Circuit Issue Help - Buck Converter with Type III Analog Voltage-Mode Controller

Thread Starter

Rborres07

Joined May 4, 2024
4
Hello there! I am working on a buck converter (Input: 24 V, Output: 10 V) with gate driver circuit and type III analog voltage-mode controller. I am facing the issue wherein when I'm inputting around 12 V it outputs 9 V but then the current is also high (around 1.4 A). The duty is around 90% already at that point and when I increase the voltage further it fluctuates at around 4-6 V output voltage. The specifications for the comparator is TL5001 with switching frequency chosen as 30k Hz. I have also attached the circuit diagram below (please also comment improvements for the circuit diagram). It also utilizes a NAND Gate (C47107B) and TLP250H for the gate driver circuit. I am not sure where the issue is but I assume it's regarding the comparator and controller part. If you have any thoughts on what the problem might be please help me. Thank you very much.
1714834407915.png
 

LowQCab

Joined Nov 6, 2012
4,290
So why are You operating it by varying the Input-Voltage far below what it was designed for ?

This Circuit is "Buck only", not "Buck-Boost".

It requires an Input-Voltage that is a certain number of Volts in excess of
the expected Output-Voltage, at all times, to insure stability of operation.
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Thread Starter

Rborres07

Joined May 4, 2024
4
So why are You operating it by varying the Input-Voltage far below what it was designed for ?

This Circuit is "Buck only", not "Buck-Boost".

It requires an Input-Voltage that is a certain number of Volts in excess of
the expected Output-Voltage, at all times, to insure stability of operation.
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.
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Even if I open the power supply at 24 V immediately, it outputs around 5 V with a varying duty cycle. I tried turning the Vcc source first then the Main Power Supply and the other way around but it still outputs an unstable 5V output voltage. I'm just wondering why it peaks at 12 V around 2 V above the required switching ON voltage for the MOSFET used.
 

LowQCab

Joined Nov 6, 2012
4,290
Please explain why You are using a special "Type-III" Voltage-Mode-Converter.

Not that I'm all that well versed in various Buck-Converter-Feedback schemes,
but I've never heard of a "Type-III" Buck-Converter,
and the Schematic rendering program that You are using
makes it impossible to decipher what's going on in this Circuit.
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ronsimpson

Joined Oct 7, 2019
3,200
There are several things that I don't understand.
1. There is a 6V battery that appears to have the negative end not connected.
2. In all but one case where wires come together, I cannot tell if they connect or just pass over.
3. Put part numbers on the ICs and MOSFET.
4. I can't see how (IC on the left) gets powered.
1714838059881.png
 

Thread Starter

Rborres07

Joined May 4, 2024
4
Th
There are several things that I don't understand.
1. There is a 6V battery that appears to have the negative end not connected.
2. In all but one case where wires come together, I cannot tell if they connect or just pass over.
3. Put part numbers on the ICs and MOSFET.
4. I can't see how (IC on the left) gets powered.
View attachment 321601
Thank you for your reply.

1. The negative end is connected to the ground and shoulb be parallel to both the bypass capacitors. I'll fix the diagram for this.
2&3. I really appreciate the comments with regards to the circuit diagram. I'll be sure to fix it.
4. The IC on the left is powered by the "bootstrap circuit" which is composed of the diode, resistor, and capacitor on top.

You circled something on the comparator part which I do not understand. Would it be possible to clarify it?
 

Thread Starter

Rborres07

Joined May 4, 2024
4
Please explain why You are using a special "Type-III" Voltage-Mode-Converter.

Not that I'm all that well versed in various Buck-Converter-Feedback schemes,
but I've never heard of a "Type-III" Buck-Converter,
and the Schematic rendering program that You are using
makes it impossible to decipher what's going on in this Circuit.
.
.
.
Type III basically just refers to the controller wherein I used 2 poles, 2 zeroes, and 1 integrator to adjust the controller GM and PM. This is what it would like in PLECS as well as the controller design from MATLAB.

1714840235464.png
 

Attachments

Ian0

Joined Aug 7, 2020
10,232
Please explain why You are using a special "Type-III" Voltage-Mode-Converter.

Not that I'm all that well versed in various Buck-Converter-Feedback schemes,
but I've never heard of a "Type-III" Buck-Converter,
and the Schematic rendering program that You are using
makes it impossible to decipher what's going on in this Circuit.
.
.
.
Types I II and III refer to this application note from TI.
Type III is a voltage-mode converter, so it needs more complicated feedback.
 

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