impulse generator circuit design

[[email protected]]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

 

[Tom Bruhns]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

What voltage? What capacitance? What load? (Is it resistive,
inductive, what? What sort of peak current are you looking for? How
long do you expect the output pulse to be? How much energy per pulse?)
Are you thinking to essentially just have the circuit connect the
capacitor to the load and let it discharge, then disconnect? How did
you have in mind charging the capacitor? (That is, would you just put
a resistor between the voltage source/battery and the capacitor, or do
you want to do something more complicated? -- A resistor will dissipate
half the energy provided by the voltage source, if the capacitor is
allowed to discharge to zero volts.) The simple form of what you
describe is just a relaxation oscillator, and there are some easy ways
to do it, but the easy ways usually have some limitation or other, and
their usefulness would depend on just what you're trying to accomplish.

Cheers,
Tom

 

[Jamie]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

Look for 555 timer examples

 

[Don Lancaster]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

You are pretty much describing a plain old switchmode power controller.


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[ehsjr]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

Is this what you want?

PNP
Vbatt+ ---- -----+-----------+
e\ /c | |
--- [CAP] [LOAD]
| | |
[R] | |
| | /c
Timer ------+----------[R]---| NPN
| \e
| |
Ground ------------+-----------+

When the timer goes low the PNP charges the cap and
the NPN is cutoff, preventing current through the
load. When the timer goes high, the PNP is cutoff,
disconnecting the cap from the battery, and the NPN
allows the cap to discharge through the load.

Ed

 

[[email protected]]

What voltage? What capacitance? What load? (Is it resistive,
inductive, what? What sort of peak current are you looking for? How
long do you expect the output pulse to be? How much energy per pulse?)

The load is going to be mainly inductive (an electromagnet actually).
Not sure about my voltage source yet. Probably be in the 5-10V range.
Figured I'd adjust the capcacitance to get a frequency-pulse power
combination I could live with.

Basically, I'm just looking for a general circuit design that I can
play with to get what I want after I get some idea of what I'll be
using for voltage source and load.

Are you thinking to essentially just have the circuit connect the
capacitor to the load and let it discharge, then disconnect?

Yeah, I think so.

How did
you have in mind charging the capacitor? (That is, would you just put
a resistor between the voltage source/battery and the capacitor, or do
you want to do something more complicated? -- A resistor will dissipate
half the energy provided by the voltage source, if the capacitor is
allowed to discharge to zero volts.)

Well, if I wind up using a battery with a small maximum current, I
might just connect it straight to the capacitor. If there's a better
way to do that, I'd be open to suggestion.

 

[Robert Baer]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

Start with a 555 which does almost everything you mentioned.

 

[Don Lancaster]

Start with a 555 which does almost everything you mentioned.

A 555 should NEVER be used for ANYTHING.

Start with a PIC instead.


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Jamie]

A 555 should NEVER be used for ANYTHING.

Start with a PIC instead.

ha.
a 555 is good choice if all you need is a simply timer.
why waste time and effort with such a sensitive device
for such a simple job.
Now, i suppose if one wanted to get fancy with in making
a motor controller? then a pic would be a good choice how ever..
have fun.

 

[[email protected]]

A 555 should NEVER be used for ANYTHING.

Start with a PIC instead.

I don't think a 555 or PIC is going to do me any good.

What I want is to be able to take a relatively small constant current
(i.e., from a battery) and generate large amplitude/short duration
current pulses. That is to say I want to build up some energy for a
period of time, release it all in a burst, and repeat that process ad
infinitum.

 

[Jamie]

I don't think a 555 or PIC is going to do me any good.

What I want is to be able to take a relatively small constant current
(i.e., from a battery) and generate large amplitude/short duration
current pulses. That is to say I want to build up some energy for a
period of time, release it all in a burst, and repeat that process ad
infinitum.

Drive a relay contactor to charge a capacitor then.

 

[[email protected]]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit

This sounds like a typical unijunction transistor application. GE
semiconductors
used to h ave lots of application notes on these, typically for
delivering a stiff
turn-on current to low sensitivity SCRs.

 

[jasen]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating.

sounds like an LM555

So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

yup 555 is sounding even better.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

google for LM555 datasheet. The application notes ner the back will get you
started.

Bye.
Jasen

 

[YD]

Late at night, by candle light, [email protected] penned
this immortal opus:

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

Look up neon lamp oscillator. Just place your load in series with the
lamp. Can't get much simpler.

