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ZeGas

Transistor Sizing And Other Q's

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Right, that time again where the electrically ignorant (me) try to expand their horizons.

 

I am looking at the following diagram.

 

20160216083625-0ca5e3b5-me.jpg

 

Most of which I understand, of that I didn't Dr. Google helped out.

  1. The simple Q first, are the "?" marked item what I think they are, I am guessing they are and that it is assumed that all LED's have the same output so the ones I have marked as "LED Tail" would be dimmer due to diode resistance.
  2. R1 says 1.2K that seems rather large so I'm guessing it is not 1200 ohms so what does it mean
  3. How are the diodes labelled 1N4148 defined (sized), I ID them and they are rated for 1v and 200mA, this circuit appears to have both 6v & 12v, so how does the diode cope.
  4. What size transistor would 0.8A do or should I look larger to 1.5A. Most seem to handle 40v but how do I figure out the saturation for the switching. I have read and watched youtube videos but most of it 747'ed me.
    This is the most simple explanation I found
    http://www.penguintu...ansistor-switch
    and although I sort of understand most of it can someone simply apply it to this circuit.
    Will one of these transistors do.
    2SB772
    http://www.ebay.com....aMAAOSw3ydV4SnX
    or 2n2222
    http://www.ebay.com....UEAAOSwLVZVjSTx
  5. One other question, in this circuit is the transistor NPN or PNP I think the later as 1 & 2 seem to be +ve.

 

Thanks in advance for any advice.

Edited by ZeGas

Cheers Grant

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Hi ZeGas,

 

The transistor is a PNP, and any generic 100mA+ transistor should work fine in that circuit...

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Thanks Michael,

 

I did find Phil's sketch and diagram that explains most

gallery_89_128_29833.jpg

 

Figured out 2 so just questions

(3) unresolved as Phil uses different diode does a diode need to be sized and

(4) if the voltage regulator is replaced by a 5.5v zener is the ground leg redundant and zener runs through. I think it is just checking (read showing my ignorance) :wacko:


Cheers Grant

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Given the low currents that these circuits run at, virtually any diode will work...

 

In Phil's diagram, a 5.5v Zenner, that is used to replace the voltage regulator, would sit parallel to C1.

That said, ~150mA @ up to 7.5v is quite a bit for a Zenner to absorb...

 

Also, Phil's circuit won't have 'realistic brake lights' like the one above does...

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If you need a small regulator, I've used a few of these...

http://www.jaycar.com.au/Active-Components/Regulators/Fixed-Voltage/78L05-%2B5V-100mA-Voltage-Regulator/p/ZV1539

 

They will just run 2x 30mA Front lights, and 2x 20mA Rear lights.

 

If you wish to run brighter lights, you can fit one transistor near each pair of lights and go up to ~50mA LED's, which is similar to how the SCX light boards work...

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Or you could just buy a ready made board from Ace Hobbies with all LEDs pre wired.

 

This one is $28 and has 2 headlights, 2 rear lights with tail and brake, plus the LEDs will flash for a couple of minutes if the car is removed from the track. Makes it easy for marshals to find the car in the dark when night racing.

 

165.jpg

 

http://acehobbies.co...roducts_id=1097

 

 

 

And there's a 4 headlight version for $33

 

165Q.jpg

 

http://acehobbies.co...roducts_id=1098

Edited by Garry J

Cheers,

 

Garry J

 

Slotworx_Logo_Small.jpg

 

Old age and treachery will overcome youth and skill

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Now your just confusing me Michael I haven't got a handle on how transistors work yet.

 

I was going to set up as per first diagram but adjust the resistors to suit the LEDS I was going to use.

I planned on using SMD LEDS

2x tail lights (3528 - 3v - 30mA) Red

2x brake lights (3528 - 3v - 30mA) Red

2x headlights (5050 - 3.5v - 60mA) White

2x spot lights (3528 - 3.5v - 30mA) White

 

So the modifications to the first diagram would be

Input voltage = 5.5v

R2 = 0.5w 50ohm

R3 & R4 = 0.5w 40ohm

And spots = 0.5w 40ohm in series.

 

Guess the questions now are

will a 5.5v zener run this if all in parallel, I can't see why not as voltage doesn't drop

and Is R5 calculated by R1 and R6 or just R6 as R1 doesn't complete the circuit.


Cheers Grant

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Home Track..........Corvette C1 Build..........McLaren M1A Build..........Maserati 300S Build..........Allard J2 Build..........50's Diner..........Iso Griffo A3C

 

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Hi Gary,

 

Thanks for that.

Yes I realise that Werner sells them and I have bought a couple off him previously but they have the annoying, IMO, flashing tail lights.

He did have ones that didn't flash but they didn't have the brake lights and I think when I bought the last one he said he wasn't getting them anymore, could be wrong though.

The cost is also a bit prohibitive, especially if you can build it for only a few dollars.

And I like learning how things work so wouldn't mind a simple circuit to start with and see how I go.


Cheers Grant

20191120172309-193d8f3b.gif.......................................................20170306174707-b4015afe.gif

Home Track..........Corvette C1 Build..........McLaren M1A Build..........Maserati 300S Build..........Allard J2 Build..........50's Diner..........Iso Griffo A3C

 

3D Printed Adjustable Chassis..........3D Print Projects

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