Capacitor charging and discharging circuit

Thread Starter

Tajerek

Joined Jul 14, 2017
7
Hi guys,

I would like to have a capacitor charged into one circuit then as it fills up it, I switch it to a circuit where it gets discharged into a load , below is very simple example where a square signal controls charging and discharging cycle.

1) I want equivalent of this in solid state version, where I can apply a signal to control the switching of capacitor between the charging circuit and the discharging circuit.
2) it should be able to reach very high frequencies in from KH up to 1 MHZ
3) I want a self oscillating version where instead of controlling the frequency of charging and discharging manually from a frequency counter, it gets triggered automatically as a feedback from the capacitor.ie. when it's charged it switches to discharge into the circuit B then when C is discharged it is switched to circuit A to recharge back again.


 

wayneh

Joined Sep 9, 2010
17,153
Lots of options. 1MHz is ‘high’ for a 555 circuit but I think it can be done. The voltage in the timing capacitor varies from 2/3 to 1/3 of the supply voltage.

A comparator oscillator can reach that frequency and get you closer to the power rails, if that’s what you want.
 

crutschow

Joined Mar 14, 2008
27,898
when it's charged it switches to discharge into the circuit B then when C is discharged it is switched to circuit A to recharge back again.
Define charged and discharged.
How close to the supply voltage and how close to ground do you want to switch?

What R1, R2 and C2 values will you be expecting to use for 1MHz operation?
 
Last edited:

Thread Starter

Tajerek

Joined Jul 14, 2017
7
thank you all.

LMC555C or 555 timer would work but I need help with the circuit for solid state version , should it use mosphets or transistors to switch back and forth the two parts of the circuit ?

The next question is whether there is a self-oscilating version.

Define charged and discharged.
How close to the supply voltage and how close to ground do you want to switch?

What R1, R2 and C2 values will you be expecting to use for 1MHz operation?
The closer to supply voltage and to ground the better. Regardless of frequency I want to charge the capacitor up to 95% for example then discharge it close to zero and switch. I can keep frequency variable until I reach that sweet spot.

Actually I do not plan to use R1 I put it there to simulate the impedance of the capacitor and to show the charging waveform. And R2 will be a load so you can consider it variable resistance..that's the reason I preferred self-oscillating version over manually setting the frequency in that way for different values of R2 the discharge speed would be different and therefore the switching frequency adjusts itself.
I am not sure it can reach mhz it depends how fast i can charge and discharge the cap. but i am interested in the a circuit schematic that can acheive this.
I am planning to use this with high supply voltages like 2kv coming out of flyback or other type of transformer. and 0.1uF cap.
 

crutschow

Joined Mar 14, 2008
27,898
I am planning to use this with high supply voltages like 2kv coming out of flyback or other type of transformer. and 0.1uF cap.
It is likely not feasible to charge and discharge a 0.1μF cap to 2kV at a 1 MHz rate. :eek:
Don't know of any semiconductors that can do that.
Suggest you generate more modest plans on what you intend to do.
 

Thread Starter

Tajerek

Joined Jul 14, 2017
7
It is likely not feasible to charge and discharge a 0.1μF cap to 2kV at a 1 MHz rate. :eek:
Don't know of any semiconductors that can do that.
Suggest you generate more modest plans on what you intend to do.
frequency is not the issue, like i said previously it will depend how fast the capacitor is charging and discharging . it can be few khz that's fine, but my question is what solid state circuit can do the switching...any help ?
 
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