Using two transistors to create regulator?

[realflow100]

is it possible to use a darlington transistor with a 1-2K resistor and a low breakdown collector/emitter reverse voltage transistor as if it were a zener diode?
and how accurate would it be? would it not work at specific voltages?
I tried to build one myself and it seemed to work.. from 19V it changed it to 7.5V regardless of load applied to the output. but I don't know how reliable it'd be or if theres a transistor of 5V or specific voltages that would do the same thing?

I'm trying to create a reliable voltage of 5V to power a usb hub with a power transistor running from 9-10V or around that voltage

but I don't know or believe that there would be a specific transistor that would change the voltage output to 5V specifically.. as the emitter collector reverse breakdown voltage varies wildly between different transistors..

I dont have a diagram but it should be simple to imagine a scenario of a darlington transistor with a 1-2K resistor and another transistor acting as a zener. but I dont know if a darlington would be more efficient than a non-darlington transistor.. using common NPN transistors.

Is there a zener diode that would account for voltage drop of the transistor and resistor and itself to make the output consistent 5V?

 

[ronsimpson]

Look at the data sheet for the LT431.
It is a programmable Zener.
There is a diagram TL431 + transistor= regulator.
The base to emitter voltage changes with temperature (some with load). This will cause errors in a simple design. A TL431 can correct for these errors.

 

[realflow100]

Is it possible though to use a high power 5W 5.1V zener instead of using a transistor as a zener

 

[MikeMl]

Why bother with any of this when a genuine 7805 costs ~$0.44?

 

[Colin]

Zener regulators are very wasteful.

 

[AnalogKid]

is it possible to use a darlington transistor with a 1-2K resistor and a low breakdown collector/emitter reverse voltage transistor as if it were a zener diode? and how accurate would it be? would it not work at specific voltages?

Yes it is possible, but it will not be very accurate at all.

if theres a transistor of 5V or specific voltages that would do the same thing?

No.

I'm trying to create a reliable voltage of 5V to power a usb hub with a power transistor running from 9-10V or around that voltage but I don't know or believe that there would be a specific transistor that would change the voltage output to 5V specifically.. as the emitter collector reverse breakdown voltage varies wildly between different transistors..

No, there is not a specific transistor for what you want; and yes, the reverse breakdown voltage will vary from part to part and with temperature.

I dont know if a darlington would be more efficient than a non-darlington transistor.. using common NPN transistors.

For a fixed set of application conditions (input voltage, output voltage, output current), the efficiency of all linear regulator circuits is almost exactly the same. The only variation comes from the current that is used to power the regulator circuit, but this usually is much less than the output current so it does not contribute much to the efficiency calculation.

Is there a zener diode that would account for voltage drop of the transistor and resistor and itself to make the output consistent 5V?

Yes, 5.6 V and a standard power transistor, or 6.2 V and a Darlington transistor. Note that the output probably will be a bit below 5 V, and will not be adjustable. Also, while this is a very simple regulator circuit, it has no feedback so the output voltage will decrease as the load current increases, possibly to the point that it is outside of the USB specification.

ak

 

[realflow100]

how do I make it stay at 5V even if theres a short on the output? do would I need a higher power supply voltage to account for voltage drops? or something else? or will nothing be able to do that?

https://solarbotics.com/product/17185/?gclid=CJ3grJvswssCFcYdgQoda_wMdQ should I try to get this one? and how easy would it be able to set up with minimal components? minimal filtering components? is it possible to use it by itself even?

 

[chemelec]

NO Regulator can deliver 5 Volts with a SHORTED OUTPUT!

And WHY would you want that anyway?

 

[Ian Rogers]

Roman Black did a cracking two transistor linear power supply

https://www.romanblack.com/smps/smps.htm

 

[ronsimpson]

I try to get this one? and how easy would it be able to set up with minimal components? minimal filtering components? is it possible to use it by itself even?

From the data sheet. This is using the 5 volt version not the adjustable!
This is the minimal component circuit.
This is a "LDO" (Low Drop Out) part and they need these capacitors more than a non-LDO version.

If you have 10V in and 5V out at 1A there will be 5 watts loss in the regulator. It will be too hot with out a heat sink. A big heat sink.

 

[realflow100]

I have a massive heatsink used for a high power 75W amplifier that ive got so it should be more than overkill for heatsinking.. two of them actually..

 

[AnalogKid]

Roman Black did a cracking two transistor linear power supply
https://www.romanblack.com/smps/smps.htm

Two transistors *and two diodes*, **and one diode is a reference**. It's a great circuit, but with fewer semiconductors you can do a linear regulator with feedback and no switching noise.

https://electronics.stackexchange.c...r2-in-this-discrete-voltage-regulator-circuit

https://www.angelfire.com/planet/funwithtransistors/Book_TS_CHAP-5.html - Figures 5.2 and 5.2b

ak

 

[realflow100]

I was thinking of doing a linear solid state regulator because I dont have the time parts or effort for a switching regulator.

