Re: Voltage rating on SMD capacitors
Alright I am reading and will now run some tests on my caps to see how they behave! What I was worried about was that reaching or exceeding the voltage ratings might cause irreversible damage, maybe even unnoticeable. like temperature coefficient worsening, or ESR worsening or whatever the capacitor meter won't tell me.
akis
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Last Activity: 04-30-2015, 03:09 PM
Joined: 06-19-2012
Location: Surrey
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Re: Voltage rating on SMD capacitors
/bump
anyone?Leave a comment:
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Voltage rating on SMD capacitors
I am using three SMD MLCC X7R 10uF/25V (total 30uF measured 40uF) at the output of a push-pull amp powered by +/-23V, the other side of the cap being a transformer.
On a purely resistive load I think I'd be within the voltage levels of the cap.
It is possible depending on the behaviour of the load on the transformer that higher voltages may develop even for very short periods of time.
Can these theoretical (not observed, just academic) voltages harm the capacitor? How could I check a random capacitor for "good operation" other than plugging... -
Cross conduction and thermal runaway
Hello all
I have posted this problem on other forums too, hoping for some ideas and suggestions.
I have designed a power amp to deliver around 20W into a 1 Ohm load at 200KHz sine. The amplitude is more or less constant, the frequency is constant, the load varies a bit. The supply rails are +/-12V. My design uses 2 or 3 pairs of output transistors (2 pairs did not work well, tried 3 pairs still no go).
The amplifier works perfectly until we reach a point where the load gets too heavy (too small) in conjunction with a high amplitude signal. At that moment,... -
Re: switched capacitors for DC to DC
Reading from Maxim's documentation, it should be possible to monitor the charge capacitor's voltage - it should not have to charge to full charge instantly. At least that is how they build their own switched capacitor ICs.
In practice however, as you said, I am discovering that the only way to keep that capacitor from charging to the full voltage, is to interrupt the charge cycle, in other words NOT to allow the pass transistor/MOSFET to open fully. And that right there is the problem, since the transistor is not...Leave a comment:
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Re: switched capacitors for DC to DC
I also tried simulating the two caps in series and then in parallel, but could not create a suitable circuit (too many switches were needed), was becoming very complex.
I have also many times fallen foul of efficiency - I design something which I think is great only to realise it still spends just as much power as a linear approach would do. Here is a schematic of such an attempt.
Voltage supply is 15V. Output voltage is 4.5V/1A. A 555 generates a fixed frequency of about 7.3KHz. A switching transistor arrangement...Leave a comment:
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Re: switched capacitors for DC to DC
Thanks. I have found a few not only from MAxim and Linear, but also NS : LM 2751 - but they all seem to be low voltages and currents (eg 5V at 80mA). I have not discovered an equivalent to, say, LM317 but in a switched capacitor topology.
I have built and tested a very simple switched capacitor DC inverter circuit that is good for any voltages (I think it was tested to 15-20V and 500mA), so I was confident that the idea(s) could also be applied/scaled to other DC-DC conversions and currents, especially DC step ...Leave a comment:
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Re: switched capacitors for DC to DC
Hoped I would find something more here. No thanks to you.Leave a comment:
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switched capacitors for DC to DC
Hello
Has anyone built a practical circuit that uses capacitors (not coils) to convert DC to DC? I have experimented a little and have made these topologies so far:
all the below with common ground which is also important
DC -> 555 -> inverter
DC -> 555 -> doubler
DC -> 555 -> +Vs/2 -Vs/2 (ie split a 20V into +/-10V)
I have not taken some of these circuits beyond a few mA on the load.
I am looking for ideas/circuits to step down, eg DC -> 555 -> Vs/2 or Vs/3 as an example, or even variable.... -
Re: Capacitor choice for 200KHz
I did not see the question in time, sorry it has been a while, this has been made in a PCB and works quite well with tiny changes needed to the PCB. Now designing version 2
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Re: Capacitor choice for 200KHz
Hi guys, been a while. I have gone through many iterations since I last posted here. Rial supply is now increased to +/-12V DC. There are two biasing diodes one of which is bypassed with 1KOhm trimmer so I can adjust the bias. My capacitor is a 10uF/25V surface mount on which I have soldered two wires. It is a tiny little thing but works really well. [url]http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=2070524[/url]Re: Capacitor choice for 200KHz<br /...t posted here.Leave a comment:
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Re: Capacitor choice for 200KHz
As you suggested I am looking to buy MLCC 10uF/25V and 20uF/25V X7R from Mouser and try them to see how they look on the scope. They are not that expensive at 25V.
Regarding biasing and overheating, the circuit works well at +/-6V which is the expected rail voltage. On the test circuit the transistors have tiny local heatsinks and they do not even get warm. The final device will have a proper larger heat sink.
From the theory that I know I can increase the 0.15R to something larger, maybe even 1R, to stop any single transistors...Leave a comment:
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Re: Capacitor choice for 200KHz
This is the prototype which I am using, except the capacitor I used is as I said a combination of 2 * 1000uF and 2*470u...Leave a comment:
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Re: Capacitor choice for 200KHz
The circuit is an op-amp oscillator at 200KHz pure sinusoidal at +/-4V. This is then fed to a current amplification stage to drive a transformer. The current amplification stage is push-pull using complementary pairs at the output. The output of this stage, which is +/-4V, is fed to the transformer, whose primary resistance is expected to be as low as 2.5R. I have used a capacitor to isolate the transformer's primary from the output. I started by using 2 * 680nF capacitors, but then I got slightly better output with 2 * 1000 uF and 2 * 470uF all in...Leave a comment:
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Re: Capacitor choice for 200KHz
ah that is a clever idea, buy the cheap surface mount and attach two terminals to it. sounds fiddly but possible.Leave a comment:
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Re: Capacitor choice for 200KHz
ahh thank you. so Farnell UK does not sell them (the through hole ones) and mouser are so expensive. mouser have them but demand a minimum order of 30 pounds and delievery of 12 pounds unless your order is over 50 pounds... why are capacitors are so expensive...Leave a comment:
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Re: Capacitor choice for 200KHz
The power supply of the amplifier is +/-6 Volts. I cannot pretend I understand what the MLCC is.Leave a comment:
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Re: Capacitor choice for 200KHz
Hello
I want to couple the output of a push-pull power amplifier (sinusoidal 4V peak, 200KHz) into a transformer and want to make sure there is no DC so I used a capacitor. Because the "load" maybe as low or lower than 4R the capacitor should not add to that, and at 200 KHz a 20uF capacitor is roughly 1/10 of 4R [ Zc = 1 / (2 * pi * F * C) ] - hence the 20uF.
As I did not have a ceramic 20uF, while testing on the prototype, I used 2 * 1000 uF cans, and it works OK under load, although I feel I am mis-using the...Leave a comment:
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Capacitor choice for 200KHz
I need a capacitor at 20uF and 200KHz and 4V peak AC voltage. Ideally I should use a ceramic or film capacitor, but do not have one.
So I used a pair of electrolytics at 1000uF each. I know that the electrolytics are not good at 200KHz so hopefully the 2*1000uF will suffice.
However I am thinking of buying non-electrolytics at 20uF, except I am not sure what I need and they do cost a lot, so I'd rather ask before.
At 20uF, it seems that there are all made for high voltages (200V, 300V) and have class qualifiers like "X2"...
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