12V to ±80V adjustable isolated half bridge converter.

Thread Starter

Gianluca2000

Joined Dec 13, 2023
7
I really appreciate if someone can help me a bit with this project.

Its a half bridge topology DC-DC converter that takes 12V on the Input and transphorms it into a simmetrical 80V output (Maximum). The output voltage will be adjustable from ±18V to ±80V.

I am using the SG3525 IC for this design. The switching converter frequency is 100Khz. I wound the transformer myself and it works fine but there is one problem:

To drive a half bridge, a high + low side gate driver is needed. I tried to use IR2104 but there might be a problem with this SG3525 & IR2104 combination.

SG3525 gives out two square waves to drive two MOSFETs, and the duty cycle of both of those square waves will vary according to the feedback. But both outputs are designed only for LOW SIDE switching, so its impossible to connect them directly to the half bridge. So i decided to use IR2104 but the problem is that this gate driver has only one Input. Basically, a single square wave (That can change its duty cycle) can be feeded into the Input of IR2104, and that IC will be able to drive BOTH mosfet of the half bridge.
It seems like the IC is 'duplicating' the input square wave signal to switch both output MOSFETs alternately. So you can basically control a half bridge with just a single square wave, which is simpler. But here is the catch: SG3525 has TWO outputs. So i tried to connect only one output of SG3525 to the IR2104, thinking that nothing will change because the IR2104 will 'duplicate' the square wave again resulting in the same outcome. But this is probably where i'm screwing up. Something in my brain tells me that this setup is wrong. I tested the system (with the feedback set to 40V) and it works but the output voltage does not increase to more than 22V at 12V supply Input. If i increase the supply input, the output voltage rises as well, which is of corse wrong. I tried the same transformer in a different System and it works, increasing the voltage all the way to 80V or even more.

So the reason this System isn't working is because of the 'incompatibility' between the IR2104 and SG3525??

It seems like the duty cycle remains limited and wont rise up from a certain threshold.

Now i know there is a better IC which is IR2110. It has two independent inputs and outputs, which is probably what i need. It is still a half bridge driver, but it has independent channels.

So will the system work correctly after using IR2110? Can you help me figuring out if what i explained here is the actual problem? Because i already designed the PCB layout for the whole system, but in my test system i've got into this problem that i cant fully understand, it just confuses me.

This system is actually two equal circuits with their outputs connected in series. Thats why i am making them isolated. A single circuit takes 12V from the input and converts it into 18 - 80V. The feedback is designed around a comparator with its own isolated supply (B1212S - 1W) and an optocoupler.

Also, the MOSFETS heat up a bit too much.
They are 3.3 milliohms when fully turned on, and the gate driver drives their gates with a current of 2.5A (source and sink are both 2.5A). The gate capacitance of those MOSFETs is 9400pF.

So the fact that the MOSFETs do heat up a lot is probably related to the main problem i tried to explain here, i hope.

So i really appreciate if someone can help me understanding if THIS is the actual problem and if i can solve it by using the IR2110.

Because if there is another problem i will waste both components and PCBs that i am about to order for this project.

If my test circuit fully works then i am going with the final project.
 
Last edited:

Ian0

Joined Aug 7, 2020
9,834
For 12V input, I would go for the push-pull circuit rather than the half-bridge. At higher input voltages half-bridges might be better. The SG3525 is already equipped to drive the transistors in a push-pull circuit (although it doesn't have the drive current that more modern devices do). So, I agree with @LowQCab on topology, but would prefer the 3525 to the 3524.
 

Thread Starter

Gianluca2000

Joined Dec 13, 2023
7
I May try new systems in the future...

So what i am trying to do now wont work?

If i use IR2110 the half bridge should work right?

I will modify the system to run with 36V or 48V input. I think the voltage on the output can also be stepped down below the maximum input voltage.

Now, with 36, 48, or maybe even 56V input, will my half bridge solution work? I want to stick with the half bridge for now because i designed the PCB and everything around it...

So first lets see it is possible to increase the input voltage without changing the topology and ICs (SG3525 and IR2110).

For now the main doubt i have is the IR2110. Can it drive the half bridge in combination with the SG3525's output square waves? Or are the output signals of SG3525 not right to drive a half bridge to start with?

