Hi everyone;
I'm trying to build my boost converter using TL494 PWM controller, I've read the datasheet and the manual on how to correctly use it, then I've build the schematic shown in the attachments.
The main purpose of my circuit is to be a variable-output boost converter , the desired output voltage is being adjust using a pot, a soft-start is added to the circuit; everything else in the schematic has been token from the datasheet and the manual.
My problem is that the circuit boosts the voltage up to 13.5v then a short-circuit happens as my power supply shows, my power supply is UTP3704S which has an output current up to 3A, the current exceeds this value and thus the voltage drops to 5V at the input while the short-circuit happens.
I've tried to change the values of the output feedback resistors and that didn't help me.

I'll be very pleased if anyone can help me understand my issue.

Best Regards

 

You are probably saturating L1.

 

You are probably saturating L1.

sorry but what do you mean by "saturating" if I'm setting the frequency to 100kHz and calculate the needed inductance ?
what shall I do to overcome this ?

 

You turn off transistors badly. They turn off using 10 kΩ very slowly. This is not the correct use of the IC.

 

You turn off transistors badly. They turn off using 10 kΩ very slowly. This is not the correct use of the IC.

Shall I decrease the value of resistors or use another topology ?

 

Saturating a core means the strength of the magnetic field (due to the current) exceeds the amount that the core can support. It no longer acts as an impedance and you get maximum current flow.

 

Saturating a core means the strength of the magnetic field (due to the current) exceeds the amount that the core can support. It no longer acts as an impedance and you get maximum current flow.

OK but I'm not attaching any loads yet ! and I've chosen the core that is 2 times the Lmin value.
Have I got anything wrong ?

 

What is the saturation current value on the specification? (Not the inductance.)

 

Consider a Complementary MOSFET Gate Driver ( something like this ) ...
https://www.acmesystems.it/www/pcb_pwm/GateDriver.png
Fast Turn-On and fast Turn-Off.

Also, why do you have C2 and E2 grounded?
Should your C2/E2 output be in parallel with C1/E1 output?

 

I'm not attaching any loads yet !

You need to at least attach a dummy load, otherwise you won't get good data.

 

What is the saturation current value on the specification? (Not the inductance.)

I've designed the circuit to withstands 5A.

 

Consider a Complementary MOSFET Gate Driver ( something like this ) ...
https://www.acmesystems.it/www/pcb_pwm/GateDriver.png
Fast Turn-On and fast Turn-Off.

Also, why do you have C2 and E2 grounded?
Should your C2/E2 output be in parallel with C1/E1 output?

why to connect them in parallel as I don't consume too much power from the IC ?
I'm grounding them so I can get rid of any noise .
I've tried to minimize the value of the resistor and I've got better results, I'll try the circuit you attached, but is there any limitations for choosing the transistors ?

 

What did you calculate for your Gate current ?

 

Shall I decrease the value of resistors or use another topology ?

You could try using the IC in push-pull mode, with the Output Control pin connected to Ref instead of ground, and with the presently-unused output transistor being used instead to pull down the FET gates. That will speed up the FET switch-offs.

 

What did you calculate for your Gate current ?

sorry I haven't got what do you mean
if you mean the MOSFET gate current it's very small value in nA, and the drop across each 10K is about 1.2mA , but I guess this isn't your question

 

You could try using the IC in push-pull mode, with the Output Control pin connected to Ref instead of ground, and with the presently-unused output transistor being used instead to pull down the FET gates. That will speed up the FET switch-offs.

would it give me the same result as connecting the circuit that mvas has attached ? it works a little bit good, the voltage reaches 24V and then the same problem happens at 100KHz and 10Khz.

 

another question, how can I decide the value of the gate resistors (R14 & R16) ?? I know that we can choose it in the range of (10ohm- 1Kohm).

 

would it give me the same result as connecting the circuit that mvas has attached ? it works a little bit good, the voltage reaches 24V and then the same problem happens at 100KHz and 10Khz.

It should help to speed up switch-off, so in that respect is similar to the linked FET driver. It involves only a simple re-configuration of the circuit, so why not try it?

 

It should help to speed up switch-off, so in that respect is similar to the linked FET driver. It involves only a simple re-configuration of the circuit, so why not try it?

I'll try it of course, but I'm asking about the BEST way to deal with 100KHz as I haven't deal with speeds in this range.
but there is still a problem in the case that I can't reach an output voltage above 24V, what can it be ?

 

Consider a Complementary MOSFET Gate Driver ( something like this ) ...
https://www.acmesystems.it/www/pcb_pwm/GateDriver.png
Fast Turn-On and fast Turn-Off.

Also, why do you have C2 and E2 grounded?
Should your C2/E2 output be in parallel with C1/E1 output?

also do I need a resistor between the PWM and the bases of the transistors ? if yes what's its value ?
also can I connect two MOSFETs in parallel at the same Push-Pull circuit ? as I want to use the internal push-pull configuration of the TL494