naveenlp
Newbie level 3
Hi,
I am currently doing a undergraduate project in my university and need some help rgd my circuit design. I am trying to experiment with resonant inductive transfer to wirelessly transmit power.
The setup is:
I have a load which is an LC circuit with a capacitor connected in parallel to a copper coil. I need to drive power into this LC circuit using a 1mhz signal at around 6.8V p-p so that the power delivered to the coil is around 100mW. This gives a current requirement of around 80mA p-p if I am not wrong. This amt of power can approximately light up 3 LEDs connected in series.
I am using a Colpitts Oscillator (CO) to generate a signal at 1mhz with 3.8V p-p. This can possibly be increased to 6.8V p-p. Now I cannot connect the CO output directly to the coils because one, the BJT I use cannot supply high currents and two, the oscillation will be affected because of the reactive loads (which might affect the LC filter in the CO) So instead, I am trying to connect the CO output to an inverting opamp (or alternatively a class AB amplifier, but I cannot find power MOSFETs that respond at high frequencies) so that the CO output looks into a high impedance gate/base of transistor. Also, the current reqd can be supplied by opamp instead of the CO
I initially used a LM318 opamp (available in lab). This gave a highly distorted output for 1mhz. But it did drive some power into the coils. Estimate at around 10-20 mW as LED lit up brightly.
I thought if I chose an opamp with better specs than LM318, I should get my results. I chose a high output current opamp, OPA561, which had 17 mhz GBWP and 50V/us slew rate, 50-70mA quiescent supply current and 1.2A p-p maximum output current. (15mhz, 50V/us and 10mA supply current for LM318) However, when I tested, output was again distorted and could not even light up a single LED.
Can forumers please advise me on how to choose opamps that are suitable for my application?
1. I have looked for GBWP >= 20Mhz, slew rate >= 50V/us and (output current >= 300mA OR supply current >= 15mA). Are the parameters AND values I am looking at correct or should I look at some additional parameters?
2. What is the significance of each of these parameters in my application?
3. What is the difference between supply current and output current and what values should these be for my purpose?
4. Why is there a high distortion for a 1Mhz input although the GBWP for both OPA561 and LM318 is about 15-17 Mhz?
5. Also, from the list below, could you please advise me if any of the opamps are suitable for my purpose?
6. Lastly, I am also looking at class AB amplifiers. However, these do not respond at frequencies greater than 100khz as there is heavy distortion in the power MOSFETs. How can I overcome this problem?
LM318 - http://www.mit.edu/~6.301/LM118.pdf
OPA561 - **broken link removed**
Other possibly suitable opamps. I looked under 2 categories, high frequency and high output current/power amplifiers. Checked in RS components and Farnell:-
LM8261 - **broken link removed**
TSH73CD/TSH74CD - **broken link removed**
OPA2604 - **broken link removed**
AD8017 - **broken link removed**
I know this is a long question (and my first). Thank you if you actually read through till the end! I shall try to post a video regarding this as soon as i can.
Thanks and regards,
Naveen LP
I am currently doing a undergraduate project in my university and need some help rgd my circuit design. I am trying to experiment with resonant inductive transfer to wirelessly transmit power.
The setup is:
I have a load which is an LC circuit with a capacitor connected in parallel to a copper coil. I need to drive power into this LC circuit using a 1mhz signal at around 6.8V p-p so that the power delivered to the coil is around 100mW. This gives a current requirement of around 80mA p-p if I am not wrong. This amt of power can approximately light up 3 LEDs connected in series.
I am using a Colpitts Oscillator (CO) to generate a signal at 1mhz with 3.8V p-p. This can possibly be increased to 6.8V p-p. Now I cannot connect the CO output directly to the coils because one, the BJT I use cannot supply high currents and two, the oscillation will be affected because of the reactive loads (which might affect the LC filter in the CO) So instead, I am trying to connect the CO output to an inverting opamp (or alternatively a class AB amplifier, but I cannot find power MOSFETs that respond at high frequencies) so that the CO output looks into a high impedance gate/base of transistor. Also, the current reqd can be supplied by opamp instead of the CO
I initially used a LM318 opamp (available in lab). This gave a highly distorted output for 1mhz. But it did drive some power into the coils. Estimate at around 10-20 mW as LED lit up brightly.
I thought if I chose an opamp with better specs than LM318, I should get my results. I chose a high output current opamp, OPA561, which had 17 mhz GBWP and 50V/us slew rate, 50-70mA quiescent supply current and 1.2A p-p maximum output current. (15mhz, 50V/us and 10mA supply current for LM318) However, when I tested, output was again distorted and could not even light up a single LED.
Can forumers please advise me on how to choose opamps that are suitable for my application?
1. I have looked for GBWP >= 20Mhz, slew rate >= 50V/us and (output current >= 300mA OR supply current >= 15mA). Are the parameters AND values I am looking at correct or should I look at some additional parameters?
2. What is the significance of each of these parameters in my application?
3. What is the difference between supply current and output current and what values should these be for my purpose?
4. Why is there a high distortion for a 1Mhz input although the GBWP for both OPA561 and LM318 is about 15-17 Mhz?
5. Also, from the list below, could you please advise me if any of the opamps are suitable for my purpose?
6. Lastly, I am also looking at class AB amplifiers. However, these do not respond at frequencies greater than 100khz as there is heavy distortion in the power MOSFETs. How can I overcome this problem?
LM318 - http://www.mit.edu/~6.301/LM118.pdf
OPA561 - **broken link removed**
Other possibly suitable opamps. I looked under 2 categories, high frequency and high output current/power amplifiers. Checked in RS components and Farnell:-
LM8261 - **broken link removed**
TSH73CD/TSH74CD - **broken link removed**
OPA2604 - **broken link removed**
AD8017 - **broken link removed**
I know this is a long question (and my first). Thank you if you actually read through till the end! I shall try to post a video regarding this as soon as i can.
Thanks and regards,
Naveen LP