Thank you for your help.
 

Thread Starter

Gianluca2000

Joined Dec 13, 2023
7
I know what the input voltage is, of course.

I initially designed for 12V input, but if the half bridge is not very good for low input voltages such as 12V, i can very easily modify it for... lets say 48v.

Now, with a input voltage of 48V, will my system work?

(I will modify the transformer accordingly, of course).

I am sorry but i am not very expert in everything because i am literally learning now...

What's difficult to understand for me now are the SG3525's outputs.

If they are good already to drive the half bridge i will add the IR2110 driver for it. The problem is that i dont have IR2110 for now so i cant test it.

So i just wanted some help into understanding only if the SG3525 outputs are good to drive the half bridge.

Again, sorry if i am not very clear in some arguments. I think i explained it better now.

Again thanks for your help, it is really appreciated.
 

LowQCab

Joined Nov 6, 2012
4,075
You shouldn't try to create a project based only on what You have in your junk-drawer.

The first step in designing a project like this,
is to establish what type of Input-Power-Supply that You have to work with.

A substantial amount of engineering is required to create an efficient Transformer,
and any change that You make to the overall design of your Project
will require adjustments to the design of the Transformer.

Driving the Transformer with a "Push-Pull" Primary configuration, ( like the Schematic that I posted ),
simplifies many aspects of the overall design,
and most especially the Current-Limiting aspect.

What is the overall purpose of Your project ?
.
.
.
 

Thread Starter

Gianluca2000

Joined Dec 13, 2023
7
I need it to power and test dual rail supply audio amplifiers from a single battery. To be honest, i already tried building a push pull converter but it didnt work for reasons i cant understand.

I saw that push pull is more complex to design than half bridge.

It seems like all of this is not for me... I thought it was a bit simpler. I have to learn a lot more.

Thank you for your help anyway, i will still test my system with IR2110.

(New stock including those ICs will arrive tomorrow at the shop where i buy components).

II just wanted to know earlier if my system could actually work.

Lets close the discussion here, i realized that i have really a lot more to learn.

Again, thank you for your help anyway.
 

LowQCab

Joined Nov 6, 2012
4,075
You should test Audio-Amplifiers using the Power-Supply that they were designed to operate with,
otherwise, You won't be able to test them under actual "real-world" conditions,
so your testing would basically mean nothing.
.
.
.
 

MisterBill2

Joined Jan 23, 2018
18,566
A "dual rail" audio amplifier is quite common. When they are powered from a single battery with an inverter type supply they are a two component system that can be quite a challenge if not all of the pieces are right. Is this to be a production line test or an end of the line test?
For production testing it might make more sense to check each section separately prior to the final assembly. That would immediately show which section needs to be repaired, and which section has production issues. Quickly locating the source of a production problem is important.
 

Thread Starter

Gianluca2000

Joined Dec 13, 2023
7
This is not meant to be cutting edge technology or top of the line hardware. I am just a hobbist trying to make a DC-DC converter to test... actually... my OWN amplifiers. I built powerful and working amplifiers but i cant test them at full power because i dont have such a split high power dual rail supply system. Each amplifier i built has a different input voltage, hence why i am doing this DC-DC converter adjustable. I am not working for something ultra serious, i am just a hobbist. And, actually, i am learning really a lot of things. And this is great for me.

Now i've just ran into this problem, and i wanted just a simple solution. I just wanted to know if the IR2110 is capable to drive a half bridge PROPERLY in combination with the SG3525's square wave outputs.

Guess what? Now after buying the IR2110 and using it as a replacement instead of the IR2104... THE SYSTEM WORKS PERFECTLY FINE. And the efficency is around 88% at all output voltages.

I just wanted to know before if this could actually work so that i wont waste components for nothing. I risked it, and luckily it went well.

Maybe this site is not my cup of tea, i dont know...
 

MisterBill2

Joined Jan 23, 2018
18,566
I am happy that it works for you. Half-bridge inverters are not my area of expertise, but I have done work with industrial testing. It was not clear to me that you were not working to set up production testing of a new product. Personal projects are different.
 
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