R1 220 R2 750 and 0.5FV schottky will give you 5V.

What wattage shoould resistors be?

 

http://www.fort777.co.za/index.php?main_page=index&cPath=269_456_605_607_611
1N5817 Schottky Barrier Rectifier (DOD817)
1N5817 Schottky Barrier Rectifier (DOD817)
1N5817 Schottky Barrier Rectifier 1A 20V Low switching noise. Low forward voltage drop 0.45V max. High surge capability 25A for 8.3ms. High...
R2.68

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1N5819 Schottky Barrier Rectifier (DOD819)
1N5819 Schottky Barrier Rectifier (DOD819)
1N5819 Schottky Barrier Rectifier 1A 40V Low switching noise. Low forward voltage drop 0.6V max. High surge capability 25A for 8.3ms. High...
R0.76

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1N5822 Schottky Barrier Rectifier (DOD822)
1N5822 Schottky Barrier Rectifier (DOD822)
1N5822 Schottky Barrier Rectifier 3A 40V Low switching noise. Low forward voltage drop 0.525V max. High surge capability 80A for 8.3ms. High...
R2.68

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BAT85 Fast Recovery Schottky Barrier (SEQ87H)
BAT85 Fast Recovery Schottky Barrier (SEQ87H)
BAT85 Fast Recovery Schottky barrier. Planar Schottky barrier diode with an integrated protection ring against static discharges, DO-34 package....
R5.71

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MBR1090 Schottky Rectifier Diode (SEN03H)
MBR1090 Schottky Rectifier Diode (SEN03H)
Schottky Rectifier Diode FEATURES • Guard–Ring for Stress Protection • Low Forward Voltage • 150°C Operating Junction Temperature •...
R17.64

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MBR3045PT Schottky Rectifier Diode (SER23H)
MBR3045PT Schottky Rectifier Diode (SER23H)
Schottky Rectifier Diode FEATURES • Low power loss, high efficiency. • High surge capacity. • For use in low voltage, high frequency inverters,...
R17.16

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FML33S Ultra Fast Diode 300V/10A (SEQ81H)
FML33S Ultra Fast Diode 300V/10A (SEQ81H)
Ultra Fast Schottky Diode Rated 300V at 10A
R24.49

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Displaying 1 to 7 (of 7 products)



The only schottky I can easily attain, give me a part no, see if mantech.co.za will have it, but don't know when I'll be able to pick it up from Mantech :-/

 

You can use 1W.Pot can be 0.5W LINEAR. 1N5822 diode is close enough.

 

The tolerance of the regulator reference voltage will also give some variation in the output voltage from the ideal, even with exact resistors. If you want exactly 5V then you can use a pot (connected as a rheostat) for one of the resistors, but note that 5V circuits are typically designed to operate properly with +/- 5% tolerance on their supply voltage.

I see Crutschow has already said this.

what wattage should trimpot be, I can get cement trimmers for 0.75W

Since this is a learning exercise try calculating for yourself.

What is the voltage and/ or current through the trim pot?
Either will lead you to the power dissipated. add 25% for safety.

I have two MJ2955 transistors listed.

These are TO3 metal can 150 watt devices
The MJ2955A has better guaranteed gain (20 to 70 at 4 amps) than the MJ2955 (5 at 10 amps)

The MJE2955s are what we call plastic transistors and have lower power ratings.

You need to be a bit more careful about these since there are three versions with different pinouts.

The MJE2955 has a TO127 case and a guaranteed gain of 20 -70 at 4 amps and a power max of 90 watts. Pinout is E-C-B
The MJE2955T has a TO220 case and a guaranteed gain of 20 min at 4 amps and a power max of 75 watts. Pinout is B-C-E
The MJE2955K has a TO220 case and a guaranteed gain of 5 at 10 amps and a power max of 90 watts. Pinout is B-C-E

There are similar variations in the 3055 range

So check with your supplier if you get these.

 

Are you going to use your 12 volt camera supplies?

You do not need fast schotty rectifiers for this, ordinary cheaper ones will do.

The schotty's are for the switching supply that you already have.

 

I see Crutschow has already said this.



Since this is a learning exercise try calculating for yourself.

What is the voltage and/ or current through the trim pot?
Either will lead you to the power dissipated. add 25% for safety.

I have two MJ2955 transistors listed.

These are TO3 metal can 150 watt devices
The MJ2955A has better guaranteed gain (20 to 70 at 4 amps) than the MJ2955 (5 at 10 amps)

The MJE2955s are what we call plastic transistors and have lower power ratings.

You need to be a bit more careful about these since there are three versions with different pinouts.

The MJE2955 has a TO127 case and a guaranteed gain of 20 -70 at 4 amps and a power max of 90 watts. Pinout is E-C-B
The MJE2955T has a TO220 case and a guaranteed gain of 20 min at 4 amps and a power max of 75 watts. Pinout is B-C-E
The MJE2955K has a TO220 case and a guaranteed gain of 5 at 10 amps and a power max of 90 watts. Pinout is B-C-E

There are similar variations in the 3055 range

So check with your supplier if you get these.

