MC34063 DC-DC BUCK CONVERTER

[TuralH]

Hello everyone,
I need to assemble a circuit to control a DC motor, my 60V battery needs to be reduced to 12V,
I have an mc34063 in my hands but its maximum voltage is 40V VCC,
I assembled a circuit in LTSPICE with an external pmos but the circuit does not work in the simulation. that is,
I supply 60 volts separately to pmos and 12 volts to IC separately, maybe someone will advise assembling the circuit differently,
I need to get 12V 3A at the output to control DC motor

 

[KlausST]

Hi,

my 60V battery needs to be reduced to 12V,

Your circuit shows you already have a 12V supply ..

I_sns seems not to be wired correctly.
1N4148 diodes are far too small .. they are SIGNAL diodes .. but you use them in a POWER path. SIGNAL and POWER are two different things.
The manufacturer provides a datasheet and most probalbly design notes. --> use them.

***

but the circuit does not work

This is far from being a useful error description..

We need to know
* What do you expect
* what does not work as expected

What did you do to investigate the problem on your own?
I mean: you have a simulation tool --> so use it.
You can - and should - measure each single node in your scheamtic.

Best strategy is to FIRST decide how a signal of a node should look like regarding voltages and timing. Use paper and pencil to sketch it down.
THEN use the scope function to verify it.

I have an idea what´s happening. But I don´t have your simulation files ... and if I had .. I´m not very experienced with circuit simulation software.

Please see it as your job ... to debug "at least something" ... and report us the details of your expectations and results.

Klaus

 

[stenzer]

Hi,

on first glance I would say your P-channel MOSFET is turned on the whole time, as its maximum gate voltage is 12 V. To turn it off the MOSFET VGS has to be 0 V. Further, here your VGS is larger than 20 V, which is usually the typically maximum voltage difference a MOSFET can handle.

Also your circuitry (approach) does not match your problem desciption.

BR

 

[TuralH]

Hi,


Your circuit shows you already have a 12V supply ..

I_sns seems not to be wired correctly.
1N4148 diodes are far too small .. they are SIGNAL diodes .. but you use them in a POWER path. SIGNAL and POWER are two different things.
The manufacturer provides a datasheet and most probalbly design notes. --> use them.

***

This is far from being a useful error description..

We need to know
* What do you expect
* what does not work as expected

What did you do to investigate the problem on your own?
I mean: you have a simulation tool --> so use it.
You can - and should - measure each single node in your scheamtic.

Best strategy is to FIRST decide how a signal of a node should look like regarding voltages and timing. Use paper and pencil to sketch it down.
THEN use the scope function to verify it.

I have an idea what´s happening. But I don´t have your simulation files ... and if I had .. I´m not very experienced with circuit simulation software.

Please see it as your job ... to debug "at least something" ... and report us the details of your expectations and results.

Klaus

yes, about the 12 volt power supply, I get it using another converter to power the IC, but there the maximum current consumption is 700 mA, and I want to reduce the second converter with mc34063 for a DC motoryes, regarding the 12 volt power supply, I get it using another converter to power the microcircuit, but there the maximum current consumption is 700 mA, and I want to reduce the second converter with mc34063 for the DC motor

 

[KlausST]

Hi,

why handstands ...
* building one 12V 700mA supply
* a second 12V 3A supply
* with unsuitable controller and thus the need for extra circuitry.

Are you sure this makes sense?

Why not one single 60V (Battery) down to 12V one. Using an IC that is designed to do this..

Klaus

 

[TuralH]

Hi,

why handstands ...
* building one 12V 700mA supply
* a second 12V 3A supply
* with unsuitable controller and thus the need for extra circuitry.

Are you sure this makes sense?

Why not one single 60V (Battery) down to 12V one. Using an IC that is designed to do this..

Klaus

I have xl7005 and MC34063 for supplying MC34063 i use xl7005 can buck from 80v to 12v but current rate is 700mA for dc motor control i used MC34063 where input is 60V i want to get 12v 3A but with external transistor. But it works with 20V-40V if i supply VCC but my goal is buck from 60v to 12v

 

[KlausST]

Hi,

But it works with 20V-40V if i supply VCC but my goal is buck from 60v to 12v

did you read what Stencer wrote?
Did you cross check with your 60V circuit? --> that´s what a simulation is made for.
Did you check whether your mosfet is ON all the time .. and if so: why?

Just connect a virtual scope to measure V_GS ...

Please give us some evidence that you do something (no only want us to do something)

Klaus

 

[TuralH]

Hi,


did you read what Stencer wrote?
Did you cross check with your 60V circuit? --> that´s what a simulation is made for.
Did you check whether your mosfet is ON all the time .. and if so: why?

Just connect a virtual scope to measure V_GS ...

Please give us some evidence that you do something (no only want us to do something)

Klaus

pmos gate waveform in simulation. works if everything is from one source. but according to the datasheet, the maximum voltage for mc34063 is 40V.

 

[FvM]

34063 doesn't work for 60 V. Output transistor driver can be optionally supplemented with discrete level shifter, but current sense must be operated at positive supply input.

34063 is low price switcher controller with limited features. Why not using a full featured 60 V capable controller?

 

[TuralH]

34063 doesn't work for 60 V. Output transistor driver can be optionally supplemented with discrete level shifter, but current sense must be operated at positive supply input.

34063 is low price switcher controller with limited features. Why not using a full featured 60 V capable controller?

I ordered a Chinese pmic eg1163 which has a built-in gate driver for n channel mosfet, among the converters that I currently have in my hands are mc34063 and pwm controllers tl494, uc3843 for which an additional driver is needed, yes you are right mc34063 does not work with 60v, but I wanted I would like to know if it is possible?

 

[FvM]

Possible candidates are e.g. LM5085 or MIC2176.

 

[TuralH]

Possible candidates are e.g. LM5085 or MIC2176.

thanks for the advice, I know that the capabilities of mc34063 are limited, but I will consider the ICs you suggest as candidates for mc34063

 

[mtwieg]

I think the MC34063 could be made to work at 60V. Would have to fix the PMOS drive circuitry. Could generate the VCC bias from a simple LDO circuit, then bootstrap it from Vout. If you post your simulation (along with the MC34063 model and symbol files) I could show how.

The main issue will be that the MC34063's peak current limiting function will not work (unless you were to add some complex circuitry to translate the switch current signal to the Ipk sense pin, maybe with a current transformer). If you want current limiting, I would not use the MC34063.

 

[Easy peasy]

a small CT would serve to provide the current signal to the IC

 

[TuralH]

I think the MC34063 could be made to work at 60V. Would have to fix the PMOS drive circuitry. Could generate the VCC bias from a simple LDO circuit, then bootstrap it from Vout. If you post your simulation (along with the MC34063 model and symbol files) I could show how.

The main issue will be that the MC34063's peak current limiting function will not work (unless you were to add some complex circuitry to translate the switch current signal to the Ipk sense pin, maybe with a current transformer). If you want current limiting, I would not use the MC34063.

thank you very much for the advice, my eg1163 chip, ready for this solution, has already arrived, mc34063 is not for such things, I think so

 

[cupoftea]

Cheapest 60V to 12v at 3A Buck is with low side Buck and UCC28C43.
The 12Vout wont be input ground referenced, but does it need to be?
Alternative is low side buckboost with motor ground at the 60V input voltage.

Each of the above uses one low side nFET only, and is useable with any cheap current mode control IC.

 

[Easy peasy]

.....