624
Yes I already checked datasheets but they don't mention about the exact reverse recovery time. They mention that the diodes are extremely fast switching. I think it's enough for my work. Isn't it?
That's a really good question. The datasheets that I found are abbreviated, which often happens with parts that are no longer manufactured or obsolete. If the information is not on the datasheet or the part comes from a secondary source you may not be getting what you think you are getting. On the Digi-Key site, both diodes are claimed to have a "switching speed", whatever that is, of ≤ 500 ns. IMHO that is a pretty slow recovery time. I'm not certain that those two things are the same. The datasheet does not mention either "Revers Recovery Time" or "switching speed", so I am at a loss on how to advise you, except that you can measure this parameter if you have a mind to do it.

In your application of "Wireless Power Transfer", every source of loss is potentially important. It is kind of like building a fire in a fireplace to heat your cabin, and opening the front door to improve the draft. One problem you are facing is that many discrete, leaded parts are obsolete and no longer manufactured. They have been replaced by Pb-Free surface mount parts. Going forward your choices are going to be further limited.

I have some simulations of this you might find useful. It surprised me that the small signal diode was the fastest, the Schottky was in 2nd place, and the supposedly Fast Recovery Rectifiers brought up the rear.

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#### myaeaindrathein1996

Joined Jun 11, 2021
16
That's a really good question. The datasheets that I found are abbreviated, which often happens with parts that are no longer manufactured or obsolete. If the information is not on the datasheet or the part comes from a secondary source you may not be getting what you think you are getting. On the Digi-Key site, both diodes are claimed to have a "switching speed", whatever that is, of ≤ 500 ns. IMHO that is a pretty slow recovery time. I'm not certain that those two things are the same. The datasheet does not mention either "Revers Recovery Time" or "switching speed", so I am at a loss on how to advise you, except that you can measure this parameter if you have a mind to do it.

In your application of "Wireless Power Transfer", every source of loss is potentially important. It is kind of like building a fire in a fireplace to heat your cabin, and opening the front door to improve the draft. One problem you are facing is that many discrete, leaded parts are obsolete and no longer manufactured. They have been replaced by Pb-Free surface mount parts. Going forward your choices are going to be further limited.

I have some simulations of this you might find useful. Stay tuned.
Thanks for your advice. So I better look for small reverse recovery time diodes for rectifiers that would be suitable for my work. What do you suggest besides UF4002?

#### Papabravo

Joined Feb 24, 2006
17,624
Thanks for your advice. So I better look for small reverse recovery time diodes for rectifiers that would be suitable for my work. What do you suggest besides UF4002?
I am currently retired and have not looked at specific components for more than a decades so my knowledge is somewhat out of date. I can take a look at the UF4002. BTW I'm not saying the parts you are considering won't work at all, I'm just saying you need to know what your are dealing with because efficiency is critical and you really can't afford to use parts that will defeat your purpose.

EDIT: the datasheet is encouraging, and it lists the trr as 50 ns. going from 0.5 amp forward to 1 Amp reverse. There was a time (ca. 1987), that I would have killed for that level of performance.

UF4001-UF4007 Fast Rectifiers (onsemi.com)

I could not find a model for the UF4002, but there was on for the UF4007

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#### Alec_t

Joined Sep 17, 2013
12,479
I used IR21844S for half bridge converter
Your schematic is missing a diode from the 15V supply to the VB pin of the IC.