The supplier I can easily get parts from is Yebo Electronics (www.fort777.co.za) local. The suppplier that have more parts is www.mantech.co.za, but it's in another suburb, so difficult to get to with my VERY limited transport options...

At Yebo I can get "MJ2955 - High Power PNP Silicon Transistor, T0220 (SEM62H)" If that one will work, then it's way more possible to get the part, dunno when I'll be able to get a lift to www.mantech.co.za, but they have MJE2995T

 

You can use 1W.Pot can be 0.5W LINEAR. 1N5822 diode is close enough.

1N5822 Schottky Barrier Rectifier (DOD822)
R2.68
1N5822 Schottky Barrier Rectifier 3A 40V

Low switching noise.
Low forward voltage drop 0.525V max.
High surge capability 80A for 8.3ms.
High reliability.

Specifications
Max. Recurring Peak Reverse Voltage: 40V
Max. RMS Voltage: 28V
Max. DC Blocking Voltage: 40V
Max. Average Forward Rectified Current at 95°C: 3A
Max. Instantaneous Forward Voltage at 3A DC: 0.525V
Max. Forward Voltage at 9.4A: 0.95V
Max. Average Reverse Current at 40V DC: 2mA
Case style 5 x 2.6 (dia) mm: DO-41

How will this diode rectify 5V? says blocking voltage 40V

 

I see Crutschow has already said this.



Since this is a learning exercise try calculating for yourself.

What is the voltage and/ or current through the trim pot?
Either will lead you to the power dissipated. add 25% for safety.

I have two MJ2955 transistors listed.

These are TO3 metal can 150 watt devices
The MJ2955A has better guaranteed gain (20 to 70 at 4 amps) than the MJ2955 (5 at 10 amps)

The MJE2955s are what we call plastic transistors and have lower power ratings.

You need to be a bit more careful about these since there are three versions with different pinouts.

The MJE2955 has a TO127 case and a guaranteed gain of 20 -70 at 4 amps and a power max of 90 watts. Pinout is E-C-B
The MJE2955T has a TO220 case and a guaranteed gain of 20 min at 4 amps and a power max of 75 watts. Pinout is B-C-E
The MJE2955K has a TO220 case and a guaranteed gain of 5 at 10 amps and a power max of 90 watts. Pinout is B-C-E

There are similar variations in the 3055 range

So check with your supplier if you get these.

I=V/R V=5v R =220, I=0.0227272727273 P=V*I = 5*0.022=0.113636363636
please step me through it If you have the time and this isn't correct.

(I'm using circuit from http://diyaudioprojects.com/Technical/Voltage-Regulator/)

 

We are not rectifying anything if your input in the power supply is pure DC.We are going to use the diode at the output to drop the voltage from 5.5V to 5V so you can use it for microcontrollers.

 

We are not rectifying anything if your input in the power supply is pure DC.We are going to use the diode at the output to drop the voltage from 5.5V to 5V so you can use it for microcontrollers.

yes, but how does that work? the DC block rating is 40V, and I believe that packaging is like a resistor.

 

Diode blocks current only on one side. In case of Schottky's diode it has Forward voltage of 0,5V which means it going to turn on and let the current pass when you put more than 0.5V on it.So if you have 5,5V and you place diode in circuit its going to drop the the voltage by 0,5V since it needs it to turn on and pass the current.If you pass current from cathode towards anode its going to get blocked.

 

Diode blocks current only on one side. In case of Schottky's diode it has Forward voltage of 0,5V which means it going to turn on and let the current pass when you put more than 0.5V on it.So if you have 5,5V and you place diode in circuit its going to drop the the voltage by 0,5V since it needs it to turn on and pass the current.If you pass current from cathode towards anode its going to get blocked.

This is what we're looking for? :

Low forward voltage drop 0.525V max

Gets me to 4.986 (5.511- 0.525) but you're saying the voltage drop is 0.5V, is that where the "max" comes in after: Low forward voltage drop 0.525V *max*

 

Yes,because it drops the voltage from 5,5v to ~5V which we need.If you use a pot you won't need the diode to get 5V since you can adjust the voltage but you will need to have VU meter to see the voltage.

 

I really don't know how to calculate power ratings on the resistors @ http://diyaudioprojects.com/Technical/Voltage-Regulator/ <-- their lm350 circuit , The highest wattage I can get from yebo on the 750R is 0.5w; 220R I can get at 2W

 

Ok, let me try again:

220+750=970
Voltage will drop over both, so its I= V/R=5/970=0.00515463917526 P=V*I=5*0.00515463917526=0.0257731958763
is that right?

 

0,5W will be enough,there is really small current going through them.You can find the adj current in the datasheet.

 

50-100uA
Adjustment Pin Current 50(typical) 100(max) µA
but this is with a 10mA load

 

It needs 5-10mA load to regulate,0,5W resistor is fine.

 

For learning purposes you could make a simple transistor regulator.

 

Ok, let me try again:

220+750=970
Voltage will drop over both, so its I= V/R=5/970=0.00515463917526 P=V*I=5*0.00515463917526=0.0257731958763
is that right?

are these correct?