Need some help for a circuts newb... simple question line filtering type question....

Have a 3.3V IC circut with a component that needs 5V. Rather than adding a second regulator, would it cause issues to simply use a voltage divider for the lower voltage. The 22Ω and 47Ω resistors are there as a voltage divider...

The 3.3V and the 5V are providing power, neither are a signal line...

Would the following present me with any issues ???

Any and all input is greatly appreciated.

Thanks!

 

A voltage divider is fine if you do not draw any current from it. In other words no.

Actually if you use low enough value resistors and do not mind wasting all that power you can get a low enough output impedance so it can work.

So suck it up, get another regulator would be my advice.

 

What is the current needed by your 3.3 volt circuit?

 

Russ, thanks... a second regulator is not an issue...

And ronv, haven't measured it yet but should be around 50 mA with short maximums of no more than 200 mA...

 

I would use two regulators both being fed from the power jack input.

 

I would use two regulators both being fed from the power jack input.

Aren't there any better ways to do it than 2 voltage regs or what he posted ???

 

I am doing exactly that on my boards right now, i.e. using two regulators.

Here is a good reason for using two independent regulators.

The 3.3V regulator is used to power digital circuits.
The 5V regulator is used to power analog circuits. It is imperative to keep the digital and analog supplies separate.

 

You can buy a bag of fifty 3.3v regulators on ebay for a few dollars. They are fine with a 5.0v input, so they turn 5.0v into 3.3v. Then you are set for life!

They are usually a SMD package but still with 3 pins and they can be hand soldered without too many problems.

 

I am doing exactly that on my boards right now, i.e. using two regulators.

Here is a good reason for using two independent regulators.

The 3.3V regulator is used to power digital circuits.
The 5V regulator is used to power analog circuits. It is imperative to keep the digital and analog supplies separate.

You can buy a bag of fifty 3.3v regulators on ebay for a few dollars. They are fine with a 5.0v input, so they turn 5.0v into 3.3v. Then you are set for life!

They are usually a SMD package but still with 3 pins and they can be hand soldered without too many problems.

Couldn't he use one of those cheap chinese bread power supplies ??

 

Using two 1N4001 and one Schottky diode, if you want then you can in parallel with a 2K false load from the output to GND.

 

You can buy a bag of fifty 3.3v regulators on ebay for a few dollars. They are fine with a 5.0v input, so they turn 5.0v into 3.3v. Then you are set for life!

They are usually a SMD package but still with 3 pins and they can be hand soldered without too many problems.

Yep... have a pretty tight board and was looking for a way to eliminate a component... still have some work to do...

 

there are 4 options:

1) use voltage divider, but u need to calculate current u need for ur 3.3v circuit and choose resistances accordingly. it's a very bad idea if the 3.3v circuit needs somewhat higher current anywhere near to 100mA.
2) use 3x 1N4007 in series before the 3.3v circuit. but the voltage drop each diode offers is current defendant, so u need to check the voltage drop with a multimeter, and a pot before u connect these to 3.3v circuit.
3) use ldos like LM1117 / AMS1117 as THE_RB suggested, its the best alright, will supply 500-600mA easily, provided the 5v can sustain that much.
4) if 3.3 circuit draws steady current like 50mA, then u can simply add a 1.7v drop resistance. i.e. 1.7/0.05=34ohm resistance in series to 3.3v circuit. wattage requirement for the resistance should be 34x(0.05^2) watts. if the current draw is 100mA, then i need 1/2 w resistance minimum, and it will generate heat.....etc

 

I googled ebay and found these;
http://www.ebay.com/itm/100-PCS-AMS...A-LOW-DROPOUT-VOLTAGE-REGULATOR-/290964901871

100 pieces for $7.99 with FREE shipping. They are SOT223 SMD pack, which is a nice large SMD device and the pin spacing is close enough to 0.1" that you can solder them directly on stripboard or padboard, or solder them to a 3 pin header to plug into a breadboard. No more excuses.