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UC3842 IC used for voltage mode control of Buck & Boost converter

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abhijithsinghs

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Hello,

I am finding it very difficult to design the voltage mode control of Buck & Boost converter using UC3842. If anyone has the design procedure then please share it. It would be of great help.
Thank you soo much in advance.
 

Have you focussed on getting success with a buck converter? It is the easier type to regulate automatically, for two reasons:
(a) You turn on the switching component when output drops. Turn it off when output rises.
(b) The reference voltage (or desired output voltage) is available from the moment of powerup.

In contrast, the boost converter is not so easy to regulate.
(a) It must be kept oscillating continuously. This requires a control system which is not dependent solely on voltage sensing.
(b) A reference voltage is not available immediately at powerup, making it necessary to use some indirect manner of regulation.

That's all I can reply since I have no hands-on experience with control IC's such as UC3842.
 

Have you focussed on getting success with a buck converter? It is the easier type to regulate automatically, for two reasons:
(a) You turn on the switching component when output drops. Turn it off when output rises.
(b) The reference voltage (or desired output voltage) is available from the moment of powerup.

In contrast, the boost converter is not so easy to regulate.
(a) It must be kept oscillating continuously. This requires a control system which is not dependent solely on voltage sensing.
(b) A reference voltage is not available immediately at powerup, making it necessary to use some indirect manner of regulation.

That's all I can reply since I have no hands-on experience with control IC's such as UC3842.

Have worked on both Buck and Boost converter and able to get the desired output.

The problem am facing is with the control IC UC3842 where the pin number 3 plays a major role as it is the switch current sensing pin.
I want to use this IC as Voltage Mode Control for the converter.
As the Pin number 3 is the Input to R pin of SR Latch it cannot be grounded or left floating. Then what has to be done with this pin number 3????
 

The problem am facing is with the control IC UC3842 where the pin number 3 plays a major role as it is the switch current sensing pin.
I want to use this IC as Voltage Mode Control for the converter.
I doubt that it's a good idea to use a dedicated current mode controller for voltage mode. Better use a voltage mode controller IC.

To make it work at all, you would feed a ramp signal from CT to CS pin, review the 3842 slope compensation reference circuits.
 

As you know, when you use a voltage mode converter, you still need fet source current sensing so that you can turn the fet off in cases of overload.
In fact, during startup, many voltage mode converters work in peak current mode, since their error amplifier is railed high then.

It is diffuclt to find voltage mode control chips....some of the LM**** series active clamp converters from ti.com use voltage mode control, and you can adapt them for your use.
 

There are ways of defeating the CS pin by creating an artificial current signal from the gate drive o/p...
 

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