Indeed, I was wondering initially how that capacitor is actually discharged, nice circuit and ideal for applications where you need to have a small on/off switch.
That reminds me, I have a whole bunch of those things in a very tiny package, SOT-23-6??? that I used for small H-bridges a few years ago. Sadly they are too tiny for me to use anymore. Wish our eyes kept up with things getting smaller and smaller.
I used the same with a uC to do a soft on/off latch circuit. Working very well. Even on battery powered device. All is on my instructable page for more detail. DMG6601LVT, SIL2308, DMC3021LSD-13, IRF7319TRPBF, are all pin compatible together. Thanks for sharing.
Before you added the resistor the P channel FET turned off momentarily when the switch was pressed a second time. That allowed the capacitor to charge up to whatever voltage is required to turn the N channel FET back on. The brief duration of the P channel FET being off is sometimes noticeable as the LED blinks. A much shorter button press would work. With the added resistor the capacitor can't charge up enough to turn the N channel FET back on. If you look at the original circuit with a scope you will see how the P channel FET turns off momentarily, allowing the N channel FET to turn back on. Another circuit built at random with no analysis.
The thing I wonder about the fix is what is the gate voltage at the n-channel when the circuit is on? It's only 1/2 the output voltage. As long as that's "well above" the threshold of the nfet, that's fine, but if it's close to the threshold, the nfet might not be fully on. Maybe it doesn't matter because the nfet doesn't carry any significant current in this circuit anyway. If it was an issue, I'd increase the value of the pull down so that the voltage divider is biased towards the high side, and the nfet gate voltage is a bit higher during "on" phase.
I'm thinking that if the circuit was connected to a larger circuit load, the pull-down resistor may not have been needed but I think its a good idea. Better safe than sorry.
To ascertain the reason why the original circuit didn't turn off for you, we need to analyse the circuit. When the led is on, the voltage at the gate of the N-channel is close to the output voltage, which is close to the input voltage because the gate of the P-channel is then close to ground and it is in ohmic mode with a low resistance. That assumes that the supply voltage is larger than the threshold voltage of the mosfets (1V to 2.8V). That means that the capacitor is discharged close to ground via the 100K resistor. When the switch is closed, you are then trying to dump the N-channel's gate charge into the capacitor causing the gate voltage to drop and the drain voltage to rise, but the Miller effect will tend to oppose that, with the result that the N-channel's drain does not rise high enough fast enough to turn off the P-channel before the capacitor has charged sufficiently to keep the N-channel from turning off any further. I suspect that this is likely to happen when the supply voltage is 5V or more as that gives sufficient opportunity for charging the capacitor before the N-channel gate voltage can drop below its threshold voltage.
It can count in binary 👍 Only up to 1 but it CAN count. If you had two of them then it could count up to 3. Three of them could count up to 7. So, someone with altogether too much time on their hands could build a computer out of them. Lol.
I have some Si4599DY chips, same pinout, slightly different specs (mine are mounted on a small breakout board). Ralph Bacon did a video using them to drive a bi-colour LED from one pin.
Good job. I have used the traditional npn-pnp circuit working similarly but carrying a few components more. I noted with it that in noisy environments it is required to have capacitors 10 nF to ground or so, at the bases to prevent glitches. I assume this circuit may be just as sensitive and needs to be slowed down a bit.
Indeed, I was wondering initially how that capacitor is actually discharged, nice circuit and ideal for applications where you need to have a small on/off switch.
That reminds me, I have a whole bunch of those things in a very tiny package, SOT-23-6??? that I used for small H-bridges a few years ago. Sadly they are too tiny for me to use anymore. Wish our eyes kept up with things getting smaller and smaller.
I used the same with a uC to do a soft on/off latch circuit. Working very well. Even on battery powered device. All is on my instructable page for more detail. DMG6601LVT, SIL2308, DMC3021LSD-13, IRF7319TRPBF, are all pin compatible together. Thanks for sharing.
I speculate that the origin circuit loves (needs) resistive load, hates capacitive load and confused by non linear load.
N and P-CH in one package is also convenient to use in H bridge motor driver.
We used to use the IRF7389 (very similar to this one) in a tiny motor drive.
Before you added the resistor the P channel FET turned off momentarily when the switch was pressed a second time. That allowed the capacitor to charge up to whatever voltage is required to turn the N channel FET back on. The brief duration of the P channel FET being off is sometimes noticeable as the LED blinks. A much shorter button press would work. With the added resistor the capacitor can't charge up enough to turn the N channel FET back on. If you look at the original circuit with a scope you will see how the P channel FET turns off momentarily, allowing the N channel FET to turn back on. Another circuit built at random with no analysis.
Easiest circuit you can make with such a package is a logic inverter. Don't need any external components, just the 2 complementary CMOS transistors.
The thing I wonder about the fix is what is the gate voltage at the n-channel when the circuit is on? It's only 1/2 the output voltage. As long as that's "well above" the threshold of the nfet, that's fine, but if it's close to the threshold, the nfet might not be fully on. Maybe it doesn't matter because the nfet doesn't carry any significant current in this circuit anyway. If it was an issue, I'd increase the value of the pull down so that the voltage divider is biased towards the high side, and the nfet gate voltage is a bit higher during "on" phase.
Thank for this video. Very cool schematic, i will try it!
Good chip to know about. Thanks.
I'm thinking that if the circuit was connected to a larger circuit load, the pull-down resistor may not have been needed but I think its a good idea. Better safe than sorry.
To ascertain the reason why the original circuit didn't turn off for you, we need to analyse the circuit. When the led is on, the voltage at the gate of the N-channel is close to the output voltage, which is close to the input voltage because the gate of the P-channel is then close to ground and it is in ohmic mode with a low resistance. That assumes that the supply voltage is larger than the threshold voltage of the mosfets (1V to 2.8V). That means that the capacitor is discharged close to ground via the 100K resistor. When the switch is closed, you are then trying to dump the N-channel's gate charge into the capacitor causing the gate voltage to drop and the drain voltage to rise, but the Miller effect will tend to oppose that, with the result that the N-channel's drain does not rise high enough fast enough to turn off the P-channel before the capacitor has charged sufficiently to keep the N-channel from turning off any further. I suspect that this is likely to happen when the supply voltage is 5V or more as that gives sufficient opportunity for charging the capacitor before the N-channel gate voltage can drop below its threshold voltage.
I wonder if it truly stays latched on indefinitely due to the eventual capacitor leakage.
There's a similar circuit using a 555 timer that does the same thing in the same manner.
It can count in binary 👍 Only up to 1 but it CAN count. If you had two of them then it could count up to 3. Three of them could count up to 7. So, someone with altogether too much time on their hands could build a computer out of them. Lol.
RANT OF THE WEEK! RANT OF THE WEEK! RANT OF THE WEEK! :)
I have some Si4599DY chips, same pinout, slightly different specs (mine are mounted on a small breakout board). Ralph Bacon did a video using them to drive a bi-colour LED from one pin.
zamzam water
Good job. I have used the traditional npn-pnp circuit working similarly but carrying a few components more. I noted with it that in noisy environments it is required to have capacitors 10 nF to ground or so, at the bases to prevent glitches. I assume this circuit may be just as sensitive and needs to be slowed down a bit.