Joined Jan 15, 2015
6,324
I made an experiment for 100W wireless power transfer for my research. I used IR21844S for half bridge converter using IRFP360 MOSFETs. I designed the transmitter and receiver coils. I used full bridge rectifier using 1N4002 diodes and 2.2uF filter capacitor. I tested 10.5 ohms as a load by using an electronic load and measure voltage and current. I gave 24V dc supply for MOSFETs and 15V for gate driver. But the problem is that there is no current from the supply for MOSFETs and the power at the load is not even 0.1W. I planned to use schottky diodes in parallel with MOSFETs to reduce voltage spike and change schottky diodes in the rectifier of the receiver circuit. I used the frequency around 80kHz. I have no idea where I have the problems. I also simulated using LT spice and the simulation results are not that bad. Can someone help me or suggest any ideas?
The diodes you show in your drawing should be fine and with a Google of "wireless charging circuits" you will see the 1N4000 series used extensively. There are a wide range of circuits used as the oscillator source. The Tx and Rx coils need to be identical and with 100 Watts you are asking quite a bit. Circuits I have seen average between 70% and 80% efficient and the latter is really reaching. Magnetic induction transfer of energy relying on air has quite a bit of loss even with the coils tightly packed together. The greater the distance the higher the number of inductor turns needed. 12 Volts 100 Watts you are looking at greater than 8 Amps on the secondary and even with a 12 Volt 8 Amp primary drive at 70% efficiency you would only get about 70 Watts out and I have never seen a wireless power transfer through an air core yet. If you could do it your secondary diodes would need chosen to handle the load. Anything 1N4000 is an amp.

Ron

#### myaeaindrathein1996

Joined Jun 11, 2021
16
I am currently retired and have not looked at specific components for more than a decades so my knowledge is somewhat out of date. I can take a look at the UF4002. BTW I'm not saying the parts you are considering won't work at all, I'm just saying you need to know what your are dealing with because efficiency is critical and you really can't afford to use parts that will defeat your purpose.

EDIT: the datasheet is encouraging, and it lists the trr as 50 ns. going from 0.5 amp forward to 1 Amp reverse. There was a time (ca. 1987), that I would have killed for that level of performance.

UF4001-UF4007 Fast Rectifiers (onsemi.com)

I could not find a model for the UF4002, but there was on for the UF4007

View attachment 242634
Thank you so much for your simulations and suggestions. I will firstly test with the diodes that I have (1N5819, Mbr1645). If not work, I will change with the ones you recommend.

#### myaeaindrathein1996

Joined Jun 11, 2021
16
The diodes you show in your drawing should be fine and with a Google of "wireless charging circuits" you will see the 1N4000 series used extensively. There are a wide range of circuits used as the oscillator source. The Tx and Rx coils need to be identical and with 100 Watts you are asking quite a bit. Circuits I have seen average between 70% and 80% efficient and the latter is really reaching. Magnetic induction transfer of energy relying on air has quite a bit of loss even with the coils tightly packed together. The greater the distance the higher the number of inductor turns needed. 12 Volts 100 Watts you are looking at greater than 8 Amps on the secondary and even with a 12 Volt 8 Amp primary drive at 70% efficiency you would only get about 70 Watts out and I have never seen a wireless power transfer through an air core yet. If you could do it your secondary diodes would need chosen to handle the load. Anything 1N4000 is an amp.

Ron
I used 2mm diameter solid copper wire, 13 turns and the ansys maxwell simulations show that coil self inductance is 18uH and mutual is 4uH. I used acrylic to fix the coils and the coils are almost touched (no air gap distance). The problem is that even though I increase the dc supply voltage to MOSFETs, the current is not increased at all (0.0mA). I don't know where my circuit has the problems.

#### myaeaindrathein1996

Joined Jun 11, 2021
16
S
a resistor, or more likely a pile of resistors is the answer.

These are normally inside a metal "box" so as not to break local rules and radiate,
local authorities take very badly to jamming,

there even used to be one that every one used to us
but alas now long gone

#### myaeaindrathein1996

Joined Jun 11, 2021
16
Your schematic is missing a diode from the 15V supply to the VB pin of the IC.
Your schematic is missing a diode from the 15V supply to the VB pin of the IC.
I used Mbr1645 schottky diodes for boot strap.

#### Martin_R

Joined Aug 28, 2019
103
There's a shut down pin on the ic shown on the datasheet. Is it connected correctly? I can't see reference to it on your circuit diagram