- YD.

 

[Jan Panteltje]

I don't think a 555 or PIC is going to do me any good.

What I want is to be able to take a relatively small constant current
(i.e., from a battery) and generate large amplitude/short duration
current pulses. That is to say I want to build up some energy for a
period of time, release it all in a burst, and repeat that process ad
infinitum.

resistor
+ --===----------------------------------------------
R1 | | | | | pulse frequncy
| | | [ ]<---
12 V | | [ ] R2 | R4
battery | load | [ ]
=== | --| | R5
--- C1 --- |/-----
|Elco \ / -----------|UJT |
| ---/ | |
| |Thyristor [ ] R3 === C2
| | | |
- ---------------------------------------------

You can use a 555 if you cannot find a UJT.
Note the gate current comes from C2, and is much higher then the current
that charges C2 via R4 + R5 (time constant).
This should be enough to trigger a 30A Thyristor.
C1 should be as big as is required for the energy you need.
R1 should be such that C1 charges to an acceptable level between firings.

 

[Jan Panteltje]

I don't think a 555 or PIC is going to do me any good.

What I want is to be able to take a relatively small constant current
(i.e., from a battery) and generate large amplitude/short duration
current pulses. That is to say I want to build up some energy for a
period of time, release it all in a burst, and repeat that process ad
infinitum.

resistor
+ --===----------------------------------------------
R1 | | | | | pulse frequncy
| | | [ ]<---
12 V | | [ ] R2 | R4
battery | load | [ ]
=== | --| | R5
--- C1 --- |/-----
|Elco \ / -----------|UJT |
| ---/ | |
| |Thyristor [ ] R3 === C2
| | | |
- ---------------------------------------------

You can use a 555 if you cannot find a UJT.
Note the gate current comes from C2, and is much higher then the current
that charges C2 via R4 + R5 (time constant).
This should be enough to trigger a 30A Thyristor.
C1 should be as big as is required for the energy you need.
R1 should be such that C1 charges to an acceptable level between firings.

And I forgot to mention I in R1 should be below the hold current of the
thyristor.
Else you will have to use a transistor of sorts and not a thyristor!
Oops.

 

[Jan Panteltje]

Start with a 555 which does almost everything you mentioned.

A 555 should NEVER be used for ANYTHING.

Start with a PIC instead.




I don't think a 555 or PIC is going to do me any good.

What I want is to be able to take a relatively small constant current
(i.e., from a battery) and generate large amplitude/short duration
current pulses. That is to say I want to build up some energy for a
period of time, release it all in a burst, and repeat that process ad
infinitum.

resistor
+ --===----------------------------------------------
R1 | | | | | pulse frequncy
| | | [ ]<---
12 V | | [ ] R2 | R4
battery | load | [ ]
=== | --| | R5
--- C1 --- |/-----
|Elco \ / -----------|UJT |
| ---/ | |
| |Thyristor [ ] R3 === C2
| | | |
- ---------------------------------------------

You can use a 555 if you cannot find a UJT.
Note the gate current comes from C2, and is much higher then the current
that charges C2 via R4 + R5 (time constant).
This should be enough to trigger a 30A Thyristor.
C1 should be as big as is required for the energy you need.
R1 should be such that C1 charges to an acceptable level between firings.

And I forgot to mention I in R1 should be below the hold current of the
thyristor.
Else you will have to use a transistor of sorts and not a thyristor!
Oops.

And I also goofed on the fact that the UJT circuit should get power from
_before_ the R1, so directly from the battery.
Oops again

LOL

 

[John Fields]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating. So basically I need a circuit
that turns a constant DC voltage source into a series of current
impulses (because I want both the cyclical nature of the impulse and
also a higher current in the impulses than I would be able to get from
just the DC power supply I'm using, which will probably be a
not-too-large battery). One more thing, I would like this circuit to
run at a reasonable high frequency (maybe 50-200 Hz) so I'd prefer not
to have any mechanical components such as relays in the circuit since
it seems like they could wear out easily under those conditions.

So, any help I can get with this would be appreciated. I'm actually an
electrical engineer, but in control theory, so while I'll be able to
understand a circuit diagram I haven't done any real circuit work in
ages. Thanks.

---
You might want to download Linear Tech's free simulator and that way
you can try any circuits anyone might propose without having to
actually build anything, at first.

