Hi every one,
I'm trying to build a DC to Square wave converter using NE555 as shown in the schematic , I took it from the internet without the output driver and it seems that there are lots of problems in my design ( I know one of them that there should be a delay between the on/off time , but how can I do it ?)
if anyone can help me I will be very pleased.
My second question is about Power Electronics , I'm a pre-graduated student and trying to learn power electronics - away from lots of the non-useful theories and subjects - , if any one can help me in where to find a good references to learn it from basics up to advanced I will be very pleased again )
Thanks all.

 

Having duplicate reference numbers on the schematic makes it ambiguous.
I suggest you do some more googling for circuits which provide the dead time (delay) you want.
'Power electronics' is a very broad subject. Are there any aspects you are particularly interested in?

 

Having duplicate reference numbers on the schematic makes it ambiguous.
I suggest you do some more googling for circuits which provide the dead time (delay) you want.
'Power electronics' is a very broad subject. Are there any aspects you are particularly interested in?

thanks for replying
it's a H-Bridge , the duplicated numbers just to let the schematic be clear and to avoid long connections.
I don't prefer googling so that I post my problem here to learn from my mistakes, so is it a huge problem that there is no delay in switching the mosfets ? and if it could be added to the circuit what shall I use in this case ?
AC and DC drivers and how to deal with them practically and how to connect them correctly with the microcontrollers .
if there are some books that's will be very good.

 

"the duplicated numbers just to let the schematic be clear and to avoid long connections."

No, the just make it hard to follow.

 

"the duplicated numbers just to let the schematic be clear and to avoid long connections."

No, the just make it hard to follow.

ok but I guess that it's clear that I'm trying to make an H-bridge, anyway would you like me to post another schematic without these numbers ??

 

ok but I guess that it's clear that I'm trying to make an H-bridge,

If a H-bridge is your final result your after, you should look into something called "shoot through". Because your schematic shows a good example of the term. I'd tell you to Google, but you don't like to do that.

Your thread title also makes know sense, when compared to your schematic. You don't need a H-bridge to make a 'square wave', only one mosfet or transistor and the timer chip will do that.

 

If a H-bridge is your final result your after, you should look into something called "shoot through". Because your schematic shows a good example of the term. I'd tell you to Google, but you don't like to do that.

Your thread title also makes know sense, when compared to your schematic. You don't need a H-bridge to make a 'square wave', only one mosfet or transistor and the timer chip will do that.

thanks, but I'd like to make something like +24V then -24V ( AC square wave ) not to +24 then GND , so I used the H-bridge
I will google about the thing you talked about. but is there any logical or practical problem in my schematic here ?

 

You cannot just connect the diagonal gates together as it looks like you are trying to do on your circuit.
Q2 and Q3 gate drive will need to be higher than your 24V supply.
Have you looked for an H bridge circuit or an IC?
What is your load requirements?

 

Having duplicate reference numbers on the schematic makes it ambiguous.

Unless I missed something, there are no duplicate reference designators. 1, 2, and 3 are net names. Not my favorite practice for signal nets, but not unheard of.

ak

 

1, 2, and 3 are net names.

Not always; hence the confusion. The number '2' appears eight times in the schematic, but the points labelled '2' should not all be connected together as a net.

 

Are you saying that the difference between pin 2 of a resistor that has a wire attached that obscures the pin number, and a single-ended pin with a label floating clearly out in space, is unclear?

ak

 

Hello,

I have drawn some colored lines in your schematic, how I think they should be connected:



But I don't think the circuit will work, as all fets are equal.
I would expect some P-fets on the upper side and N-fets on the lower side.

I would also expect troubles with the driving circuit as that works on 12 Volts and the H-bridge is on 24 Volts.

Bertus

 

The circuit will not work in any useful manner. The upper FETs are configured as source followers with a maximum of 12 volts applied to the gates which means the maximum voltage across the load will be 10 volts (2 V is minimum Vgs threshold voltage for those FETs) at nearly zero current and probably around 8 volts with more than one or two amperes.

Using a 555 to control a power circuit like this is almost always the wrong thing to do. There are lots of good power control ICs that don't cost very much and actually do the job properly.

 

Hello,

I have drawn some colored lines in your schematic, how I think they should be connected:

View attachment 157409

But I don't think the circuit will work, as all fets are equal.
I would expect some P-fets on the upper side and N-fets on the lower side.

I would also expect troubles with the driving circuit as that works on 12 Volts and the H-bridge is on 24 Volts.

Bertus

that's the thing I wanted to tell you by using (1,2 and 3) they aren't relevant to anything or any purpose just to avoid these connections.
why there will be a problem when driving with 12V and the load is 24V while the ground is connected to each other ?
when I tried the circuit practically a short circuit appears , don't know the reason , but I just want to learn much more about divers and how to use them.
thanks

 

The circuit will not work in any useful manner. The upper FETs are configured as source followers with a maximum of 12 volts applied to the gates which means the maximum voltage across the load will be 10 volts (2 V is minimum Vgs threshold voltage for those FETs) at nearly zero current and probably around 8 volts with more than one or two amperes.

Using a 555 to control a power circuit like this is almost always the wrong thing to do. There are lots of good power control ICs that don't cost very much and actually do the job properly.

the load is getting 24V - 2V = 22V and it could be increased so the voltage can be 24V
what another type of IC's do you suggest me to use to do that purpose ? that I can change the duty cycle and the frequency ?
thanks

 

why there will be a problem when driving with 12V and the load is 24V while the ground is connected to each other ?

It is not a matter of grounds, but of having the gate voltage being able to drive some volts higher than the source.
If you expect Q2 and Q3 to turn on, the gate voltage will have to go to 30V for example.
Then that 30V being applied to the gates of Q1 and Q4 would probably pop them.

Read up on how FETs work.
As has been mentioned, just go and use a FET bridge IC or the correct driver ICs.

 

the load is getting 24V - 2V = 22V

No, it isn't. It is getting around 8 to 10V, depending on the load current anf FET characteristics.

To discuss cross-conduction, those unseen connections are important.

ak

 

You could try the IR2110 driver chips,
https://www.infineon.com/dgdl/ir2110.pdf?fileId=5546d462533600a4015355c80333167e

 

https://www.aliexpress.com/item/Fre...VC6qWCh3exg8tEAQYAyABEgKrx_D_BwE&gclsrc=aw.ds
https://www.sparkfun.com/datasheets/Robotics/L298_H_Bridge.pdf

 

thanks for all your replies <3 <3
the last thing I want if there is a book about FETs and how to practically deal with them I'll be sooo pleased