open loop feed forward Buck converter

[matouk]

feedforward buck

Hi
Please any one can help me to design feed forward open loop voltage mode Buck (step down) converter using TL494 IC I,ve done the circuit that in the data sheet but in my task I couldnot get the PWM changing with varying in the refernce voltage . so I need correct conections of TL494 to do this jobe .I am runing out of time aod I need it badly please reply

 

[VVV]

feed forward buck converter

If it's feedforward, you need to adjust the PWM with respect to the input voltage, rather than the output. SO feed the input voltage through a divider to the input of the error amp. Then I would integrate the PWM output and feed that back to the other input of the error amp. You do not need to change the reference in this.

 

[matouk]

buck open loop

Dear VVV
Thank you very much for your reply and answer. the task need a changing in reference voltage as you can see in the attchment file . so please could you provide circuit diagrame of tl494 and buck converter. as i Know that tl494 can do all controling task,with out extra external voltage supply just Vcc.
best regards

 

[VVV]

input voltage feedforward buck

I am sorry, but I don't understand the actual requirement.
What is the circuit supposed to achieve? Can you explain?
What is PV?

According to your picture I would say that what I explained should be valid.

 

[FvM]

buck converter tl494

PV is simply an Ue source, I think. The purpose of the converter is to provide roughly constant Ua with variable Ue through feedforward.

The feedforward control scheme implies setting of d ~ 1/Ue, provided the buck converter is always operated in continuous mode by a sufficient output current.

The intended characteristic could be achieved by making the sawtooth voltage respectively Vref proportional to Ue. However, I don't see, that TL494 provides this option. There is neither a hint, if and how Vref may be overridden nor a specification of a voltage range above or below 5V, that would allow reliable PWM generator operation. Thus I think, an external oscillator would be the obvious requirement.

 

[matouk]

buck converter by tl494

Thank you all for your reply and help , the follwing may make it clear
the PV is photovoltaic or solar cell it has IV characterstics as in atachment file.The fig. shows the (current / voltage )and ( Power / Voltage ) of the Solar cell (Photovoltaic) under changing of illumination and temperature which vary the output current and out put voltage respectively. So to make sure that the solar cells delivering its maximum power (mpp) under climat change , we have to very the reference voltage Vref to track maximum power point of the photovoltaic cells. External supply voltage should be used in this system also voltage divider at the input voltage (Vpv) . Calculation will be made at final task by using relation between photovoltaic surface temperature and the Vref . at the beginning I have to get duty cycle (d) changing with change of Vref by feed forward open loop using tl494, so please if any one provide me the circuit connections buck converter using tl494.
best regards for all of you