About ZCS

MrCU204

About ZCS [Copy link]

 

For me, ZVS is easier to understand, but ZCS is difficult to understand.

The key is how to achieve true zero current, so I think,

The only method that truly conforms to the concept of zero current is blocking, even the reverse conducting diode is omitted.

MrCU204

If the Cr voltage is equal to or slightly higher than Vcc, the tube will indeed be blocked, and it will be difficult for Ic to be non-zero.

Then, the tube is turned off, and Cr must discharge to the load. When the tube needs to be turned on, it can only rely on Lr to limit the current, there is no other way!

At the moment the tube is turned on at high speed, the impedance of the inductor is quite large, making the entire circuit almost without current (note, only almost). There is only one way to turn on the tube with "zero current" in an environment without any bypass configuration.

qwqwqw2088

It is mainly soft switching. The PWM driver adds a dynamic pulse width modulation signal. Before the shutdown signal, the current has dropped to 0.

led2015

ZVS technology is to switch the switch tube, by controlling the resonant frequency and phase of the circuit, so that the switch switching occurs at the moment when the voltage waveform transition is zero, so as to achieve zero voltage switching.

MrCU204

qwqwqw2088 posted on 2023-9-23 08:54 It is mainly soft switching. The PWM drive adds a dynamic pulse width modulation signal. Before the shutdown signal, the current has dropped to 0.

Buck is a DC circuit, and its property is DC→DC.

The two inductors and the load are connected in series to form a voltage divider, but the voltage of the capacitor can rise to (or even slightly higher than) Vcc.

This is not the series resonance in the classic scenario, but a similar phenomenon does occur. The tube can be blocked and zero current shutdown is achieved, which is a success. However, when the tube is turned on, only the inductor limits the current.

MrCU204

led2015 Published on 2023-9-23 21:38 ZVS technology is to switch the switch tube, by controlling the resonant frequency and phase of the circuit, so that the switch switching occurs at the moment when the transition of the voltage waveform is zero, so as to...

ZVS and ZCS seem to be the difference between clamping and equipotential.

MrCU204

There are several ZCS tank topologies.

The key is, is there a solution to truly and thoroughly achieve zero current switching? !

For example, if the load current is 10A, the Lr inductance is 10mH, the coil resistance is 1Ω, and the switching time of the tube is 1nS, do you think that the Ic can be less than 1% (0.1A) at the moment when the tube is fully turned on, and is the working condition when the tube is turned on actually a bit like a hard switch? !

MrCU204

MrCU204 posted on 2023-9-23 23:28 There are several topologies of ZCS tank circuits. The key is, is there a solution to truly and thoroughly achieve zero current switching? ! ...

I think only the one in the lower right corner meets my definition of ZCS!

Soft switching is aimed at the safety of the tube at the moment of switching on and off. Things before or after the switch are not within the scope of care.

Therefore, reverse-conducting diodes are acceptable, but capacitors should not be connected in parallel with the tube in any way, otherwise it will have ZVS components or even become completely ZVS.

The diode in the circuit on the lower right corner is a non-reverse diode. When the voltage of Cr is equal to (or higher than) Vcc, the non-reverse diode bears all the reverse pressure, and the switch tube is like being suspended (if the voltage of Cr can be guaranteed not to be much higher than Vcc, the non-reverse diode does not need to be added).

xjtburden

Theoretically, soft switching is ZVS on and ZCS off. When the current is equal to zero, the switch is turned off to reduce the turn-off loss.