Switching pre-regulator

Hi Bros,

I am designing a switching pre-regulator to monitor the output voltage of a variable linear regulator. I need some help on this. What is a switching pre-regulator? Is it the same as a Switching regulator?

The pre-regulator is supposed to operate up to 160vdc and supply 100W of output power.
Any ideas how should I start this project? A million thanks in advance.

Regards,
Derrick

It is an SMPS that is operating before a down stream supply. For example, using a two stage supply, PFC as the front end before a downstream SMPS - PFC would be considered a Pre-regulator since it is a switcher that is being operated before the downstream supply. The output bus of the PFC voltage is constant and is used as the input to the downstream supply.

You have not mentioned the input voltage and some application detail. Is the output voltage variable or fixed.

Hi,

The input voltage of the Switching pre-regulator is to operate up to 160Vdc and supply 100W power. The pre-regulator must monitor the output voltage of the variable linear regulator and maintain 2-4v across the input-output of the linear regulator. To minize power dissipation in the linear regulator.

Is there any books or websites that can help me kick start my project? Thanks in advance.

From your post it seems the output voltage of the switcher is variable to maintain 2-4V across the input- output of the linear regulator.
Depending on the range of output voltage that is required: if output voltage is lower than input, then you can use buck converter and if the output voltage is higher than you can use boost converter. Buck-Boost converter can be used for application where the output voltage is both higher and lower than the input voltage.
Linear has a collection of app note than might be helpful. https://www.linear.com/pc/viewCategory.jsp?navId=H0,C1,C1003,C1042
One thing to think about: Why can't you use the output of the regulator without using a linear regulator provided it is a single output supply.

Hi Bro,

The aim of building the Switching Pre-regulator is to minimize the power dissipation in the variable linear regulator. It must also maintain good line regulation.

From your post, i should consider using a Buck-Boost converter as my linear regulator is to have variable voltage outputs.

I am thinking of the safety features too. Heard of crowbar protection. Is it feasible?
Thanks in advance.

The point I was making is the use of the linear regulator, unless you have a good reason to use it. If it is a single output supply and you are planning on using an SMPS for your design: you could easily design a single stage output flyback which would be isolated and give you the ability to have a variable output voltage. What is the range of output voltage that is required in your design.? I guess I am failing to see the end application.

Flyback is also a buck-boost but is generally isolated.

Crowbar can be used as long as you use the circuit properly.

Hi Bro,

I am still unsure.. What are the actual differences between a Switching regulator and a Switching Pre-regulator? I need some theories on this. Any website that i can refer to? Thanks.

I attached a design example from ST which uses a PFC pre-regulator. A pre-regulator is a regulator that sets up the necessary condition for the downstream converter to work properly. In this case, a PFC pre-regulator is used to improve efficiency over a wide input range, improve power factor and also, provide a steady bus voltage to the downstream converter.

cant seem to find any preregulating circuit which can have input voltage up to 160vdc... Do i need something to amplify the input voltage? Any feel?

First the specs for your design:
Things we know:
Input voltage: 160Vdc
Output voltage: Still unknown?

A pre-regulator is not a special circuit. It is a regulator like any other regulator (smps, linear supply etc). A regulator controls the output voltage or current, maybe both. A pre-regulator simply means it is a regulator before another downstream regulator and provides all the necessary condition so the downstream regulator functions appropriately.

You say your input voltage is 160Vdc which makes me think that there might be an AC input voltage of 110~120 being rectified or maybe not. But examples where AC-DC input voltage range from 100~120Vac should be looked at which is close to your application need. After rectification and bulk capacitor, the bus voltage is close to ~160Vdc. AC-DC converter examples with a single stage are plenty on ST, TI and Power Integration website. Remember they are only reference design which will be close to you application but the leg work still needs to be done to complete your specific design. I will provide the link for power int.
**broken link removed**

my input voltage should take up to 160vdc. There is a variable input range for the preregulator. Hence, i am looking at design a DC input into the preregulator.

However, i cant find any circuit that can take in a voltage that is up to 160vdc.
Should i add some circuit in front to magnify the voltage?

Look at the AC-DC application especially the one's that have a range of 85-120Vac. I am guessing this is the range around the 160Vdc you keep on referring.

After rectification, peak voltage is 85*1.41=119V~120*1.41=169.2. To keep the bus voltage stable at the peak rectified voltage, a input bulk capacitor is used. A flyback circuit is most appropriate for your application. An application note of a flyback circuit is attached.

Switching Power Supply Design, Abraham Pressman (Author), Keith Billings (Author), Taylor Morey (Author) would be a good book to start.

I had discussion with my supervisor. The input to the pre-regulator is 160vdc and will have 100W of peak output power.

1)I plan to use a Buck converter to step down to 80vdc with 1A current. Hence, a
DC input supply.

2)The output will regulate the linear regulator to produce 76vdc to 78vdc output.
Remember regulating 2v to 4v from pre-regulator. This way, the efficiency of
the linear regulator will be higher too. Am i correct?

3)User can select a voltage from 78vdc and below. Or just 76vdc to 78vdc..

4)I need a microcontroller to monitor the safety of the linear regulator too. Any
better ideas?

Thanks a lot.... regards

How come your project is same as my friend Mr. Lau to me.

You can find some idea from VICOR V375A24C600A, or attached paper.

I have attached an app note for forward converter. It is a buck stage and as input accepts dc voltage. Some calculation needed during the design of the converter is also explained in the app note.
In your application , the microcontroller can be used to change the reference voltage based on the desired output voltage.