40-pulses Monoshot (200ms/1A) design_help

[vinodquilon]

Help me to design a Monoshot with the following specifications

1. 200ms pulse width
2. Magnitude 0.5V steps in 0-20V range (total 40 pulses). That is 0,0.5V, 1V, 1.5V,......,19.5V & 20V.
3. capacity to drive maximum 1A load.

 

[E-design]

Are you looking at a staircase generator?

 

[chuckey]

Looks as though you have to divide your circuit into two areas.the first is the 40 step stair case, the second an amplifier to get the out put current.
For the first you need a 5 bit binary counter with a three input gate*, so that on the 41st count the counter can be reset. From the MSB (count =32) take a feed via a 1X resistor to the negative input of an opamp, from the count =16, a 2X resistor, count =8 via a 4X resistor etc. I would make X = 10K. Use a 10K feedback resistor. When you use a N555 oscillator running at 20KHZ as your input signal, you should get your 40 step staircase.
Frank

* connect count = 32 as one input, count = 8 as another, count = 1 as the final input, connect output to counter reset line

 

[BigBoss]

An DAC ( incremental ) that drives a low Rds MOS can work with a one-shot trigger circuit.
One shot should also be driven by a clock circuit up to 40.
Clock circuit counts up to 40 to trig one-shot (200ms) and one-shot will drive DAC to increase the voltage.And this voltage drives MOS tha is connected to 20+ V power supply..
And at the end, a reset pulse make them to inital state..
Just an idea..

 

[D.A.(Tony)Stewart]

Although you didn't specify repetition rate , a Schmitt trigger clock @ 2.5Hz can drive both a binary counter and tristate parallel buffer with a resistor ladder out 2R (Series)> R ( to ground) from each of 6 output stages to do 64 levels. Using logic you can reset the up-counter at 40. The tristate is pulled down to ground at 50% duty cycle every 200ms and steps up in linear increments. A power Op Amp such as the LM1875 can normalize the gain or step size and drive up to 4 Amps from a 24~30V supply.

Your biggest problem is to handle the wasted power and to minimize the VI drop on the driver. Since you did not specify efficiency, cost or heat sinking as not an issue, then this will do it.

You can always use a different buffer such as a Darlington. which would require some method to produce small pulses near ground such as two diodes to drop the base input voltage such as a PNP Darlington to NPN Darlington emitter Follower.
These tend to oscillate on capacitve loads without adding a small Rs like 1 Ohm or a large ferrite bead.

The above circuit needs a -negative supply such as --5V for the lower voltage pulses.

Usually a better answer will rise when you define why you need this.

 

[vinodquilon]

why you need this.

In order to do the Step Method for PickUp/Pull In Voltage measurement of Relays. Also I want to generate one pulse at a time by manual control. I am using 28V relays, so that I have to increase the step voltage from 0-20V in 0.5V steps. And manual stepping is required since when the relay pull-in happens I have to note down the corresponding pick-up voltage.

 

[chuckey]

for manual pulsing just use a switch connected to Vcc instead of the oscillator.

If you are testing 28V relays, if they are plugin types then I would use their own contacts to signal that they have pulled in and stop further increasing the voltage. Also you would want to alter the voltage range as no 28V relay will pull in at 2V. I would try for 16 - 30V. so if you connect the oscillator in series with a normally closed contact, then when the relay operates it stops the clock and its voltage can be checked. The speed would need to be reduced, to, say 20mS/step.
Frank

 

[D.A.(Tony)Stewart]

Pickup Voltage is usually between 50 and 75% so there is no need for 0 to 100%.

Pulses are better for operation but for quality testing, all you need is a sawtooth that ramps starting below where you do expect Vpick triggers a Sample & Hold when the contacts close for ADC reading, then ramps down for release voltage and repeat for if you have statistical reasons.

If you expect a weak current transition time of 20ms and wish to have a resolution of 0.1V then your ramp rate is 5V/s starting from 50%. You could even test as many relays in parallel as you want.