Their simulator page doesn't seem to be available right now, but
when it comes back up you can get to it easily from:

http://www.linear.com/designtools/index.jsp

 

[Tom Bruhns]

The load is going to be mainly inductive (an electromagnet actually).
Not sure about my voltage source yet. Probably be in the 5-10V range.
Figured I'd adjust the capcacitance to get a frequency-pulse power
combination I could live with.

Basically, I'm just looking for a general circuit design that I can
play with to get what I want after I get some idea of what I'll be
using for voltage source and load.



Yeah, I think so.


Well, if I wind up using a battery with a small maximum current, I
might just connect it straight to the capacitor. If there's a better
way to do that, I'd be open to suggestion.

OK, I've looked over the other suggestions, and there seem to be some
good ideas. I'd avoid a PIC: the 555 is a lot better at handling a
range of voltages gracefully, especially ones above 5V. And, it's easy
to use. It can generate narrow pulses easily. I'd recommend the CMOS
version (with due care about zapping the CMOS inputs). You didn't say
what peak current you want, but at such low voltage, and running from a
battery, certainly a power MOSFET can be found to do what you want.

Because you want to have fairly fast recharging of the capacitor and
you're planning a small (?) battery for power, I'd recommend you
consider a couple different things: first, do like one poster
suggested and disconnect the recharge circuit when you're conducting
current in the load. Second, provide some much larger capacitor across
the battery, so you don't draw relatively high current pulses from the
battery. A capacitor likely will be much better at delivering the AC
part of the recharge current.

And finally, if you want the best battery life, by all means use a
resonant recharge circuit. If you connect the battery "directly" to
the capacitor, you will lose the same power in the battery's internal
resistance and the circuit resistance as you would if you put in an
external series resistor. The net resistance changes the time it takes
to recharge, but not the energy lost in heating the resistance. A
typical resonant charging circuit would be: battery, with large energy
storage capacitor, C2, in parallel. Negative side to common/ground.
Positive side to a P-channel power mosfet source. Pull the gate of the
power mosfet low to turn it on when the load is disconnected. Power
mosfet drain to the anode of a diode (Schottky nice, to keep the
voltage drop low). Cathode of the diode to an inductor, L1. Other end
of the inductor to the capacitor you're recharging, C1. Pick the
inductance of L1 such that the resonant frequency of C1 and L1 has a
period LESS THAN two time the length of time you have to recharge C1.
For example, if C1=1000uF and you want a 200Hz rep rate with a
discharge time of 1 millisecond, that leaves 4 milliseconds to
recharge. You need to pick L1 to give a resonant frequency with C1 of
at least 125Hz, which is 8 milliseconds for a full cycle. The recharge
takes place in half a cycle. So L1 should be less than 1.6
millihenries. Since a 1000uF capacitor will have a pretty loose
tolerance, I'd suggest 1.0 millihenries. NOTE: the capacitor will
charge to a voltage such that the average of the final voltage and the
initial voltage (just before you started the charging) is equal to the
battery voltage less a diode drop -- not accounting for a little
additional drop in resistances. So if you have a 9V battery, C1 could
charge to nearly 18V with this circuit. The peak current in the
inductor (important that the inductor can handle this current without
saturating) will be such that Ipeak^2*L1=0.25*Vpeak^2*C1. (That
overstates the current, if you don't discharge C1 to zero each cycle,
but it's a safe limit.) In this case, note that it's a pretty high
current, about 9 amps! Why? Because 1000uF charged to 18 volts
represents (18^2)*0.001/2 joules = .162 joules, and at 200 discharges
per second, that's over 32 watts. From a 9V battery, that's an average
of 3.6 amps. -- In other words, be sure to set you expectations
correctly with regard to how much power it will take to run your little
experiment, before you start. And...C2>>C1; I'd say C2 >= 10*C1 Be
sure to size the parts right for the job.

Cheers,
Tom

 

[Ancient_Hacker]

Howdy. I'm looking for an electronic circuit design that accomplishes
the following: using a DC voltage source first charge a capacitor to
a certain voltage level and then (automatically) discharge that
capacitor through another circuit, then start charging the capacitor
again so the process keeps repeating.

The simplest and most rugged might be a thyristor, they're swell at
switching high current and voltage. You can trigger it with a diac.
Two components! Hard to beat that.