 

[audioguru]

I want to see a video of regulator that keeps its output at 5V when its output is shorted. I wonder if the BANG will be very loud? The big spark at the output will probably weld the short together.

 

[chemelec]

I want to see a video of regulator that keeps its output at 5V when its output is shorted. I wonder if the BANG will be very loud? The big spark at the output will probably weld the short together.

And Keep it RED HOT

 

[realflow100]

I dont think there would be any noise especially if the regulator was rated 5A and the battery/powersupply/voltage couldn't deliver anywhere near that it'd just go into protection mode repeatedly.

 

[spec]

is it possible to use a darlington transistor with a 1-2K resistor and a low breakdown collector/emitter reverse voltage transistor as if it were a zener diode?
and how accurate would it be? would it not work at specific voltages?
I tried to build one myself and it seemed to work.. from 19V it changed it to 7.5V regardless of load applied to the output. but I don't know how reliable it'd be or if theres a transistor of 5V or specific voltages that would do the same thing?

I'm trying to create a reliable voltage of 5V to power a usb hub with a power transistor running from 9-10V or around that voltage

but I don't know or believe that there would be a specific transistor that would change the voltage output to 5V specifically.. as the emitter collector reverse breakdown voltage varies wildly between different transistors..

I dont have a diagram but it should be simple to imagine a scenario of a darlington transistor with a 1-2K resistor and another transistor acting as a zener. but I dont know if a darlington would be more efficient than a non-darlington transistor.. using common NPN transistors.

Is there a zener diode that would account for voltage drop of the transistor and resistor and itself to make the output consistent 5V?

View attachment 98215
From the data sheet. This is using the 5 volt version not the adjustable!
This is the minimal component circuit.
This is a "LDO" (Low Drop Out) part and they need these capacitors more than a non-LDO version.

If you have 10V in and 5V out at 1A there will be 5 watts loss in the regulator. It will be too hot with out a heat sink. A big heat sink.

Why bother with any of this when a genuine 7805 costs ~$0.44?

OBSOLETE: PLEASE SEE POST #26

ERRATA
(1) Connect a 1N400x (x= 2 to 9) rectifier diode, cathode to the regulator input and anode to the regulator output. Any 1A or more, 50V or more rectifier diode will be suitable. This diode protects the regulator when the power is switched off.

NOTES
(1) The circuit will provide a constant 5V for load currents from 0A to 1A. Above around 1A drain the output voltage will drop to 0V. By fitting different three terminal regulators the maximum output current can be increased to 3A or 5A- see data sheets below.
(2) The three terminal regulator should be bolted to a heat sink using insulating washers and a mica washer between the lower metal face of the regulator case and the heat sink. A thin coating of thermal grease should be smeared on both faces of the mica washer.


DATA SHEETS
(1) LM78xx Voltage Regulator (1A output. Input voltage range 8V to 35V)
https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf
(2) LM1085-5 (3A output. Input voltage range 6.5V to 29V)
**broken link removed**
(3) LM1084-5 (5A output. Input voltage range 6.5V to 29V)

 

[chemelec]

What are you Driving with this 5 Volts?
And What Current do you really Need?

Noise is only a Problem when driving certain Items.
(Amplifiers, Transmitters, ETC, But not for things like Relays or Solenoids)

Considering your Input Supply Voltage is 9 to 10 Volts, It Doesn't require a Low Drop Out Regulator.
Any 5 Volt Regulator should be Ok.

 

[realflow100]

I wanted to power a 5V usb hub with a very reliable 5V that doesnt drop voltage much on load Noise isn't a large issue but I just want the voltage to be reasonably stable at no load and high load. (voltage increases back up to 5V when load is increased to keep 5V on the output and decreases V to 5V when theres no load or very small load.) and has plenty overhead for charging a phone. running xbox controllers and such so that windows doesn't report insufficient power issues.
because all my usb ports are filled up with things.

I have a 2A power supply (switch on the front to change output voltage between 3V 5V 6V 6.5V 7V 7.5V and such up to 11.7V but i checked the voltage on its 5V setting and it was much too high to be safe plugged into anything that requires a consistant 5V like a usb hub.

trying to run my usb headphones off the usb hub off that setting is unreliable and makes the bottom half of the audio waveform below 0V completely cut off! and even does that to the microphone. so thats why I want a consistant 5V output. but my computer can't supply enough current to all the devices at once.

 

[chemelec]

Almost Any 5 Volt Regulator will be OK for your needs.
Even a Cheap 7805, With a Suitable Heat Sink.
But Considering your POOR Quality 2 Amp Power Supply, I would recommend Including Both the Input and Output Capacitors on the Regulator.