DC Voltage Converter

Figure 1: Voltage divider

A simple example of a voltage divider consists of two resistors in series or a potentiometer. It is commonly used to create a reference voltage, and may also be used as a signal attenuator at low frequencies.

Hi Thanks a lot for ur response.

I make my requirements clear here.

Vin = 24V to 64V

Only for this range of input i should get 5V output. Incase Vin less than 24V my output shall be 0V. For Vin greater than 65V my output can be 5V but i should have protective circuit at initial stage.

How about replacing Z1 with a zener diode rated at ~19Volts and replace Z2 with a 5 Volt zener.

This would be closer to what you want.... voltage less than 24 volt output less than 5 volt (tending to zero)

Voltage 24 to 65 volts output is 5 Volts

Voltage above 65 volts output is regulated at 5 volts???

Watchout for power dissipation though... Oh and you will need a current limiting resistor as well.

Regards An idea! but:

Sorry below 24V even it will drop linearly till Z1 [19V zener] stops conducting somewhere below 20/19V.

More over you have to place a resistor before Z1 and after 24V + to limit current through zeners to protect overheating. Can you imagine current throuh a zener with a higher input voltage than the rated without a series resisor?

What you are describing is a simple comparator circuit.

http://en.wikipedia.org/wiki/Comparator

This can be implemented cheaply with a comparator chip and a couple of resistors. For overvoltage protection of the op amp input (voltage being monitored) simply use a zener diode regulator.

http://en.wikipedia.org/wiki/Zener_diode

Still the spec is not clear. i understand as - when voltage raises above 64 volt the out put should be 5 volt and during falling down below 24 volt output should falls to zero, upto 25 it will still high at 5 volt. again in the next cycle (till input reaches 64 volt out put will be zero) >64V input out put will be 5 volt and. it means you require a schmidt trigger with large hysteresis. as stated by one of our friends in this section with potential dividers you can reduce the in coming voltage range to may be 0 to 8 volt or so and use a comparator chip with hysteresis. input can be protected with zener diode.

seetharaman

Too lossy a network.

5v from 24~64V & 64V Loss = [59 x 20]/1000 = 1.8W while power used =5 x 20=0.1 W

HI

Thank U all for all ur suggestions.

Here i concluded for my Req.

Considering the cost constrain i end up with the following sollution.

Let the input vary between 24V to 64V. I will put a resistor divitor network and make sure that i get max of 30V and followed by 7805 reg.

For Vin greater than 64V input Zener and some other protection will take care.

Thank u ..

R1 is too high, you have to supply at least 20+ mA on the divider. In addition I would replace R2 with a 30 (24?) V Zener.

Take R1 133K in series to 7805 regulator:

@ 24V 24 ÷ 133000= <0.2mA

@ 30V 30÷133000= <0.25 mA

@ 64V 60÷133000= <0.5mA

How the regulator will function at such a low current & how 20mA can be taken?

It is possible to reduce Dc voltage by a suitable Voltage Divider which consists of some resistances connected in series and required voltage can be obtained by proportionate tapping . This is a rather in expensive devise but for proportionate tapping , correct resistance is required to be tapped and so standard resistances are required to be used .

In series with 1Kohm 2W resistor connect 5 to 7 diodes (1N4148) in series (forward bias) so as give you total 5V "forward voltage drop will solve your purpose. Due some technical reasons I am not able to provide you schematic.

What's wrong with this?

The 820 Ω resistor is too large. When the supply voltage is 24 V the current will only be about 10 mA. I'm starting to think that a low-power switcher is the best solution.

Why do you say that: current through the Zener perhaps?

Because in case the load current is higher than 10 mA the Zener will not conduct, the output voltage will drop below the Zener-voltage.

I made 19V through 820Ω about 23mA.

The TZX5V1A,B,CorD looks pretty good to me from 3mA up to 75mA

They might cost a bit more than 1½ cents for anything but the C version:-

http://gb.mouser.com/ProductDetail/Vishay-Semiconductors/TZX5V1C-TR/?qs=sGAEpiMZZMsnCtsnHQqDlTQnV0SrzyvbY8YqNFxP18w%3d

Regards all.

Voltage divider in a conventional way is not a good choice @ such a high input range i.e. 24~64V for constant job unless it is for a Voltage Ref purpose.

Though it is a small power cct but the ideas be technically the best choice or the concept to have that much range be re-thought.

Even series regulators in that much range will overheat on higher range area as ideal is to have minimun volatage drop across the regulator is kept within the range of 2~10V.

More drop-out across the series regulator is not rcommended.

Everyone is getting hung up on power supplies. I believe the OP wants 2 output voltages only: 0 volts or 5 volts. I took a look at a comparator I used Jeez 30 years ago... The LM340 by National Semiconductor. It can source an amp of current, and if one wanted to get tricky with resistor networks, you could add a hysteresis loop to it. I don't have time to crunch the numbers right now, but it might be worth looking at.

Bill

GA, but are you sure you meant an LM340

Chandu,
...........Can you put a 5V supply on the board. If so four LM339s (quad comparators) with a transistor on the output would do the job.

You are quite correct!! As I indicated, I was in a rush. BUT Look at LM319. It is open collector, but it sinks 25 ma... and has a max voltage of 36 volts. Hmmm on the output of the comparator, run a resistor to + voltage, and a 5 volt zener (1N751?) to ground. This would give to 5v or 0v output. Just an idea.

Bill