# Schematic Diagram

Discussion in 'General Electronics Chat' started by imraneesa, Jan 28, 2015.

1. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4

If I have a small circuit board with components, can we find the schematic of the circuit? I am attaching pictures.

2. ### bwilliams60 Active Member

Nov 18, 2012
851
136
That circuit is small enough that you could draw your own. Good luck finding one from manufacturer. Who soldered this board?

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3. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
What is the first top left component in the first image? Don't know who is the manufacturer. How to draw a circuit using board? Is it finding with continuity?

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4. ### ScottWang Moderator

Aug 23, 2012
5,478
864
You can draw in two circuits and another is to mix them to one circuit, three pins could be mosfet or bjt, when you drawing that you just draw them as three pins, after completed the circuit and then we can analyze the circuit.

5. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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It is labeled U1, which suggests it might be an IC, such as a voltage regulator; Q1 on the reverse is probably some sort of single component, like a BJT or mosfet (http://en.wikipedia.org/wiki/Reference_designator). Considering the inductor and diodes, I suspected it might be a small switching supply. However, it would be nice to know where it came from.

John

6. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
I am trying to figure out the connections. as soon as I draw the diagram. I am going to post it here. after that I need help to finish the schematic and I have to make this pcb. this circuit is the constant current supply driver for weak laser (may be 20mw). This was working fine until my friend used wrong side battery. and after that it stopped working. so I want to make one of this may be more to make pointers. I am in the middle of drawing the circuit.

7. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
from y2 is the backside. so up to y2 component it is front side. i hope somebody will give me a best schematic for this which will enable me to print pcb and work on it. Thank you for the replies and help.

8. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
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Maybe just U1 is blown, and you can just replace it, if you can find out what it is. Here's a typical "boost" converter with a minimum of pins. CE = enable. So, only 3 pins are really involved in the boost. At least the inductor connection looks similar. I didn't check the rest that carefully.

John

9. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
can we use this for laser diodes? how to control the current in this. I am not seeing no pot or resistors. I want to make a constant current of 300mA.

10. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
912
You implied it is a constant current supply. My suspicion is that there is a boost component and that the transistor on the back may be for the constant current part. Your drawing for U1's connections is similar to the NCP1402. The pot may be involved in setting the current.

John

11. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
yes you are very correct i thin. the front side is the boost component and back transistor is to control the current (constant current). can you put all these components in a schematic for me? so according to you we can use ncp1402 instead of that first component which we don't know about?

Jul 18, 2013
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I have had similar SMT boards come from China that were obviously soldered crudely with a hand operated iron.
Max.

13. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
yes Sir, this board is from china also. lol. But how to find what component is that? is there a way that I can find about it?

14. ### bwilliams60 Active Member

Nov 18, 2012
851
136
That's very sketchy. I've had students solder better on their first attempts. Amazing some of the junk that is out there.

15. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
912
SparkFun has that converter in 3.3V and 5V versions for little more than the parts' cost (https://www.sparkfun.com/products/10968). I just ordered 2 on Sunday and they are sitting in my mailbox now. SFE also gives the Eagle schematic and board designs. They are limited to 200 mA, which I suspect is enough, but do you have any data on that? Do you know what voltage and current your laser needs?

John

16. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
I am looking for something from 200 to 500mA adjustable current type driver.

17. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
912
I just checked ebay for constant current LED driver (http://www.ebay.com/bhp/constant-current-led-driver). Some are quite inexpensive. My concern is that without knowing the voltage and current requirement for your laser, you stand to ruin it.

If you do know those operating values, then only you can balance the fun and cost of building with the likely lower cost of buying.

John

Last edited: Jan 28, 2015
18. ### imraneesa Thread Starter Member

Dec 18, 2014
198
4
I know the ratings. I have different diodes. one is 405nm 20mw diode which need 250mW current and 4.5~5V voltage. and I also have red diode which is 658nm and 300mw and it requires 350 mw current and only 3V voltage. they are very sensitive so I need to keep current constant. else they will die. Right now I am using linear driver using lm117 voltage regulator. I will attach the schematic. this need at least two lithium 3.7v batteries to function. but I want to use single battery to run the diodes.

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