Hi,
I have designed a switching amplifier - BTL, LPF to drive a capacitive load.
The modulation method I have used is SPWM.
I tried to calculate the efficiency of my amplifier using the measured input rms current and DC voltage over the measured rms current and voltage at my load.
It seems that my efficiency is as low as 50%.
Hence, I would like to consult everyone whether I have done the measurement correctly? If it is correct, where has my power gone to?
Lastly, I would like to check whether efficiency will change with frequency for a capacitive load?
Hope to have some link or paper that I could study and read up.
Thanks.
I have designed a switching amplifier - BTL, LPF to drive a capacitive load.
The modulation method I have used is SPWM.
I tried to calculate the efficiency of my amplifier using the measured input rms current and DC voltage over the measured rms current and voltage at my load.
It seems that my efficiency is as low as 50%.
Hence, I would like to consult everyone whether I have done the measurement correctly? If it is correct, where has my power gone to?
Lastly, I would like to check whether efficiency will change with frequency for a capacitive load?
Hope to have some link or paper that I could study and read up.
Thanks.
Hi Dug,
I am operating at about 90W.
Hence, I am wondering whether I have been doing things right.
Thanks.
I am operating at about 90W.
Hence, I am wondering whether I have been doing things right.
Thanks.
On a constant DC bus, you measure the AVERAGE current to get the amps input power.
On the output side, rms voltage and rms current can only be used to measure power if the load is purely ohmic. Universally, with different loads, only the integration method can tell you about the real power output (mulitplying rms values gives only the apparent power).
In case of a purely capacitive load, there is NO real power output, just apparent power.
Efficiency is based on REAL POWER.
On the output side, rms voltage and rms current can only be used to measure power if the load is purely ohmic. Universally, with different loads, only the integration method can tell you about the real power output (mulitplying rms values gives only the apparent power).
In case of a purely capacitive load, there is NO real power output, just apparent power.
Efficiency is based on REAL POWER.
Apex has (had) some good app notes on reactive loads.
Or at least they used to.
http://www.apexanalog.com/products/power-operational-amplifiers/
Or at least they used to.
http://www.apexanalog.com/products/power-operational-amplifiers/
Hi Vienna,
Thank you for your reply.
On my oscilloscope, for input power, could I say that I should set at average reading for my current reading?
Also, as my load do consist of resistive components, could I measure the average value of I*V (a reading which I could obtain from oscilloscope) - just like I*V*cos (deta)?
Lastly, the portion that I am confuse. If efficiency is based on real power, then how about all the reactive power drawn from the source? Why dont we consider them in for the calculation?
Thanks.
Hi Dug,
Thank you for your link and I suppose you are referring to the link: http://www.apexanalog.com/wp-content/uploads/2012/10/AN25U_G.pdf.
I have read the application note. However, it cover mainly linear amplifier.
Can really get the idea of measuring the loss or efficiency of switching PA.
Thanks.
Thank you for your reply.
On my oscilloscope, for input power, could I say that I should set at average reading for my current reading?
Also, as my load do consist of resistive components, could I measure the average value of I*V (a reading which I could obtain from oscilloscope) - just like I*V*cos (deta)?
Lastly, the portion that I am confuse. If efficiency is based on real power, then how about all the reactive power drawn from the source? Why dont we consider them in for the calculation?
Thanks.
Hi Dug,
Thank you for your link and I suppose you are referring to the link: http://www.apexanalog.com/wp-content/uploads/2012/10/AN25U_G.pdf.
I have read the application note. However, it cover mainly linear amplifier.
Can really get the idea of measuring the loss or efficiency of switching PA.
Thanks.
- Status
- Not open for further replies.