What is power, voltage, current you are trying to switch ?
Thanks guys, but I'm really looking for a discrete circuit rather than an IC solution.Something like these?
Probably because I'm a Mech.Eng. swimming in water over my headwhy not just use an inverter circuit? it does the same thing...
i've used this circuit in the past to drive non-rectifying flyback transformers:
removing the diode on the secondary gives you an AC output.
WOW. That is a staggering amount of information to leave out of your original question.Thanks guys, but I'm really looking for a discrete circuit rather than an IC solution.
I'm driving a piezo chip which requires ~125V @ ~145kHz from a Li-ion cell voltage. I'm going to wind a toroidal transformer to do the lifting, but need to switch the DC to AC to drive the transformer. (I don't need PWM; this thing will either be on or off.)
My basic idea is to wind a tapped primary and switch the battery between the two halves of the primary coil so as to double the voltage range in the secondary.
Each half of the switch will need to control upto 4.2V @ ~10A. The 'switches' themselves will be used to drive mosfets to handle the current.
I hope to reduce the secondary current needs by tuning the secondary coil inductance to cancel some or all of the piezo's capacitance at the antiresonant frequency.
That part deserved an encore.Each half of the switch will need to control upto 4.2V @ ~10A.
WOW. That is a staggering amount of information to leave out of your original question.
That part deserved an encore.
That's pretty much where I've arrived at (since asking the question): https://tinyurl.com/ydvf78maMOSFETs would work and can switch fast enough. To make the equivalent of a DPDT switch you'd need at least 4 MOSFETs, and possibly 8.
You'll also need a driver circuit. You've got to switch two branches on after the other two branches turn off.
When switching power, it is important that you never allow both branches to be on at the same time.
Its not a motor. It's a transformer that steps up the voltage to drive a piezo, that is resonance coupled with the secondary inductance.Would it be simpler to use a h-bridge designed to drive inductive loads (motors) both ways without the need for a center tap.
It’s increasingly difficult and expensive to obtain high voltage and still achieve a high-frequency and high-current PZT driver amplifier. Fortunately, there’s simple solution to enable a lower-voltage piezoelectric amplifier to boost to higher volt-ages. A series-resonant technique can boost the driving volt-age and become a high-voltage driver and generator. Voltage boosting can be accomplished by adding a series inductor (Fig. 3). The next three sections offer detailed explanations on how a series-resonance circuit can boost voltage for capacitive devices.
Referring to Figures 3 and 5, the series inductor is acting as impedance cancellation device. At the resonance frequency, both the inductor and the PZT capacitor have the same im-pedance, but an opposite polarity. They are 180 degrees out of phase. These two impedances cancel each other out. Thus, the inductor is a device that cancels capacitor impedance.Impedance cancellation is modeled as a virtual short circuit at resonance frequency. As shown in Figure 5, there’s a short circuit between the inductance and capacitor. This is because the two impedances cancel each other. The net impedance is zero. Because the impedance is always zero, the voltage is also zero at any current. By definition, it’s a short circuit.
My needs are higher frequency and lower voltage )145kHz and 125V; but using a simple flyback circuit from a Li-ion battery; not the huge and expensive laboratory piezo driver units in the article.For example, consider the setup in Figure 7 with 1-μF piezo-electric actuator capacitance and a 0.25-mH resonant induc-tor, plus a 100-V dc supply. At 10-kHz resonant frequency, the voltage across the PZT is 200 V p-p with ±6.5-A peak current. This is equivalent to 1300-W power. It’s achieved with just a 6.5-A and 6.5-V driver (42 W).
Thanks. I'm getting closer There is still a weird asymmetry between the two halves of the primary I do not understand.)The transformer winding connected to the piezo, plus the piezo capacitance, need to form a tuned circuit at the piezo resonant frequency.
Then play with the drive impedance - taps on the same winding, or a coupling winding - to get the most output for a given drive power.
Look at an IR2153, a combined oscillator and push-pull FET driver:Now I'm looking for an oscillator chip that can do kHz and be tuned quite finely?
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no hint of how fast,
Has to be electronic as it has to operate at ~100kHz
*I* would assume both directions.does current flow one direction or two?, etc..
You knew about the transformer but I did not.
Clearly, but that does not mean that they are not relevant, only that you don't know why. Can you see the difference?I do not see what relevance the presence of a transformer has to the question I asked.
Because a 2N7001 cannot handle 10 amps. And, we still do not know about the power source(s) for the circuit, which might rule out using MOSFETs.Nor for that matter, why the voltage/current/power are relevant either
That is because your confining was based on your understanding of the overall circuit. If that understanding were correct, you wouldn't be having a problem.I hoped that by confining myself to the specific part of the problem I was having trouble with, I could avoid all the meta discussion. I failed miserably.