Hello everyone.
I could really use some guidance right now...
I am designing a circuit, its a voltage controlled current sink. As shown in attachment 1. The circuit is pretty simple. It will provide current pulses to a Load of 1kΩ. Those pulses, need to be: current amplitude = 10-100mA, pulse width = 200-500µsec, frequency of 20-100Hz. To apply this current amplitude to a 1kΩ, a high voltage is needed (100V at the load).
Here is where I need your help.
To obtain this voltage, I bought a "miniature DC converter". Here is the datasheet: (http://www.datasheets360.com/pdf/5050517326450757206) It is a 5 to 200V converter. It's limitations are that it can only source 6.25mA at max load. Attachment 2 shows a schematic from an article that used this converter. The converter's datasheet says that a 0.1µF, 1000V DC capacitor is needed at the output, and the article says "R10(220kΩ) ensures minimum load for the converter, and R11(47kΩ) ensures the current it sources is always below maximum." That leaves the other 2 capacitors, which are charged up to 200µF total and used for delivering the voltage/current needed.
However, if the math is right, this might fulfill my requirements.
I have two parallel 100µF caps, = 200µF = 200(µA·sec)/Volt
The load is 500µsec times 0.1A = 50µA·sec
C = Q/V; => V = (50µA·sec)/200µF = 0.25 V drained from caps EACH PULSE.
Now say for 1 second, I would have 500µsec· 100 pulses = 0.5 sec of ON time, now 0.5sec · 0.1A = .005A·sec per second = Thats 5000µA·sec per second.
Since the caps have 200(µA·sec)/Volt, thats 5000/200 = 25V loss from the capacitors EACH SECOND.
If the capacitors ran continuously after this point at 175 volts instead of 200 volts, the replenishment current through R11 (47k) would be 25V/47k = 532µa sec per second. As you can see this is not enough to keep the caps fully charged because the full load will require 5000µA·sec per second!
I was hoping you guys could help me in figuring out what changes I should make to this design so that I can deliver the current/voltage I need, considering that the converter sources only 6.25mA MAX. I see that the capacitors are key here, but I dont have a lot of experience with them so I'm having a hard time figuring things out.
If anything is not clear just let me know. I'm a beginner so any help at all is appreciated.
I could really use some guidance right now...
I am designing a circuit, its a voltage controlled current sink. As shown in attachment 1. The circuit is pretty simple. It will provide current pulses to a Load of 1kΩ. Those pulses, need to be: current amplitude = 10-100mA, pulse width = 200-500µsec, frequency of 20-100Hz. To apply this current amplitude to a 1kΩ, a high voltage is needed (100V at the load).
Here is where I need your help.
To obtain this voltage, I bought a "miniature DC converter". Here is the datasheet: (http://www.datasheets360.com/pdf/5050517326450757206) It is a 5 to 200V converter. It's limitations are that it can only source 6.25mA at max load. Attachment 2 shows a schematic from an article that used this converter. The converter's datasheet says that a 0.1µF, 1000V DC capacitor is needed at the output, and the article says "R10(220kΩ) ensures minimum load for the converter, and R11(47kΩ) ensures the current it sources is always below maximum." That leaves the other 2 capacitors, which are charged up to 200µF total and used for delivering the voltage/current needed.
However, if the math is right, this might fulfill my requirements.
I have two parallel 100µF caps, = 200µF = 200(µA·sec)/Volt
The load is 500µsec times 0.1A = 50µA·sec
C = Q/V; => V = (50µA·sec)/200µF = 0.25 V drained from caps EACH PULSE.
Now say for 1 second, I would have 500µsec· 100 pulses = 0.5 sec of ON time, now 0.5sec · 0.1A = .005A·sec per second = Thats 5000µA·sec per second.
Since the caps have 200(µA·sec)/Volt, thats 5000/200 = 25V loss from the capacitors EACH SECOND.
If the capacitors ran continuously after this point at 175 volts instead of 200 volts, the replenishment current through R11 (47k) would be 25V/47k = 532µa sec per second. As you can see this is not enough to keep the caps fully charged because the full load will require 5000µA·sec per second!
I was hoping you guys could help me in figuring out what changes I should make to this design so that I can deliver the current/voltage I need, considering that the converter sources only 6.25mA MAX. I see that the capacitors are key here, but I dont have a lot of experience with them so I'm having a hard time figuring things out.
If anything is not clear just let me know. I'm a beginner so any help at all is appreciated.
Attachments
-
46.7 KB Views: 21
-
47.7 KB Views: 26