Proportional DC-DC Design

[ChubbyChubby]

Hi all,

I need some suggestion on how to design as per below requirement:

I need my Output Voltage to be proportional to my Input Voltage (range from 0-10V) as below:

Input Voltage proportional Output Voltage (approximate)
0V = 0V
1V = ~2.4V
2V = ~4.8V
3V = ~7.2V
4V = ~9.6V
5V = ~12.0V
6V = ~14.4V
7V = ~16.8V
8V = ~19.2V
9V = ~21.6V
10V = ~24.0V

My meaning is when I supply Input Voltage of 1V, Output must be ~2.4V, when Input Voltage = 2V, Output = ~4.8V and so on. My output current must at least able drive load on min 1A.

Can anyone suggest me how to implement this circuitry? Can I use am Op-Amp to implement it or any better suggestion ( e.g. microcontroller)?

Kindly advise me.

Thanks,
Cheryl

 

[Tunelabguy]

Most DC-DC converters used as power supplies have a regulated output that is sort of independent of the input voltage, so that won't work for you. Also they usually work only over a certain voltage range, not down to zero volts. It will be very hard to get something that is powered by 1volt and puts out 2.4 volts at 1 amp, and still work when powered by 10 volts. This design would be easier if you had a separate power supply to power the whole thing. Then you would consider the 0 to 10 volt input as merely a control signal. The real power would come from a separate (and constant) power supply. But if you are forced to derive all the power from this one 0 - 10v input, I think you will have a very difficult time of it.

 

[ChubbyChubby]

Dear Tunelabguy,

Thanks for your reply.

Actually what you wrote is what I trying to ask, only the way I write it was wrong.

Yes I use separate power supply to power the whole thing and actually treated the 0 to 10Volt input as control signal.

If so is there any circuitry or design you could possible recommended to me or advise me?

Thanks,
Cheryl

 

[betwixt]

So your specification is:

Input voltage range 0 - 10V
Output voltage range 0 - 24V at 1A load

More questions:
How much current can the 0 - 10V control voltage itself supply?
How fast does it have to react to the control voltage? (what does the 0 - 24V connect to?)
You need a power source providing at least 24V to produce the maximum output you want but to get down to zero you may also need a negative supply, do you have one?

Brian.

 

[ChubbyChubby]

Hi Betwixt

My power source derive from a switching power supply 24VDC which is also use to power up a PLC.

My input signal is actually from a PLC analog voltage output. I need a circuitry to receive this analog voltage from PLC (0-10V) and give an output voltage ranging (0-24V). The output voltage is use to control small DC motor (300mA motor). The reason need at least 1A load is for protection purpose.

Thanks,
Cheryl

 

[dick_freebird]

If you have this power supply then all you really want is
a noninverting amplifier, gain=2.4. The problem for a
switcher, aside from some unusual voltage mode types,
is getting to true zero and true VIN (+24); all the current
mode control types I've seen have min on time, min off
time limits preventing a truly zero or 100% duty.

But I have built prototypes that can do that. They are
simple enough - reference, error amp, ramp generator
and comparator. Make the error amp single supply and
below-ground capable, make the ramp such that its
excursions lie entirely within the error amp's output
range, then your comparator (and downstream FET
drive) can run a "Class D audio" sync rect output
stage stop-to-stop duty cycle wise.

Now you're on your own for the current limiting,
and how to get that without an intolerable voltage
drop is a question. But one with some possible
solutions.

 

[betwixt]

.... which is why I queried whether a negative supply was available. What concerns us Cheryl is that you are asking for a system that can give any output from 0% to 100% of the available input power. That leaves no overhead for any current limiting circuit. Normally a current limiter would deliberately drop a small voltage which is proportional to the current being drawn, it's easy to use such a voltage to set the limit. However, in your specification that isn't possible. Additionally, going right down to zero is difficult for two reasons, the first is the same current limit issue, the other is that it's difficult to measure voltages very close to zero when that is also the same ground point of the measurement system. Usually, a negative supply is used so the measurement system is still working within it's range while the voltage it is measuring is at or close to zero.

It isn't impossible to do what you want but it gets a whole lot easier if you can supply say +30V and -5V to the circuit.

Within your constraints, the most promising method I can think of is similar to that suggested by dick_freebird, a PWM based regulator but that inevitably involves some digital, inductive and high speed components. Before going further, is that something you are comfortable with?

Brian.

 

[ChubbyChubby]

Dear dick_freebird & betwixt,

I have try out the non-inverting amp as suggested by dick_freebird and I am I able to get the result. But still there some tuning I might need to make.

Yes betwixt I can supply both the +30V and -5V to my circuitry as I plan to use regulator to obtain the negative voltage. The concept I am actually looking is similar to PWM.

Anyhow I am trying it out to see the outcome first. Any help I will post here for advise. Thanks for all parties advise..