TL494 synchronous buck converter LOW output voltage

codemaster11

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that's picture of an inverter based on TL494 & HIGH LOW side mosfet driver IR2101. i modefied this picture for my
synchronous buck converter placed a ferrite inductor instead of transformer. use IR2110 as driver while output side is
as like shown in following picture.
feedback loop of the converter is as shown in above picture of TL494 and IR2101. frequency of the converter is set to 45KHz & duty cycle is greater than 90%.
these are my reference picture of my schematic diagram. i m facing one problem that is "the converter max output voltage is half of the input voltage
where i need more output voltage than half" Vin 16.5vdc but max Vout = 8.25 volt . the feedback loop of TL494 works upto 8.25 volts mean it decrease below this
level but not going to increase above 8.25 volts changing feedback resistors but nothing happens to increase output voltage. here what to do increase the output voltage.
 

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The shown TL494 configuration produces symmetrical duty cycle as required for push-pull converter. It's not suited for buck converter application.
 

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can i use here "IR2104 LOW HIGH side driver" there is one Input pulse to IR2104 by little changing above circuit
configuration. Pin#9 & 10 of TL494 to GND and using either pin#8 or 9 for input pulse to IR2104 to avoid symmetric pulse
problem in IR2110.
 

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The IRFP460 has an RdsOn of 0.25 ohm . If you are losing 50% something is wrong.

Check that you are getting 16Vpp out of the switches. If your filter is too lossy or too low in impedance, then ... wrong RLC values. Measure Rs or show links to specs for L,C. and load.
Show waveforms. Show test setup.
 
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Yes IR2104 has the required function. To allow higher duty cycles than 45%, you can connect pin 9 and 10 in parallel.

Consider that the controller has no features to disable low side switch in case of back current and isn't suited e.g. as battery charger.
 

    codemaster11

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the problem is "max half output voltage" if to connect LIN to GND and remove R6 and R9. can it solve the
voltage regulation at max 11vdc or less. will the driver will do the synchronous buck voltage conversion at only Hin?
--- Updated ---

"in the schematic diagram posted in post#1 pin#13 of TL494 is connected with Vref. both PWM output
of TL494 is anti phase" here i don't have any idea will it works by connecting them together as only HIN for the driver.
 
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please study answer given just above - for simplicity replace bottom fet with diode - as TL494 can never control a bottom fet correctly.
 

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Solution
OP mentioned to use IR2104 instead of IR2101. As far as I see, it can control push-pull converter (or synchronous buck) with TL494.
 

    codemaster11

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the outputs are not complementary, and if you don't combine the outputs you can only ever get 48% max ON time on the high side ( and the low side ).
 

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Yes, the output should be combined, as suggested in post #5 and #6. That's independent of using a suitable push-pull driver inverting low-side gate signal.
 

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replacing the low side mosfet with high power shotcky diode like 20H100 works by only using high side mosfet
for converter operation but here another problem comes with the output voltage that is the output voltage swing upto 6vdc
in my circuit i set output voltage using potentiometer at Vout = 12Vdc. the output fluctuate from 12vdc to 6.2vdc not giving constant voltage at output
i done this test with my circuit.

now i 'm going to try the synchronous converter with IR2104. previous time i received IR2104 from an online store
but all of them are faulty. now i will test with new one.
 

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here is sync buck with ltc4449...you find sim of (the free) ltspice in there
 

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  • Synchronous Buck.zip
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I am sending you a schematic diagram of the 494 half bridge that is currently in mass production.
 

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    codemaster11

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as suggested in post#5 i use the new one good IR2104 and the converter has starts working as expected
connect pin#9 and 10 of TL494 in parallel for higher duty cycle. currently i test the converter with only 12 watt Vin = 12vdc & Iin = 1Amp dc input and
set the Vout = 10 volt and Iout = 1Amp approximatly with complete voltage regulation no Vout drop occur at this load. in my testing circuit i'm using
75nf75 FET not irfp460.

but i will do further more test to ensure that it is working at higher input let say Vin = 60 to 70 volt dc and higher output load without any damage
to the circuitry. after that i will upload complete final schematic diagram.
 

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after some experiments the synchronous converter starts working with 83 to 90% power conversion efficiency using irf4115 mosfets on high & low side.
connect it to Vin = 48 vdc from a 540 watts solar panel set output voltage Vout = 14vdc and Iout = 23 amp getting 8.8 amp from solar panel while Vin drop to 41Vdc.
here another problem arise with efficiency that is when connect two such solar panel in series now Vin no-load = 96 to 100vdc set the converter output Vout = 48vdc. by putting a load of 400 watts Vload = 48vdc & Iout = 8.3amp the converter efficiency drop giving Vout = 31vdc ( vin drop to 43vdc) while Iout and Iin is same that is Iout = Iin now here how to stabelize the output at Vout = 48vdc. the converter is not working well at vin = 80 to 100vdc.
 

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as IN4148 has max current of 150mA and reverse voltage of 75v. i used here FR106 instead of IN4148.
 

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switching losses are proportional to Vin, also higher vin = higher RF noise - which can affect the controller

unfortunately, if the duty cycle changes towards holding the bottom fet on longer - you can get reverse current in this mosfet - as the TL494 is not designed for synch rec control - this is why a fast diode only in the bottom is a good idea.
 

    codemaster11

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i change my design from synchronous to asynchronous by using shotcky barrier 20H100 instead bottom FET as bottom FET is heating a lot. now at Vout = 14vdc and Iout = 23Amp dc with a little heating but still efficiency drop occure at high Vin-dc
 

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