About regulator and DC/DC converter

[Analog_starter]

Hi all,

What is the difference between regulator and DC-DC converter? The same thing?

Is it the simplest regulator: Bandgap+OPA+external resistor? And adjust the resistance value to obtain the output voltage which is wanted to get?

Does most regulator use bipolar transistor? Why not use CMOS except for the reference？

Thanks & Best Regards
Analog_starter

 

[markty]

Well, they both output the dc supply. But i can give you one example. Most DC/DC converter, as far as i know, output a voltage larger than the input voltage. For a regulator, you can not get this.

 

[olemp]

regulator terms is used to describe to hold constant something(voltage or current). you are asking linear and switching regulators.
with this information you can search on the web.
for example:
**broken link removed**
shortly in linear regulators quality of the output power is better. but efficiency is terrible.even if switching regulators hold lesser area their structure is more complex.............

 

[Kevin Weddle]

A DC to DC converter does not regulate. A regulator uses the output as feedback and directly affects the output voltage. It is a simple loop. The value of the voltage of a DC to DC converter can be very constant. So yes in some cases you don't need a regulator. Very interesting. The nice thing about a regulator is that it is fool proof. Whereas it will regulate against any variation of the DC. You know of course that the DC has fluctuation, and that a regulator will by construction negate this fluctuation. As it is used to dealing with a changing DC.

 

[Analog_starter]

Thank you all,

But I can not get a uniform conclusion form your answers. I am puzzled.

Who can tell me the best way to implement this regulator spec: input 3.3v output 1.5v? And what is the important parameter for regulator, power efficiency and ...??

Thanks & Best Regards
Analog_starter

 

[IanP]

Here you can read about dc-dc converters:

**broken link removed**

These two terms are often used for the same circuit and I think you have to make up your mind by yourself...

Back to your last question: I think stability of the output voltage, efficiency will be next as you do not want to have heaters tha waste energy...

Depending on power requirements (current consumption) convertion of 3.3V to 1.5V can be done by some simple ICs: see MAXIM-ICs for examples or LM1086CT-3.3 from National Semiconductors..etc


PS: I would ignore some statements from previous posts....

 

[Analog_starter]

Hi IanP,

I mean that I want to design a regulator circuit converting from 3.3V to 1.5V, not use existing ICs. What's the best way to realize it? Sorry for my unclear question.

Thanks & Best Regards
Analog_starter

 

[andy1]

Use an Opamp as your error correction. Use a bipolar or Fet at the output as a current source.

 

[nicleo]

I mean that I want to design a regulator circuit converting from 3.3V to 1.5V, not use existing ICs. What's the best way to realize it? Sorry for my unclear question.

From your first post, I guess you wish to design regulator IC?

 

[IanP]

Hera are some examples:

https://www.onsemi.com/pub/Collateral/NCP5424DEMO-D.PDF
**broken link removed**
https://www.altera.com/literature/hb/cyc/cyc_c51012.pdf

I know these examples are not exactly what you would like to do but have a look at them and maybe you will find some intresting solutions.

Designing this from scratches? It is not ease to find components which will operate at as low as 3.3V. However, have a look at LM358, LM6142, ....or TLV2466.. They all can operate at voltages ≤3Vdc and on them you can base a PWM which will convert 3.3 to 1.5V...

 

[Analog_starter]

Hi andy1,

What is the purpose for bipolar or Fet current source?
Is it workable that Bandgap(as voltage reference)+opa(as error correction)+two resistors(as voltage divider 1.5V/1.2XXXV "the bandgap output")? If it is ok what I should pay attention to?

Thanks & Best Regards
Analog_starter

Added after 2 minutes:

Yes, nicleo, you got it.

Thanks & Best Regards
Analog_starter

 

[andy1]

Analog_Starter:

Please look at this doc. It has the schematic for a simple linear voltage regulator.

Look under Low Drop Out (LDO) section since the spec you specify does not leave much for head room.

One tricky thing is that you need to supply voltage for the op amp. I don't know what type of voltage supply available to you but choosing an opamp with only 3.3 V supply is a little tricky or I guess you can build an opamp from discrete part which is even more trickier.

As for switching supply, I think it's a lot harder to build using discrete parts.