Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Help with boost converter please :)

Status
Not open for further replies.

throbscottle

Well-Known Member
Attached is the badly drawn schematic for my first attempt at a simple boost converter, using a dual nand gate oscillator and a transistor used as a voltage controlled resistor to control the duty/frequency. It's intended to drive a pretty constant, light load, with a zener to clamp the output voltage, but has kept within a couple of volts over the range of load shown, so I'm feeling quite pleased. The output can be adjusted by means of the feedback resistor.

The test run is at 9v since that's the only psu I have at the moment, with outputs tested at 13v, 17v and 20v

I have a couple of issues with this circuit I'd like some help with:
1) it's not very stable, and can go into a state where the oscillator runs with an approximately 50/50 duty cycle, and the output goes up quite high, to around 35v. Don't know how it's doing that.
2) I'd like to be able to create a feedback circuit with reference for greater stability - any pointers how to do this?

TIA
 
Hi,

There are much simpler designs using an inductor, two transistors, a capacitor or two, a diode, and a couple resistors. Are you sure you want to be bothered by the complexity of the circuit you are looking at now? There are many more parts in that one which are basically just a waste of time, money, space, and trouble.

Feedback to stabilize the output voltage often comes in the form of an op amp and a few more resistors and small caps.
 
Last edited:
Please tell me there is a diode missing!
There are ICs that do all this! One simple 6 or 8 pin IC.
Your 'error amplifier' does not have much gain.
 
Thanks for the feedback!

Yes, there's a diode missing from the output - well spotted! It /is/ in the actual circuit. Of course, that was a deliferate mistale to make sure you're paying attention (ahem)...

I started with just the inductor/output transistor/rectifier/smoothing driven by a signal generator, and the output voltage changes terribly with load. The 2 nand gate oscillator was the simplest way I could think of to get a square wave, then I found a variable duty version on the net, so adapted that so there was a transistor instead of one of the resistors.

I did want to make a self oscillating version but I guess that would have to be some kind of relaxation oscillator and I don't know how to make one. Could a circuit like this be able to be regulated?

I didn't want to use a converter chip because I want to learn how these things work - also it would cost money I haven't got to spend and I wanted to use parts I already have.

Well, anyway, it's good enough for what I want it for, I just wanted to pick peoples brains and see what else I can learn, and how to improve it.
 
Hi,

I cant help but wonder why you'd want to start with such a complex circuit when much simpler ones are already out there.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top